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1、 Center butterfly valve

The structural feature of the butterfly valve is that the stem axis, butterfly plate center and body center are at the same position. The structure is simple and the manufacture is convenient. The common rubber lined butterfly valve belongs to this kind. The disadvantage is that the butterfly plate and the valve seat are always in the state of extrusion and scraping, with large resistance distance and fast wear. In order to overcome extrusion, scraping and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or polytetrafluoroethylene, but it is also limited by temperature in use. This is why traditionally people think that butterfly valve is not resistant to high temperature.

2、 Single eccentric butterfly valve

In order to solve the extrusion problem between the butterfly plate and the valve seat of concentric butterfly valve, the single eccentric butterfly valve is produced. Its structural feature is that the shaft axis 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 rotation axis, which disperses and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, due to the single eccentric structure in the whole process of valve opening and closing, the scraping phenomenon between the butterfly plate and the valve seat does not disappear, and its application scope is similar to that of concentric butterfly valve, so it is rarely used.

3、 Double eccentric butterfly valve

On the basis of single eccentric butterfly valve, the double eccentric butterfly valve which is widely used at present is further improved. The structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the body. The effect of double eccentricity enables the butterfly plate to break away from the valve seat immediately after the valve is opened, greatly eliminates the unnecessary over extrusion and scratch phenomenon between the butterfly plate and the valve seat, reduces the opening resistance distance, reduces the wear and improves the service life of the valve seat. At the same time, the double eccentric butterfly valve can also use metal seat, which improves the application of butterfly valve in high temperature field. But because its sealing principle is a position sealing structure, that is, the sealing surface of butterfly plate and valve seat is in line contact, and the elastic deformation caused by squeezing the valve seat through the butterfly plate produces sealing effect, so it has high requirements on the closing position (especially the metal valve seat) and low pressure bearing capacity. This is why traditionally people think that butterfly valve is not resistant to high pressure and has large leakage.

4、 Triple eccentric butterfly valve

To be high temperature resistant, hard seal must be used, but the leakage is large; To be zero leakage, must use soft seal, but not resistant to high temperature. In order to overcome the contradiction of double eccentric butterfly valve, the butterfly valve is eccentric for the third time. Its structural features are that the conical axis of the sealing surface of the butterfly plate is inclined to the cylinder axis of the main body while the axis position of the double eccentric valve stem is eccentric, that is to say, after the third eccentric, the sealing section of the butterfly plate is no longer true circle, but ellipse, and the shape of the sealing surface is asymmetric, one side is inclined to the center line of the main body, and the other side is parallel to the center line of the main body.