The check valve can also be used to replenish the auxiliary system where the pressure may rise above the system pressure. Check valves can be divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis).

The role of this type of check 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 the fluid pressure flowing in one direction, the valve flap opens; when the fluid flows in the opposite direction, the self-coincidence of the fluid pressure and the valve flap acts on the valve seat, thereby cutting off the flow.

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 flap like a door freely rests on the inclined seat surface. In order to ensure that the valve flap can reach the proper position of the valve seat surface every time, the valve flap is designed in the hinge mechanism, so that the valve flap has enough unscrewed space, and the valve flap is truly and fully contacted with the valve seat. The valve flap can be made entirely of metal, or it can be inlaid with leather, rubber, or a synthetic cover, depending on the performance requirements. When the swing check valve is fully open, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The valve flap of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except for the valve flap which can be lifted and lowered freely, the rest of the valve is like a shut-off valve. The fluid pressure lifts the valve flap from the sealing surface of the valve seat. The medium backflow causes the valve flap to fall back to the valve seat and cut off the flow. According to the conditions of use, the valve flap can be an all-metal structure, or in the form of a rubber pad or rubber ring inlaid on the valve flap 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 of the swing check valve is restricted. Very little.