Check Valve Working Principle

Check valves can also be used in pipelines supplying auxiliary systems where the pressure may rise above the system pressure. Check valves are mainly divided into swing check valves (rotating around a center of gravity) and lift check valves (moving along an axis).

The function of this type of valve is to allow the medium to flow in only one direction and prevent flow in the opposite direction. These valves are usually automatic. Under the pressure of fluid flowing in one direction, the valve disc opens; when the fluid flows in the opposite direction, the fluid pressure and the weight of the valve disc combine to force the disc against the valve seat, thus cutting off the flow.

Check valves belong to this type of valve, including swing check valves and lift check valves. Swing check valves have a hinge mechanism and a valve disc, like a door, that rests freely against an inclined valve seat surface. To ensure that the valve disc always reaches the correct position on the valve seat, the valve disc is designed in the hinge mechanism to have sufficient swing space and to ensure true and full contact between the valve disc and the valve seat. Valve discs can be made entirely of metal, or inlaid with leather, rubber, or synthetic coverings, depending on performance requirements. In a fully open swing check valve, fluid pressure is almost unimpeded, resulting in a relatively small pressure drop across the valve. In a lift check valve, the valve disc sits on the valve seat sealing surface on the valve body. Except for the freely moving disc, this valve functions like a gate valve; fluid pressure lifts the disc from the seat sealing surface, and backflow causes the disc to fall back onto the seat, cutting off the flow. Depending on the application, the disc can be all-metal or have rubber pads or rings embedded in the disc holder. Like gate valves, the flow path through a lift check valve is narrow, resulting in a larger pressure drop than a swing check valve, while the flow rate of a swing check valve is less restricted.