slide valve

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A valve that slides back and forth over ports, especially one in the cylinder wall of a steam engine that permits the intake and outflow of steam to move the piston.

Century Dictionary and Cyclopedia

1. n. In steam, hydraulic, and pneumatic engineering, a valve which slides over and upon its seat without lifting in opening or closing a port or ports formed in the seat; specifically, a flat-faced plain slide working, or adapted to work or slide, upon a flat-faced seat which includes a port or ports to be alternately opened and closed by the reciprocation of the slide. It is in extensive use in the cheaper forms of steam-engines, compressed-air engines, hydraulic motors, gas-and water-meters, in some kinds of air-compressors, and in some compressed-air ice-machines. In England the slide-valve is very commonly called simply a slide.

GNU Webster's 1913

1. n. A particular kind of sliding valve, often used in steam engines for admitting steam to the piston and releasing it, alternately, having a cuplike cavity in its face, through which the exhaust steam passes. It is situated in the steam chest, and moved by the valve gear. It is sometimes called a D valve, -- a name which is also applied to a semicylindrical pipe used as a sliding valve.

WordNet 3.0

1. n. valve that opens and closes a passageway by sliding over a port