Check valves refer to valves whose clacks open and close automatically by flows and forces of the medium to prevent the media flowing back to the valves, the motors' reversal of pumps and drives and the leakage of media inside containers. Check valves, belonging to automatic valves, are mainly for the pipelines where the media can only flow in one direction. Typically, the fluid makes the clack open under the pressure and it flows from the inlet side to the outlet side. When the pressure of inlet side is lower than that of the outlet side, the valve clack will automatically shut down the channel under the effects of fluid pressure and its own gravity to prevent back flow of fluid. According to the different movement modes of clacks, check valves can be divided into 3 categories: lift check valves, swing check valves and butterfly check valves. The valve body of a lift check valve is similar to that of a globe valve. A lift check valve can produce large resistance force for fluid. The clack of a lift check valve is on the sealing surface of the valve seat on the valve body and is free to lift. The fluid pressure lifts the valve from the sealing surface of the valve seat and the back flow of the media makes the clack fall to the valve seat and cuts off the flow. Depending on the operating conditions, the clack may be in the all-metal structure or in a rubber gasket or ring embedded on the valve frame form. A swing check valve produces small resistance force for fluid and generally are applicable to pipelines with medium or low pressure and large diameters. The shape of a butterfly check valve is like a butterfly. It has a simple structure and produces small resistance forces for fluid. If check valves are closed too fast, it may cause liquid hammer in the pipes full of liquid, resulting in noises and even leading to damage to the valve parts. In order to avoid this situation, when necessary, you can use a check valve with the buffer function to extend the closing time.

Check valves are to prevent the impacts on the water pump impellers in the pump water supply system, which is brought by water flowing back under high pressure. When the system is running, if the pump suddenly stops running for some reasons, the pump pressure will disappear, and the high-pressure water connected to the pump outlet will flow to the pump reversely. When the pump outlet is equipped with a check valve, the check valve will close immediately to prevent high-pressure water flowing back to the pump. Otherwise, high-pressure water will flow to the pump reversely and the pump impeller will reverse under the impact of high-pressure water. It can further causes the pump impeller or other spare parts to be loose or damaged. When the pump is running again, it may cause the impeller to fly out, causing a great threat to safe production.