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Butterfly Valve Classification

  • 2021-05-04 09:00

        1. Concentric butterfly valve:  The structural feature of this kind of butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate and the center of the body are in the same position. The structure is simple and the manufacturing is convenient. Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of squeezing and scratching, with a large resistance distance and rapid wear. In order to overcome squeezing, scratching, and to ensure sealing performance, the valve seat is basically made of rubber or polytetrafluoroethylene and other elastic materials, but it is also subject to temperature restrictions in use. This is why traditionally people think that butterfly valves are not resistant to high temperatures. the reason.

     
   2. Single eccentric butterfly valve:  is to solve the problem of the extrusion of the butterfly plate and the valve seat of the concentric butterfly valve, resulting in a single eccentric butterfly valve. Its structural feature is that the stem axis deviates from the center of the butterfly plate, so that the lower end of the butterfly plate is no longer It becomes the axis of rotation, disperses, and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, because the single eccentric structure does not disappear from the scratching phenomenon of the butterfly plate and the valve seat during the entire opening and closing process of the valve, and the scope of application is similar to that of the concentric butterfly valve, it is not used much.



         3. Double eccentric butterfly valve: On the basis of the single eccentric butterfly valve, the double eccentric butterfly valve is the most widely used double eccentric butterfly valve. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching between the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The life of the valve seat is improved. The scraping is greatly reduced, and at the same time, the double eccentric butterfly valve can also use a metal seat, which improves the application of the butterfly valve in the high temperature field. But because its sealing principle is a positional sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, and the elastic deformation caused by the butterfly plate squeezing the valve seat produces a sealing effect, so the closing position is very demanding (especially metal Valve seat), low pressure bearing capacity, which is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.
 

         4. Triple eccentric butterfly valve:  must be resistant to high temperatures and must use a hard seal, but the leakage is large; if there is no leakage, a soft seal must be used, but it is not resistant to high temperatures. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time. Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body, that is to say, after the third eccentricity, the sealing section of the butterfly plate is not Furthermore, it is a true circle, but an ellipse, and the shape of the sealing surface is therefore asymmetrical. One side is inclined to the center line of the body, and the other side is parallel to the center line of the body. The biggest feature of this third eccentricity is that the sealing structure is fundamentally changed. It is no longer a position seal, but a torsion seal, that is, it does not rely on the elastic deformation of the valve seat, but completely relies on the contact surface pressure of the valve seat to achieve the seal. Therefore, the problem of zero leakage of the metal valve seat is solved in one fell swoop, and because the contact surface pressure is proportional to the medium pressure, the high pressure and high temperature resistance is also solved.
 

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