LOCOMOTIVES. There are now used for passenger and freight traffic in the United States four principal types of locomotives: 1, the passenger or light-freight locomotive, which is designated the "American " type, having four coupled drivers and a four-wheel truck or bogie in front (see Vol. I,p. 304 el seq.): 2, engines for heavy passenger or fast-freight service, having six-coupled wheels with a leading four-wheeled truck, known as the "Ten-wheel" type; 3, those with six-coupled wheels and a pony-truck or single radiating pair of wheels in front, called the "Mogul" type; 4,,heavy freight-engines. "Consolidation " type, having eight-coupled wheels and a pony-truck in front. Besides these, a great variety of types has been worked out to meet special conditions of service: as four-wheel and six-wheel switching-engines, without trucks. and with tank and fuel carried on the engine or on a sepa rate tender. For elevated railroad service, light locomotives of the Forney type are used, with four-coupled wheels under the engine, and a four-wheel rear truck carrying the water tank and fuel. For local or suburban passenger-trains, fonr-coupled engines are employed, having a two-wheel truck front and rear, or a two-wheel truck front, and a four-wheel truck at the rear. Decapod or ten-coupled engines have been constructed to some extent for freight service on steep gradients. The accompanying table gives dimensions, weights, and weights of trains, for some of the types of American locomotives constructed by the Baldwin Locomotive Works.
Each of the types named in the table is constructed of several sizes. Of the principal types two examples are given: (1), the average used on the greater mileage of lightly built roads, and (2) the heaviest which has come into use on railways of maximum traffic. The form of boiler in general use for bituminous coal-burning engines of the American " Ten wheel " and " Mogul " types, is one with a deep fire-box placed between the rear driving axle and the one preceding it. For burning anthracite a larger fire-box is required, which is made shallower, and extended over the rear driving-axle. The larger grade area necessary in the larger bituminous engines, now coining into general use, has led to the adoption of the same arrangement. Locomotives of the "American" type, and frequently the "Mogul" and "Ten-wheel" types, are usually constructed with boilers of the wagon-top pattern—that is, with the outer shell elevated and enlarged over the frames to give increased steam-space, and to increase the weight on the driving-wheels. The crown-sheets of the furnaces are sup
ported either by crown-bars placed transversely and supported at their ends on the side sheets, or by radial stay-bolts tapped through the crown-sheet and roof of the boiler and riveted over. The latter construction is coming largely into use in connection with the wagon-top form, the dome being located on the wagon-top portion. which is extended in front of the fur nace to receive it. Crown-bars placed longitudinally are unusual.
In the United States all locomotives for road service, as distinguished from switching and pushing engines, have leading trucks. Not only do American engineers depend upon the truck to guide the engine safely, at fast speed, around curves of short radius, but the ability of the locomotives to traverse such curves has had its natural effect upon the construction of the roadway. Curves are employed which would be impracticable but for the flexibility of the locomotives, and the cost of construction is correspondingly reduced. The trucks are either two-wheeled or four-wheeled. The two-wheeled trucks invariably have a swinging bolster and radius-bar, Radial axle-boxes are rarely used. Four-wheeled trucks are always center-bearing and swiveling, and are either with or without a swinging bolster to give lateral motion. To facilitate traversing curves, it is usual to omit the flanges from either the inter mediate or leading coupled wheels. In the "Mogul" and "Consolidation " types the front and back pairs of coupled wheels have flanges, while the intermediate wheels are without flanges. In the " Ten-wheel" type the leading and trailing coupled wheels can he flanged, the intermediate wheels plain, and the truck or bogie made with a swinging bolster ; or the middle and back pairs flanged, the front pair plain, and the truck without swing motion. The first method is considered better for roads having sharp curvatures, but the second is preferred by many, and answers satisfactorily on straight roads or those having only easy curvature.