Page:Popular Science Monthly Volume 12.djvu/159

Rh the steam-passages between them, permitting a symmetrical distribution of strain, and the use of the usual general type of beam-engine. A readily-adjustable valve-gear is attached, and its cut-off gives an expansion of about ten times, the boiler steam-pressure being about eighty pounds per square inch. The cylinders are steam-jacketed, and very thoroughly clothed with a non-conducting felting and lagging. This engine has given the best economical results yet reported in this country, attaining a "duty" on a test-trial of more than 100,000,000 pounds of water raised one foot high by each 100 pounds of fuel burned.

Still another recent form of steam pumping-engine, noted for its cheapness combined with efficiency, is that of Worthington (Fig. 22), in which two pairs of steam cylinders, A, B, are placed side by side, each pair driving a pump-plunger, F, attached to its piston-rod, and each having its valve-gear, H L, M N, actuated by the movement of the piston of the other. The cylinders together form a compound engine; the steam exhausted from the smaller, A, passing into the



larger, B, where it is further expanded. The valve-gear of this engine is peculiarly well adapted to this type of engine. There is no fly-wheel, and the motion of each of the two independent engines, which together form the pair, is controlled by its neighbor, the valve-gear of the one being moved by the piston of the other. This ingenious combination permits each piston to move from end to end of its cylinder, holds it stationary an instant while the pump-cylinders