Railway stations are either " terminal " or " intermediate." A terminal station embraces (I) the passenger station; (2) the goods station; (3) the locomotive, carriage and waggon depots, where the engines and the carrying stock are kept, cleaned, examined and repaired. At many intermediate stations the same arrangements, on a smaller scale, are made; in all of them there is at least accommodation for the passenger and the goods traffic. The stations for F - FIG. Q. - American Rail, 90 lb to the yard, showing rail joint.
a |
FIG. 14. - Points and Crossings. FP =Facing points.
TP =Trailing points.
a=Stock rail.
b =Switch rail.
V =Single or V-crossing. D= Diamond crossing.
c = Check rails.
d = Wing rails.
e = Winged check rails.
f = Diamond points.
passengers and goods are generally in different and sometimes in distant positions, the place selected for each being that which is most convenient for the traffic. The passenger station abuts on the main line, or, at termini, forms the natural terminus, at a place as near as can conveniently be obtained to the centre of the population which constitutes the passenger traffic; and preferably its platforms should be at or near the ground level, for convenience of access. The goods station is approached by a siding or fork set off from the main line at a point short of the passenger station. In order to keep down the expense of shunting the empty trains and engines to and from the platforms the carriage and locomotive depots should be as near the passenger station as possible; but often the price of land renders it impracticable to locate them in the immediate vicinity and they are to be found at a distance of several miles.
In laying out the approaches and station yard of a passenger station ample width and space should be provided, with welldefined means of ingress and egress to facilitate the Passenger ci rculation of vehicles and with a long setting-down stations. g g pavement to enable them to discharge their passengers and luggage without delay. The position of the main buildings - ticket offices, waiting and refreshment-rooms, parcels offices, &c. - relative to the direction of the lines of rails may be used as a means of classifying terminal stations. They are placed either on the departure side parallel to the platform (" side " stations) or at right angles to the rails and platforms (" end " stations). Many large stations, however, are of a mixed type, and the offices are arranged in a fork between two or more series of platforms, or partly at the end and partly on one side. Where heavy suburban traffic has to be dealt with, the expedient is occasionally adopted of taking some of the lines round the end in a continuous loop, so that incoming trains can deposit their passengers at an underground platform and immediately proceed on their outward journey. Intermediate stations, like terminal ones, should be convenient in situation and easy of approach, and, especially if they are important, should be on the ground level rather than on an embankment or in a cutting. The lines through them should be, if possible, straight and on the level; the British Board of Trade forbids them being placed on a gradient steeper than i in 260, unless it is unavoidable. Intermediate stations at the surface level are. naturally constructed as side stations, and whether offices are provided on both sides or whether they are mainly concentrated on one will depend on local circumstances, the amount of the traffic, and the direction in which it preponderates. When the railway lies below the surface level the bulk of the offices are often placed on a bridge spanning the lines, access being given to the platforms by staircases or lifts, and similarly when the railway is at a high level the offices may be arranged under the lines. Occasionally on a double-track railway one platform placed between the tracks serves both of them; this " island " arrangement, as it is termed, has the advantage that more tracks can be readily added without disturbance of existing buildings, but when it is adopted the exit from the trains is at the opposite side to that which is usual, and accidents have happened through passengers alighting at the usual side without noticing the absence of a platform. At stations on double-track railways which have a heavy traffic four tracks are sometimes provided, the two outside ones only having platforms, so that fast trains get a clear road and can pass slow ones that are standing in the station. In Great Britain, it may be noted, trains almost invariably keep to the left, whereas in most other countries right-handed running is the rule.
The arrangement and appropriation of the tracks in a station materially affect the economical and efficient working of the traffic. There must be a sufficient provision of sidings, connected with the running tracks by points, for holding spare rolling stock and to enable carriages to be added to or taken off trains and engines to be changed with as little delay as possible. At terminal stations, especially at such as are used by short-distance trains which arrive at and start from the same platform, a third track is often laid between a pair of platform tracks, so that the engine of a train which has arrived at the platform can pass out and place itself at the other end of the train, which remains undisturbed. At the new Victoria station (London) of the London, Brighton & South Coast railway - which is so long that two trains can stand end to end at the platforms - this system is extended so as to permit a train to start out from the inner end of a platform even though another train is occupying the outer end. One of the advantages of electric trains on the multiple control system is that they economize terminal accommodation, because they can be driven from either end indifferently, and therefore avoid the necessity for tracks by which engines can change from one end of the train to the other.
The platforms on British railways have a standard elevation of 3 ft. above rail level, and they are not now made less than 2 ft. in height. In other countries they are generally lower; in the United States they are commonly level with, or only a few inches higher than, the top of the rails. They may consist of earth with a retaining wall along the tracks and with the surface gravelled or paved with stone or asphalt, or they may be constructed entirely of timber, or they may be formed of stone slabs supported on longitudinal walls. They should be of ample dimensions to accommodate the traffic - the British Board of Trade requires them to be not less than 6 ft. wide at small stations and not less than 12 ft. wide at large ones - and they should be as free as possible from obstructions, such as pillars supporting the roof. At intermediate stations the roofs are often carried on brackets fixed to the walls of the station buildings, and project only to the edge of the platforms. At larger stations where both the platforms and the tracks are covered in, there are two broad types of construction, with many intermediate variations: the roof may either be comparatively low, of the " ridge and furrow " pattern, borne on a number of rows of pillars, or it may consist of a single lofty span extending clear across the area from the side walls. The advantage claimed for roofs formed with one or two large spans is that they permit the platforms and tracks to be readily rearranged at any time as required, whereas this is difficult with the other type, especially since the British Board of Trade requires the pillars to be not less than 6 ft. away from the edges of the platforms. On the other hand, wide spans are more expensive both in first cost and in maintenance, and there is the possibility of a failure such as caused the collapse in December 1905 of the roof of Charing Cross (S.E.R.) station, London, which then consisted of a single span. Whatever the pattern adopted for the roof, a sufficient portion of it must be glazed to admit light, and it should be so designed that the ironwork can be easily inspected and painted and the glass readily cleaned. For the illumination of large stations by night electric arc lamps are frequently employed, but some authorities favour high-pressure incandescent gas-lighting.
At busy stations separate tracks are sometimes appropriated to the use of light engines and empty trains, on which they may be run between the platforms and the locomotive and Loco- carriage depots. A carriage depot includes sheds in motive which the vehicles are stored, arrangements for wash- depots. ing and cleaning them, and sidings on which they are marshalled into trains. At a locomotive depot the chief building is the " running shed " in which the engines are housed and cleaned. This may be rectangular in shape (" straight " shed), containing a series of parallel tracks on which the engines stand and which are reached by means of points and crossings diverging from a main track outside; or it may take a polygonal or circular form (round house or rotunda), the lines for the engines radiating from a turn-table which occupies the centre and can be rotated so as to serve any of the radiating lines. The second arrangement enables any particular engine to enter or leave without disturbing the other; but on the other hand an accident to the turn-table may temporarily imprison the whole of them. In both types pits are constructed between the rails on which the engines stand to afford easy access for the inspection and cleaning of their mechanism. Machine shops are usually provided to enable minor repairs to be executed; the tendency, both in England and America, is to increase the amount of such repairing plant at engine sheds, thus lengthening the intervals between the visits of the engines to the main repairing shops of the railway. A locomotive depot further includes stores of the various materials required in working the engines, coal stages at which they are loaded with coal, and an ample supply of water. The quality of the last is a matter of great importance; when it is unsuitable, the boilers will suffer, and the installation of a water-softening plant may save more in the expenses of boiler maintenance than it costs to operate. The water cranes or towers which are placed at intervals along the railway to supply the engines with water require similar care in regard to the quality of the water laid on to them, as also to the water troughs, or track tanks as they are called in America, by which engines are able to pick up water without stopping. These consist of shallow troughs about 18 in. wide, placed between the rails on perfectly level stretches of line. When water is required, a scoop is lowered into them from below the engine, and if the speed is sufficient the water is forced up it into the tender-tanks. Such troughs were first employed on the London & North-Western railway in 1857 by John Ramsbottom, and have since been adopted on many other lines.
Goods stations vary in size from those which consist of perhaps a single siding, to those which have accommodation for thousands of wagons. At a small roadside station, where the traffic is of a purely local character, there will be some sidings to which horses and carts have access for handling bulk goods like coal, gravel,. manure, &c., and a covered shed for loading and unloading packages and materials which it is undesirable to expose to the weather. The shed may have a single pair of rails for wagons running through it along one side of a raised platform, there being a roadway for carts on the other side; or if more accommodation is required there may be two tracks, one on each side of the platform, which is then approached by carts at the end. In either case the platform is fitted with a crane or cranes for lifting merchandise into and out of the wagons, and doors enable the shed to be used as a lock-up warehouse. In a large station the arrangements become much more complicated, the precise design being governed by the nature of the traffic that has to be served and by the physical configuration of the site. It is generally convenient to keep the inwards and the outwards traffic distinct and to deal with the two classes separately; at junction stations it may also be necessary to provide for the transfer of freight from one wagon to another, though the bulk of goods traffic is conveyed through to its destination in the wagons into which it was originally loaded. The increased loading space required in the sheds is obtained by multiplying the number and the length of lines and platforms; sometimes also there are short sidings, cut into the platforms at right angles to the lines, in which wagons are placed by the aid of wagon turn-tables, and sometimes the wagons are dealt with on two floors, being raised or lowered bodily from the ground level by lifts. The higher floors commonly form warehouses where traders may store goods which have arrived or are awaiting despatch. An elaborate organization is required to keep a complete check and record of all the goods entering and leaving the station, to ensure that they are loaded into the proper wagons according to their destination, that they are unloaded and sorted in such a way that they can be delivered to their consignees with the least possible delay, that they are not stolen or accidentally mislaid, &c.; and accommodation must be provided for a large clerical and supervisory staff to attend to these matters. British railways also undertake the collection and delivery of freight, in addition to transporting it, and thus an extensive range of vans and wagons, whether drawn by horses or mechanically propelled, must be provided in connexion with an important station.
It may happen that from a large station sufficient traffic may be consigned to certain other large stations to enable full train-loads to be made up daily, or several times a day, and despatched direct to their destinations. In general, however, the conditions are less simple. Though a busy colliery may send off its product by the train-load to an important town, the wagons will usually be addressed to a number of different consignees at different depots in different parts of the town, and therefore the train will have to be broken up somewhere short of its destination and its trucks rearranged, together with those of other trains similarly constituted, into fresh trains for conveyance to the various depots. Again, a: station of moderate size may collect goods destined for a great variety of places but not in sufficient quantities to compose a full train-load for any of them, and then it becomes impossible; except at the cost of uneconomical working, to avoid despatching trains which contain wagons intended for many diverse destinations. For some distance these wagons will all travel over the same line, but sooner or later they will reach a junction-point where their ways will diverge and where they must be separated. At this point trains of wagons similarly destined for different places will be arriving from other lines, and hence the necessity will arise of collecting together from all the trains all the wagons which are travelling to the same place.
The problem may be illustrated diagrammatically as follows` (fig. 15): A may be supposed to be a junction outside a large FIG. 15. - Diagram to illustrate use of Shunting Yards.
seaport where branches from docks a, b, c and d converge, and where the main line also divides into three, going to B, C and D respectively. A train from a will contain some wagons for B,, some for C and some for D, as will also the trains from a, b, c and d. At A therefore it becomes necessary to disentangle and group together all the wagons that are intended for B, all that are intended for C, and all that are intended for D. Even that is not the whole of the problem. Between A and B, A and C, and A and D, there may be a string of stations, p, q, r, s, &c., all receiving goods from a, b, c and d, and it would manifestly be inconvenient and wasteful of time and trouble if the trains serving those intermediate stations were made up with, say, six wagons from a to p next the engine, five from b to p at the middle, and four from c to p near the end. Hence at A the trucks from a, b, c and d must not only be sorted according as they have to travel along A B, A C, or A D, but also must be marshalled into trains in the order of the stations along those lines. Conversely, trains arriving at A from B, C and D must be broken up. and remade in order to distribute their wagons to the different, dock branches.
To enable the wagons to be shunted into the desired order yards containing a large number of sidings are constructed at important junction points like A. Such a yard consists essentially of a group.. or groups of sidings, equal in length at least to the longest train run on the line, branching out from a single main track and often again converging to a single track at the other end; the precise design,.. however, varies with the amount and character of the work that has to be done, with the configuration of the ground, and also with the mode of shunting adopted. The oldest and commonest method of shunting is that known as " push-and-pull," or in America as " link-and-pin " or " tail " shunting. An engine coupled to a batch of wagons runs one or more of them down one siding, leaves them there, then returns back with the remainder clear of the points where the sidings diverge, runs one or more others down another siding, and so on till they are all disposed of. The same operation is repeated with fresh batches of wagons, until the sidings contain a number of trains, each intended, it may be supposed, for a particular town or district. In some cases nothing more is required than to attach an engine and brake-van (" caboose ") and despatch the train; but if, as will happen in others, a further rearrangement of XXII. 27 a the wagons is necessary to get them into station order this is effected on the same principle.
Push-and-pull shunting is simple, but it is also slow, and therefore efforts have been made at busy yards where great numbers of trains are dealt with to introduce more expeditious methods. One of these, employed in America, is known as " poling." Alongside the tracks on which stand the trains that are to be broken up and from which the sidings diverge subsidiary tracks are provided for the use of the shunting engines. These engines have a pole projecting horizontally in front of them, or are attached to a " polecar " having such a pole. The method of working is for the pole to be swung out behind a number of wagons; one engine is then started and with its pole pushes the wagons in front of it until their speed is sufficient to carry them over the points, where they are diverted into any desired siding. It then runs back to the train to repeat the operation, but while it is doing so a second engine similarly equipped has poled away a batch of wagons on the opposite side. In this way a train is distributed with great rapidity, especially if the points giving access to the different sidings are worked by power so that they can be quickly manipulated.
Another method, which was introduced into America from Europe about 1890, is that of the summit or " hump." The wagons are pushed by an engine at their rear up one slope of an artificial mound, and as they run down the other slope by gravity are switched into the desired siding. Sometimes a site can be found for the sorting sidings where the natural slope of the ground is sufficiently steep to make the wagons run down of themselves. One of the earliest and best known of such " gravity " yards is that at Edgehill, near Liverpool, on the London & North-Western railway, which was established in 1873. Here, at the highest level, there are a number of " upper reception lines " converging to a single line which leads to a group of " sorting sidings " at a lower level. These in turn converge to a pair of single lines which lead to two groups of marshalling sidings, called " gridirons " from their shape, and these again converge to single lines leading to " lower reception and departure lines " at the bottom of the slope. The wagons from the upper reception lines are sorted into trains on the sorting sidings, and then, in the gridirons, are arranged in the appropriate order and marshalled ready to be sent off from the departure lines. (H. M. R.) Locomotive Power The term " power " is used in technical sense to mean the rate at which work is done against a resistance, and is measured in units of energy expended per unit of time. The unit of power commonly used by engineers is the horse-power, and this unit corresponds to a rate of working of 550 foot-lb of work per second. The problems arising out of the special consideration of the power required to propel a railway train against the resistances opposing its motion, the way the power is applied to trains, the agent by means of which the power is exerted, are conveniently grouped together under the general heading of Locomotive Power. There are certain fundamental relations common to all tractive problems, and these are briefly considered in §§ i and 2, after which the article refers particularly to steam locomotives, although §§ 4, 5, 7, 8, 9, and 10 have a general application to all modes of traction.
§ 1. Fundamental Relations. - The resistance against which a train is moved along a railway is overcome by means of energy obtained from the combustion of fuel, or in some few cases by energy obtained from a waterfall. If the total resistance against which the train is maintained in motion with an instantaneous velocity of V feet per second is R, the rate at which energy is expended in moving the train is represented by the product RV, and this must be the rate at which energy is supplied to the train after deducting all losses due to transmission from the source of power. Thus if R is equal to 10,000 lb when the velocity is 44 ft. per second, equivalent to 30 m. per hour, the rate of working against the resistance is 440,000 foot-lb per second.
In whatever form energy is produced and distributed to the train it ultimately appears as mechanical energy applied to turn one or more axles against the resistance to their rotation imposed by the weight on the wheels and the motion of the train.
The rate at which work is done on a particular axle is measured by the product where T is the torque or turning moment exerted on the axle by the motor or mechanism applied to it for this purpose, and is the angular velocity of the axle in radians per second. Hence if all the energy supplied to the train is utilized at one axle there is the fundamental relation RV (I) Continuing the above arithmetical illustration, if the wheels to the axle of which the torque is applied are 4 ft. diameter, w = 44/2 = 22 radians per second, and therefore T= 440,000/22=20,000 lb ft. If the energy supplied is distributed between several axles the relation becomes l l 2 3 w 3. = RV (2) where T 1, T2, T3, &c. are the torques on the axles whose respective angular velocities are wl,w2, W3, &c.
The fundamental condition governing the design of all tractive machinery is that the wheels belonging to the axles to which torque is applied shall roll along the rails without slipping, and exert a tractive force on the train.
The fundamental relation between the applied torque and the tractive force F will be understood from fig. 16, which shows in a diagrammatic form a wheel and axle connected to the framework of a vehicle, in the way adopted for railway trains. The journal of the axle A, is carried in a bearing or axle-box B, which is free to move vertically in the wide vertical slot G, formed in the frame and called generally " the horns," under the control of the spring. The weight W 1 carried by the part of the frame supported by the wheel (whose diameter is D) is transmitted first to the pins P 1, P2, which are fixed to the frame, and then to the spring links L 1, L2, which are jointed at their respective ends to the spring S, the centre of which rests on the axle-box.
Let a couple be applied to the axle tending to turn it in the direction shown by the arrow. This couple, we may assume, will be equally divided between the two wheels, so that the torque acting on each will be T. Assuming the wheels to roll along the rail without slipping, this couple will be equivalent to the couple formed by the equal opposite and parallel forces, F 1 acting in the direction shown, from the axle-box on to the frame, and F 1 =µ0, acting along the rail. The torque corresponding to this couple is F 1 X z D = 2µWID, and hence follows the fundamental relation, 2T = 2F 1 D = 2µWID, or if W now represents the weight supported by the axle, F will be the tractive force exerted on the frame by the two axle-boxes to propel the vehicle, and the more convenient relation is established, T=2FD=2µWD (3) If T has a greater value than this relation justifies the wheels will slip. F is called the " tractive force " at the rail. The coefficient of friction is a variable quantity depending upon the state of the rails, but is usually taken to be This is the fundamental equation between the forces acting, however the torque may be applied. Multiplying through by w we obtain Tw = 2FwD = 2µWwD = RV (4) This is a fundamental energy equation for any form of locomotive in which there is only one driving-axle.
The couple T is necessarily accompanied by an equal and opposite couple acting on the frame, which couple endeavours to turn the frame in the opposite direction to that in which the axle rotates. The practical effect of this opposite couple is slightly to tilt the frame and thus to redistribute slightly the weights on the wheels carrying the vehicle.
If there are several driving-axles in a train, the product Tw must be estimated for each separately; then the sum of the products will be equal to RV. In equation (4) there is a fixed relation between w, V and D given by the expression.
w=2V /D (5) Here D is in feet, V in feet per second and w in radians per second. If the speed is given in miles per hour, S say, V =1.466 S (6) The revolutions of the axle per second, n, are connected with the radians turned through per second by the relation n =w/27r = w/6.38 (7) § 2. Methods of Applying Locomotive Power. - By locomotive power is to be understood the provision of power to maintain the rates of working on the driving-axles of a train indicated by the relation (4). The most usual way of providing this power is by the combustion of coal in the fire-box of a boiler and the utilization of the steam produced in a steam-engine, both boiler and engine being carried on a frame mounted on wheels in such a way that the crank-shaft of the steam-engine becomes the driving-axle of the train. From equation (3) it is clear that the wheels of the driving-axle must be heavily loaded in order that F may have a value sufficiently great to propel the train. The maximum weight which one pair of wheels are usually allowed to carry on a first-class track is from 18 to 20 tons. If a larger FIG. 16. - Wheel and Connexion to Frame.
value of the tractive force is required than this provides for, namely from 4 to 5 tons, the driving-wheels are coupled to one or more pairs of heavily loaded wheels, forming a class of what are called " coupled engines " in contradistinction to the " single engine " with a single pair of loaded driving-wheels. Mechanical energy may be developed in bulk at a central station conveniently situated with regard to a coal-field or a waterfall, and after transformation by means of electric generators into electric energy it may be transmitted to the locomotive and then by means of electric motors be retransformed into mechanical energy at the axles to which the motors are applied. Every axle of an electric locomotive may thus be subjected to a torque, and the large weight which must be put on one pair of wheels in order to secure sufficient adhesion when all the driving is done from one axle may be distributed through as many pairs of wheels as desired. In fact, there need be no specially differentiated locomotive at all. Motors may be applied to every axle in the train, and their individual torques adjusted to values suitable to the weights naturally carried by the several axles. Such an arrangement would be ideally perfect from the point of view of the permanent-way engineer, because it would then be possible to distribute the whole of the load uniformly between the wheels. This perfection of distribution is practically attained in present-day practice by the multiple control system of operating an electric train, where motors are applied to a selected number of axles in the train, all of them being under the perfect control of the driver.
The fundamental difference between the two methods is that while the mechanical energy developed by a steam engine is in the first case applied directly to the driving-axle of the locomotive, in the second case it is transformed into electrical energy, transmitted over relatively long distances, and retransformed into mechanical energy on the driving-axles of the train. In the first case all the driving is done on one or at most two axles, sufficient tractive force being obtained by coupling these axles when necessary to others carrying heavy loads. In the second case every axle in the train may be made a driving-axle if desired, in which case the locomotive as a separate machine disappears. In the second case, however, there are all the losses due to transmission from the central station to the train to be considered, as well as the cost of the transmitting apparatus itself. Ultimately the question resolves itself into one of commercial practicability. For suburban traffic with a service at a few minutes' interval and short distances between the stations electric traction has proved itself to be superior in many respects to the steam locomotive, but for main line traffic and long distance runs it has not yet been demonstrated that it is commercially feasible, though it is known to be practically possible. For the methods of electric traction see Traction; the remainder of the present article will be devoted to the steam locomotive.
§ 3. General Efficiency of Steam Locomotive. - One pound of good Welsh coal properly burned in the fire-box of a locomotive yields about 15,000 British thermal units of heat at a temperature high enough to enable from 50 to 80% to flow across the boiler-heating surface to the water, the rest escaping up the chimney with the furnace gases. The steam produced in consequence of this heat transference from the furnace gas to the water carries heat to the cylinder, where 7 to II % is transformed into mechanical energy, the remainder passing away up the chimney with the exhaust steam. The average value of the product of these percentages, namely o65 Xo09 =0.06 say, may be used to investigate generally the working of a locomotive; the actual value could only be determined by experiment in any particular case. With this assumption, 0.06 is the fraction of the heat energy of the coal which is utilized in the engine cylinders as mechanical work; that is to say, of the 15,000 B.Th.U. produced by the combustion of 1 lb of coal, 15,000 Xo06 =900 only are available for tractive purposes.
Coals vary much in calorific value, some producing only 12,000 B.Th.U. per lb when burnt, whilst 15,500 is obtained from the best Welsh coals. Let E represent the pounds of coal burnt per hour in the fire-box of a locomotive, and let c be the calorific value in B.Th.U. per lb; then the mechanical energy available in footpounds per hour is approximately 0-06 X 778 X Ec, and this expressed in horse-power units gives I.H.P. - o06X778XEc _648.1,980,000.
A " perfect engine " receiving and rejecting steam at the same temperatures as the actual engine of the locomotive, would develop about twice this power, say 1400 I.H.P. This figure represents the ideal but unattainable standard of performance. This question of the standard engine of comparison, and the engine efficiency is considered in § 15 below, and the boiler efficiency in § It below.
The indicated horse-power developed by a cylinder may always be ascertained from an indicator diagram and observations of the speed. Let p be the mean pressure in pounds per square inch, calculated from an indicator diagram taken from a particular cylinder when the speed of the crank-shaft is n revolutions per second. Also let l be the length of the stroke in feet and let a be the area of one cylinder in square inches, then, assuming two cylinders of equal size, I.H.P. =2 planl550 (8) The I.H.P. at any instant is equal to the total rate at which energy is required to overcome the tractive resistance R. The horsepower available at the driving-axle, conveniently called the brake horse-power, is from 20 to 30% less than the indicated horse-power, and the ratio, B.H.P./I.H.P. =E, is called the mechanical efficiency of the steam engine. The relation between the b.h.p. and the torque on the driving-axle is 55 o B.H.P. =Tu., (9) It is usual with steam locomotives to regard the resistance R as including the frictional resistances between the cylinders and the driving-axle, so that the rate at which energy is expended in moving the train is expressed either by the product RV, or by the value of the indicated horse-power, the relation between them being 55 0 I.H.P. =RV (Io) or in terms of the torque 55 0 I.H.P.X€=RVe=TW (II) The individual factors of the product RV may have any value consistent with equation (to) and with certain practical conditions, so that for a given value of the I.H.P. R must decrease if V increases. Thus if the maximum horse-power which a locomotive can develop is woo, the tractive resistance R, at 60 m. per hour (=88 ft. per second) is R = (woo X550)/88 =6250 lb. If, however, the speed is reduced to 15 m. per hour (= 22 ft. per second) R increases to 25,000 lb. Thus an engine working at maximum power may be used to haul a relatively light load at a high speed or a heavy load at a slow speed.
§ 4. Analysis of Train Resistance. - Train resistance may be analysed into the following components: (i) Journal friction and friction of engine machinery.
(2) Wind resistance.
(3) Resistance due to gradients, represented by R9. (4) Resistance due to miscellaneous causes.
(5) Resistance due to acceleration, represented by Ra. (6) Resistance due to curves.
The sum of all these components of resistance is at any instant equal to the resistance represented by R. At a uniform speed on a level straight road 3, 5 and 6 are zero. The total resistance is conveniently divided into two parts: (1) the resistance due to the vehicles hauled by the engine, represented by R q ; (2) the resistance of the engine and tender represented by R 4. In each of these two cases the resistance can of course be analysed into the six components set out in the above list.
§ 5. Vehicle Resistance and Draw-bar Pull. - The power of the engine is applied to the vehicles through the draw-bar, so that the draw-bar pull is a measure of the vehicle resistance. The draw-bar pull for a given load is a function of the speed of the train, and numerous experiments have been made to find the relation connecting the pull with the speed under various conditions. The usual way of experimenting is to put a dynamometer car (see Dynamometer) between the engine and the train. This car is equipped with apparatus by means of which a continuous record of the draw-bar pull is obtained on a distance base; time indications are also made on the diagram from which the speed at any instant can be deduced. The pull recorded on the diagram includes the resistances due to acceleration and to the gradient on which the train is moving. It is usual to subtract these resistances from the observed pull, so as to obtain the draw-bar pull reduced to what it would be at a uniform speed on the level. This corrected pull is then divided by the weight of the vehicles hauled, in which must be included the weight of the dynamometer car, and the quotient gives the resistance per ton of load hauled at a certain uniform speed on a straight and level road. A series of experiments were made by J. A. F. Aspinall on the Lancashire & Yorkshire railway to ascertain the resistance of trains of bogie passenger carriages of different lengths at varying speeds, and the results are recorded in a paper, " Train Resistance," Proc. Inst. C.E. (1901), vol. 147. Aspinall's results are expressed by the formula S 5+ 50.8 12 r„ =2 -}-00278,L where r ro is the resistance in pounds per ton, S is the speed in miles per hour, and L is the length of the train in feet measured over the carriage bodies. The two following expressions are given in the Bulletin of the International Railway Congress (vol. xii. p. 1275), by Barbier, for some experiments made on the Northern railway of France with a train of 157 tons mean weight; they are valid between 37 and 77 m. per hour: - rv= 3.58-I 165S(I 61S } 50) for 4-wheel coaches, (13) 1000 rv= 3-58+ I 645(1 61S +IO) for bogie coaches. 1000 The Baldwin Locomotive Company give the formulae 0.565 r =3.36+ 3 and r z ,= 1.68 +0.2245 for speeds from 47 to 77 m. per hour. (16) All the above formulae refer to carriage stock. The resistance of goods wagons has not been so systematically investigated. In the paper above quoted Aspinall cites a case where the resistance of a train of empty wagons 1830 ft. long was 18.33 lb per ton at a speed of 26 m. per hour, and a train of full wagons 1045 ft. long gave only 9.12 lb per ton at a speed of 29 m. per hour. The resistance found from the above expressions includes the components I, 2 and 4 of § 4. The resistance caused by the wind is very variable, and in extreme cases may double the resistance found from the formulae. A side wind causes excessive flange friction on the leeward side of the train, and increases the tractive resistances therefore very considerably, even though its velocity be relatively moderate. The curves corresponding to the above expressions are plotted in fig. 17, four values of L being taken for formula (12) corresponding to trains of 5, 10, 15 and 20 bogie carriages.
The resistance at starting is greater than the running resistance at moderate speeds. From Aspinall's experiments it appears to be about 17 lb per ton, and this value is plotted on the diagram.
The resistance to motion round a curve has not been so systematically studied that any definite rule can be formulated applicable to all classes of rolling stock and all radii of curves. A general result could not be obtained, even from a large number of experiments, because the resistance round curves depends upon so many variable factors. In some cases the gauge is laid a little wider than the standard, and there are varying amounts of superelevation of the outer rail; but the most formidable factor in the production of resistance is the guard-rail, which is sometimes put in with the object of guiding the wheel which runs on the inner rail of the curve on the inside of the flange.
From experiments made on the NorthEastern railway (see a paper by W. H. Smith on " Express Locomotive Engines," Proc. Inst. Mech. Eng., October 1898), it appeared that the engine resistance was about 35% of the total resistance, and in the train-resistance experiments on the Lancashire & Yorkshire railway quoted above the engine resistance was also about 35% of the total resistance, thus confirming the North-Eastern railway results. Barbier (loc. cit.) gives as the formula for the engine resistance re = 8.51 +3.24S(I. 61S+30)/Iooo (17) where S is the speed in miles per hour. This formula is valid between speeds of 37 and 77 m. per hour, and was obtained in connexion with the experiments previously quoted on the Northern railway of France with an engine and tender weighing about 83 tons. Barbier's formula is plotted in fig. 17, together with a curve expressing generally the results of some early experiments on the Great Western railway carried out by Sir D. Gooch. The extension of the Barbier curve beyond the above limits in fig. 17 gives values which must be regarded as only very approximate.
70 FIG. 17.
§ 7. Rate at which work is done against the resistances given by the curves fig. z7. - When the weight of the engine and tender and the weight of the vehicles are respectively given, the rate at which work must be done in the engine cylinders in order to maintain the train in motion at a stated speed can be computed by the aid of the curves plotted in fig. 17. Thus let an engine and tender weighing 80 tons haul vehicles weighing 200 tons at a uniform speed on the level of 40 m. per hour. As given by the Barbier curves in fig. 17, the engine resistance at 40 m. per hour is 20 lb per ton, and the vehicle resistance 8.5 lb per ton at the same speed. Hence Engine resistance, R e = 80 X20 = 1600 lb Vehicle resistance, R v =200 X8.5 = 1700 „ Train resistance, R = 3300 „ The speed, 40 m. per hour, is equal to 58.6 ft. per second; therefore the rate of working in foot-pounds per second is 3300 X58.6, from which I.H.P. _ (3300 X58.6)/550 = 354. This is the horse-power, therefore, which must be developed in the cylinders to maintain the train in motion at a uniform speed of 40 m. per hour on a level straight road with the values of the resistances assumed.
§ 8. Rate at which work is done against a gradient. - Gradients are measured either by stating the number of feet horizontally, G say, in which the vertical rise is I ft., or by the vertical rise in too ft. measured horizontally expressed as a percentage, or by the number of feet rising vertically in a mile. Thus a gradient of I in 200 is the same as a half per cent. grade or a rise of 26.4 ft. per mile. The difference between the horizontal distance and the distance measured along the rail is so small that it is negligible in all practical calculations. Hence if a train is travelling up the gradient at a speed of V ft. per second, the vertical rise per second is V/G ft. If W I is the weight of the train in pounds, the rate of working against the gradient expressed in horse-power units is H.P.=W,V/550 G. (18) Assuming the data of the previous section, and in addition that the train is required to maintain a speed of 40 m. per hour up a gradient of I in 300, the extra horse-power required will be H.P. _280X2240X58.6 =22 300 X 550 3.
This must be exerted in addition to the horse-power calculated in the previous section, so that the total indicated horse-power which must be developed in the cylinders is now 354+223 =577. If the train is running down a gradient this horse-power is the rate at which gravity is working on the train, so that with the data of the previous section, on the assumption that the train is running down a gradient of I in 300, the horse-power required to maintain the speed would be 354-223=131.
Rate at which work is done against acceleration. - If W 1 is the weight of the train in pounds and a the acceleration in feet per second, the force required to produce the acceleration is f = Wi a / g (19) And if V is the average speed during the change of velocity implied by the uniform acceleration a, the rate at which work is done by this force is fV= W1Va /g (20) or in horse-power units Time occupied in the change - 13 - 0 113. Therefore the horse-power which must be developed in the cylinders to effect this change of speed is from (21) H.P.280X2240X0113X59 = _237 55 0 X 32 The rate of working is negative when the train is retarded; for instance, if the train had changed its speed from 41 to 40 m. per hour in 13 seconds, the rate at which work would have to be absorbed by the brake blocks would represent 237 H.P. This is lost in heat produced by the friction between the brake blocks and the wheels, though in some systems of electric driving some of the energy stored in the train may be returned to the central station during retardation. The principal condition operating in the design of locomotives intended for local services with frequent stops is the degree of acceleration required, the aim of the designer being to produce an engine which shall be able to bring the train to its journey speed in the shortest time possible. For example, suppose it is required to start a train weighing 200 tons from rest and bring it to a speed of 30 m. per hour in 30 seconds. The weight of the engine may be assumed in advance to be 80 tons. The acceleration, a, which may be supposed uniform, is 1.465. The average velocity is 15 m. per hour, which is equal to 22 ft. per second; therefore the tractive force required is, from (19), (280 X2240XI. 465)/32 = 28,720 ib, and the corresponding horse-power which must be developed in the cylinders is, from (20), f V/550, and this is with f and V equal to the above values, 1149. To obtain the tractive force the weight on the coupled wheels must be about five times this amount - that is..
LOCOMOTIVE POWER] |
- 20 ton Speed in Miles per Hour 30 40 50 60 90 100 H.P. = W, Va /55 og (21) Assuming the data of § 7, suppose the train to change its speed from 40 to 41 m. per hour in 13 seconds. The average acceleration in feet per second is measured by the fraction Change of speed in feet per sec. 60.07-58.6 64 tons; and to obtain the horse-power the boiler will be one of the largest that can be built to the construction gauge. After acceleration to the journey speed of 30 m. per hour the horse-power required is reduced to about one-third of that required for acceleration alone.
§ 10. General expression for total rate of working. - Adding the various rates of working together R. H.P. - (Were ?-W v r v)V ?2240WV ?2240WVa (22) 55 0 550 550G 550g where W e is weight of engine and tender in tons, Wv the weight of vehicles in tons, W the weight of train in tons =W e r e and r z , the respective engine and vehicle resistances taken from the curves fig. 17 at a speed corresponding to the average speed during the acceleration a, G the gradient, g the acceleration due to gravity, and V the velocity of the train in feet per second. In this expression it is assumed that the acceleration is uniform, and this assumption is sufficiently accurate for any practical purpose to which the above formula would be applieu in the ordinary working of a locomotive. If a is variable, then the formula must be applied in a series of steps, each step corresponding to a time interval over which the acceleration may be assumed uniform.
Dividing thr Hugh by V and multiplying through by 550, 2240W 2240Wa R =Were+W vry t G (23) ' 'an expression giving the value of R the total tractive resistance. If the draw-bar pull is known to be R v, then applying the same principles to the vehicle alone which above are applied to the whole train, total draw-bar pull = Wvry 2240Wv 2240Wva. (24) G g This expression may be used to find r„ when the total draw-bar pull is observed as well as the speed, the changes of speed and the gradient. The speed held to correspond with the resistance must be the mean speed during the change of speed. The best way of deducing r„ is to select portions of the dynamometer record where the speed is constant. Then a disappears from all the above expressions. These expressions indicate what frequent changes in the power are required as the train pursues its journey up and down gradients, against wind resistance, j ournal friction and perhaps the resistance of a badly laid track; and show how both the potential energy and kinetic energy of the train are continually changing: the first from a change in vertical position due to the gradients, the second from changes in speed. These considerations also indicate what a difficult matter it is to find the exact rate of working against the resistances, because of the difficulty of securing conditions which eliminate the effect both of the gradient and of acceleration.
Maximum Power. - The maximum power which can be developed by a locomotive depends upon the maximum rate of fuel combustion which can be maintained per square foot of grate. This maximum rate depends upon the kind of coal used, whether small, friable, bituminous or hard, upon the thickness of the fire, and upon the correct design and setting of the blast-pipe. A limit is reached to the rate of combustion when the draught becomes strong. enough to carry heavy lighted sparks through the tubes and chimney. This, besides reducing the efficiency of the furnace, introduces the danger of fire to crops and buildings near the line. The maximum rate of combustion may be as much as so lb of coal per square foot of grate per hour, and in exceptional cases even a greater rate than this has been maintained. It is not economical to force the boiler to work at too high a rate, because it has been practically demonstrated that the boiler efficiency decreases after a certain point, as the rate of combustion increases. A few experimental results are set forth in Table XX., from which it will be seen that with a relatively low rate of combustion, a rate which denotes very light service, namely lb of coal per square foot of grate per hour, the efficiency of the boiler is %, which is as good a result as can be obtained with the best class of stationary boiler or marine boiler even when using economizers.
The first group consists of experiments selected from the records of a large number made on the boiler of the locomotive belonging to the Purdue University, Indiana, U.S.A.
The second group consists of experiments made on a boiler belonging to the Great Eastern Railway Company. The first one of the group was made on the boiler fixed in the locomotive yard at Stratford, and the two remaining experiments of the group were made while the engine was working a train between London and March.
The third group consists of experiments selected from the records of a series of trials made on the London & South-Western railway with an express locomotive.
§ 12. Draught. - One pound of coal requires about 20 lb of air for its proper combustion in the fire-box of a locomotive, though this quantity of air diminishes as the rate of combustion increases.
Dry coal fired per | Pounds of water eva- | Boiler | ||
Kind, and calorific value of coal. | square foot of grate | poratedper lb of coal | effici- | Reference. |
per hour. lb | from and at 212° F. | enc y. | ||
Indiana block coal | 49 | 7.83 | 0.58 | Prof. Goss |
from the neigh- | 109 | 6.59 | 0.49 | (Amer. Soc. |
bourhood of | 181 | 5.71 | 0.42 | of Mech. |
Brazil. Esti- mated calorific value, 13,000 | Eng., vol. 22, 1900). | |||
B.Th.U. per lb | ||||
Nixon's Naviga- | 35'5 | 13 | 0.80 | " Experi- |
tion. Calorific | 28.1 | 13.3 | 0.82 | ments on |
value, 15,560 B.Th.U. per lb | 31.7 | 13.1 | 0.81 | SteamBoil- ers," Don- kin and |
Kennedy, (Engineer- ing, Lon- don,t897) | ||||
Calorific value, 13,903 | 62.5 | II.15 | 0.77 | Adams and Pettigrew |
Calorific value, 12840 , | 80.9 | 8.86 | o66 | (Proc. Inst. C.E., vol. t25). |
For instance, an engine having a grate area of 30 sq. ft. and burning too lb of coal per square foot of grate per hour would Table Xx require that 60,000 ib of air should be drawn through the furnace per hour in order to burn the coal. This large quantity of air is forced through the furnace by means of the difference of pressure established between the external atmospheric pressure in the ash-pan and the pressure in the smoke-box.
FIG. 18. - Smoke-box, L. & N.W.R. four-coupled 6 ft. 6 in. passenger engine, scale 24.
The exhaust steam passing from the engine through the blastpipe and the chimney produces a diminution of pressure, or partial vacuum, in the smoke-box roughly proportional to the weight of steam discharged per unit of time. The difference of pressure between the outside air and the smoke-box gases may be measured by the difference of the water levels in the limbs of a U tube, one limb being in communication with the smokebox, the other with the atmosphere. The difference of levels varies from r to as much as 10 in. in extreme cases. The draught corresponding to the smallest rate of combustion shown in Table XX. in Professor Goss's experiments, was 172 in. of water, and for the highest rate, namely 181, 7.48 in. of water. To get the best effect the area of the blast-nozzle must be properly proportioned to the size of the cylinders and be properly set with regard to the base of the chimney. The best proportions are found by trial in all cases.
Figs. 18 and 19 show two smoke-boxes typical of English practice. Fig. 18 is the smoke-box of the 6 ft. 6 in. six-coupled express passenger engines designed by G. Whale for the London & North-Western Railway Company in 1904, and fig. 19 shows the box of the fourcoupled express passenger engine designed by J. Holden for the FIG. lg. - Smoke-box and Spark Arrester, G.E.R. four-coupled express engine, scale A.
Great Eastern Railway Company. In the case of the London & North-Western engine (fig. 18), the blast-pipe orifice B is placed at about the centre of the boiler barrel, and the exhaust steam is discharged straight into the trumpet-shaped end of the chimney, which is continued down inside the smoke-box. In fig. 19 the blast orifice B is set much lower, and the steam is discharged through a frustum of a cone set in the upper part of the smoke-box into the short chimney. Fig. 20 shows the standard proportions recommended - by the committee of the Railway Mas * ter Mechanics' Association on Exhaust _ Pipes and Steam Passages (Prot. Amer. Railway Master Mechanics' Assoc., Ig06).
D According to the Report, for the best results both H and h should be made as great as practicable, and then d= o21D-l-o16h, b=2d or o. 5D, P=o32D, p=o22D, L=o6D or o9D, but not of intermediate values. This last relation is, however, not well established. For much detailed information regarding American smoke-box practice, reference may be made to Locomotive Sparks, by Professor W. F. M. Goss (London, 1902). The arrangements for arresting sparks in American practice and on the continent of Europe are somewhat elaborate. In English practice where a spark-arrester is put in it usually takes the form of a wire-netting dividing the smoke-box horizontally into two parts at a level just above the top row of tubes, or arranged to form a continuous connexion between the blast-pipe and the chimney.
Fig. 19 illustrates an arrangement designed by J. Holden. The heavy sparks are projected from the tubes in straight lines and are caught by the louvres L, L, L, and by them deflected downwards to the bottom of the smoke-box, where they collect in a heap in the space D round a tube which is essentially an ejector. At every blast a small quantity of steam is caught by the orifice 0 and led to the ejectors, one on each side, with the result that the ashes are blown out into the receptacles on each side of the engine, one of which is shown at E. The louvres 1, 1, l are placed to shield the central region occupied by the blast-pipe.
As the indicated horse-power of the engine increases, the weight of steam discharged increases, and the smoke-Lox vacuum is increased, thereby causing more air to flow through the furnace and increasing the rate of combustion. 'I hus the demand for more steam is automatically responded to by the boiler. It is this close automatic interdependence cf engir e and boiler which makes the locomotive so extraordinarily w ell suited for the purpose of locomotive traction.
The steam engine of a locomotive has the general characteristics of a double-acting non-condensing engine (see Steam Engine). Distribution of steam is effected by a slide valve, sometimes fitted with a balancing device, and sometimes formed into a piston valve. All types of valves are with few exceptions operated by a link motion, generally of the Stephenson type, occasionally of the Allan type or the Gooch type, or with some form of radial gear as the Joy gear or the Walschaert gear, though the latter gear has characteristics which ally it with the link motions. The Stephenson link motion is used almost universally in England and America, but it has gradually been displaced by the Walschaert gear on the continent of Europe, and to some extent in England by the Joy gear. The general characteristics of the distribution effected by these gears are similar. Each of them, besides being a reversing gear, is an expansion gear both in forward and backward running. The lead is variable in the Stephenson link motion, whilst in the Walschaert and the Joy gears it is constant. Illustrations of these gears are given in the article Steam Engine, and the complete distribution of steam for both forward and backward running is worked out for a typical example of each of them in Valves and Valve Gear Z1 ecl.cnisms by W. E. Dalby (London, 1906).
Adhesion. - Tractive Fcrce. - A locomotive must be designed to fulfil two conditions. First, it must be able to exert a tractive force sufficient to start the train under the worst conditions possible on the railway over which it is to operate - for instance, when the train is stopped by signal on a rising gradient where the track is curved and fitted with a guard-rail. Secondly, it must be able to maintain the train at a given speed against the total resistances of the level or up a gradient of given inclination. 7 hose conditions are to a certain extent mutually antagonistic, since an engine designed to satisfy either condition independently of the other R euld Le a different engine from that designed to make the best ccmpromise between them.
Equation (3), § I expresses the fundamental condition which must be satisfied when a locomotive is starting a train. 7 he torque exerted on the driving-axle by the steam engine just at starting may be that due to the full boiler pressure acting in the cylinders, but usually the weight on the coupled wheels is hardly sufficient to enable advantage to be taken of the full boiler pressure, and it has to be throttled down by the regulator to prevent slipping. Sand, driven between the wheel and the rail by a steam jet, used just at starting, increases the adhesion beyond the normal value and enables a larger pressure to be exerted on the piston than would otherwise be possible. V hen the train is started and is moving slowly, the toroue acting on the driving-axle may be estimated as that due to about 85°/, of the full boiler pressure acting in the cylinders. The torque;?i H ti l ' --- L-- - -Tt FIG. 20. - Smoke-box, American Railway Master Mechanics' Association.
due to the two cylinders is variable to a greater or less extent, depending upon the degree of expansion in the cylinders and the speed. The form of the torque curve, or crank effort curve, as it is sometimes called, is discussed in the article Steam Engine, and the torque curve corresponding to actual indicator diagrams taken from an express passenger engine travelling at a speed of 65 m. per hour is given in The Balancing of Engines by W. E. Dalby (London, 1906).
The plotting of the torque curve is laborious, but the average torque acting, which is all that is required for the purposes of this article, can be found quite simply, thus: - Let p be the mean effective pressure acting in one cylinder, a, the area of the cylinder, and 1, the stroke. Then the work done during one revolution of the crank is 2pla per cylinder. Assuming that the mean pressure in the other cylinder is also p, the total work done per revolution is 4pla. If T is the mean torque, the work done on the crank-axle per revolution is 27rT. Hence assuming the mechanical efficiency of the engine to be and substituting ! d 2 for the area a, 4 27-T = 4 plae = plird2e, so that T = z pd2le. But from § I, T=2DF; therefore F = pd 2 lE/D (25) F in this expression is twice the average magnitude of the equal and opposite forces constituting the couple for one driving-wheel illustrated in fig. 16, one force of which acts to propel the train whilst the other is the value of the tangential frictional resistance between the wheel and the rail. This force F must not exceed the value. V or slipping will take place. Hence, if p is the maximum value of the mean effective pressure corresponding to about 85% of the boiler pressure, ,uW = pd 2 le /D (26) is an expression giving a relation between the total weight on the coupled wheels, their diameters and the size of the cylinder. The magnitude of F when p and e are put each equal to unity, is usually called the tractive force of the locomotive per pound of mean effective pressure in the cylinders. If p is the mean pressure at any speed the total tractive force which the engine is exerting is given by equation (25) above. The value of is variable, but is between 7 and 8, and for approximate calculations may be taken equal to unity. In the following examples the value will be assumed unity.
These relations may be illustrated by an example. Let an engine have two cylinders each 19 in. diameter and 26 in. stroke. Let the boiler pressure be 175 lb per square inch. Taking 85% of this, the maximum mean effective pressure would be 149 lb per square inch. Further, let the diameter of the driving-wheels be 6 ft. 3 in. Then the tractive force is, from (25), (149 X 19 2 X2.166)/6.25 =18,600lb =8.3 tons.
Assuming that the frictional resistance at the rails is given by the weight on the wheels, the total weight on the driving-wheels necessary to secure sufficient adhesion to prevent slipping must be at least 8.3 X5 =41.5 tons. This would be distributed between three coupled axles giving an average of 1.38 tons per axle, though the distribution might not in practice be uniform, a larger proportion of the weight falling on the driving-axle. If the starting resistance of the whole train be estimated at 16 lb per ton, this engine would be able to start 1.163 tons on the level, or about 400 tons on a gradient of I in 75, both these figures including the weight of the engine and tender, which would be about 100 tons.
The engine can only exert this large tractive force so long as the mean pressure is maintained at 149 lb per square inch. This high mean pressure cannot be maintained for long, because as the speed increases the demand for steam per unit of time increases, so that cut-off must take place earlier and earlier in the stroke, the limiting steady speed being attained when the rate at which steam is supplied to the cylinders is adjusted by the cut-off to be equal to the maximum rate at which the boiler can produce steam, which depends upon the maximum rate at which coal can be burnt per square foot of grate. If C is the number of pounds of coal burnt per square foot of grate per hour, the calorific value of which is c B.Th.U. per pound, the maximum indicated horse-power is given by the expression I.H.P. maximum - CcA X778 1980000 where A is the area of the grate in square feet, and is the combined efficiency of the engine and boiler. With the data of the previous example, and assuming in addition that the grate area is 24 sq. ft., that the rate of combustion is 150 lb of coal per square foot of grate per hour, that the calorific value is 14000, and finally that n =0.06, the maximum indicated horse-power which the engine might be expected to develop would be o06 X 150 x14000 X24 X 778/1980000 = I 190, corresponding to a mean effective pressure in the cylinders of 59.5 lb per square inch.
Assuming that the train is required to run at a speed of 60 m. per hour, that is 88 ft. per second, the total resistance R, which the engine can overcome at this s p eed, is by equation (10) R=(1190X550)/88=7.400 lb.
Thus although at a slow speed the engine can exert a tractive force of 18,600 lb, at 60 m. per hour, the tractive force falls to 7400 lb, and this cannot be increased except by increasing the rate of combustion (neglecting any small changes due to a change in the efficiency 7 Knowing the magnitude of R, the draw-bar pull, and hence the weight of vehicle the engine can haul at this speed, can be estimated if the resistances are known. Using the curves of fig. 17 it will be found that at 60 m. per hour the resistance of the engine and tender is 33 lb per ton, and the resistance of a train of bogie coaches about 14 lb per ton. Hence if W is the weight of the vehicles in tons, and the weight of the engine and tender be taken at too tons, the value of W can be found from the equation 1 4 W +33 00= 744 0, from which W =296 tons. This is the load which the engine would take in ordinary weather. With exceptionally bad weather the load would have to be reduced or two engines would have to be employed, or an exceptionally high rate of combustion would have to be maintained in the fire-box.
It will be seen at once that with a tractive force of 7400 lb a weight of 37,000 lb (=16.5 tons) would be enough to secure sufficient adhesion, and this could be easily carried on one axle. Hence for a level road the above load could be hauled at 60 m. per hour with a " single " engine. When the road leads the train up an incline, however, the tractive force must be increased, so that the need for coupled wheels soon arises if the road is at all a heavy one.
§15. Engine Efficiency. Combined Engine and Boiler Efficiency. - The combined engine and boiler efficiency has hitherto been taken to be o06; actual values of the boiler efficiencies are given in Table XX. Engine efficiency depends upon many variable factors, such as the cut-off, the piston speed, the initial temperature of the steam, the final temperature of the steam, the quality of the steam, the sizes of the steam-pipes, ports and passages, the arrangement of the cylinders and its effect on condensation, the mechanical perfection of the steam-distributing gear, the tightness of the piston, &c. A few values of the thermal efficiency obtained from experiments are given in Table XXI. in the second column, the first column being added to give some idea of the rate at which the engine was working when the data from which the efficiency has been deduced were observed. The corresponding boiler efficiencies are given in the third column of the table, when they are known, and the combined efficiencies in the fourth column. The figures in this column indicate that o06 is a good average value to work with.
0 | ||||||
Indi- | Engine | Boiler | Corn- | Boiler | ||
- 5 | Effici- | Effici- | bined | Pressure | ||
c.> ri | horse- | Effici- | lb per | |||
C '+ 4 atz 0 | power. | ency. | ency. | ency. | sq. in. | |
---|---|---|---|---|---|---|
128 | 0.073 | Mean | Deduced from | |||
w | 205 | 0.075 | about | data given by | ||
° L.' | 222 | 0.080 | 128 but | Professor Goss | ||
o a) | 399 | 0.088 | throttled. | (Trans. Am. Mech. | ||
H ---.-- | mean | Eng. vol. 14). | ||||
I | 129 | 0.057 | 0.815 | 0.047 | mean about | Deduced from Kennedy and |
120 | Donkin's trials | |||||
(Engineering, London, 1887). | ||||||
2 | 490 | 0.098 | 0.775 | 0.077 | 167 | Deduced from |
3 | 582 | 0.11 | 0.665 | 0.073 | 169 | Adams and |
Pettigrew's trials (Proc. | ||||||
Inst. C.E. vol. | ||||||
125). | ||||||
4 | 520 | 0.084 | 0.52 | 0.044 | 140 | Deduced from |
5 | 692 | 0.083 | o65 | 0.054 | 175 | Smith's experi- |
6 | 558 | 0.074 | 0.69 | 0.051 | 175 | ments (Proc. |
7 | 603 | o. 086 | o63 | 0.054 | 175 | Inst. Mech. |
8 | 570 | o08 i | o64 | 0.052 | 160 | Eng. October |
1898) . |
[LOCOMOTIVE PO W ER |
Table Xxi It is instructive to inquire into the limiting efficiency of an engine consistent with the conditions under which it is working, because in no case can the efficiency of a steam-engine exceed a certain value which depends upon the temperatures at which it receives and rejects heat. Thus a standard of comparison for every individual engine may be obtained with which to compare its actual performance. The standard of comparison generally adopted for this purpose is obtained by calculating the efficiency of an engine working according to the Rankine cycle. That is to say, expansion is adiabatic and is continued down to the back pressure which in a non-condensing engine is 14.7 lb per square inch, since any back pressure above this amount is an imperfection which belongs to the actual engine. The back pressure is supposed to be uniform, and there is no compression.
Fig. 21 shows the pressure-volume diagram of the Rankine cycle for one pound of steam where the initial pressure is 175 lb per square inch by the 19t, gauge, equivalent to 190 lb per square inch absolute. In no case could an engine receiving steam at the tem perature corresponding to this pressure and rejecting heat at 212° F. convert more heat into work than is represented by the area of this diagram. The area of the diagram may be measured, but it is usually more convenient to calculate the number of B.Th.U. which the area represents from the following formula, which is expressed in terms of the absolute temperature T, of the steam at the steam-pipe, and the temperature T2= 461°H-212° =673° absolute corresponding to the back pressure: - Maximu per pound oflsteaelwork =U=(T - T) (i -f -Lr--.1) - T2loge.Tr--2.
With the initial pressure of 190 11; per square inch absolute it will be found from a steam table that T =838° absolute. Using this and the temperature 673° in the expression, it will be found that U =185 B.Th.U. per pound of steam. If h is the water heat at the lower temperature, h l the water heat at the higher temperature, and L the latent heat at the higher temperature, the heat supply per pound of steam is equal to h1 - h2+L1, which, from the steam tables, with the values of the temperatures given, is equal to 1013 B.Th.U. per pound. The thermal efficiency is therefore 185/1013 =0.183.
That is to say, a perfect engine working between the limits of temperature assigned would convert only 18% of the total heat supply into work. This would be an ideal performance for an engine receiving steam at 190 lb initial pressure absolute, and rejecting steam at the back pressure assumed above, and could never be attained in practice. When the initial pressure is 100 lb per square inch by the gauge the thermal efficiency drops to about nearly 15% with the same back pressure. The way the thermal efficiency of the ideal engine increases with the pressure is exhibited in fig. 22 by the curve AB. The curve was drawn by calculating the thermal efficiency from the above expression for various values of the initial temperature, keeping the final temperature constant at 673°, and then plotting these efficiencies against the corresponding values of the gauge pressures.
The actual thermal efficiencies observed in some of the cases cited in Table XXI. are plotted on the diagram, the reference numbers on which refer to the first column in the table. Thus the Fio. 22. - Engine Efficiency Curves.
cross marked 3 in fig. 22 represents the thermal efficiency actually obtained in one of Adams and Pettigrew's experiments, namely, 0-I I, the pressure in the steam-pipe being 167 lb per square inch. From the diagram it will be seen that the corresponding efficiency of the ideal engine is about 0.18. The efficiency ratio is therefore o11 /o. 18 =0.61. That is to say, the engine actually utilized 61% of the energy which it was possible to utilize by means of a perfect engine working with the same initial pressure against a back pressure equal to;the atmosphere. Lines representing efficiency ratios of o6, 0.5 and 0.4 are plotted on the diagram, so that the efficiency ratios corresponding to the various experiments plotted may be readily read off. The initial temperature of the standard engine of comparison must be the temperature of the steam taken in the steam-pipe. For further information regarding the standard engine of comparison see the article Steam Engine and also the " Report of the Committee on the Thermal Efficiency of Steam Engines," Proc. Inst. C.E. (1898).
The expression for the indicated horse-power may be written I.H.P. =pay/550 (27) where v is the average piston speed in feet per second. For a stated value of the boiler pressure and the cut-off the mean pressure p is a function of the piston speed v. For the few cases where data are available - data, however, belonging to engines representing standard practice in their construction and in the design of cylinders and steam ports and passages - the law connecting p and v is approximately linear and of the form p=c - bv (28) where b and c are constants. (See W. E. Dalby, " The Economical Working of Locomotives," Proc. Inst. C.E., 1905-6, vol. 164.) Substituting this value of p in (27) I.H.P. _ (c av (29) 550 the form of which indicates that there is a certain piston speed for which the I.H.P. is a maximum. In a particular case where the boiler pressure was maintained constant at 130 lb per square inch, and the cut-off was approximately 20% of the stroke, the values c =55 and b=o031 were deduced, from which it will be found that the value of the piston speed corresponding to the maximum horsepower is 887 ft. per minute. The data from which this result is deduced will be found in Professor Goss's paper quoted above in Table XXI. The point is further illustrated by some curves published in the American Engineer (June 1901) by G. R. Henderson recording the tests of a freight locomotive made on the Chicago & North-Western railway. Any modification of the design which will reduce the resistance to the flow of steam through the steam passages at high speeds will increase the piston speed for which the indicated horse-power is a maximum.
The thermal efficiency of a steam-engine is in general increased by carrying out the expansion of the steam in two, three or even more stages in separate cylinders, notwithstanding the inevitable drop of pressure which must occur when the steam is transferred from one cylinder to the other during the process of expansion. Compound working permits of a greater range of expansion than is possible with a simple engine, and incidentally there is less range of pressure per cylinder, so that the pressures and temperatures per cylinder have not such a wide range of variation. In compound working the combined volumes of the low-pressure cylinders is a measure of the power of the engine, since this represents the final volume of the steam used per stroke. The volume of the high-pressure cylinder may be varied within wide limits for the same low-pressure volume; the proportions adopted should, however, be such that there is an absence of excessive drop between them as the steam is transferred from one to the other. Compound locomotives have been built by various designers, but opinion is still uncertain whether any commercial economy is obtained by their use. The varying load against which a locomotive works, and the fact that a locomotive is non-condensing, are factors which reduce the margin of possible economy within narrow limits. Coal-saving can be shown to the extent of about 1% in some cases, but the saving depends upon the kind of service on which the engine is employed. The first true compound locomotive was constructed in 1876 from designs by A. M. Mallet, at the Creusot works in Bayonne. The first true compound locomotive in England was constructed at Crewe works in 1878 by F. W. Webb. It was of the same type as Mallet's engine, and was made by simply bushing one cylinder of an ordinary two-cylinder simple engine, the bushed cylinder being the high-pressure and the other cylinder the low-pressure cylinder. Webb evolved the type of threec y linder compound with which his name is associated in 1882.
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FIG. 21. |
LOCOMOTIVE POWER] |
020 610 3 30 140 150 160 170 180 190 200 210 220 230 240 250 260 Area is Equivalent to 185 8. Thar equal to 148930 foot pounds 4 2.37 cubic feet. Indicator diagram corresponding to 1 lb. of steam for the Rankine Engine of Comparison when is 190 lbs sq. inch absolute, and exhaust pressis lbs sq. inch absolute There were two high-pressure cylinders placed outside the frames and driving on a trailing wheel, and one low-pressure cylinder placed between the frames and driving on a wheel placed in front of the driving-wheel belonging to the highpressure cylinders. The steam connexions were such that the two high-pressure cylinders were placed in parallel, both exhausting into the one low-pressure cylinder. The first engines of this class were provided with high-pressure cylinders, i i in. diameter and 24 in. stroke, a low-pressure cylinder 26 in. diameter, 24 in. stroke, and driving-wheels 6 ft. 6 in. diameter; but subsequently these dimensions were varied. There were no coupling rods. A complete account of Webb's engines will befound in a paper, " The Compound Principle applied to Locomotives," by E. Worthington, Proc. Inst. C.E., 1889, vol. xcvi. Locomotives have to start with the full load on the engine, consequently an outstanding feature of every compound locomotive is the apparatus or mechanism added to enable the engine to start readily. Generally steam from the boiler is admitted direct to the low-pressure cylinder through a reducing valve, and valves and devices are used to prevent the steam so admitted acting as a back pressure on the high-pressure cylinder. In the Webb compound the driver opened communication from the high-pressure exhaust pipe to the blast-pipe, and at the same time opened a valve giving a supply of steam from the boiler direct to the lowpressure valve chest. T. W. Worsdell developed the design of the two-cylinder compound in England and built several, first for the Great Eastern railway and subsequently for the North-Eastern railway. The engines were built on the Worsdell and Von Borries plan, and were fitted with an ingenious startingvalve of an automatic character to overcome the difficulties of starting. Several compounds of a type introduced by W. M. Smith on the North-Eastern railway in 1898 have been built by the Midland railway. In these there are two lowpressure cylinders placed outside the frame, and one highpressure cylinder placed between the frames. All cylinders drive on one crank-axle with three cranks at 120°. The drivingwheels are coupled to a pair of trailing wheels. A controlling valve enables the supply of steam to the low-pressure cylinders to be supplemented by boiler steam at a reduced pressure. For a description and illustrations of the details of the starting devices used in the Webb, Worsdell and Smith compounds, see an article, " The Development of the Compound Locomotive in England," by W. E. Dalby in the Engineering Magazine for September and October 1904. A famous type of compound locomotive developed on the continent of Europe is the four-cylinder De Glehn, some of which have been tried on the Great Western railway. There are two high-pressure cylinders placed outside the frame, and two low-pressure placed inside the frames. The low-pressure cylinders drive on the leading crank-axle with cranks at right angles, the highpressure cylinders driving on the trailing wheels. The wheels are coupled, but the feature of the engine is that the couplingrods act merely to keep the high-pressure and low-pressure engines in phase with one another, very little demand being made upon them to transmit force except when one of the wheels begins to slip. In this arrangement the whole of the adhesive weight of the engine is used in the best possible manner, and the driving of the train is practically equally divided between two axles. The engine can be worked as a four-cylinder simple at the will of the driver. S. M. Vauclain introduced a successful type of four-cylinder compound in America in 1889. A highand low-pressure cylinder are cast together, and the piston-rods belonging to them are both coupled to one cross-head which is connected to the driving-wheels, these again being coupled to other wheels in the usual way. The distribution of steam to both cylinders is effected by one piston-valve operated by a link motion, so that there is considerable mechanical simplicity in the arrangement. Later Vauclain introduced the " balanced compound." In this engine the two piston-rods of one side are not coupled to a common cross-head, but drive on separate cranks at an angle of 180°, the pair of 180° cranks on each side being placed at right angles.
The unbalanced masses of a locomotive may be divided into two parts, namely, masses which revolve, as the crank-pins, the crank-cheeks, the couplingrods, &c.; and masses which reciprocate, made up of the piston, piston-rod, cross-head and a certain proportion of the connecting-rod. The revolving masses are truly balanced by balance weights placed between ' the spokes of the wheels, or sometimes by prolonging the crank-webs and forming the prolongation into balance weights. It is also the custom to balance a proportion of the reciprocating masses by balance weights placed between the spokes of the wheels, and the actual balance weight seen in a driving-wheel is the resultant of the separate weights required for the balancing of the revolving parts and the reciprocating parts. The component of a balance weight which is necessary to balance the reciprocating masses introduces a vertical unbalanced force which appears as a variation of pressure between the wheel and the rail, technically called the hammer-blow, the magnitude of which increases as the square of the speed of the train. In consequence of this action the compromise is usually followed of balancing only 3 of the reciprocating masses, thus keeping the hammer-blow within proper limits, and allowing 3 of the reciprocating masses to be unbalanced in the horizontal direction. It is not possible to do anything better with two-cylinder locomotives unless bobweights be added, but with four-cylinder four-crank engines complete balance is possible both in the vertical and in the horizontal directions. When the four cranks are placed with two pairs at 180°, the pairs being at 90°, the forces are balanced without the introduction of a hammer-blow, but there remain large unbalanced couples, which if balanced by means of revolving weights in the wheels again reintroduce the hammerblow, and if left unbalanced tend to make the engine oscillate in a horizontal plane at high speed. The principles by means of which the magnitude and position of balance weights are worked out are given in the article Mechanics (Applied Mechanics), and the whole subject of locomotive balancing is exhaustively treated with numerous numerical examples in The Balancing of Engines by W. E. Dalby, London, 1906.
Locomotives may be classified primarily into " tender engines " and " tank engines," the water and fuel in the latter being carried on the engine proper, while in the former they are carried in a separate vehicle. A tender is generally mounted on six wheels, or in some cases on two bogies, and carries a larger supply of water and fuel than can be carried by tanks and the bunker of a tank engine. A tender, however, is so much dead-weight to be hauled, whilst the weight of the water and fuel in a tank engine contributes largely to the production of adhesion. A classification may also be made, according to the work for which engines are designed, into passenger engines, goods engines, and shunting or switching engines. A convenient way of describing any type of engine is by means of numerals indicating the number of wheels - (I) in the group of wheels supporting the leading or chimney end, (2) in the group of coupled wheels, and (3) in the group supporting the trailing end of the engine. In the case where either the leading or trailing group of small wheels is absent the numeral o must be used in the series of three numbers used in the description. Thus 4-4-2 represents a bogie engine with four-coupled wheels and one pair of trailing wheels, the wellknown Atlantic type; 4-2-2 represents a bogie engine with a single pair of driving-wheels and a pair of trailing wheels; 0-4-4 represents an engine with four-coupled wheels and a trailing bogie, and 4-4-o an engine with four-coupled wheels and a leading bogie. A general description of the chief peculiarities of various kinds of locomotives is given in the following analysis of types: (I) " Single-driver " type, 4-2-2 or 2-2-2. Still used by several railways in Great Britain for express passenger service, but going out of favour; it is also found in France, and less often in Germany, Italy, and elsewhere in Europe. It is generally designed as a 4-2-2 engine, but some old types are still running with only three axles, the 2-2-2. It is adapted for light, high-speed service, and noted for its simplicity, excellent riding qualities, low cost of maintenance, and high mechanical efficiency; but having limited adhesive weight it is unsuitable for starting and accelerating heavy trains.
(2) " Four-coupled " type, 4-4-0, with leading bogie truck. For many years this was practically the only one used in America for all traffic, and it is often spoken of as the " American " type. In America it is still the standard engine for passenger traffic, but for goods service it is now employed only on branch lines. It has been extensively introduced, both in Great Britain and the continent of Europe, for passenger traffic, and is now the most numerous and popular class. It is a safe, steady-running and trustworthy engine, with excellent distribution of weight, and it is susceptible of a wide range of adaptability in power requirements.
(3) " Four-coupled " three-axle type, 2-4-0. Used to some extent in France and Germany and considerably in England for passenger traffic of moderate weight. Engines of this class, with 78-inch driving wheels and the leading axle fitted with Webb's radial axle-box, for many years did excellent work on the London & North-Western railway. The famous engine " Charles Dickens " was one of this class. Built in 1882, it had by the 12th of September 1891 performed the feat of running a million miles in 9 years 219 days, and it completed two million miles on the 5th of August 1902, having by that date run 5312 trips with express trains between London and Manchester.
(4) " Four-coupled " three-axle type, with trailing axle, 0-4-2. Used on several English lines for fast passenger traffic, and also on many European railways. The advantages claimed for it are: short coupling-rods, large and unlimited fire-box carried by a trailing axle, compactness, and great power for a given weight. Its critics, however, accuse it of lack of stability, and assert that the use of large leading wheels as drivers results in rigidity and produces destructive strains on the machinery and permanent way.
(5) " Four-coupled " type, with a leading bogie truck and a trailing axle, 4-4-2. It is used to a limited extent both in England and on the continent of Europe, and is rapidly increasing in favour in the United States, where it originated and is known as the " Atlantic " type. It has many advantages for heavy high-speed service, namely, large and well-proportioned boiler, practically unlimited grate area, fire-box of favourable proportions for firing, fairly low centre of gravity, short coupling-rods, and, finally, a combination of the safe and smooth riding qualities of the fourcoupled bogie type, with great steaming capacity and moderate axle loads. Occasionally a somewhat similar type is designed with the bogie under the fire-box and a single leading axle forward under the smoke-box - an arrangement in favour for suburban tank engines. In still rarer cases both a leading and a trailing bogie have been fitted.
(6) " Six-coupled " with bogie, or " Ten-wheel " type, 4-6-0. A powerful engine for heavy passenger and fast goods service. It is used to a limited extent both in Great Britain and on the continent of Europe, but is much more common in America. The design combines ample boiler capacity with large adhesive weight and moderate axle loads, but except on heavy gradients or for unusually large trains requiring engines of great adhesion, passenger traffic can be more efficiently and economically handled by four-coupled locomotives of the eight-wheel or Atlantic types.
(7) " Six-coupled " total-adhesion type (all the weight carried on the drivers), o-6-o. This is the standard goods engine of Great Britain and the continent of Europe. In America the type is used only for shunting. It is a simple design of moderate boiler power.
(8) " Six-coupled " type, with a leading axle, 2-6-0. This is of American origin, and is there known as the " Mogul." It is used largely in America for goods traffic. In Europe it is in considerable favour for goods andpassenger traffic on heavy gradients. The type is, however, less in favour than either the ten-wheel or the eight-coupled " Consolidation " for freight traffic.
(9) " Eight-coupled " total-adhesion type, o-8-o; now found on a good many English railways, and common on the continent of Europe for heavy slow goods traffic. In America it is comparatively infrequent, as total-adhesion types are not in favour.
(io) " Eight-coupled " type, with a leading axle, 2-8-0. This originated in America, where it is termed the " Consolidation." In the United States it is the standard heavy slow-speed freight engine, and has been built of enormous size and weight. The type has been introduced in Europe, especially in Germany, where the advantages of a partial-adhesion type in increased stability and a larger boiler are becoming appreciated. Occasionally the American eight-coupled type has a bogie instead of a single leading axle (4-8-0), and is then termed a " Twelve-wheeler," or " Mastodon." (11) " Ten-coupled " type, with a leading axle, 2-10-0. This originated in America, where it is known as the " Decapod." It is used to a limited extent for mountain-grade goods traffic, and has the advantage over the " Consolidation " or eight-coupled type of lighter axle loads for a given tractive capacity.
In addition to the foregoing list, various special locomotive types have been developed for suburban service, where high rates of acceleration and frequent stops are required. These are generally tank engines, carrying their fuel and water on the engine proper.
Their boilers are of relatively large proportions for the train weight and average speed, and the driving wheels of small diameter, a large proportion of their total weight being " adhesive." Other special types are in limited use for " rack-railways," and operate either by engagement of gearing on the locomotive into a rack between the track rails, or by a combination of this and rail adhesion.
§ 20. Current Developments. - The demand of the present day is for engines of larger power both for passenger and goods service, and the problem is to design such engines within the limitations fixed by the 4 ft. 82 in. gauge and the dimensions of the existing tunnels, arches, and other permanent works. The American engineer is more fortunately situated than his English brother with regard to the possibility of a solution, as will be seen from the comparative diagrams of construction gauges, figs. 23, 24, 25, 26. Fig. 23 shows the construction L.& N.W. Ry. FIGS. 23-26.
gauge for the London & North-Western railway, fig. 24 that for the Great Western' railway, fig. 25 that for the Great Eastern railway, whilst fig. 26 gives a general idea of the American gauge in a particular case, generally typical, however, of the American limits. In consequence of this increasing demand for power, higher boiler pressures are being used, in some cases 225 lb per sq. in. for a simple two-cylinder engine, and cylinder volume is slightly increased with the necessary accompaniment of heavier loads on the coupled wheels to give the necessary adhesion. Both load and speed have increased so much in connexion with passenger trains that it is necessary to divide the weight required for adhesion between three-coupled axles, and the type of engine gradually coming into use in England for heavy express traffic is a six-coupled engine with a leading bogie, with wheels which would have been considered small a few years ago for the speed at which the engine runs. The same remarks apply to goods engines. There is a general increase in cylinder power, boiler pressure and weight, and in consequence in the number of coupled axles. Not only are the load and speed increasing, but the distances run without a stop are increasing also, and to avoid increasing the size of the tenders, water-troughs, first instituted by J. Ramsbottom on the London & North-Western railway in 1859, have been laid in the tracks of the leading main lines of Great Britain. For local services where stoppages are frequent the demand is for engines capable of quickly ' At the beginning of 1908 the Great Western's loading gauge on its main lines was widened to 9 ft. 8 in. from a height of 5 ft. above rail level.
ROLLING STOCK] |
Cylinders. | Diam | Weight(Ton= 2240 lb). | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
of | Grate | Total | ||||||||||
No | Type. | Driving. | Total | Total | Area . | Heating | ||||||
Position. | Diam. | Stroke. | Wheels. | of Engine. Engi | on Coupled Wheels. | Total with Tender. | Surface. | |||||
In | In. | In. | Tons. | Tons. | Tons. | Sq. Ft. | Sq. Ft. | |||||
" Rocket " (Liverpool & Z | 6 | 2 In Victoria and Albert Museum,South | ||||||||||
Manchester).. j | 0-2-2 | Outside | 8 | 1 61 | 561 | 4'25 | 7 45 | 137.75 | Kensington. | |||
I | Caledonian.. . | 4-4-0 | Inside | Ig | 26 | 78 | 51'70 | 34'65 | 96'7 | 23 | 1600 | "Dunalastair III." (goo) class. Fittedfire-box |
2 | London & South-Western | 4-4- o | Inside | 18' | 26 | 79 | 8'8 4 5 | 3345 | 930 | 24 4 | 1500 ? | face. giving 165 sq. ft. of heating surface. giving 165 sq. ft. of heating |
3 | Midland. . | 4-4 - o | Inside | 19 | 26 | 782 | 58'5 | 38'75 | 10 44 | 28'4 | 1557 | S Belpaire fire-box. Pressure 220 IB per in. |
4 | Great Western.. . | 4 - 6 - o | Outside | IS | 30 | 805 | 72 | 54'8 | 112 | 27 | 2000 ' | I Fitted with superheater contributin 360 sq. ft. of heating surface to the total. Boiler pressure 20otb pr sq.in. |
S Fired with Holden's system of liquid | ||||||||||||
5 | Great Eastern.. . | 4-4-0 | Inside | 19 | 26 | 84 | 50'3 | 3320 | 85'35 | 21'3 | 1630 | 5 fuel. |
6 | London & North-Western | 4-6-o | Inside | 19.1 ' | 26 | 75 | 65-75 | 6' 4 75 | Ioz'^ r 5 | 25 5 | 1 o 99 | 1 Experiment class. Boiler pressure 1 185 lb per sq. in. |
14-cylinder simple. Fitted with super- | ||||||||||||
7 | Great Western | 4- 6 0 | 2 inside t 2 outside 1 | 14{ | 26 | 80, | 75 6 | 55'4 | 115 6 | 27 | 2076 | heater contributing 269 sq. ft. of ) heating surface to the total. Boiler l pressure 225 lb per sq. in. |
inside | + 4-cylinder simple. Working pressure | |||||||||||
8 | London & South-Western . | 4- | . 2 Z 2 outside S | r6 | 24 | 72 | 73 | 51'5 | 31.5 | 2727 | , c ro ss -t u b es i n fi re-box. Fitted cross-tubes | |
q | Lancashire & Yorkshire . | 4-4-2 | Inside | 19 | 26 | 87 | 58'75 | 35'0 | 89.4, | 26'05 | 2052 | Belpaire fire-box. |
Io | Great Northern.. . | 4-4-2 | Outside | 19 | 24 | 78 | 58 | 31 | 99 | 26"75 | 1 44 2 | 990 class. |
I I | North-Eastern. . | 4-4-2 | 220 uts d | 146 | 26 | 85 | 73.6 | 39'15 | 116'2 | 2g | 196q | .. |
12 | Highland.. . | 4-6-0 | Outside | 191 | 26 | 69 | 58'85 | 43'85 | 96'95 | 26 | 2050 | Steam pressure 200 Tt, per sq. in. |
1 3 | Midland | 4_4_0 | 2 L.-P. outside i H.-P. inside | 21 19 | 26 2 26 S | 84 | 59'8 | 39'1 | 102'7 | 28'4 | 1458 | S 3-cylinder compound. Working pres- Z sure 220 lb per sq. in. |
Midland | o-6-o | Inside | ,81 | 26 | 63 | 43.8 | 43'8 | 8495 | 21'1 | 1512 | 175 per sq. in. | |
15 16 | . North-Eastern Caledonian | o-6-o 4-6-o | Inside Outside | 182 19 | 26 26 | 55 60 | 34.4 60'4 | 34'4 45'9 | 82'05 98'4 | 20'0 21 | 1658 20,8 | .. Pressure 175 lb per sq. in. |
17 | Lancashire & Yorkshire | o-8-o | Inside | 20 | 26 | 54 | 5378 | 5378 | 8445 | 2605 | 2038 | |
,8 | . Great Western | 4 4-2 | 2 H.-P. outside 2 L.-P. inside | 14'2 23'6 | 25'2 | 80'5 | 73'8 | 38'5 | 108'9 | 33'3 | 2755 | S De Glehn compound. Boiler pressure 227 per sq. i n. |
Chicago & Alton | 4-4-2 | Outside | 20 | 28 | 80 | 82'8 | 43.7 | 155 | 33'5 | 2696 | Balanced piston valves. | |
20 | Atchison, Topeka | outside | ?5 | 26 | 79 | 86'5 '5 | 3 45 | 160 | 49'5 | 3215 | S 4-cylinder balanced compound. | |
Sante F4.. .) | 4 4 2 | 1 2 inside | 15 | 26 S | Vauclain type. Balanced valve. | |||||||
21 | Central of Georgia. . | 4-6-2 | Outside | 20 | 28 | 68 | 84'0 | 50'7 | 150 | 46 8 | 3357 | |
22 | P.nnsylvania | 2- 6-o | Outside | 20 | 28 | 62 | 71'43 | 62'09 | 125 | 30'2 | 2431.3 | |
23 | Chicago, Rock Island & ! | Outside | 23 | 30 | 63 | 88'8 | 79'2 | 147 | 49'7 | 2912 | ||
Pacific. S | 2--0 | |||||||||||
2 4 | Atchison, Topeka & | S Outside | 39 | 32 } | 57 | 128'4 | 104.5 | 201 | 58'5 | 4796 | Tandem compound. | |
25 | Sante Fe S Great Northern, U.S.A. | 2 _ IO 2 2 - 6 - 6 - 2 | Outside (Outside Outsi de | 33 158'5 | 32 S | 14, | 22 5 | 78 | 5658 | Driving-wheels divided into two groups of six-coupled wheels. Leading group driven by L.-P. cylinders, trailing group by 11.-P. cylinders. Mallet type. | ||
26 | Erie Railroad | 0-8-8-o | S Outside Outside | ?5 39 | 28 28 | 51 | 183 | 183 | .. | 6108 | Mallet type. | |
27 23 | Argentine Great Western Belgian State. . | 2 - 10--o 2-6-0 | Outside 2 outside Z 2 inside S | 17) | 28 24 | 51 78 | 79'5 82'0 | 70' 8 52'0 | 124'17 .. | 36 3 2'4 | 2440 1672 | 5 ft. 6 in. gauge. 4 cylinder simple expansion. Pres- sure 205 lb per sq. in. |
13.4 | 2 5 2 | 66'2 | 32 5 | 107'3 | x9'7 | 23 60 | Serve tubes. Boiler pressure 235 lb | |||||
29 30 | Nord Est | 4 4 4 - 6 | 2 2 0 i ut s ide nside 2 H.-P. outside 2 L.-P. inside | z2 13,78 ? 21:',5t | 25'2 | 70 | 62'4 | 48'7 | 27'6 | 2155 | r sq. n. Serve tubes. | |
31 | Austro-Hungarian State . | 2-10-0 | S 2 H -P. inside 2 L.-P. outside | ?4 5 1 2480 S | 2 8' 34 | 57 | 77 2 | 6 7'4 | 49.5 | 2 777 | S Fitted with superheater contributing 678 ft. to the total. Articulated tank engine on two motor | |
32 | Nord. ... . | 6- 2-2- 6 | 2 outside 2 outside | 1575 Z 24 8 S | 26 8 | 57.2 | 71 | 32'3 | 2660 | bogies mounted on a central girder, splayed at ends to take buffer beams. H.-P. cylinders drive one bogie, L.-P. the other. | ||
33 | P aris, Orleans | 4 6 - 0 | 2 outside -' 2 inside | 14.17 Z 23'62 | 2 I 9 5 | 73 | 72 6 | 53 | 1095 | 3 3'37 | 2577 | S Serve tubes. Boiler pressure 2 35 lb per sq. in. |
2 H.-P. on one Z | ||||||||||||
34 | I talian State | 6 -o 4 | side | 14 17 | z 62 3 | 75 6 | 69.5 9.5 | 4 z'6 | z'2 3 9 | 221 7 | S Serve tubes. Boiler pressure 220 lb -. er i | |
2 L.-P. on other | 23'22 | |||||||||||
35 | Austrian State.. . | 2-6-2 | ` 2 H.-P. inside outside H.P. outside | 14'56 ?5- 24'80 S | 28.34 | 71'5 | 63'9 | 42'9 | 107'9 | 43.0 | 2775 | Boiler pressure 220 tb per sq. in. Lentz double-beat equilibrium valves. |
36 3 | Prussian State . | 4-4-2 4-4 | t 2 L.-P. i ns e | 14'17 22'04 j | 2 6z 3 | 61'0 | z 9.9 | Io 9 | z 9 | 52 | Serve tubes. Boiler pressure 205 p 205 lb per sq. in |
G.WI. Ry. Table Xxii. - Comparative Data Of Locomotives accelerating the train to the journey speed. The nature of this problem is illustrated by the numerical example in § g. When the service is frequent enough to give a good power factor continuously, the steam locomotive cannot compete with the electric motor for the purpose of quick acceleration, because the motors applied to the axles of a train may for a short time absorb power from the central station to an extent far in excess of anything which a locomotive boiler can supply.
With regard to the working of the locomotive, J. Holden developed the use of liquid fuel on the Great Eastern railway to a point beyond the experimental stage, and used it instead of coal with the engines running the heavy express traffic of the line, its continued use depending merely upon the relative market price of coal and oil. Compound locomotives have been tried, as stated in § 17, but the tendency in England is to revert to the simple engine for all classes of work, though on the continent of Europe and in America the compound locomotive is largely adopted, and is doing excellent work. A current development is the application of superheaters to locomotives, and the results obtained with them are exceedingly promising.
The leading dimensions of a few locomotives typical of English, American and European practice are given in Table Xxii. (W. E. D.) Rolling Stock The rolling stock of a railway comprises those vehicles by means of which it effects the transportation of persons and things over its lines. It may be divided into two classes, according as it is intended for passenger or for goods traffic.
In the United Kingdom, as in Europe generally, the vehicles used on passenger trains include firstclass carriages, second-class carriages, third-class carriages, composite carriages containing compartments for two or more classes of passengers, dining or restaurant carriages, sleeping carriages, mail carriages or travelling post offices, luggage brake vans, horse-boxes and carriage-trucks. Passenger carriages were originally modelled on the stage-coaches which they superseded, and they are often still referred to as " coaching stock." Early examples had bodies about 15 ft. long, 61 ft. wide and 44 ft. high; they weighed 3 or 4 tons, and were divided into three compartments holding six persons each, or eighteen in all.
The distinction into classes was made almost as soon as the railways began to carry passengers. Those who paid the highest fares (22d. or 3d. a mile) were provided with covered vehicles, on the roofs of which their luggage was carried, and from the circumstance that they could book seats in advance came the term " booking office," still commonly applied to the office where tickets are issued. Those who travelled at the cheaper rates had at the beginning to be content with open carriages having little or no protection from the weather. Gradually, however, the accommodation improved, and by the middle of the 19th century second-class passengers had begun to enjoy " good glass windows and cushions on the seat," the fares they paid being about 2d. a mile. But though by an act of 1844 the railways were obliged to run at least one train a day over their lines, by which the fares did not exceed the " Parliamentary " rate of id. a mile, third-class passengers paying 14 d. or 12 d. a mile had little consideration bestowed on their comfort, and were excluded from the fast trains till 1872, when the Midland railway admitted them to all its trains. Three years later that railway did away with second-class compartments and improved the third class to their level. This action had the effect, through the necessities of competition, of causing travellers in the cheaper classes to be better treated on other railways, and the condition of the third-class passenger was still further improved when Parliament, by the Cheap Trains Act of 1883, required the railways to provide " due and sufficient " train accommodation at fares not exceeding id. a mile. In the United Kingdom it is now possible to travel by every train, with very few exceptions, and in many cases to have the use of restaurant cars, for id. a mile or less, and the money obtained from third-class travellers forms by far the most important item in the revenue from passenger traffic. Since the Midland railway's action in 1875 several other English companies have abandoned second-class carriages either completely or in part, and in Scotland they are entirely unknown.
On the continent of Europe there are occasionally four classes, but though the local fares are often appreciably lower than in Great Britain, only first and second class, sometimes only first class, passengers are admitted to the fastest trains, for which in addition a considerable extra fare is often required. In Hungary and Russia a zone-tariff system is in operation, whereby the charge per mile decreases progressively with the length of the journey, the traveller paying according to the number of zones he has passed through and not simply according to the distance traversed. In the United States there is in most cases nominally only one class, denominated first class, and the average fare obtained by the railways is about id. per mile per passenger. But the extra charges levied for the use of parlour, sleeping and other special cars, of which some of the best trains are exclusively composed, in practice constitute a differentiation of class, besides making the real cost of travelling higher than the figures just given.
In America and other countries where distances are great and passengers have to spend several days continuously in a train sleeping and restaurant cars are almost a necessity, and accordingly are to be found on most important through trains. Such cars in the United States are largely owned, not by the railway companies over whose lines they run, but by the Pullman Car Company, which receives the extra fees paid by passengers for their use. Similarly in Europe they are often the property of the International Sleeping Car Company (Compagnie Internationale des Wagons-Lits), and the supplementary fares required from those who travel in them add materially to the cost of a journey. In the United Kingdom, where the distances are comparatively small, sleeping and dining cars must be regarded rather as luxuries; still even so, they are to be met with very frequently. The first dining car in England was run experimentally by the Great Northern railway between London and Leeds in 1879, and now such vehicles form a common feature on express trains, being available for all classes of passengers without extra charge beyond the amount payable for food. The introduction of corridor carriages, enabling passengers to walk right through the trains, greatly increased their usefulness. The first English sleeping cars made their appearance in 1873, but they were very inferior to the vehicles now employed. In the most approved type at the present time a passage runs along one side of the car, and off it open a number of transverse compartments or berths resembling ships' cabins, mostly for one person only, and each having a lavatory of its own with cold, and sometimes hot, water laid on. A charge of 7s. 6d. or 10s., according to distance, is made for each bed, in addition to the first-class fare. In the United States the standard sleeping car has a central alley, and along the sides are two tiers of berths, arranged lengthwise with the car and screened off from the alley by curtains. To some extent cars divided into separate compartments are also in use in that country. On the continent of Europe the typical sleeping car has transverse compartments with two berths, one placed above the other.
The first railway carriages in England had four wheels with two axles, and this construction is still largely employed, especially for short-distance trains. Later, when increased length became desirable, six wheels with Passenger g g three axles came into use; vehicles of this kind were carria es. made about 30 ft. long, and contained four compartments for first-class passengers or five for second or third class, carrying in the latter case fifty persons. Their weight was in the neighbourhood of 10 tons. In both the four-wheeled and the six-wheeled types the axles were free to rise and fall on springs through a limited range, but not to turn with respect to the body of the carriage, though the middle axle of the six-wheeled coach was allowed a certain amount of lateral play. Thus the length of the body was limited, for to increase it involved an increase in the length of the rigid wheel base, which was incompatible with smooth and safe running on curves. (On the continent of Europe, however, six-wheeled vehicles are to be found much longer than those employed in Great Britain.) This difficulty is avoided by providing the vehicles with four axles (or six in the case of the largest and heaviest), mounted in pairs (or threes) at each end in a bogie or swivel truck, which being pivoted can move relatively to the body and adapt itself to the curvature of the line. This construction was introduced into England from America about 1874, and has since been extensively adopted, being now indeed standard for main line stock. It soon led to an increase in the length of the vehicles; thus in 1885 the Midland railway had four-wheeled bogie third-class carriages, with bodies 43 ft. long, holding seventy persons in seven compartments and weighing nearly 18 tons, and sixwheeled bogie composite carriages, 54 ft. long and weighing 23 tons, which included 3 first-class and .4 third-class compartments, with a cupboard for luggage, and held 58 passengers. The next advance, introduced on the Great Western railway in 1892, was the adoption of corridor carriages having a passage along one side, off which the compartments open, and connected to each other by vestibules, so that it is possible to pass from one end of the train to the other. This arrangement involves a further increase of length and weight. For instance, fourwheeled bogie third-class corridor carriages employed on the Midland railway at the beginning of the 10th century weighed nearly 25 tons, and had bodies measuring 50 ft.; yet they held only 36 passengers, because not only had the number of compartments been reduced to six, as compared with seven in the somewhat shorter carriage of 1885, by the introduction of a lavatory at each end, but each compartment held only 6 persons, instead of 10, owing to the narrowing of its width by the corridor.
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It will be seen from these particulars - which are typical of what has happened not only on other British railways, but also on those of other countries - that much more space has to be provided and more weight hauled for each passenger than was formerly the case. Thus, on the Midland railway in 1885, each third-class passenger, supposing the carriage to have its full complement, was allowed o62 ft. of lineal length, and his proportion of the total weight was 5.7 cwt. Less than 20 years later the lineal length allowed each had increased to nearly 1.4 ft., and the weight to nearly 14 cwt. Passengers in sleeping cars appropriate still more space and weight; in Great Britain some of these cars, though 40 tons in weight and over 65 ft. in length, accommodate only 11 sleepers, each of whom thus occupies nearly 6 ft. of the length and requires over 31 tons of dead weight to be hauled.
In America the long open double-bogie passenger cars, as originally introduced by Ross Winans on the Baltimore & Ohio railway, are universally in use. They are distinguished essentially from the British type of carriage by having in the centre of the body a longitudinal passage, about 2 ft. wide, which runs their whole length, and each car having communication with those on either side of it, the conductor, and also vendors of books, papers and cigars, are enabled to pass right through the train. The cars are entered by steps at each end, and are provided with lavatories and a supply of iced water. The length is ordinarily about 50 ft., but sometimes 80 or go ft. The seats, holding two persons, are placed transversely on each side of the central passage, and have reversible backs, so that passengers can always sit facing the direction in which the train is travelling. Cars of this saloon type have been introduced into England for use on railways which have adopted electric traction, but owing to the narrower loading gauge of British railways it is not usually possible to seat four persons across the width of the car for its whole length, and at the ends the seats have to be placed along the sides of the vehicle. A considerable amount of standing room is then available, and those who have to occupy it have been nicknamed " straphangers," from the fact that they steady themselves against the motion of the train by the aid of leather straps fixed from the roof for that purpose. Cars built almost entirely of steel, in which the proportion of wood is reduced to a minimum, are used on some electric railways, in order to diminish danger from fire, and the same mode of construction is also being adopted for the rolling stock of steam railways.
End doors opening on end platforms have always been characteristic of American passenger equipment. Their use secures a continuous passage-way through the train, but is attended with some discomfort and risk when the train is in motion. The opening of the doors was apt to cause a disagreeable draught through the car in cold weather, and passengers occasionally fell from the open platform, or were blown from it, when the train was moving. To remedy these defects vestibules were introduced, to enclose the platform with a housing so arranged as to be continuous when the cars are made up into trains, and fitted with side doors for ingress and egress when the trains are standing. A second advantage of the vestibule developed in use, for it was found that the lateral swaying of the cars was diminished by the friction between the vestibule frames. The fundamental American vestibule patent, issued to H. H. Sessions of Chicago in November 1887, covered a housing in combination with a vertical metallic plate frame of the general contour of the central passage-way, which projected slightly beyond the line of the couplings and was held out by horizontal springs top and bottom, being connected with the platform housing by flexible connexions at the top and sides and by sliding plates below. A common form is illustrated in fig. 27. Subsequent improvements on the Sessions patent have resulted in a modified form of vestibule in which the housing is made the full width of the platform, though the contact plate and springs and the flexible connexions remain the same as before. The application of vestibules is practically limited to trains making long journeys, as it is an obstruction to the free ingress and egress of passengers on local trains that make frequent stops.
FIG. 27. - A " Vestibule "; the " lazytongs " gate is folded away when two cars are coupled together, giving free passage from end to end of the train.
In the United States the danger of the stoves that used to be employed for heating the interiors of the cars has been realized, and now the most common method is by steam taken from the locomotive boiler and circulated through the train in a line of piping, rendered continuous between the cars by flexible coupling-hose. The same method is finding increased favour in Great Britain, to the supersession of the old hot-water footwarmers. These in their simplest form are cans filled with water, which is heated by immersing them in a vessel containing boiling water. In some cases, however, they are filled with fused acetate of soda; this salt is solid when cold, but when the can containing it is heated by immersion in hot water it liquefies, and in the process absorbs heat which is given out again on the change of state back to solid. Such cans remain warm longer than those containing only hot water. On electric railways the trains are heated by electric heaters. As to lighting, the oil lamp has been largely displaced by gas and electricity. The former is often a rich oil-gas, stored in steel reservoirs under the coaches at a pressure of six or seven atmospheres, and passed through a reducing valve to the burners; these used to be of the ordinary fish-tail type, but inverted incandescent mantles are coming into increasing use. Gas has the disadvantage that in case of a collision its inflammability may assist ally fire that may be started. Electric light is free from this drawback. The current required for it is generated by dynamos driven from the axles of the coaches. With " set" or " block" trains, that is, trains having their vehicles permanently coupled up, one dynamo may serve for the whole train, but usually a dynamo is provided for each coach, which is then an /..,F?? o..? .................._ -..
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independent unit complete in itself. It is necessary that the voltage of the current shall be constant whatever be the increase of the speed of the train, and therefore of the dynamo. In most of the systems that have been proposed this result is attained by electrical regulation; in one, however, a mechanical method is adopted, the dynamo being so' hung that it allows the driving belt to slip when the speed of the axle exceeds a certain limit, the armature thus being rotated at an approximately constant speed. In all the systems accumulators are required to maintain the light when the train is at rest or is moving too slowly to generate current.
In all countries passenger trains must vary in weight according to the different services they have to perform; suburban Weight trains, for example, meant to hold as many pas ah d sengers as possible, and travelling at low speeds, do not weigh so much as long-distance expresses, which include dining and sleeping cars, and on which, from considerations of comfort, more space must be allowed each occupant. The speed at which the journey has to be completed is obviously another important factor, though the increased power of modern locomotives permits trains to be heavier and at the same time to run as fast, and often faster, than was formerly possible, and in consequence the general tendency is towards increased weight as well as increased speed. An ordinary slow suburban train may weigh about loo tons exclusive of the engine, and may be timed at an inclusive speed, from the beginning to the end of its journey, as low as 12 or 15 m. an hour; while usually the fastest express trains maintaining inclusive speeds of say 45 m. an hour, and made up of the heaviest and strongest rolling stock, do not much exceed 300 tons in any country, and are often less. The inclusive speed over a long journey is of course a different thing from the average running speed, on account of the time consumed in intermediate stops; the fewer the stops the more easily is the inclusive speed increased, - hence the advantage of the non-stop runs of 150 and zoo m. or more which are now performed by several railways in Great Britain, and on which average speeds of 54 or 55 m. per hour are attained between stopping-places. Over shorter distances still more rapid running is occasionally arranged, and in Great Britain, France and the United States there are instances of trains scheduled to maintain an average speed of 60 m. an hour or more between stops. Still higher speeds, up to 75 or even 80 m. an hour, are reached, and sustained for shorter or longer distances every day by express trains whose average speed between any two stoppingplaces is very much less. But isolated examples of high speeds do not give the traveller much information as to the train service at his disposal, for on the whole he is better off with a large number of trains all maintaining a good average of speed than with a service mostly consisting of poor trains, but leavened with one or two exceptionally fast ones. If both the number and the speed of the trains be taken into account, Great Britain is generally admitted still to remain well ahead of any other country.
The vehicles used for the transportation of goods are known as goods wagons or trucks in Great Britain, and as freight cars in America. The principal types to be found in the United Kingdom and on the continent of Europe are open wagons (the lading often protected from the weather by tarpaulin sheets), mineral wagons, covered or box wagons for cotton, grain, &c., sheep and cattle trucks, &c. The principal types of American freight cars are box cars, gondola cars, coal cars, stock cars, tank cars and refrigerator cars, with, as in other countries, various special cars for special purposes. Most of these terms explain themselves. The gondola or flat car corresponds to the European open wagons and is used to carry goods not liable to be injured by the weather; but in the United States the practice of covering the load with tarpaulins is unknown, and therefore the proportion of box cars is much greater than in Europe. The long hauls in the United States make it specially important that the cars should carry a load in both directions, and so bcx cars which have carried grain or merchandise one way are filled with wool, coal, coke, ore, timber and other coarse articles for the return journey. On this account it is common to put small end doors, in American box cars, through which timber and rails may be loaded.
The fundamental difference between American freight cars. and the goods wagons of Europe and other lands is in carrying capacity. In Great Britain the mineral trucks can ordinarily hold from 8 to io tons (long tons, 2240 lb), and the goods trucks rather less, though there are wagons in use holding 12 or 15 tons, and the specifications agreed to by the railway companies associated in the Railway Clearing House permit private wagon owners (who own about 45% of the wagon stock run on the railways of the United Kingdom) to build also wagons holding 20, 30, 40 and 56 tons. On the continent of Europe the average carrying capacity is rather higher; though wagons of less than io tons capacity are in use, many of those originally rated at io tons have been rebuilt to hold 15, and the tendency is towards wagons of 15-20 tons as a standard, with others for special purposes holding 40 or 45 tons.
The majority of the wagons referred to above are comparatively short, are carried on four wheels, and are often made of wood. American cars, on the other hand, have long bodies mounted on two swivelling bogie-trucks of four wheels each, and are commonly constructed of steel. About 1875 their average capacity differed little from that of British wagons of the present day, but by 1885 it had grown to zo or 22 short tons (z000 ib) and now it is probably at least three times that of European wagons. For years the standard freight cars have held 60,000 lb and now many carry 80,000 lb or 100,000 lb; a few coal cars have even been built to contain 200,000 lb. This high carrying capacity has worked in several ways to reduce the cost of transportation. An ordinary British 10-ton wagon often weighs about 6 tons empty, and rarely much less than 5 tons; that is, the ratio of its possible paying load to its tare weight is at the best about 2 to 1. But an American car with a capacity of 10o,000 lb may weigh only 40,000 lb, and thus the ratio of its capacity to its tare weight is only about 5 to 2. Hence less dead weight has to behauled for each ton of paying load. In addition the increased size of the American freight car has diminished the interest on the first cost and the expenses of maintenance relatively to the work done; it has diminished to some extent the amount. of track and yard room required to perform a unit of work;, it has diminished journal and rolling friction relatively to thetons hauled, since these elements of train resistance grow relatively less as the load per wheel rises; and finally, it has tended to reduce the labour costs as the train loads have become greater, because no more men are required to handle a heavy train than; a light one.
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It is sometimes argued that if these things are true for one country they must be true for another, and that in Great Britain, for example, the use of more capacious cars would bring down. the cost of carriage. It may be pointed out, however, that the social and geographical conditions are different in the United - Kingdom and the United States, and in each country the. methods of carrying goods and passengers have developed in accordance with the requirements of those conditions. In the one country the population is dense, large towns are numerous and close to one another, the greatest distances to be travelled are short, and relatively a large part of the freight to be carried is merchandise and manufactured material consigned in small quantities. In the other country precisely the opposite conditions exist. Under the first set of conditions quickness and flexibility of service are relatively more important than under the second set. Goods therefore are collected and: despatched promptly, and, to secure rapid transit, are packed'. in numerous wagons, each of which goes right through to its destination, with the consequence that, so far as general merchandise is concerned, the weight carried in each is a quarter - or less of its capacity. But if full loads cannot be arranged forsmall wagons, there is obviously no economy in introducing, larger ones. On the other hand, where, as in America, the great volume of freight is raw material and crude food-stuffs, and the distances are great, a low charge per unit of transportation is more important than any consideration such as quickness of delivery; therefore full car-loads of freight are massed into enormous trains, which run unbroken for distances of perhaps 1000 m. to a seaport or distributing centre.
The weight and speed of goods trains vary enormously according to local conditions, but the following figures, which refer to traffic on the London & North-Western railway between London and Rugby, may be taken as representative of good English practice. Coal trains, excluding the engine, weigh up to Boo or 900 tons, and travel at from 18 to 22 m. an hour; ordinary goods or merchandise trains, weighing 430 tons, travel at from 25 to 30 m. an hour; and quick merchandise trains with limited loads of 300 tons make 35 to 40 m. an hour. In the United States mineral and grain trains, running at perhaps 12 m. an hour, may weigh up to about 4000 tons, and loads of 2000 tons are common. Merchandise trains run faster and carry less. Their speed must obviously depend greatly on topographical conditions. In the great continental basin there are long lines with easy gradients and curves, while in the Allegheny and Rocky Mountains the gradients are stiff, and the curves numerous and of short radius. Such trains, therefore, range in weight from 600 to 1800 tons or even more, and the journey speeds from terminus to terminus, including stops, vary from 15 to 30 m. an hour, the rate of running rising in favourable circumstances to 40 or even 60 m. an hour.
The means by which vehicles are joined together into trains are of two kinds - automatic and non-automatic, the difference between them being that with the former the impact of two vehicles one on the other is sufficient to couple them without any human intervention such as is required with the latter. The common form of non-automatic coupler, used in Great Britain for goods wagons, consists of a chain and hook; the chain hangs loosely from a slot in the draw-bar, which terminates in a hook, and coupling is effected by slipping the =chain of one vehicle over the hook of the next. For this operation, or its reverse, a man has to go in between the wagons, unless, as in Great Britain, he is provided with a coupling-stick - that is, a pole having a peculiarly shaped hook at one end by which the chain can be caught and thrown on or off the drawbar hook. This coupling gear is placed centrally between a pair of buffers; formerly these were often left " dead " - that is, consisted of solid prolongations of the frame of the vehicle, but now they are made to work against springs which take up the shocks that occur when the wagons are thrown violently .against one another in shunting. In British practice the chains consist of three links, and are of such a length that when fully extended there is a space of a few inches between opposing buffers; this slack facilitates the starting of a heavy train, since the engine is able to start the wagons one by one and the weight of the train is not thrown on it all at once. For passenger trains and occasionally for fast goods trains screw couplings are substituted for the simple chains. In these the central bar which connects the two end links has screw threads cut upon it,;and by means of a lever can be turned so as either to shorten the coupling and bring the vehicles together till their buffers .are firmly pressed together, or to lengthen it to permit the end link to be lifted off the hook.
Another form of coupler, which used to be universal in the United States, though it has now been almost entirely superseded by the automatic coupler, was the " link and pin," which differed fundamentally from the couplers commonly used in Europe, in the fact that it was a buffer as well as a coupler, no :side buffers being fitted. In it the draw-bar, connected through a spring to the frame of the car, had at its outboard end a socket into which one end of a solid link was inserted and secured by a pin. The essential change from the link and pin to the automatic coupler is in the outboard end or head of the draw-bar. 'The socket that received the link is replaced by a hook, shown at A in fig. 28, which is usually called the knuckle. This hook swings on the pivot B, and has an arm which extends backwards, practically at right angles with the working face of the hook, FIG. 28. - Automatic Coupling for Freight Cars (U.S.A.).
in a cavity in the head, and engages with the locking-pin C. This locking-pin is lifted by a suitable lever which extends to one or both sides of the car; lifting it releases the knuckle, which is then free to swing open, disconnecting the two cars. The knuckle stands open until the coupling is pushed against another coupling, when the two hooks turn on their pivots to the position shown in fig. 28, and, the locking-pin dropping into place, the couplers are made fast. This arrangement is only partly automatic, since it often happens that when two cars are brought together to couple the knuckles are closed and must be opened by hand. There are various contrivances by which this may be done by a man standing clear of the cars, but often he must go in between their ends to reach the knuckle.
This form of automatic coupler has now gained practically universal acceptance in the United States. To effect this result required many years of discussion and experiment. The Master Car Builders' Association, a great body of mechanical officers organized especially to being about improvement and uniformity in details of construction and operation, expressed its sense of the importance of " self-coupling " so far back as 1874, but no device of the kind that could be considered useful had then been invented. At that time a member of the Association referred to the disappearance of automatic couplers which had been introduced thirty or forty years before. This body pursued the subject with more or less diligence, and in 1884 laid down the principle that the automatic coupler should be one acting in a vertical plane - that is, the engaging faces should be free to move up and down within a considerable range, in order to provide for the differences in the height of cars. By the fixing of this principle the task of the inventor was considerably simplified. In 1887 a committee reported that the coupler question was the " knottiest mechanical problem that had ever been presented to the railroad," and over 4000 attempted solutions were on record in the United States Patent Office. The committee had not found one that did not possess grave disadvantages, but concluded that the " principle of contact of the surfaces of vertical surfaces embodied in the Janney coupler afforded the best connexion for cars on curves and tangents "; and in 1887 the Association recommended the adoption of a coupler of the Janney type, which, as developed later, is shown in fig. 28. The method of constructing the working faces of this coupler is shown in fig. 29. The principle was patented, but the company owning the patent undertook to permit its free use by railway companies which were members of the Master Car Builders' Association, and thus threw open the underlying principle to competition. From that time the numerous patents have had reference merely to details. Many different couplers of the Janney type are patented and made by different firms, but the tendency is to equip new cars with one of only four or five standard makes. The adoption of automatic couplers was stimulated in some degree by laws enacted by the various states and by the United States; and the Safety Appliance Act passed by Congress in 1893 made it unlawful for railways to permit to be hauled on their lines after the ist of January 1898 any car used for interstate commerce that was not equipped with couplers which coupled automatically by impact, and which could be uncoupled without the necessity for men going in between the ends of the cars. The limit was extended to the 1 st of August 1900 by the Interstate Commerce Commission, which was given discretion in the matter.
Automatic couplers resembling the Janney are adopted in a few special cases in Great Britain and other European countries, FIG. 29. - Development of the Working Faces of the Janney Coupler. The sides of the square are 6 in., and the centres AA are taken at 2 in. from the top and bottom of the square. The circles A'A', which are struck with 2-inch radius, define the first portion of the knuckle. The inner circle B has a radius of 12 in. From its intersection with A'A' arcs are struck cutting B in two points. These intersections determine the centres of the semicircles CC which form the ends of the respective knuckles. These semicircles and the circles A'A' are joined by tangents and short arcs struck from the centre of the figure.
but the great majority of couplings remain non-automatic. It may be pointed out that the general employment of side buffers in Europe greatly complicates the problem of designing a satisfactory automatic coupling, while to do away with them and substitute the combined buffer-coupling, such as is used in the United States, would entail enormous difficulties in carrying on the traffic during the transition stage.
In the United States the Safety Appliance Act of 1893 also forbade the railways, after the 1st of January 1898, to run trains which did not contain a " sufficient number " of cars equipped with continuous brakes to enable the speed to be controlled from the engine. This law, however, did not serve in practice to secure so general a use of power brakes on freight trains as was thought desirable, and another act was passed in 1903 to give the Interstate Commerce Commission authority to prescribe what should be the minimum number of power-braked cars in each train. This minimum was at first fixed at 50%, but on and after the 1st of August 1906 it was raised to 75%, with the result that soon after that date practically all the rolling stock of American railways, whether passenger or freight, was provided with compressed air brakes. In the United Kingdom the Regulation of Railways Act 1889 empowered the Board of Trade to require all passenger trains, within a reasonable period, to be fitted with automatic continuous brakes, and now all the passenger stock, with a few trifling exceptions, is provided with either compressed-air or vacuum brakes (see Brake), and sometimes with both. But goods and mineral trains so fitted are rare, and the same is the case on the continent of Europe, where, however, such brakes are generally employed on passenger trains. (H. M. R.) Intra-Urban Railways The great concentration of population in cities during the 19th century brought into existence a class of railways to which the name of intra-urban may be applied. Such l i nes are primarily intended to supply quick means of passenger communication within the limits of cities, and are to be distinguished on the one hand from surface tramways, and on the other from those portions of trunk or other lines which lie within city boundaries, although the latter may incidentally do a local or intra-urban business. Intra-urban railways, as compared with ordinary railways, are characterized by shortness of length, great cost per mile, and by a traffic almost exclusively passenger, the burden of which is enormously heavy. For the purpose of connecting the greatest possible number of points of concentrated travel, the first railways were laid round the boundaries of areas approximately circular, the theory being that the short walk from the circumference of the circle to any point within it would be no serious detention. It has been found, however, in the case of such circular or belt railways, that the time lost in traversing the circle and in walking from the circumference to the centre is so great that the gain in journey speed over a direct surface tramway or omnibus is entirely lost. Later intra-urban railways in nearly every case have been built, so far as possible,. on straight lines, radiating from the business centre or point of maximum congestion of travel to the outer limits of the city; and, while not attempting to serve all the population through the agency of the line, make an effort to serve a portion in the best possible manner - that is, with direct transit.
The actual beginning of the construction of intra-urban railways was in 1853, when powers were obtained to build a line, 24 m. long, from Edgware Road to King's Cross, in London, from which beginning the Metropolitan and Metropolitan District railways developed. These railways, which in part are operated jointly, were given a circular location, but the shortcomings of this plan soon became apparent. It was found that there was not sufficient traffic to support them as purely intra-urban lines, and they have since been extended into the outskirts of London to reach the suburban traffic.
The Metropolitan and Metropolitan District railways followed the art of railway building as it existed at the time they were laid out. Wherever possible the lines were constructed in open cutting, to ensure adequate ventilation; and where this was not possible they were built by a method suggestively named " cut and cover." A trench was first excavated to the proper depth, then the side walls and arched roof of brick were put in place, earth was filled in behind and over the arch, and the surface of the ground restored, either by paving where streets were followed, or by actually being built over with houses where the lines passed under private property. Where the depth to rail-level was too great for cut-and-cover methods, ordinary tunnelling processes were used; and where the trench was too shallow for the arched roof, heavy girders, sometimes of cast iron, bridged it between the side walls, longitudinal. arches being turned between them (fig. 30).
-- ice _ 1 - /f r- - f? h - - 2 FIG. 30. - Type-Section of Arched Covered Way, Metropolitan District railway, London.
The next development in intra-urban railways was an elevated line in the city of New York. Probably the first suggestion for an elevated railway was made by Colonel Stevens, of Hoboken, New Jersey, as early as 1831, when the whole art of railway construction was in its infancy. He proposed to build an elevated railway on a single line of posts, placed along the curb-line of the street: a suggestion which embodies not only the general plan of an elevated structure, but the most striking feature of it as subsequently built - namely, a railway supported by a single row of columns. The first actual work, however, was not begun till 1870, when the construction of an iron structure on a single row of columns was undertaken. The superiority, so far as the convenience of passengers is concerned, of an elevated over an underground railway, when both are worked by steam locomotives, and the great economy and rapidity of construction, led to the quick development and extension of this general design. By the year 1878 there were four parallel lines in the city of New York, and constructions of the same character had already been projected in Brooklyn and Chicago and, with certain modifications of details, in Berlin. In the year 1894 an elevated railway was built in Liverpool, and in 1900 a similar railway was constructed in Boston, U.S.A., and the construction of a new one undertaken in New York. These elevated railways as a rule follow the lines of streets, and are of two general types. One (fig. 31), the earliest form, consisted of a single row of columns supporting two lines of longitudinal girders carrying the rails, the lateral stability of the structure being obtained by anchoring the feet of the columns to their foundations. The other type (fig. 32) has two rows of columns connected at the top by transverse girders, which in turn carry the longitudinal girders that support the railway. In Berlin, on the Stadtbahn - which for a part of its length traverses private property - masonry arches, or earthen embankments between retaining walls, were substituted for the metallic structure wherever possible.
The next great development, marking the third step in the progress of intra-urban railway construction, took place in 1886, when J. H. Greathead (q.v.) began the City & South London railway, extending under the Thames from the Monument to Stockwell, a distance of 32 m. Its promoters recognized the unsuitability of ordinary steam locomotives for underground railways, and intended to work it by means of a moving cable; but before it was completed, electric traction had developed so far as to be available for use on such lines. Electricity, therefore, and not the cable, was installed (fig. 33). In the details of construction the shield was the novelty. In principle it had been invented by Sir Marc I. Brunel for the construction of the original Thames tunnel, and it was afterwards improved by Beach, of New York, and finally developed by Greathead. (For the details of the shield and method of its operation, see Tunnel.) By means of the shield Greathead cut a circular hole at a depth ranging from 40 to 80 ft.
below the surface, with an external diameter of 10 ft. 9 in.; this he lined with cast-iron segments bolted together, giving a sr 2 / FIG. 33. - Section of Tunnel and Electric Locomotive, City & South London railway.
clear diameter of 10 ft. 2 in. Except at the shafts, which were sunk on proposed station sites, there was no interference with the surface of the streets or with street traffic during construction. Two tunnels were built approximately parallel, each taking a single track. The cross-section of the cars was made to conform approximately to the section of the tunnel, the idea being that each train would act like a piston in a cylinder, expelling in front of it a column of air, to be forced up the station shaft next ahead of the train, and sucking down a similar column through the station shaft just behind. This arrangement was expected to ensure a sufficient change in air to keep such railways properly ventilated, but experience has proved it to be ineffective for the purpose. This method of construction has been used for building other railways in Glasgow and London, and in the latter city alone the " tube railways " of this character have a length of some 40 m. The later examples of these railways have a diameter ranging from 13 to 15 ft.
The fourth step in the development of intra-urban railways was to go to the other extreme from the deep tunnel which Greathead introduced. In 1893 the construction was completed in Budapest of an underground railway with a thin, flat roof, consisting of steel beams set close together, with small longitudinal jack arches between them, the street pavement .
`,I FIG. 34. - Electric Underground Railway, Budapest.
resting directly on the roof thus formed (fig. 34). The object was to bring the level of the station platforms as close to the . FIG. 31. - Single-Column Elevated Structure Z9' 1'7 5-3 " FIG. 32. - Double-Column Elevated Structure (half-section).
[INTRA-URBAN RAILWAYS |
surface of the street as the height of the car itself would permit; in the case of Budapest the distance is about q ft. This principle of construction has since been followed in the construction of the Boston subway, of the Chemin de Fer Metropolitain in Paris, and of the New York underground railway. The Paris line is built with the standard gauge of 4 ft 82 in., but its tunnels are designedly made of such a small crosssection that ordinary main line stock cannot pass through them.
The New York underground railway (fig. 35) marks a still further step in advance, in that there are practically two different railways in the same structure. One pair of tracks is used for a local service with stations about one-quarter of a mile apart, following the general plan of operation in vogue on all other intra-urban railways. The other, or central, pair of tracks is for trains making stops at longer distances. Thus there is a differentiation between the long-distance traveller who desires to be carried from one extreme of the city to the other and the short-distance traveller who is going between points at a much less distance.
To sum up, there are of intra-urban railways two distinct classes: the elevated and the underground. The elevated is used where the traffic is so light as not to warrant the expensive underground construction, or where the construction of an elevated line is of no serious detriment to the adjoining property. The underground is used where the congestion of traffic is so great as to demand a railway almost regardless of cost, and where the conditions of surface traffic or of adjoining property are such as to require that the railway shall not obstruct or occupy any ground above the surface.
Underground railways are of three general types: the one of extreme depth, built by tunnelling methods, usually with the shield and without regard to the surface topography, where the stations are put at such depth as to require lifts to carry the passengers from the station platform to the street level. This type has the advantage of economy in first construction, there being the minimum amount of material to be excavated, and no interference during construction with street traffic or subsurface structures; it has, however, the disadvantage of the cost of o p eration of lifts at the stations. The other extreme type is the shallow construction, where the railway is brought to the minimum distance below the street level. This system has the advantage of the greatest convenience in operation, no lifts being required, since the distance from the street surface to the station platform is about 12 to 15 ft.; it has the disadvantages, however, of necessitating the tearing up of the street surface during construction, and the readjustment of sewer, water, gas and electric mains and other subsurface structures, and of having the gradients partially dependent on the surface topography. The third type is the intermediate one between those two, followed by the Metropolitan and Metropolitan District railways, in London, where the railway has an arched roof, built usually at a sufficient distance below the surface of the street to permit the other subsurface structures to lie in the ground above the crown of the arch, and where the station platforms are from 20 to 30 ft. beneath the surface of the street - a depth not sufficient to warrant the introduction of lifts, but enough to be inconvenient.
In the operation of intra-urban railwa y s, steam locomotives, cables and electricity have severally been tried: the first having been used in the earlier examples of underground lines and in the various elevated systems in the United States. The fouling of the air that results from the steam-engine, owing to the production of carbonic acid gas and of sulphurous fumes and aqueous vapour, is well known, and its use is now practically abandoned for underground working. The cable is slow; and unless development along new lines of com p ressed air or some sort of chemical engine takes place, electricity will monopolize the field. Electricity is applied through a separate locomotive attached to the head of the train, or through motor carriages attached either at one end or at both ends of the train, or by putting a motor on every axle and so utilizing the whole weight of the train for traction, all the motors being under a single control at the head of the train, or at any point of the train for emergency. The distance between stations on intra-urban railways is governed by the density of local traffic and the speed desired to be maintained. As a general rule the interval varies from one-quarter to one-half mile; on the express lines of the New York underground railway, the inter-station interval averages about r1 m. On steam-worked lines the speed of trains is about i r to 15 m. per hour, according to the distance between stations Later practice takes advantage of the great increase in power that can be temporarily developed by electric motors during the period of acceleration; this, in proportion to the weight of the train to be hauled, gives results much in advance of those obtained on ordinary steam railways. Since high average speed on a line with frequent stops depends largely on rapidity of acceleration, the tendency in modern equipment is to secure as great an output of power as possible during the accelerating period, with corresponding increase in weight available for adhesion. With a steam locomotive all the power is concentrated in one machine, and therefore the weight on the drivers available for adhesion is limited. With electricity, power can be applied to as many axles in the train as desired, and so the whole weight of the train, with its load, may be utilized if necessary. Sometimes, as on the Central London railway, the acceleration of gravity is also utilized; the different stations stand, as it were, on the top of a hill, so that outgoing trains are aided at the start by having a slope to run down, while incoming ones are checked by the rising gradient they encounter.
The cost of intra-urban railways depends not only on the type of construction, but more especially upon local conditions, such as the nature of the soil, the presence of subsurface structures, like sewers, water and gas mains, electric conduits, &c.; the necessity of permanent underpinning or temporary supporting of house foundations, the cost of acquiring land passed under or over when street lines are not followed, and, in the case of elevated railways, the cost of acquiring easements of light, air and access, which the courts have held are vested in the abutting property. The cost of building an ordinary two-track elevated railway according to American practice varies from $300,000 to $400,000 a mile, exclusive of equipment, terminals or land damages. The cost of constructing the deep tubular tunnels in London, whose diameter is about 15 ft. exclusive, in like manner, of equipment, terminals or land damages, is about b70,000 to L200,000 a mile. The cost of the Metropolitan and Metropolitan District railways of London varied greatly on account of the variations in construction. The most difficult section - namely, that under Cannon Street - where the abutting buildings had to be underpinned, and a very dense traffic maintained during construction, while a network of sewers and mains was readjusted, cost at the rate of about r,000,000 a mile. The contract price of the New York underground railway, exclusive of the incidentals above mentioned, was $35,000,000 for 21 m., of which 16 m. are underground and 5 are elevated. The most difficult portion of the road, 41 m. of four-track line, cost $15,000,000. (W. B. P.) FIG. 35. - New York Rapid Transit railway, showing also the tracks and conduits of the electric surface tramway.
LIGHT RAILWAYS] |
The term light railways is somewhat vague and indefinite, and therefore to give a precise definition of its significance is not an easy matter. No adequate definition is to be found even in the British statute-book; for although g parliament has on different occasions passed acts dealing with such railways both in Great Britain and Ireland, it has not inserted in any of them a clear and sufficient statement of what it intends shall be understood by the term, as distinguished from an ordinary railway. Since the passing of the Light Railways Act of 1896, which did not apply to Ireland, it is possible to give a formal definition by saying that a light railway is one constructed under the provisions of that act; but it must be noted that the commissioners appointed under that act have authorized many lines which in their physical characteristics are indistinguishable from street tramways constructed under the Tramways Act, and to these the term light railways would certainly not be applied in ordinary parlance. Still, they do differ from ordinary tramways in the important fact that the procedure by which they have been authorized is simpler and cheaper than the methods by which special private acts of parliament have to he obtained for tramway projects. Economy in capital outlay and cheapness in construction is indeed the characteristic generally associated with light railways by the public, and implicitly attached to them by parliament in the act of 1896, and any simplifications of the engineering or mechanical features they may exhibit compared with the standard railways of the country are mainly, if not entirely, due to the desire to keep down their expenses.
The saving of cost is effected in two ways: (I) Instead of having to incur the expenses of a protracted inquiry before parliament, the promoters of a light railway under the act of 1896 make an application to the light railway commissioners, who then hold a local inquiry, to obtain evidence of the usefulness of the proposed railway, and to hear objections to it, and, if they are satisfied, settle the draft order and hand it over to the Board of Trade for confirmation. The Board may reject the order if it thinks the scheme to be of such magnitude or importance that it ought to come under the direct consideration of parliament, or it may modify it in certain respects, or it may remit it to the commissioners for further inquiry. But once the order is confirmed by the Board, with or without modifications, it has effect as if it had been enacted by parliament, and it cannot afterwards be upset on the ground of any alleged irregularity in the proceedings. (2) The second source of economy is to be sought in the reduced cost of actually making the line and cf working it when made. Thus the gauge may be narrow, the line single, the rails lighter than those used in standard practice, while deep cuttings and high embankments may be avoided by permitting the curves to be sharper and the gradients steeper: such points conduce to cheapness of construction. Again, low speeds, light stock, less stringent requirements as to continuous brakes, signals, block-working and interlocking, road-crossings, stations, &c., tend to cheapness in working. On the lines actually authorized by the Board of Trade under the 1896 act the normal minimum radius of the curves has been fixed at about 600 ft.; when a still smaller radius has been necessary, the speed has been reduced to 10 m. an hour and a guard-rail insisted on inside the curve. Again, the speed has been restricted to 20 m. an hour on long inclines with gradients steeper than i in 50, and also on a line which had scarcely any straight portions and in which there were many curves of 600 ft. radius and gradients of 1 in 50. In the case of a line of 22 ft. gauge, with a ruling gradient of I in 40, a maximum speed of 15 m. an hour and a minimum radius of curve of 300 ft. have been prescribed. Curves of still smaller radius have entailed a maximum speed of io m. an hour. It must be understood that a railway described as " light " is not necessarily built of narrower gauge than the standard. Many lines, indeed, have been designed on the normal 4 ft. 82 in. gauge, and laid with rails weighing from 50 to 70 lb per yard; a flat-footed 60 lb rail, with the axle load limited to 14 tons, has the advantage for such lines that it permits the employment of a proportion of the locomotives used on main lines. The orders actually granted have allowed 50 lb, 56 lb, 60 lb and 70 lb rails, with corresponding axle loads of 10, 12, 14 and 16 tons. On a line of 2 ft. gauge, rails of 40 lb have been sanctioned. In regard to fencing and precautions at level-crossings, less rigid requirements may be enforced than with standard railways; and in some cases where trains are likely to be few, it has been provided that the normal position of the gates at crossings shall be across the line. Again, if the speed is low and the trains infrequent, the signalling arrangements may be of a very simple and inexpensive kind, or even dispensed with altogether. It should be mentioned that the act provided that the Treasury might advance a portion of the money required for a line in cases where the council of any county, borough or district had agreed to do the same, and might also make a special advance in aid of a light railway which was certified by the Board of Agriculture to be beneficial to agriculture in any cultivated district, or by the Board of Trade to furnish a means of communication between a fishing-harbour and a market in a district where it would not be constructed without special assistance from the s' ate.
As a general classification the commissioners have divided the schemes that have come before them into three classes: (A) those which like ordinary railways take their own line across country; (B) those in connexion with which it is proposed to use the public roads conjointly with the ordinary road traffic; and (Neutral) which includes inclined railways worked with a rope, and lines which possess the conditions of A and B in about equal porportions.
[LIGHT RAILWAY S |
The Light Railways Act 1896 was to remain in force only until the end of 1901 unless continued by parliament, but it was continued year by year under the Expiring Laws Continuance Act. In 1901 the president of the Board of Trade it troduced a bill to continue the act until 1906, and to amend it so as to make it authorize the construction of a light railway on any highway, the object being to abolish the restriction that a light railway should run into the area of at least two local authorities; but it was not proceeded with. Towards the end of 1901 a departmental committee of the Board of Trade was formed to consider the Light Railways Act, and in 1902 the president of the Board of Trade (Mr Gerald Balfour) stated that as a result of the deliberations of this committee, a new bill had been drafted which he thought would go very far to meet all the reasonable objections that had been urged against the present powers of the local authorities. This bill, however, was not brought forward. In July 1903, Lord Wolverton, on behalf of the Board of Trade, introduced a bill to continue and amend the Light Railways Act. It provided that the powers of the light railway commissioners should continue until determined by parliament, and also provided, inter alia, that in cases where the Board of Trade thought, under section (9) subsection (3) of the original act, that a proposal should be submitted to parliament, the Board of Trade itself might submit the proposals to parliament by bringing in a bill for the confirmation of the light railway order, with a special report upon it. Opposition on petition could be heard before a select committee or a joint committee as in the case of private bills. The bill was withdrawn on the 11th of August 1903, Lord Morley appealing to the Board of Trade to bring in a more comprehensive measure to amend the unsatisfactory state of legislation in relation to tramways and light railways. In 1904 the president of the Board of Trade brought in a bill on practically the same lines as the amending bill of 1903. It reached second reading but was not proceeded with. Similar amending bills were introduced in the 1905 and 1906 sessions, but were withdrawn. During the first ten years after the act came into force 545 applications for orders were received, 313 orders were made, and 282 orders were confirmed. The orders confirmed were for 1731 m., involving an estimated capital expenditure of (12,770,384. At the end of 1906 only 500 m. had been opened for traffic, and the mileage of lines opened was much less in proportion to the mileage sanctioned in the cases of lines constructed on their own land than in the case of lines more of the nature of tramways. (In other countries where the mileage of main lines of railways in proportion to area and population is roughly the same as in the United Kingdom, the mileage of light railways already constructed is considerable, while many additional lines are under construction. At the end of 1903 there were 6150 m. working in France, costing on an average £4500 per mile, earning £275 per mile per annum; 3730 miles in Prussia costing £4180 per mile, earning £310 per mile per annum; 1430 m. in Belgium at £3400 per mile, earning £320 per mile per annum.) The average cost per mile in Great Britain on the basis of the prescribed estimates is £5860, but this figure does not include the cost of equipment and does not cover the whole cost of construction. According to the light railway commissioners, experience satisfied them (a) that light railways were much needed in many parts of the country and that many of the lines proposed, but not constructed, were in fact necessary to admit of the progress, and even the maintenance, of existing trade interests; and (b) that improved means of access were requisite to assist in retaining the population on the land, to counteract the remoteness of rural districts, and also, in the neighbourhood of industrial centres, to cope with the difficulties as to housing and the supply of labour. They pointed out that while during the first five years the act was in force there were 315 applications for orders, during the second five years there were only 142 applications, and that proposals for new lines had become less numerous owing to the various difficulties in carrying them to a successful completion and to the difficulty of raising the necessary capital even when part of it was provided with the aid of the state and of the local authorities. They expressed the opinion that an improvement could be effected enabling the construction of many much-needed lines by an amendment of some of the provisions of the Light Railways Act, and by a reconsideration of the conditions under which financial or other assistance should be granted to such lines by the state and by local authorities.
The so-called light railways in the United States and the British colonies have been made under the conditions peculiar to new countries. Their primary object being the development and peopling of the land, they have naturally been made as cheaply as possible; and as in such cases the cost of the land is inconsiderable, economy has been sought by the use of lighter and rougher permanent way, plant, rolling stock, &c. Such railways are not " light " in the technical sense of having been made under enactments intended to secure permanent lowness of cost as compared with standard lines. On the continent of Europe many countries have encouraged railways which are light in that sense. France began to move in this direction in 1865, and has formulated elaborate provisions for their construction and regulation. Italy did the same in its laws in 1873, 1879, 1881, 1887 and 1889; and Germany fostered enterprise of this kind by the imperial edicts, of 1875, 1878 and 1892. Holland, Hungary and Switzerland were all early in the field; and Belgium has succeeded, through the instrumentality of the semi-official Societe Nationale de Chemins de Fer Vicinaux, started in 1885, in developing one of the most complete systems of rural railway transport in the world.
In France the lines which best correspond to British light railways are called Chemins de fer d'interit local. These are regulated by France. a decree No. 11,264 of 6th August 1881, which the Ministry of Public Works is charged to carry out. The model " form of regulation " lays down the scales of the drawings and the information to be shown thereon. For the first installation a single line is prescribed, but the concessionaire must provide space and be prepared to double when required. The gauge may be either 1.44 metres (4 ft. 8.7 in.), or 1 metre (3 ft. 3.37 in.), or 75 metre (2 ft. 5.5 in.). The radius of curves for the 1 . 44 m. gauge must not be less than 250 metres, loo metres for the 1 m. gauge and 50 metres for the 75 m. gauge. A straight length of not less than 60 metres for the largest gauge and 40 metres for the smallest must be made between two curves having opposite directions. Except in special cases, gradients must not exceed 3 in moo; and between gradients in the opposite sense there must be not less than 60 metres of level for 1.44 m. and 40 metres for i m. and .75 m. gauges. The position of stations and stopping-places is regulated by the council of the department. The undertaking, once approved, is regarded as a work of public utility, and the undertakers are invested with all the rights that a public department would have in the case of the carrying out of public works. At the end of the period of the concession the department comes into possession of the road and all its fixed appurtenances, and in the last five years of the period the department has the right to enter into possession of the line, and apply the revenue to putting it into a thorough state of repair. It has also the right to purchase the undertaking at the end of the first fifteen years, the net profits of the preceding seven years to govern the calculation of the purchase price. The maximum 1st, 2nd and 3rd class passenger fares are, per kilometre, 067 f. (. 6d.), .050 f. (.455d.) and. 037 f. (34d.) respectively, when the trains are run at grande vitesse, the fares including 30 kilogrammes weight of personal baggage.
In Belgium a public company under government control (" Societe Nationale de Chemins de Fer Vicinaux ") does all that in France forms the responsibility of the Ministry of the Interior Belgium. and of the prefect of the department. Over an average of years it appears that 27% of the capital cost was found by the state, 28% by the province, 40.9% by the communes and 4 . I % by private individuals. At the end of 1908 there were 2085 m. in operation, and the total mileage authorized was 2603, while the construction of a considerable further mileage was under consideration. As far as possible, these railways are laid beside roads, in preference to independent formation; the permanent way costs £977 per mile in the former as against £793 in the latter. If laid in paving, the price varies between £1108 and £2266 per mile. Through villages, and where roads have to be crossed, the line is of the usual tramway type. The line is of m metre gauge, with steel rails weighing 212 kilos (42 lb) per yard. In the towns a deeper rail is used, weighing about 60 lb per yard. In three lines of the Vicinaux system, in the aggregate 45 m. in length, the sharpest curves are 30 metres, 35 metres and 40 metres respectively. There are gradients of I in 20 and I in 25. The speed is limited to 30 kilometres (about 18 m.) in the country and 6 m. per hour in towns and through villages.
In Italy many railways which otherwise fulfil the conditions of a light railway are constructed with a gauge of 4 ft. 82 in. The weights are governed by what the railway has to carry Italy. and the speed. Light locomotives, light rails and light rolling stock are employed. There are no bridges, except where watercourses occur. Cuttings are reduced to a minimum; and where the roads are sufficiently wide, the rails are laid on the margins. The advantage of uniformity of gauge is in the use of trucks for goods which belong to the rolling stock of the main lines. In Italy these railways are called " economic railways," and are divided into five types. Types I., II. and III. are of 4 ft. 82 in. gauge, type IV. of 0 . 95 m. and type V. of 070 m.; but as there is no example of type V., the classification is practically one of 1 '445 m. (4 ft. 82 in.) and one of 0.95 (3 ft. 0.5 in.). The chief difference between the first three types lies in the weight of rails and rolling stock and in the radius of the curves. The real light railway of Italy is that of type IV.: gauge, 0.95 m. (3 ft. 0.5 in.); weight of rails, 12 (26.45 lb) to 20 (44 lb) kilos; mean load per axle, 6 tons; minimum curve, 70 m. (229 ft. 2.6 in.) radius; width of formation, 3.50 m. (t m ft. 5.5 in.); top width of ballast, 2.10 m. (6 ft. 10.7 in.); depth of ballast under sleepers, omo m. (3 ft. 9.5 in.); maximum gradient, I in 50; length of sleepers, 1.70 m. (5 ft. 6.92 in.); width between parapets and width of tunnels, 1 m. over width of carriage; height of tunnels, 5 m. (16 ft. 4.85 in.); locomotives, maximum weight per axle 6 tons, rigid wheel base 1 . 80 m. (5 ft. 10.86 in.), diameter of driving-wheels 1 m. (3 ft. 3.37 in.).
In Germany the use of light railways (Klein-bahnen) has made great strides. The gauges in use vary considerably between 4 ft. 82 in., the standard national gauge, and 1 ft. 114 in., Germany. which appears to be the smallest in use. They are under the control of the Post and Telegraph department, the state issuing loans to encourage the undertakings; the authorities in the provinces and communes also give support in various ways, and under various conditions, to public bodies or private persons who desire to promote or embark in the industry. These conditions, as well as the degree of control over the construction and working of the lines, are left to the regulation of the provincial governments. Similarly, the same authorities decide for themselves the conditions under which the public roads may be used, and the precautions for public safety, all subject to the confirmation of the imperial government.
What are known as " portable railways " should be included in the same category as light railways. With a 24 in. gauge,.
lines of a portable kind can be made very handily and the cost is very much less than that of a permanently railways. constructed light railway. The simplicity is great; they can be quickly mounted and dismounted; the correct gauge can be perfectly maintained; the sections of rails and sleepers (which are of iron) are very portable, and skilled labour is not required to lay or to take them up; the making of a " turn-out " is easy, by taking out a 15 ft. section of the way and substituting a section with points and crossings. The safe load per wheel varies between 12 cwt. on a io in. 16 lb wheel and 40 cwt. on an 18 in. 56 lb wheel. The rolling stock is constructed either for farm produce or heavy minerals, the latter holding io to 27 cub. ft. For timber, 4 or 5 ft. bogies can be used. A useful wagon for agricultural transport on a 24 in. gauge line is 16 ft. long by 5 ft. wide; it weighs 72 cwt. and costs X30. A portable line of this kind will have 20 lb steel rails and 2112 steel sleepers-4 ft. 6 in. long - to a mile, laid 2 ft. 6 in. apart centre to centre. The total cost per mile of such a line, including all bolts, nuts, fish-plates and fastenings, ready for laying, ,delivered in the United Kingdom, is under Soo a mile.
See Evans Austin, The Light Railways Act 1896, which contains the rules of the Board of Trade; W. H. Cole, Light Railways at Home and Abroad; Lieut.-Col. Addison, Report to the Board of Trade (1894) on Light Railways in Belgium. (C. E. W.; E. GA.)
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