A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level.
Flow control is the function regulating the rate of flow of a liquid or gas. A flow control or flow controller allows for adjusting the rate of fluid expulsion within a closed system as well as for mix adjustment. Examples of flow controllers may be as simple a manual faucet or a complex as a powered electro-mechanical multiplex mixing valve.