MISCELLANEOUS ACCIDENTS TO VALVE-MOTION.
Accidents to the valve-seat, such as the breaking of a bridge, can be fixed for running the engine home on one side, by covering the ports, and stripping that side of the engine, just as had to be done for a broken valve-yoke. If a serious break in a bridge occurs, it is indicated by a tremendous blow through the exhaust port, out by the stack. A mishap of much less consequence than a broken bridge is a “cocked” valve, and the small mishap is very liable to be mistaken for the greater one. Where the yoke is tight fitted, or out of true with the line of the stem, some engines have a trick of raising the valve away from the seat, and holding it there. This generally happens going into a station; and, when steam is applied in starting out, an empty roar sounds through the stack. Moving the valve with the reverse-lever by quick jerks will generally reseat a cocked valve, but sometimes it gets stuck so fast that it has to be hammered out of the yoke.
When a locomotive shows the symptoms which indicate a broken valve, a broken bridge, or a cocked valve, the engineer should exhaust every means of testing the matter from the outside before he begins an interior inspection by raising the steam-chest cover. If jerking the valve with the reverse-lever, or moving the engine a little, will not stop the blow, he should disconnect the valve-stem, and shake the valve by that means.
When a valve breaks, disabling its side of the engine so badly that it can not be used, the valve should be taken out, and a piece of strong pine-plank secured over the ports.