Author:Site Editor Publish Time: 2018-12-07 Origin:Site
Butterfly valve is a valve in which a closing part is a disc that rotates around the valve shaft to open and close, and is mainly used for cutting and throttling on the pipeline. The butterfly valve opening and closing part is a disc-shaped butterfly plate that rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjusting.
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 and scraped, and the resistance is large and the wear is fast. In order to overcome the extrusion, scratching and sealing performance, the valve seat is basically made of elastic materials such as rubber or Teflon, but it is also limited in temperature. This is why the butterfly valve is not considered to be high temperature.
Single offset 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 offset 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 offset 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.
Further improved molding on the basis of the single offset butterfly valve is the widely used double offset 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 offset 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 offset 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.
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 offset 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 at the same time as the offset position of the double offset stem, 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, with one side inclined to the center line of the body and the other side parallel to the center line of the body.