Holt's patent cylinder drain and relief valve

Cylinder drain and relief valve by Percy Holt, 1879

This arrangement of valve, patented by Mr. Holt in 1878, combines in one fitting the drainage and relief safety valves for both ends of a steam engine cylinder. Pipes from the two ends enter the casing shown, and the discharged water from the cylinder is carried off by a central pipe. In the casing is a valve for each end of the cylinder, and each of these valves consists of a central disc or relief valve, and also of a double-seated annular valve outside, which is the drain valve; these annular valves are kept on their seats by springs. action is such that, when steam is in one end of the cylinder, its pressure opens the drain valve of the other end or exhaust side, while, at any time, the central or relief portion of the valve will open should the pressure, through priming, exceed the limit determined by the springs.