Butterfly valves are divided into concentric butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and three eccentric butterfly valve. What are the main differences between these four butterfly valves? Now, Dervos will introduce to you:

1. Concentric Butterfly Valve (Midline Butterfly Valve)

The structural feature of the concentric butterfly valve is that the valve stem axis, the center of the butterfly plate and the center of the body are in the same position. It has the advantages of simple structure and convenient manufacture. The disadvantage is that the butterfly plate and valve seat are always in the state of extrusion and scratch, with large resistance distance and fast wear. In order to overcome extrusion and scratch and ensure sealing performance, the valve seat basically adopts elastic materials such as rubber or polytetrafluoroethylene, but the use of sealing materials is limited by temperature.

2. Single Eccentric Butterfly Valve

The structural feature of the single eccentric butterfly valve is that the 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, and solves the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve. However, the scratch phenomenon between the butterfly plate and the valve seat has not disappeared in the whole opening and closing process of the valve. Therefore, the application range of single eccentric butterfly valve is similar to concentric butterfly valve, and there are few applications.

3. Double Eccentric Butterfly Valve

The double eccentric butterfly valve is further improved on the basis of the single eccentric butterfly valve. Its structural feature is that the axis of the valve rod deviates from the center of the butterfly plate and the center of the body. The effect of double eccentricity enables the butterfly plate to leave the valve seat immediately after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scratch between the butterfly plate and the valve seat, reduces the opening resistance and wear, improves the service life of the valve seat. The scratch is greatly reduced, so that the double eccentric butterfly valve can adopt metal seat, which improves the application of butterfly valve in high temperature field. However, the sealing effect is produced by the elastic deformation caused by the extrusion of butterfly plate and valve seat. It has high requirements for the closing position (especially the metal valve seat), low pressure bearing capacity and large leakage.

4. Three Eccentric Butterfly Valve

To withstand high temperature, hard seal must be used, but the leakage is large; to achieve zero leakage, soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of double eccentric butterfly valve, three eccentric butterfly valve came into being. Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the sealing surface of the butterfly plate deviates from the cylindrical axis of the body. After the third eccentricity, the sealing section of the butterfly plate is no longer circular, but elliptical. Therefore, the shape of the sealing surface is asymmetric, one side is inclined to the center line of the body, and the other side is parallel to the center line of the body.