Piston valve
A piston valve is a device used to control the motion of a fluid or gas along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder. Examples of piston valves are: The valves used in many brass instruments The valves used for pneumatic propulsion The valves used in many stationary steam engines and steam locomotives == Brass instruments == Cylindrical piston valves called Périnet valves (after their inventor François Périnet) are used to change the length of tube in the playing of most brass instruments, particularly the trumpet-like members of the family (cornet, flugelhorn, saxhorn, etc.).