In order to solve the extrusion problem between the disc and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve is produced. Disperse and reduce the excessive extrusion of the upper and lower ends of the butterfly plate and the valve seat. However, due to the single eccentric structure, the scraping phenomenon between the disc and the valve seat does not disappear during the entire opening and closing process of the valve, and the application range is similar to that of the concentric butterfly valve, so it is not used much.
On the basis of the single eccentric butterfly valve, the most widely used double eccentric butterfly valve is further improved and formed. Its structural feature is that the shaft center of the valve stem deviates from the center of the disc and the center of the body. The effect of double eccentricity enables the disc to break away from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching between the disc and the valve seat, reduces the opening resistance, reduces wear, and improves the performance of the valve. Seat life.
The scraping is greatly reduced, and at the same time, the double eccentric butterfly valve can also use a metal valve seat, which improves the application of the butterfly valve in the high temperature field. However, because its sealing principle is a positional sealing structure, that is, the sealing surface of the disc and the valve seat is in line contact, and the elastic deformation caused by the disc extrusion of the valve seat produces a sealing effect, so it requires high closing position and pressure bearing capacity. Low, which is why traditionally it is believed that butterfly valves are not resistant to high pressure and have large leakage.
To withstand high temperature, a hard seal must be used, but the amount of leakage is large; to zero leakage, a soft seal must be used, but it is not resistant to high temperature. 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 is eccentric, the conical axis of the disc sealing surface is inclined to the cylinder axis of the body, that is to say, after the third eccentricity, the sealing section of the disc does not change. Then it is a true circle, but an ellipse, and the shape of its sealing surface is also 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 the triple eccentric high-performance butterfly valves 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 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 is also solved.
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