Check valve is a kind of valve whose opening and closing parts are round disc, and its action is produced by its own weight and medium pressure to block medium backflow. Belong to automatic valve class, also known as check valve, one-way valve, return valve or isolation valve. Check valve the function of this type of valve is to only allow the medium to flow in one direction and prevent the flow in the opposite direction. Usually this kind of valve works automatically. Under the action of fluid pressure flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the fluid pressure and the self weight of the valve disc act on the valve seat, thus cutting off the flow.