A valve is a component that stops and runs the flow of fluid (water, air, water vapor, gas and oil, etc.) as a faucet or controls the quantity of flow.  Valves that open and shut with the power of solenoid are called solenoid valves.

Pneumatic valve (directional control valve) switches the flowing direction (flow path) of supplied air pressure to cylinder or other actuators in the pneumatic circuit.
Directional control valves are briefly classified into switching valve, non-return valve, check valve and shuttle valve.