The Tender. The tender of a locomotive is used to carry the coal and water supply for the boiler. It is carried on two four-wheeled trucks having a frame work of wood or steel, the latter being mostly used at the present time. This frame supports the tank in which the water is stored, which, in the case of passenger and freight locomotives, is usually constructed in the shape of the letter U, the open end of which faces the fire door. The open space between the legs of the U is used for coal storage. The water is drawn from the tank near the two front corners. In these two front corners are placed tank valves which are connected by means of the tank hose and pipes to the two injectors. Near the back end of the tank is a manhole which permits a man to enter the inside to make repairs. This opening is also used in filling the tank at water towers. Tanks are made of open hearth steel, usually about ¼ of an inch in thickness, the sheets being carefully riveted together to prevent leaks. The interior of the tank is well braced and contains baffle plates which prevent the water from surging back and forth, due to curves and shocks in the train itself. The tank is firmly bolted to the frame.
Many of the engines designed for southern and western traffic burn oil and, as a rule, the railroads themselves furnish the specifications for the oil-burning equipment. Cylindrical tanks are used on the tender with the water tank forward, as a rule. Otherwise, the tender design is the same as for coal-burning locomotives.
The capacity of tenders has been increased as the locomotives which they serve have grown in size and power. Modern heavy locomotive tenders have a water capacity of from 3,000 to 9,000 gallons and a coal capacity of from 5 to 16 tons.
On switching engines, the back end of the tank is frequently made sloping in order to permit the engineer to see the track near the engine when running backward. Frequently a tool box is placed near the rear of the tank in which may be kept jacks, replacers, etc. A tool box for small tools and signals is usually placed at the front of the tender on either side. The coal is prevented from falling out at the front end by using gates or boards dropped into a suitably constructed groove. On locomotives used on northern railroads, the tanks are provided with a coil of steam pipes by means of which the water can be warmed and prevented from freezing.
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