1.Concentric butterfly valve
The structural characteristics of the butterfly valve are that the axis of the stem, the center of the butterfly plate and the center of the body are in the same position. The utility model has the advantages of simple structure and convenient manufacture. Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and valve seat are always in the state of extrusion, scratch, large resistance distance, and fast wear and tear. In order to overcome the problems of extrusion and scratch and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but it is also limited by temperature in use. This is why butterfly valves are traditionally considered to be resistant to high temperatures.
2.Single eccentric butterfly valve
In order to solve the extrusion problem of concentric butterfly valve
butterfly plate and valve seat, a single eccentric butterfly valve is produced. Its structural feature is that the axis of the stem deviates from the center of the butterfly plate, so that the lower end of the butterfly plate is no longer the center of rotation, and the excessive extrusion of the lower end of the butterfly plate and the valve seat is dispersed and alleviated. However, due to the single eccentricity structure in the whole process of the valve switch butterfly plate and seat scratch phenomenon has not disappeared, in the application range and concentric butterfly valve are similar, so the user is not much.
3.Double eccentric butterfly valve
On the basis of the single eccentric butterfly valve, the double eccentric butterfly valve, which is widely used at present, is further improved. The structure features that the axis of the valve stem deviates from both the center of the butterfly plate and the center of the body. The effect of double eccentricity enables the butterfly plate to detach from the valve seat immediately after the valve is opened, greatly eliminating unnecessary over-extrusion and scratch between the butterfly plate and the valve seat, reducing the opening resistance, reducing wear and improving the service life of the valve seat. The scratch is greatly reduced. At the same time, the double eccentric butterfly valve can also use the metal seat, which improves the application of butterfly valve in the high-temperature field. But because the sealing principle is position sealing structure, that is, the sealing surface of butterfly plate and the seat is in line contact, and the elastic deformation caused by butterfly plate extruding the seat produces a sealing effect, it requires a high closing position (especially metal seat) and low pressure bearing capacity. This is why butterfly valves are traditionally considered to be high pressure resistant and leak a lot.
4. Tri-eccentric butterfly valve
To withstand high temperature, hard seals must be used, but the leakage is large; to zero leakage, soft seals must be used, but not high temperature. In order to overcome the contradiction of double eccentricity butterfly valve, the third eccentricity of butterfly valve was carried out. The structure features that the conical axis of the butterfly plate sealing surface is oblique to the cylinder axis of the body while the axis position of the double eccentric stem is eccentric. That is to say, after the third eccentric, the sealing section of the butterfly plate is no longer a true circle, but an ellipse. Therefore, the shape of the sealing surface is asymmetrical, with one side inclined to the body center line and the other side parallel to the body center line.
The greatest feature of the third eccentricity is that it fundamentally changes the sealing structure, not position seal, but torsional seal, that is, not relying on the elastic deformation of the seat, but relying entirely on the contact surface pressure of the seat to achieve sealing effect. Therefore, the problem of zero leakage of metal seats is solved at one stroke. Because the pressure of the contact surface is proportional to the pressure of the medium, the high pressure and high-temperature resistance are also solved.