The butterfly valve also known as flap valve, is one kind of control valves with a simple structure, can be used for low-pressure pipe media switch control, the valve can be used to control the air, water, steam, corrosive media, mud, oil, liquid metal and radioactive media and other types of fluid flow. In the pipeline the main cut off and throttling effect. Butterfly valve opening and closing parts is a disc-shaped disc, in the valve body to rotate around its own axis, so as to achieve the purpose of opening or closing or adjustment.