In mechanical engineering, a Valve is a mechanical device that controls the flow of fluid and pressure within a system or process.
Valve is any device for closing or modifying the passage through a pipe, outlet, inlet, or the like, in order to stop, allow, or control the flow of a fluid media.
Valve is mechanical or electro mechanical device by which the flow of a gas, liquid, slurry, or loose dry material can be started stopped, diverted, and/or regulated or throttled.