Butterfly valve single, double, triple eccentric butterfly valve difference description

First, the central butterfly valve
The butterfly valve has the structural features of the valve stem axis, the center of the disc, and the center of the body at the same position. The structure is simple and convenient to manufacture. A common rubber-lined butterfly valve belongs to this category. The disadvantage is that the butterfly plate 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 is not resistant to high temperatures. the reason.
Second, single eccentric butterfly valve

In order to solve the problem of the pressing of the butterfly plate 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 butterfly plate, so that the lower end of the butterfly plate 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 used much.
Third, double eccentric butterfly valve
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.
Four or three eccentric butterfly valves
To withstand high temperatures, a hard seal must be used, but the amount of leakage is large; for zero leakage, a soft seal must be used, but it is not resistant to high temperatures. 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 main cylinder while the eccentric axial position of the double eccentric shaft is eccentric, that is, after the third eccentricity, the sealing section of the disc is not In addition, it is a true circle, but an ellipse, and its sealing surface shape is also asymmetrical, and the 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, thus solving the problem of zero leakage of the metal valve seat, and because the contact surface pressure is proportional to the dielectric pressure, the high pressure and high temperature are also solved.