The check valve is a check valve, and the check valve is only a one-way opening and closing valve for preventing the reverse flow of the fluid medium on various pipelines or equipment. Check valves are widely used now, and there are many types. The following is a check valve commonly used in water supply and heat:

1. Spring type: The liquid flows from bottom to top, and the valve disc controlled by the spring can be lifted up by the pressure. After the pressure disappears, the spring force will press the valve disc down to seal the liquid backflow. It is often used for check valves with small diameters.
2. Gravity type: similar to the spring type, it is closed by the gravity of the disc to prevent backflow.
3. Swing type: The liquid flows straight through the valve body, and the rotating valve disc on one side is pushed open by pressure. After the pressure is lost, the valve disc returns to its position by its own weight, and the reverse liquid pressure closes the valve disc. The principles of other one-way valves (check valves), such as sewage check valves, explosion-proof valves for civil air defense, and check valves for liquid use are similar.