An air-operated valve, also known as a pneumatic valve, is a type of power-operated pipe valve that uses air pressure to perform a function similar to a solenoid. As air pressure is increased, the compressed air starts to push against the piston or diaphragm walls which causes the valve to actuate. Whether the valve opens or closes depends on the application. These valves are used for many functions in pneumatic systems, but most often serve one of two functions. The first activates a part of the system when a specific pressure is reached. The second prevents damage by maintaining a constant pressure or flow rate inside a system, or releasing pressure when it reaches excessive levels.