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Development of Triple Eccentric Butterfly Valves

  • Publish Time: 2019-04-08
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1. Concentric butterfly valve

Concentric butterfly valve has the structural features of the valve stem axis, the center of the disc, and the center of the body are of the same line. The structure is simple and easy to manufacture. Normal rubber-lined butterfly valve belongs to this category. The disadvantage is that the valve disc and the valve seat are always in a state of being squeezed, scraped, large in resistance and fast in wear. In order to overcome the extrusion, scratching and sealing performance, the valve seat is basically made of elastic material such as rubber or Teflon, but it is also limited in temperature by use, which is why it is traditionally considered that the butterfly valve can"t resist high-temperature.




2. Single eccentric butterfly valve

In order to solve the problem of the pressing of the valve disc and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve is generated, and the structural feature is that the axial center of the valve stem deviates from the center of the valve disc, so that the lower end of the valve disc no longer becomes 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 disc 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 it is not commonly used.



3. Double eccentric(double offset) butterfly valve

As 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 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 valve disc and the valve seat is in line contact, and the sealing is based on elastic deformation caused by the disc pressing the valve seat, so the requirement on closing part is strict (especially metal seat), low pressure bearing capacity, which is why people think that butterfly valves are not resistant to high-pressure and can’t achieve low leakage.



4. Triple eccentric(triple offset) butterfly valve

To withstand high-temperatures, a hard seal must be used, but leakage occurs in the meantime; To achieve 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 subjected to the third eccentricity. The structural feature is that the conical axis of the sealing surface of the disc is deflected to the axis of the body, which means, after the third eccentricity, the sealing section of the valve disc is not eccentric at the axial position of the double eccentric valve stem. In addition, it is not a circle but an ellipse. The shape of its sealing 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, which means, 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, the high-pressure and high-temperature issue is also solved.



Features of triple eccentric butterfly valve :

The triple eccentric butterfly valve is a rotary valve. The triple eccentricities are placed on the valve disc. During the valve manufacturing process, the outer edge of the valve disc adopts a partial outer spherical structure. The outer eccentric spherical surface is polished to a roughness of Ra0.4, and the spherical chrome plated or surfacing stellite alloy. Hardness reaches HRC45~60. The triple eccentric disc valves have a withstand pressure of up to 26 MPa, a temperature resistance as low as -196°C and up to 700°C, and the sealing is zero leakage. It can be seen that due to the innovative structural characteristics of the triple eccentric butterfly valve, it has the following main features.

(1) Suitable for both adjusting and cut-off, easy to operate.

The new triple eccentric butterfly valve is designed with a double safety construction. In order to prevent deformation of the disc caused by fluid pressure and temperature, misalignment of the valve stem and engagement of the sealing surface, two independent thrust rings are respectively arranged on the lower side of the disc, thereby ensuring the valve in any working condition. In order to prevent the valve stem from being damaged or blow out, the independent valve stem anti-below out devices are designed both inside and outside of the bottom of valve body.

(2) No dead zone design, small opening torque.

The shape of the triple eccentric butterfly valve disc is an elliptical cone, the surface of which is welded with hard alloy makes it performs very good on wear resistance. The floating U-shaped stainless steel valve seat has the function of automatically center adjustment. When the valve is opened, the elliptical cone sealing face valve disc will be disengaged from the U-shaped elastic valve seat, then rotate again; when the valve is closed, the valve disc rotates under the action of the eccentric shaft, and the valve disc automatically adjusts the center to the elastic valve seat, then the valve seat will be pressed to deform the valve seat until the valve seat closely matches the elliptical conical sealing surface of the valve disc. When the valve is switched, the disc does not scrape the valve seat, and the torque of the valve stem is directly transmitted to the sealing surface through the valve disc, so the opening torque is small, thereby eliminating the common jumping phenomenon when the valve is opened, which means the dead zone is eradicated . The no dead zone design allows the triple eccentric butterfly valve to enter the regulatable zone from 90 degrees to 90 degrees, with a control ratio of up to 100:1 or more, which is twice that of a typical butterfly valve.

(3) Zero leakage, high-temperature and high-pressure resistance.

The biggest characteristic of the triple eccentricity is that the sealing structure is fundamentally changed. It is no longer a positional seal, but a torsion seal, which means 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. This sealing structure allows the triple eccentric butterfly valves to be hard-sealed at the VI level for true zero leakage. At the same time, due to the selection of the metal seat and the structural characteristics of the face seal, the problem of high-temperature and high-pressure are also solved.


In addition, the triple eccentric butterfly valve is with integral valve body seat. Which is more compact and the valve seat will barely directly contacting the medium. The valve seat will be with less washout, and the influence of minute solid matter in the medium and the sealing surface engagement caused by thermal expansion are effectively prevented. This design makes the service life of valve seat longer.



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