A flow control valve is a device used to regulate the flow or pressure of liquids or gases. It responds to signals generated by independent devices, such as flow meters or temperature gauges. It can be used in a variety of applications. 

Flow control valves are used to limit the amount of water that enters a system. The valve will keep the flow rate within its design range and will prevent overflow in downstream processes. In this way, the valve can protect the supply system from overuse and maximize the amount of water and energy that the system can deliver.

Another type of flow control valve is the plug valve. It is similar to a stopcock, but it features a tapered cylindrical part called a plug. This plug is positioned in the flow passage and is adjustable. The tapered angle of the plug determines the amount of fluid that can flow through the valve. It can be operated manually or by electric motor. It is typically made of glass or plastic and has a stopcock-like body.

A flow control valve can control the volume of liquid that flows through a pneumatic system. It can also be used to control the speed of an actuator. It is important to note that flow control valves should not be confused with pressure regulators. The relationship between flow and pressure is not linear, so using a pressure regulator for flow control can lead to wasted energy and damaged components.