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:
Joseph Riedlin is credited with the first use of rotary valves on brass instruments in 1832.
In industry, a rotary valve (which can also be called airlock) is often used to enter or extract material from two chambers with different pressure level.
As part of the material exchange process, the valve is often used as a measuring or metering device.
Coates' International Ltd. has developed a spherical rotary valve for internal combustion engines which replaces the poppet valve system. The spherical rotary valve combustion engine possesses several significant advantages over the conventional poppet valve assembly, including significantly higher compression ratios.
Rotary valves are used for loading samples on columns used for liquid or gas chromatography. The valves used in these methods are usually 6-port, 2-position rotary valves.