Classification of Butterfly Valves

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, large resistance distance, and fast wear. To overcome squeezing, scratching, and to ensure sealing performance, the valve seat is made of rubber or PTFE 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
To solve the problem of extrusion between the butterfly plate and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve was produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate so that the lower end of the butterfly plate no longer becomes the rotation axis. Disperse and reduce the excessive squeezing between the lower end 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 switching process of the valve, and the application range is similar to that of the concentric butterfly valve, it is not used much.

3. Double eccentric butterfly valve
Based on 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 of 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 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, 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, this is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.

4.Triple eccentric butterfly valve
To withstand high temperatures, hard seals must be used, but the amount of leakage is large; for zero leakage, soft seals must be used, but they are not resistant to high temperatures. 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 disc sealing surface is skewed to the cylinder axis of the body, that is to say, after the third eccentricity, the sealing section of the disc is not Furthermore, it is a true circle, but an ellipse and its sealing surface shape 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 it fundamentally changes the sealing structure. It is no longer a positional 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 sealing. 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 are also solved.