Flow valves are suitable for water systems that require flow control, especially for flow control of non corrosive liquid media such as heating and air conditioning; Installed in the water system, with one adjustment before operation, the system flow rate can automatically remain constant at the required set value. Automatically eliminating hydraulic imbalances caused by various factors in the water system, maintaining the required flow rate for users, overcoming "uneven heating and cooling", increasing the room temperature of heating and air conditioning, improving system energy efficiency, and achieving energy conservation, is an ideal supporting product for heating and air conditioning systems to achieve "metering and charging".