Check valves can also be used in pipelines to supply auxiliary systems where pressure may rise above 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).
Check valves of this type are designed to allow media to flow in only one direction and prevent reverse flow. Usually, the valve operates automatically, and the disc opens under the action of a fluid pressure flowing in one direction. When the fluid flows in the opposite direction, the disc acts on the seat by the fluid pressure and the self-coincidence of the disc, thus cutting off the flow.
Check valves belong to this type of valve, which includes swing check valves and lift check valves. Swing check valves have a hinged mechanism and a door-like disc that is free to lean against the inclined seat surface. In order to ensure that the disc can reach the proper position of the seat surface every time, the disc is designed in a hinge mechanism so that the disc has sufficient swing space and makes the disc truly and comprehensively contact with the seat. Valve discs can be made entirely of metal, or can be metal inlaid with leather, rubber, or synthetic coverage, depending on the performance requirements. When swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The disc of the lift check valve is located on the sealing surface of the seat on the valve body. In addition to the valve disc can rise and fall freely, the rest of the valve is like a globe valve. The fluid pressure causes the disc to rise from the seating surface, and the medium reflux causes the disc to fall back to the seat and cut off the flow. According to service conditions, the disc can be all-metal structure, or it can be in the form of rubber pads or rubber rings embedded on the disc rack. Like globe valves, the passage through which fluid passes through the lift check valve is narrow, so the pressure drop through the lift check valve is larger than that through the swing check valve, and the flow of the swing check valve is limited very little.