Development course of triple eccentric butterfly valve
1, concentric butterfly valve
The butterfly valve has the structural characteristics of the stem shaft, and the center of the disc and the center of the body are in the same position. It is simple in structure and convenient in manufacture. The common rubber lining butterfly valves belong to this category. The disadvantage is that the butterfly plate and valve seat are always in extrusion, scraping, resistance, wear fast. In order to overcome extrusion, scraping and sealing properties, the seat is basically made of elastic material, such as rubber or Teflon, but its use temperature is limited, which is traditionally considered to be not a high temperature resistance. Reason.
2. Single eccentric butterfly valve

In order to solve the pressure problem of butterfly plate and seat of concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the shaft center of the valve stem deviates from the center position. The butterfly plate causes the lower end of the butterfly plate to no longer become a rotating shaft, dispersing and reducing the excessive extrusion of the lower end of the disc and the seat. However, because of the single eccentric structure, the scraping of the valve and the valve seat will not disappear during the whole valve switching process, and the application range is similar to that of the concentric butterfly valve, so it is not used much.

3, double eccentric butterfly valve
The further improvement based on single eccentric butterfly valve is the most widely used double eccentric butterfly valve. The structural feature is that the axis of the valve axis deviates from the center of the disc and also deviates from the center of the body. The double eccentric effect makes the valve disconnect quickly from the seat after the valve opens, greatly eliminating unnecessary overextrusion and scraping the seat and seat, reducing the opening resistance, reducing wear and increasing the seat life. The scraping is greatly reduced, and the double eccentric butterfly valve can also be used together with the metal seat to improve the application of the butterfly valve in the high-temperature field. However, because the sealing principle belongs to the position sealing structure, that is, the butterfly plate is in contact with the sealing surface of the seat, and the elastic deformation caused by the compression seat of the butterfly plate produces the sealing effect, and the closed position is necessary (especially the metal). Seat, low pressure bearing capacity, which is why people think that butterfly valves are resistant to high pressure and large leakage.
4, triple eccentric butterfly valve
In order to withstand high temperatures, hard seals must be used, but the leakage is very large; for zero leakage, soft seals must be used, but not high temperature. In order to overcome the contradiction between the double eccentric butterfly valve, the butterfly valve is subjected to third eccentricity. The structural feature is that the conical axis of the sealing surface of the disc is deflected to the axis of the main cylinder at the same time in the eccentric position of the double eccentric rod. That is, after third eccentricity, the sealing part is not another. It is a true circle, but an ellipse, its seal surface is asymmetrical, one side is inclined to the center line of the main body, and the other is the center line of the main body. A central line parallel to the body. The biggest feature of these third eccentricity is that it fundamentally changes the seal structure, no longer a position seal, but a torsional seal, that is, it does not depend on the elastic deformation of the seat, but is completely dependent on the pressure of the seat of the contact surface to reach the seal. This effect solves the problem of zero leakage of metal valve seat at one stroke. The pressure of the contact surface is proportional to the medium pressure. It also solves the problem of high pressure and high temperature.