The difference between the center butterfly valve and the single eccentric double eccentric three eccentric butterfly valve

Center butterfly valve

The structure of the center butterfly valve is characterized by the stem axis, the center of the butterfly plate and the center of the body in the same position. Simple structure and convenient manufacture. Common rubber lined butterfly valves belong to this category. The disadvantage is that the disc and the seat are always in a state of extrusion, scratching, large resistance, and fast wear. In order to overcome extrusion, scratching and ensure sealing performance, the valve seat is basically made of rubber or polytetrafluoroethylene and other elastic materials, but it is also limited by temperature in use;

Single eccentric butterfly valve

In order to solve the problem of squeezing between the butterfly plate and the seat of the concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate are no longer the rotating axis; Disperses and reduces excessive compression of the upper and lower ends of the disc and the seat. However, because the single-eccentric structure does not disappear the scraping phenomenon between the butterfly plate and the valve seat during the whole switching process of the valve, it is not used much in the application range and the concentric butterfly valve.

Double eccentric butterfly valve

On the basis of the single eccentric butterfly valve further improved molding is the most widely used double eccentric butterfly valve. Its structural feature is that the axis of the valve stem deviates from both the center of the butterfly plate and the center of the body. The effect of double eccentricity enables the disc to be quickly removed from the seat after the valve is opened, greatly eliminating the unnecessary excessive extrusion and scratching phenomenon between the disc and the seat, reducing the opening resistance, reducing wear, and improving the life of the seat.

The significant reduction of scratch also makes the double eccentric butterfly valve can also use metal seats, which improves the application of butterfly valves in high temperature fields. However, because its sealing principle is a position sealing structure, that is, the sealing surface of the butterfly plate and the seat is in line contact, and the elastic deformation caused by the butterfly plate squeezing the seat produces a sealing effect, so the closing position is very high and the bearing capacity is low.

Three eccentric butterfly valve

To withstand high temperature must use a hard seal, but the leakage is large; A soft seal must be used for zero leakage, but it is not resistant to high temperatures. In order to overcome the contradiction of double eccentric butterfly valve, the butterfly valve is eccentric for the third time. The structure feature is that the conical axis of the sealing surface of the butterfly plate is skewed to the cylindrical axis of the body while the eccentric position of the valve stem axis is eccentric. That is to say, after the third eccentricity, the sealing section of the butterfly plate is no longer a true circle, but an ellipse, and the shape of the sealing surface is therefore asymmetric, one side is tilted 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 third eccentricity is to fundamentally change the sealing structure, no longer the position seal, but the torque seal, that is, not relying on the elastic deformation of the seat, but completely relying on the contact surface pressure of the seat to achieve the sealing effect, so it solves the problem of zero leakage of the metal seat in one stroke, and because the contact surface pressure is proportional to the medium pressure, the resistance to high pressure and high temperature is also solved.