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Sealing characteristics and principle of eccentric butterfly valve
Source: | Author:Xinsy WZ | Publish time: 354 days ago | 298 Views | Share:
Eccentric butterfly valves can be divided into three types,Single,doube and three eccentric butterfly valve

Eccentric butterfly valves can be divided into various types, generally single eccentric sealing butterfly valves, double eccentric sealing butterfly valves, and trieccentric sealing butterfly valves.


Single eccentric sealing butterfly valve features:


In order to solve the problem of the pressing of the disc and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve is generated, which is characterized in that the axial center of the valve stem is deviated from the center of the disc, so that the lower end of the disc is no longer the rotary axis. Disperses and reduces the excessive extrusion of the lower end of the disc and the valve seat. However, due to the single eccentric structure, the scraping phenomenon of the butterfly plate and the valve seat does not disappear during the whole switching process of the valve, and the application range is similar to that of the concentric butterfly valve, so that it is not used much. The single eccentric sealing butterfly valve has the following characteristics:


1. A sealing structure with reliable performance and long service life.

2. A truss structure with small flow resistance, good rigidity and low pressure loss.

3. The valve plate seal is easy to replace and easy to repair.

4. The valve plate sealing ring adopts “T” shape structure, and the sealing pair is linearly sealed.

5. The bottom end of the valve is made of bimetallic thrust washer, which has excellent thrust performance.

6. The valve can be installed either vertically or horizontally for good applicability.

7. This type of valve is recommended for one-way use and can be used in both directions when the reverse sealing requirements are not critical.

8. When the valve is completely closed, the leak test leakage is zero.

9. Replace the valve plate seal ring, O-ring, valve body, valve plate, shaft and other materials, can be applied to a variety of media and different temperatures.


Double eccentric sealing butterfly valve features:


    Further improved molding on the basis of a single eccentric butterfly valve is currently the most widely used double eccentric butterfly valve. The structural feature is that the stem axis is offset from the center of the disc and from the center of the body. The double eccentric effect allows the disc to be quickly disengaged from the valve seat after the valve is opened, which greatly eliminates unnecessary over-squeezing and scraping of the disc and the valve seat, reduces the opening resistance, reduces wear and improves The seat life. The scraping is greatly reduced, and the double eccentric butterfly valve can also be used with a metal valve seat, which improves 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 sealing surface of the butterfly plate and the valve seat is in line contact, and the elastic deformation caused by the butterfly plate pressing the valve seat produces a sealing effect, the closing position is required (especially metal). Seat), low pressure bearing capacity, which is why people think that butterfly valves are not resistant to high pressure and large leakage. Its main features are as follows:


1. Adopt full flow design, free from the influence of impurity jamming. The joint “O” type sealing line at both ends makes the pipeline installation without gasket and maintains reliable sealing. Different materials can be selected according to different use requirements.

2. The butterfly plate material adopts streamlined design, which can be used in both directions, with small flow resistance and excellent flow characteristics.

3. The axle pin adopts the unloading structure, which can tightly bond the disc valve stems without weakening the strength of the shaft and having good interchangeability.

4. The valve body connection can be applied to ANSI 125/150, DIN 2501 PN 10/16, JIS B2210 10K, JIS G5527 7.5K standard.


Three eccentric sealing butterfly valve features:Trieccentric butterfly valve diagram

1. API specifications

2. Double safety structure

3. No dead zone design

4. Body seat structure

5. Thin layer valve seat structure

6. Replaceable seal pair

7. Balanced fixed structure

8. Essential refractory structure

9. High sealing packing construction

The structure diagram of the three eccentric butterfly valve is characterized in that the eccentricity of the shaft position of the double eccentric valve is eccentric, and the conical axis of the sealing surface of the disc is deflected to the axis of the body cylinder, that is, after the third eccentricity, The sealing section of the disc is no longer a true circle, but an ellipse, and its sealing surface shape 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 this third eccentricity is that it fundamentally changes the sealing structure, 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 seal. The effect solves the problem of zero leakage of the metal valve seat in one fell swoop, and the contact surface pressure is proportional to the medium pressure, and the high pressure and high temperature are also solved. Since its inception, the three eccentric butterfly valves have undergone a process of self-improvement and continuous development in order to meet the increasingly severe working conditions. Even if the highest zero leakage is required, the triple eccentric butterfly valve can be theoretically implemented, but in reality, it still relies on careful design and precise manufacturing.