Since the check valve is qualitatively determined for quick closing in most practical applications, the medium is directional in the moment the check valve is closed, and the medium rapidly drops from a large reverse speed as the valve flap closes.

For high-pressure piping systems where multiple pumps are used in parallel, the water hammer problem of the check valve is more prominent. A water hammer is a pressure wave in a transient flow in a pressure pipe. It is a hydraulic shock phenomenon in which the pressure rises or falls due to a change in the fluid flow rate in the pressure pipe.

The check valve is installed on the pipeline, which becomes one of the fluid components of the complete pipeline. The valve flap opening and closing process is affected by the transient flow state of the system in which it is located; in turn, the closing characteristics of the valve flap are It acts on the fluid flow state.

The working characteristic is that the load changes greatly, the opening and closing frequency is small, and when the input is closed or opened, the applicable period is long, and the moving parts are not required to move. But once it is "switched", it must be flexible, which is more demanding than the usual mechanical movements.

The function of this type of valve is to allow only the medium to flow in one direction and to 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-closing valve flap of the valve disc act on the valve seat to cut off the flow.

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.

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 freely on 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.