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What is the difference between single, double and triple eccentric butterfly valves

Single eccentric butterfly valve

Single eccentric butterfly valve: In order to solve the problem of squeezing between the butterfly plate and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve is produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become The rotation axis is dispersed, and the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat is reduced.

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 of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The seat life 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. However, 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 high and the pressure bearing capacity is very high. Low, which is why it is traditionally believed that butterfly valves are not resistant to high pressure and have large leakage.

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. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric three times. 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 three eccentricities, the sealing section of the disc is no longer It is a true circle, but an ellipse, and the shape of its sealing surface is therefore asymmetrical. The biggest feature of these three eccentricities is that the sealing structure is fundamentally changed. 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 the sealing effect. 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 easily solved.

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