Rotary Valve

A rotary valve is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes. The common stopcock is the simplest form of rotary valve. Rotary valves have been applied in numerous applications, including:

Changing the pitch of brass instruments.
Controlling the steam and exhaust ports of steam engines, most notably in the Corliss steam engine.
Periodically reversing the flow of air and fuel across the open hearth furnace.
Loading sample on chromatography columns.
Certain types of two-stroke engines.
Most hydraulic automotive power steering control valves.