Fig. 19. Different Types of Corliss Valves
Fig. 20. Longitudinal Section through Corliss Engine
Fig. 21. The Gridiron Valve
Gridiron Valve.—One of the principal objects sought in the design of a valve is quick action at the points of admission and cut-off. This requires the uncovering of a large port opening with a comparatively small travel of the valve. The gridiron valve shown in [Fig. 21] is constructed especially for this purpose. This valve is of the four-valve type, one steam valve and one exhaust valve being shown in the section. Both the valve and its seat contain a number of narrow openings or ports, so that a short movement of the valve will open or close a comparatively large opening. For example, the steam valve in the illustration has 12 openings, so that if they are 1⁄4 inch in width each, a movement of 1⁄4 inch of the valve will open a space 12 × 1⁄4 = 3 inches in length.
Corliss Valve.—A section through an engine cylinder equipped with Corliss valves is shown in [Fig. 20]. There are four cylindrical valves in this type of engine, two steam valves at the top and two exhaust valves at the bottom. This arrangement is used to secure proper drainage. The action of the admission and exhaust valves is indicated by the arrows, the upper left-hand and the lower right-hand valve being open and the other two closed.