PART XXII.

DIFFERENT KINDS OF LOCOMOTIVES.

QUESTION 427. _Into what classes may locomotives be divided conveniently?_

_Answer._ 1. Locomotives for “switching,” “shunting” or “drilling” service, that is, for transferring cars from one place to another at stations; 2, for freight traffic; 3, for ordinary passenger traffic, and 4, for suburban or metropolitan railroads, where a great many light trains are run.

QUESTION 428. _What kinds of locomotives are used in this country for switching cars at stations?_

[Illustration: Fig. 220.]

_Answer._ Four-wheeled locomotives similar to that shown in Plate IV. In some cases they are made with six driving-wheels. Engines like that shown in Plate IV have separate tenders, but they are sometimes made so as to carry the water-tank and fuel on the locomotive itself, as shown in fig. 220, and are then called tank locomotives. Fig. 220 represents a switching engine built by the Taunton Locomotive Manufacturing Company.

QUESTION 429. _Why are four-wheeled locomotives used for switching?_

_Answer._ Because in such service it is constantly necessary to start trains, many of which are very heavy, and therefore a great deal of adhesion is needed. For this reason the whole weight of the locomotive and in the case of tank locomotives that of the water and fuel is placed on the driving-wheels. It is also necessary for such locomotives to run over curves of very short radius and into switches whose angle with the main track is very great, and therefore in order that they may do this and remain on the track, their wheel-bases must be very short, and consequently the wheels are all placed near together between the smoke-box and fire-box.

QUESTION 430. _Why are such locomotives not suited for general traffic?_

_Answer._ Owing to the shortness of their wheel-bases they become very unsteady at high speeds, and acquire a pitching motion, similar to that of a horse-car when running rapidly over a rough track. This unsteadiness not only becomes very uncomfortable to the men who run the locomotive, but there is danger of the engine running off the track. As nearly all switching is done at very slow speeds, it is not so objectionable for that service as it would be on the “open road”[102] at high speeds.

[102] The term “_open road_” is a literal translation from the German, for which there is no corresponding English term, and means the road between stations where trains run fast.

QUESTION 431. _What kinds of locomotives are used for freight service?_

_Answer._ The greater part of the freight service of this country is performed by locomotives like that selected for the illustrations of these articles, and represented in Plates I, II and III. Such locomotives have been called “American” locomotives because they first originated in this country and are now more generally used here than anywhere else. Side elevations of locomotives of this kind, built by the Baldwin Locomotive Works, the Grant Locomotive Works, the Danforth Locomotive and Machine Company, the Mason Machine Works and the Hinkley Locomotive Works are represented in Plates V, VI, VII, VIII and IX. Such locomotives have been described in the preceding pages.

QUESTION 432. _What are the dimensions of such engines?_

_Answer._ The principal dimensions of the engines illustrated are given in the table in the appendix, but locomotives of this plan are built of much smaller and also of larger sizes than those represented by the engravings. In some cases such locomotives do not weigh more than 35 or 36,000 lbs., with cylinders from 8 to 12 inches in diameter. In other cases they weigh as much as 66,000 lbs., with cylinders 17 or 18 inches in diameter. The wheels vary from 4 to 6 feet in diameter, but the most common sizes are 4¹⁄₂ and 5 feet.

QUESTION 433. _When it is desirable to pull heavier loads than is possible with the adhesive weight that can be placed on four driving-wheels, what is done?_

_Answer._ One or more pairs of driving-wheels are added, as in the ten-wheeled locomotive represented in Plate X, the “Mogul” engine, Plate XI, and the “Consolidation” engine, Plate XII. The ten-wheeled locomotive, it will be seen, is similar in construction to an ordinary American locomotive, excepting that it has another pair of driving-wheels in front of the main driving-wheels. It will be seen, however, that it is necessary to keep these close to the latter, because if they are brought further forward they will be too near the back truck-wheels. For this reason a truck consisting of a single pair of wheels, _A_, _A_, is placed in front of the cylinders, as represented in Plates XI and XII, is now much used. The front driving-wheels are then placed further forward, and thus bear a larger proportion of weight than they do in locomotives like that shown in Plate X.

QUESTION 434. _How are trucks with a single pair of wheels constructed?_

_Answer._ The truck frame is extended some distance behind the truck-axle, as shown in fig. 221, and the centre-pin, _a_, about which it vibrates, is placed at the back end. The weight of the locomotive, or that portion to be carried on the truck, is then made to rest over the centre of the axle, but in such a way that it can move laterally or crosswise over the track. Such trucks were first made so that the weight of the engine rested on slides on the truck frame, but recently they are nearly always suspended on links, so that they can swing like a pendulum, as shown in figs. 190 and 191. The weight of the engine then rests on the centre-plate, _H H_; which forms part of the plate, _B B_. This is suspended by links, _L L_, represented by dotted lines, which are attached by bolts to the cross-pieces, _m m_, which are fastened to the truck frame. In this way the truck-wheels can move sideways independent of the engine itself. As the wheels and axles, _A A_, must move about the centre-pin, _a_, fig. 221, the axle assumes a radial position to the curves of the track. It does this, too, quite independent of the driving-wheels, as is shown in fig. 221, which represents a plan of the wheels on a curve. It will be seen that the truck is not at all influenced by the position of the driving-wheels. This arrangement therefore gives great flexibility to the wheel-base, and enables the wheels to adjust themselves to any lateral curvature or alignment of the track.

[Illustration: Fig. 221. Scale ¹⁄₈ in. = 1 foot.]

QUESTION 435. _For what purpose are locomotives like that shown in Plates XI and XII used?_

_Answer._ “Mogul” locomotives are often used for ordinary freight service where heavy trains must be hauled, and also on steep grades. “Consolidation” locomotives, represented in Plate XII, which have eight driving-wheels, are employed almost exclusively for traffic over heavy mountain grades.

QUESTION 436. _What other kinds of locomotives are used for freight traffic?_

_Answer._ Various kinds of tank locomotives, that is, locomotives which have no separate tenders, but carry the water-tanks and fuel on the frame and wheels of the locomotive itself, have been devised and are to some extent used. Plate XIII represents a locomotive of this kind on which the tanks are placed on each side of the boiler, and the fuel on a Bissell truck at the back end. A similar truck is placed at the front end, so that a locomotive of this kind can run equally well either way. The lateral movement of the two trucks also gives great flexibility to the wheel-base, so that such an engine will adjust itself easily to the curvature of the track. If, however, the two pairs of truck-wheels should both stand on an elevated part of the track, and the driving-wheels on a depression, the latter would evidently not carry as much and the truck-wheels would carry more of the weight of the engine than they did on a level part of the track. If the reverse condition of things should occur, that is, if the driving-wheels should be on an elevation and one or both pairs of the truck-wheels on a depression, then the latter would bear less weight than they did and the driving-wheels more. For this reason, in order to distribute the weight evenly on all the wheels, it is necessary to equalize the weight on the truck and driving-wheels, by connecting them with equalizing levers, similar to those which were described in answer to Question 301. These levers distribute any undue weight which may come on one wheel to that next to it. This is important, because if the driving-wheels bore less weight at some times than at others, their adhesion and their capacity to draw loads would be reduced in like proportion.

It is evident, however, that if the water-tank or fuel is carried on the driving-wheels, there will be a greater weight on them when the tank is full than when it is empty, and that therefore there will either be so much weight on the wheels at one time as to be injurious to the rails, or else there will be too little for adhesion at another. Of course cases are conceivable, and doubtless exist in practice, where more adhesion is required to start a train and haul it during the first part of the “run” than will be needed during the latter part. In such cases doubtless the variable character of the weight might be an advantage instead of the reverse, but for ordinary practice a variable load on the driving-wheels would have the disadvantages which have been described. For this reason tank locomotives have been built like that represented in Plate XIV. In this it will be seen that the weight of the water-tank rests on a four-wheeled truck at the back end. A Bissell or two-wheeled truck is, however, placed in front in the same position as in the engine represented in Plate XIII, and carries a portion of the weight of the boiler and machinery.

In order to get all the advantages which a four-wheeled switching engine possesses in having its _whole_ weight on the driving-wheels, and at the same time avoid the disadvantages which result from a short wheel-base, and also from a varying amount of weight on the driving-wheels, a locomotive like that represented in Plate XV was designed by the writer with the whole weight of the boiler and machinery resting on the driving-wheels, and the water and fuel on a truck. By this means not only the objections to carrying the weight of the water on the driving-wheels is overcome, but at the same time the disadvantages arising from the short wheel-base of the switching locomotive, Plate IV, are also obviated. That is, all the _permanent weight_ of the boiler and machinery of such a locomotive rests on the driving-wheels, and is therefore all _adhesive weight_, as it is in the switching engine, and at the same time by extending the frame beyond the fire-box and placing the water-tank and fuel on this extension of the frame and supporting their weight on a truck, the engine has a wheel-base which is as long and as flexible as that of ordinary American engines, represented in Plates V, VI, VII, VIII and IX, and as the latter have only about _two-thirds_ of their weight on the driving-wheels, locomotives like that represented in Plate XV, of the same weight as the others, have fifty per cent. more adhesion, or they may be one-third lighter and have the same adhesion. As was explained in answer to Question 260, if an ordinary American locomotive runs backwards, that is, with the driving-wheels in front, the friction of their flanges against the rails on curves of short radius will be very excessive. To avoid this with locomotives of the design last described, they are run with the truck first, which, being at the opposite end of the boiler from the position which it usually occupies, reverses the position of the boiler and other parts relative to the motion of the engine. That is, the fire-box is then in front and the smoke-stack behind. Engines of this kind have been built and are now working and doing excellent service; but the prejudice which exists against running locomotives in the reverse direction to what has been customary seems to be the chief obstacle in the way of their use.

Another plan which possesses all the advantages of the locomotive described above and is free from the last objection is represented in Plate XVI. This plan was first adopted by Mr. Robert Fairlie in England, but has been introduced into this country and very much improved by Mr. William Mason, of Taunton, Mass. In these locomotives, the driving-wheels and cylinders are attached to a truck frame which turns around a centre-pin like any ordinary truck. The steam and exhaust pipes are connected to the boiler and cylinder with pipes which have flexible joints. By this means the truck can move independently of the boiler, and thus the driving-wheels can adjust themselves to the curvature of the track, just as the wheels of any other truck do, and therefore the driving-wheels can be run ahead just as well as the truck-wheels which carry the tank. This plan possesses the additional advantage that the fire-box can be made as wide and as long as may be desired without interfering with the driving-wheels. The flexible pipes are, however, usually considered an objection; but with the improvements which have been made in their design and construction, the difficulties which were at first encountered have probably been overcome. At any rate if there is no other objection to the use of such locomotives, ingenuity and care should in time overcome that one. Plate XVII represents a locomotive of this plan, with six driving-wheels and a six-wheeled carrying truck under the tank. This latter plan of locomotive is intended for heavy freight traffic.

QUESTION 437. _What kind of locomotives is used for passenger trains?_

_Answer._ Eight-wheeled American locomotives are used almost exclusively for passenger service. Usually the driving-wheels of such locomotives are larger in diameter than are used for freight traffic. Their size varies from 5 feet to 5 ft. 9 in. in diameter. The locomotive by the Mason Machine Works represented in Plate VIII has 5¹⁄₂ feet driving-wheels. For very heavy express trains locomotives with 17 × 24 inch cylinders and weighing 34 tons are now used on many through lines.

QUESTION 438. _What is meant by suburban and metropolitan railroads, what is the nature of their traffic, and what kinds of locomotives are needed for it?_

_Answer._ The traffic of suburban railroads consists chiefly of the transportation of passengers who do business in the city to the latter in the morning and to their homes in the evening. As the largest number of passengers must be carried during a few hours in the morning and evening, it is necessary to run very heavy trains at those times. As the passengers must be distributed at many stations which are near together, it is necessary to stop often; and in order that the average speed may be reasonably fast the trains must run very rapidly between these stations. It is therefore necessary to have heavy locomotives, with more than the usual proportion of adhesive weight, so that the trains can be started quickly without slipping the wheels. The main valves should also have a liberal amount of travel, so that steam will be admitted to and exhausted from the cylinders quickly. In some cases it is thought desirable to have locomotives which will run equally well either way, so that it will not be necessary to turn them around at each end of the “run.”

By metropolitan railroads are meant railroads in large cities. They may be divided into two classes, one for carrying freight cars from the outskirts of cities to the warehouses and stores at their business centres, and also from the terminus of one road to that of another. Metropolitan railroads of this kind are usually branches of lines which extend from the city. Locomotives for such traffic must have great tractive power, in order to pull heavy trains, and as the speed is usually slow the wheels and the boiler capacity may be small. They must generally be capable of running through curves of very short radius; and as the traffic is usually carried through streets in close proximity to buildings, the locomotives should be as nearly as possible noiseless. The other class of metropolitan roads is for carrying passengers. The traffic of the latter is similar to that usually carried on horse railroads, and consists almost exclusively of passengers. At present (1874) there are only one or two metropolitan railroads in this country for carrying passengers which are operated by steam power. It seems certain, however, that their use will soon become very general in all large cities. Their traffic will consist of many light trains run at short intervals and at comparatively slow speeds, and therefore very light locomotives are required.

QUESTION 439. _What kinds of locomotives are used for suburban railroads?_

_Answer._ The ordinary American eight-wheeled locomotive is used more than any other kind; but a number of locomotives like that represented by fig. 222 have been built and are used for this traffic. These have one pair of driving-wheels in front of the main pair and a Bissell truck in front of the cylinder. With this arrangement the driving-wheels bear a larger proportion of weight than they do if arranged on the ordinary American plan with a four-wheeled truck. Another plan is that shown in Plate XVIII. Such engines, as will be seen, have a Bissell truck at each end, and therefore they run equally well either way. In some cases the tanks of such engines are carried on the top and sides of the boiler. When they are obliged to run only a short distance, and a small supply of water is needed, this arrangement answers very well; but it is impossible to carry a large supply of water in this way without overloading the wheels of the locomotive, and at the same time increasing the evils of a varying load on the driving-wheels.

[Illustration: Fig. 222.

LIGHT PASSENGER AND FREIGHT LOCOMOTIVE, BY THE GRANT LOCOMOTIVE WORKS, PATERSON, N. J.]

Locomotives like that shown in Plate XIV are also used for suburban traffic. As shown in the engraving they have a four-wheeled truck at one end and one with two wheels at the other, so that it is thought that they can be run safely either way. The four-wheeled truck carries the weight of the water and fuel.

The plan of engine represented by Plate XV is very well adapted for this kind of traffic. Excepting on curves with a very short radius it could be run in either direction at any required speed, without encountering any other difficulty excepting the prejudices of those who run it.

As double-truck locomotives similar to that shown in Plate XVI can adjust themselves to any curve, this objection could not be urged against their use.

QUESTION 440. _What kinds of locomotives are used on metropolitan railroads?_

_Answer._ For freight traffic ordinary switching locomotives like that represented in Plate IV are often employed. In some cases these have the tanks on the locomotives. It often happens, though, that such traffic must be conducted in the streets of a city, and that the noise, especially of the exhausting steam, is thus liable to frighten horses and disturb the occupants. It is, then, necessary either to condense the exhaust steam or render its escape noiseless, which is done by allowing it to escape into the water-tanks. Street locomotives which have a condenser similar to the surface condensers used on marine engines are used on the Hudson River Railroad in New York. The exhaust steam passes through these and then escapes into the tanks. The latter are long and narrow, so as to expose a great deal of surface to radiation, and in this way cool the water which becomes heated by the steam. The engines have four driving-wheels and vertical boilers. The cylinders are connected to a crank shaft with a pinion on it, which gears with another wheel of larger size on the driving-axle. In this way the speed is reduced and great tractive power can be exerted. The whole of the engine is enclosed so as to hide the machinery, the sight of which is supposed to frighten horses. The engines were designed and patented by Mr. A. F. Smith, formerly Master Mechanic of that road.

For roads in cities carrying passengers almost exclusively, an entirely different class of locomotives is needed. To suit passengers it is of course necessary to run a great many trains at very short intervals. When this is done the trains are necessarily very light, and therefore only light locomotives are needed. Plate XIX represents the locomotives employed on the Greenwich Street Elevated Railroad in New York. These engines weigh only 10,000 lbs., and the wheels are 30 in. diameter and the cylinders 7 × 10 in. The peculiarity in their construction consists in their having an intermediate shaft between the two pairs of driving-wheels. This shaft has two cranks inside of the frames and two outside. The cylinders are connected to the inside cranks, and the coupling-rods to those on the outside. The water is carried in a tank on top of the boiler. The fuel is anthracite coal.