Silencing check valve 's role is only allowed media to flow in one direction, and stop the flow direction. The major domestic manufacturers have the right valve equipment limited company of Shanghai. Usually the valve is automatically work, in a direction of flow of fluid under pressure, the valve flap to open; fluid flow in the opposite direction, by the fluid pressure and the valve self-valve coincidence role in the valve seat, thereby cutting off the flow. Should not be used for containing solid particles and high viscosity medium. The internal thread check valve butterfly check valve, belongs to this type of valve, which includes swing check valve and lift check valve. Swing check valves are ordinary hinge, and a door like free flap valve against the valve seat sloping surface. In order to ensure that the flap valve seat face every time to reach the appropriate position, the valve flap design in the hinge, so that the valve flap is enough to swing space, and make a real flap valve, comprehensive engagement with the valve seat. Valve could be made of metal, metal can also be embedded in the leather, rubber, or synthetic coverage, depending on performance requirements. Swing check valve in the fully open position, almost unimpeded fluid pressure, so the pressure drop through the valve is relatively small. Lift check valve is located at the valve seat sealing surface. In addition to the valve disc can freely lift, like the rest of the cut-off valve, the pressure of fluid from the valve seat sealing surface lift, medium return led to the valve seat valve down, and cut off the flow. Under the conditions of use, the valve can be all-metal structure, and can also be rack mounted in the valve rubber cushion or rubber ring form. The same as the cut-off valves, fluid through the lift check valve channel is narrow, so through the lift check valve pressure drop than the swing check valve, and swing check valve flow restrictions few. This type valve in the pipeline in general should be installed horizontally.