The butterfly valve refers to a kind of valve whose closing part (valve disc or butterfly plate) is a disc and rotates around the valve shaft to achieve opening and closing. It mainly plays the role of cutting off and throttling on the pipeline. The butterfly valve opening and closing part is a disc-shaped butterfly plate, which rotates around its own axis in the valve to achieve opening and closing or adjustment. The butterfly valve is usually less than 90° from fully open to fully closed. The butterfly valve and the butterfly stem have no self-locking ability. In order to locate the butterfly plate, a turbo reducer should be installed on the valve stem.
1. Single eccentric butterfly valve. In order to solve the extrusion problem between the disc and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the axis of rotation, and are dispersed, reducing the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, since the scraping phenomenon between the disc and the valve seat of the single eccentric butterfly valve does not disappear during the entire opening and closing process of the valve, it is similar to the concentric butterfly valve in terms of application, so it is not widely used.
2. Double eccentric butterfly valve. On the basis of the single eccentric butterfly valve, this kind of China butterfly valve is improved and widely used at present. Its structural feature is that the shaft center of the valve stem deviates from the center of the disc and the center of the body. The effect of the double eccentric butterfly valve is that the butterfly plate can be quickly separated from the valve seat after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching between the butterfly plate and the valve seat, reduces the opening resistance and wear and tear, and improves seat life.
The scraping is greatly reduced, and the metal valve seat can also be used for the double eccentric butterfly valve, which improves the application of the butterfly valve in the high temperature field. However, because its sealing principle is a position sealing structure, that is, the sealing surface of the disc and the valve seat is in line contact, and the elastic deformation caused by the disc extrusion of the valve seat produces a sealing effect, so the closing position is very demanding (especially metal valve seat) and has low pressure capacity.
3. Triple offset butterfly valve. To withstand high temperature, a hard seal must be used, but the amount of leakage is relatively large. To avoid 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 eccentric for the third time. While the position of the double eccentric stem is eccentric, the triple offset butterfly valve makes the conical axis of the sealing surface of the butterfly disc deviate from the cylinder axis of the body, that is to say, after the third eccentricity, the sealing section of the disc is no longer a true circle, but an ellipse, and the shape of the sealing surface is also asymmetrical, one side is inclined to the center line of the body, and the other side is parallel to the center of the body string.