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First, the center butterfly valve The butterfly valve structure is characterized by stem axis, butterfly center, body center in the same position. Simple structure, easy to manufacture. Common rubber lining butterfly valve that belongs to this category. The disadvantage is that the disc and valve seat is always in the squeeze, scratch status, resistance, wear fast. To overcome the squeeze, scratch, and ensure the sealing performance, the seat basically uses rubber or PTFE and other elastic materials, but also in use by the temperature limit, which is why the traditional butterfly valve that people are not high temperature the reason. Single eccentric butterfly valve In order to solve the concentric butterfly valve butterfly valve seat squeeze, resulting in a single eccentric butterfly valve, the structural characteristics of the stem axis deviation from the butterfly center, so that the upper and lower disc no longer Become the axis of rotation, decentralized, reducing the over-squeeze of the upper and lower disc and valve seat. However, due to the single eccentric structure in the whole process of valve switching disc and seat scraping phenomenon has not disappeared in the application range and concentric butterfly valve is similar, so use less. Third, the double eccentric butterfly valve in the single butterfly valve based on the further improvement of the shape is currently the most widely used double eccentric butterfly valve. Its structural feature is that the valve rod axis deviates from the center of the butterfly plate as well as the center of the valve body. Double eccentric effect of the valve is opened, the disc can be quickly separated from the seat, a substantial elimination of disc and valve seat unnecessary over-squeeze, scratch phenomenon, reducing the open resistance, reducing wear and tear, improve Seat life. Significantly reduce the scratch, but also makes double eccentric butterfly valve can also be used metal seat, improve the butterfly valve in the field of high temperature applications. However, because the sealing principle is a sealing structure at the position, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, the sealing effect is generated by the elastic deformation caused by squeezing the valve seat of the butterfly plate. Therefore, the sealing position is highly demanding and pressure- Low, which is why people traditionally think that the valve is not resistant to high pressure, the reasons for the large amount of leakage. Four, three eccentric butterfly valve to high temperature, you must use a hard seal, but the large amount of leakage; to zero leakage, you must use a soft seal, but not high temperature. In order to overcome this contradiction of double eccentricity butterfly valve, the third eccentricity was performed on the butterfly valve. The structure is characterized in that the conical axis of the sealing surface of the disc is deflected to the cylinder axis of the body while being eccentric in the shaft center of the double-eccentricity, that is to say, after the third eccentricity, the sealing section of the disc does not Rectangular, but the oval, the sealing surface is therefore asymmetric shape, while tilting the body centerline, the other side is parallel to the centerline of the body. The biggest feature of this third eccentric is to fundamentally change the seal structure, is no longer the position of the seal, but the torque seal, that is not relying on the seat of the elastic deformation, but completely rely on the contact pressure of the seat to achieve the seal Effect, so in one fell swoop solves the problem of zero leakage of the metal valve seat, and because of the contact pressure and pressure is proportional to the pressure, high temperature and pressure are also solved.