The function of this type of valve is to only allow the medium to flow in one direction and prevent the direction from flowing. Usually, the valve is automatically operated, and the valve flap is opened by the fluid pressure flowing in one direction; when the fluid flows in the opposite direction, the fluid pressure and the self-reclosing valve flap of the valve disc act on the valve seat to cut off the flow.
Among them, the check valve belongs to this type of valve, which includes a swing check valve and a lift check valve. The swing check valve has a hinge mechanism and a door-like flap that rests freely against the inclined seat surface. In order to ensure that the valve flap can reach the proper position of the valve seat surface each time, the valve flap is designed in the hinge mechanism, so that the valve flap has enough swinging space and the valve flap is truly and comprehensively in contact with the valve seat. The discs can all be made of metal, or they can be inlaid with leather, rubber, or synthetic coverings depending on the performance requirements. In the fully open condition of the swing check valve, the fluid pressure is almost unimpeded, so the pressure drop across the valve is relatively small. The valve flap of the lift check valve is located on the valve seat sealing surface of the valve body. In addition to the valve flap being free to lift and lower, the valve is like a shut-off valve. The fluid pressure causes the valve flap to lift from the valve seat sealing surface. The return of the medium causes the valve flap to fall back to the valve seat and shut off the flow. Depending on the conditions of use, the flap may be of an all-metal construction or may be in the form of a rubber or rubber ring on the valve disc holder. Like the shut-off valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow rate of the swing check valve is limited. Very few.