Butterfly valve is a disc rotating with the valve stem as the opening and closing parts, to realize the valve opening, closing and adjustment. In addition to the use of the butterfly valve in the pipeline, the sealing performance has been taken as the main evaluation index in recent years, favored by the market. In addition, butterfly valve has the advantages of small size, light weight, simple structure, compared with the same parameter gate valve, the average weight reduction of 30~50%, butterfly plate rotation 90° can realize the process of opening and closing, and because of the shaft on both sides of the butterfly plate by the medium force approximately phase and so on, the torque is opposite, so the opening and closing torque is small.