Check valve refers to a valve whose opening and closing part is a round valve disc and acts by its own weight and medium pressure to block the backflow of the medium. It is an automatic valve, also known as check valve, check valve, return valve or isolation valve. The motion mode of the valve disc is divided into lifting type and swinging type. Lift check valves are similar in structure to globe valves, except for the lack of a stem that drives the disc. Media from the inlet end (swing check valves have a disc that is tilted and can rotate around the shaft, and work in a similar way to lift check valves. The check valve is often used as the bottom valve of the pumping device, which can prevent the return of water. The combination of the check valve and the globe valve can play a role in safety isolation. The disadvantage is that the resistance is large and the sealing is poor when closed.