Check valve means relying on the media flow itself automatically open and close the valve, the valve to prevent the media back, also known as non-return valve, check valve, backflow valve and back pressure valve. Check valves are an automatic valve, whose main role is to prevent the media back, to prevent reverse pump and drive motor, and discharge the container medium. Pressure valve which can also be used to exceed the system pressure may rise auxiliary systems provide supply pipeline. Check valve can be divided into the swing check valve (depending on the focus of the rotation) and lift check valves (axial movement). The role of this type of check valve is only allowed media to flow in one direction and prevent flow in the opposite direction. Usually the valve is automatically work in a direction of flow of the fluid pressure effect, the valve opens; fluid flow the opposite direction, the fluid pressure and the valve flap from the coincidence of acting on the valve seat, thereby cutting off the flow. Check them belong to this type of valve, which includes swing check valves and lift check valves. Swing Check Valve with ordinary hinge, there is a door the same as the free flap valve leaning tilt seat surface. To ensure the valve position every time to reach the right side of the seat, the valve flap design in the hinge body to valve flap has enough to swing space, and make a real flap valve, comprehensive engagement with the valve seat. Valve can all be made of metal can also be embedded in the leather, rubber on metal, or synthetic coverage, depending on performance requirements. Swing check valve in the fully open position, the fluid pressure virtually unimpeded, so by the pressure drop across the valve is relatively small. Lift check valve located on the valve body sealing surface of the valve seat is located. Addition to this valve disc is free to lift, the other part as the cut-off valves, fluid pressure lifted from the valve seat sealing surface, medium return valve flap led to a seat, and cut off the flow. Depending on conditions, the valve flap can be all metal construction, it can also be inlaid in the form of a rubber mat or rubber ring in the valve frame. Like off valves, fluid channels through the lift valve is narrow, so check valve by lifting the pressure drop than the swing check valve a little bigger, and swing check valves for flow restrictions very little.