A rotary valve (also called rotary-motion 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.

They use a closure element that rotates, usually through a quarter-turn or 90° range, to block the flow. A rotary-motion valve usually weighs less and is smaller in size than a comparable linear valve. It is also easier to control emissions through the stem packing of a rotary valve without the use of bellows seals.