STATIONARY ENGINES.

293

exists in the anterior portion. Inside the main frames there arefixed the slide bars, whicli are adjustable, top and bottom, forthe purpose of taking up the wear. The upper one is made planethroughout, but the lower one is of a trough shape. They aremade of the best forged Steel , as, indeed, are all the working partsof the engines.

The high-pressure cylinders are each fitted with a liner, thespace between this and the cylinder casting proper forming a steamjacket; the low-pressure cylinders, however, are not jacketted. Attheir forward ends each of the low-pressure cylinders is solid, and isprovided with a bracketted flange where it is in contact with themain frames; and connection between the frames and the cylinderends is effected by means of bolts, no studs being used.

The valves of these engines are of the double-piston type. Thesteam ports in the valve casings have triangulär openings into thevalve cylinders, the valve pistons having a 914 inch stroke, andbeing fitted with broad packing rings which are furnished withcylindrical springs of a V shape. A tight-working piston is therebyobtained, no escape of steam having been observed at any pressureyet employed. The object aimed at in employing this type ofvalve was to relieve the valve motion of the severe tear and wearresulting from the use of unbalanced flat-faced valves.

The valve casings are placed on the sides of the cylinders inorder that they may be easily got at for inspection or in case ofrepairs being necessary. The receiver formerly mentioned as inter-vening between the high- and low-pressure cylinders of each engineis immediately underneath the valve casings, and serves to catchup any water that might otherwise enter the cylinders. The valvespindles are of Steel , and are jointed together by means of a boxcoupling provided with cotters—an arrangement which allows ofthe pistons and spindles being easily withdrawn for repairs andreplaced in position.

Steam is admitted into the high-pressure cylinder by the pistonvalve entering between the pistons of the valve, and exhausting ateach end into the receiver. The distribution of the steam into thelow-pressure cylinder is similarly effected by its valve, the steamentering at the middle of the valve, and exhausting at each end asbefore. On the top of the low-pressure valve casing there is placeda small auxiliary slide valve, which is worked from the link motionof the main valve, and is in direct communication with the steam