1. Center Butterfly Valve
The structure of the butterfly valve is characterized in that the stem axis, 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. A common rubber-lined butterfly valve falls into this category. Disadvantages are due to the disc and seat always in extrusion, scratch state, resistance distance, wear fast. In order to overcome the extrusion, scratch, seal performance, valve seat basically use rubber or polytetrafluoroethylene, but also in the use of temperature restrictions, this is why people traditionally thought that the butterfly valve is not heat resistant.
2. Single Eccentric Butterfly Valve
In order to solve the problem of extrusion between disc and seat of concentric butterfly valve, a single Eccentric Butterfly Valve is produced, which is characterized by the deviation of the stem axis from the disc center, so that the upper and lower ends of the disc no longer become the rotary axis, disperse, reduce the excessive extrusion between the upper and lower ends of the disc and the seat. But because of the single eccentric structure in the whole valve opening and closing process of disc and seat scratch phenomenon does not disappear, in the Application Range and concentric butterfly valve similar, so not much.
3. Double Eccentric Butterfly Valve
Based on the single eccentric butterfly valve, the double eccentric butterfly valve is the most widely used at present. The structure is characterized in that the shaft of the valve stem deviates from both the center of the disc and the center of the body. The double eccentric effect makes the butterfly plate can quickly leave the valve seat after the valve is opened, and greatly eliminates the unnecessary excessive extrusion, scratch phenomenon between the butterfly plate and the valve seat, reduces the opening resistance distance, reduces the wear and tear, and increases the life of the valve seat. The greatly reduced scratch, at the same time also makes double eccentric butterfly valve can also use metal seat, improve the butterfly valve in the high-temperature field applications. But because of its sealing principle is position seal structure, namely the sealing surface of butterfly plate and valve seat is line contact, the elastic deformation caused by squeezing the valve seat through the butterfly plate produces sealing effect, so it requires very high closing position, low bearing capacity, which is why people think that the butterfly valve is not resistant to high pressure, large leakage.
4. Triple Eccentric Butterfly Valve
To be resistant to high temperature, must use hard seal, but leakage; to zero leakage, must use soft seal, but not resistant to high temperature. In order to overcome the contradiction of double eccentric butterfly valve, the triple eccentric butterfly valve was carried out. The structure features are that the conical axis of the butterfly plate sealing surface deviates from the axis of the body cylinder while the double eccentric valve stem axis is eccentric, that is to say, after the third eccentricity, the sealing section of the butterfly plate is no longer true circle, but ellipse, the sealing surface shape is also asymmetrical, one side is inclined to the center line of the body, the other side is parallel to the center line of the body.
The biggest characteristic of this triple eccentricity is to change the sealing structure fundamentally, no longer is the position seal, but the torque seal, namely is not depending on the elastic deformation of the valve seat, but completely depending on the contact surface pressure of the valve seat to achieve the sealing effect, thus solved the problem of zero leakage of the metal valve seat at one stroke, and because the contact surface pressure is proportional to the dielectric pressure, high pressure and high temperature are also solved.
Post time: Nov-25-2021