Butterfly valve, also known as flap valve, is a simple structure control valve, which can be used for low-pressure pipeline medium on-off control. Butterfly valve refers to a kind of valve whose closing piece (disc or butterfly plate) is a round plate and rotates around the valve shaft to open and close. The valve can be used to control the flow of air, water, steam, various corrosive medium, mud, oil, liquid, metal and radioactive medium. It is mainly used to cut off and throttle the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so as to achieve the purpose of opening and closing or adjustment.