Check valve The role of this type of valve is to only allow the medium to flow in one direction, but also prevent the flow in the direction. Usually this valve works automatically. Under the action of the fluid pressure in one direction, the valve flap opens; when the fluid flows in the opposite direction, the self-coincidence valve flap of the fluid pressure and the valve flap acts on the valve seat, thereby cutting off the flow. Among them, check valve belongs to this type of valve, which includes swing check valve and lift check valve. 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. Swing check valve is fully open, the fluid pressure is almost unimpeded, so the pressure drop through valve is relatively small. The disc seat of the lift check valve is located on the seat sealing surface of 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 pressure of the fluid 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 stop 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 the swing check valve, and the flow rate of the swing check is very limited less.