Butterfly valve, also known as flap valve, is a simple regulating valve, which can also be used for on-off control of low-pressure pipeline medium. Butterfly valve is a kind of valve whose closing part (disc or butterfly plate) is a disc and rotates around the valve axis to open and close. It mainly plays the role of cutting off and throttling in 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. Butterfly valve is applicable to the pipeline conveying various corrosive and non corrosive fluid medium in the engineering system of generator, gas, natural gas, liquefied petroleum gas, city gas, cold and hot air, chemical smelting, power generation and environmental protection. It is used to regulate and cut off the flow of medium.