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 and four-stroke engines. Most hydraulic automotive power steering control valves.

The French horn is a brass instrument made of tubing wrapped into a coil with a flared bell. The double horn in F/B♭ is the horn most often used by players in professional orchestras and bands, although the descant and triple horn have become increasingly popular. A musician who plays a horn is known as a horn player or hornist.