How check valve works?

Check valves may also be used on lines supplying auxiliary systems where pressure may rise above system pressure. Check valves can be mainly divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis).
The purpose of this type of valve is to allow the medium to flow in only one direction and prevent flow in the opposite direction. Usually this kind of valve works automatically. Under the action of fluid pressure flowing in one direction, the valve flap opens; when the fluid flows in the opposite direction, the fluid pressure and the self-coincident valve flap of the valve flap act on the valve seat, thereby cutting off the flow.
Among them, the check valve belongs to this type of valve, which includes swing check valve and lift check valve. Swing check valves have a hinge mechanism and a door-like disc that rests freely on the sloping seat surface. In order to ensure that the valve disc can reach the proper position of the valve seat surface every time, the valve disc is designed in the hinge mechanism, so that the valve disc has enough swing space and makes the valve disc truly and comprehensively contact the valve seat. The disc can be made entirely of metal, or inlaid with leather, rubber, or synthetic overlays, 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 disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the valve disc can rise and fall freely, the rest of the valve is like a globe valve. The fluid pressure lifts the valve disc from the sealing surface of the valve seat, and the backflow of the medium causes the valve disc to fall back to the valve seat and cut off the flow. According to the conditions of use, the disc can be of all-metal structure, or it can be in the form of a rubber pad or rubber ring embedded on the disc holder. Like the globe 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 of the swing check valve is limited rare.