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Second, the single eccentric butterfly <br> <br> to solve the problem of extruding concentric butterfly valve plate and valve seat, thereby creating a single eccentric butterfly valve, wherein the structure of the disc offset from the center axis of the stem, so that The lower end of the butterfly plate no longer becomes the axis of rotation, dispersion, and the excessive extrusion of the lower end of the butterfly plate and the valve seat is relieved. However, due to the single eccentric structure, the scraping phenomenon of the butterfly plate and the valve seat did not disappear during the entire switching process of the valve, and the application scope was similar to the concentric butterfly valve, so it was not used much.
Third, the double eccentric butterfly <br> <br> further improved molding is the most widely used double eccentric butterfly valve on the basis of a single eccentric butterfly valve on. Its structural feature is that the stem axis is both offset from the center of the disc and away from the center of the body. The effect of double eccentricity makes the butterfly plate quickly disengage from the valve seat after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scraping of the butterfly plate and the valve seat, reduces the open distance, reduces wear, and improves Seat life. The drastic reduction of the scratches also allows the use of metal seats for the double-eccentric butterfly valve, which increases the application of the butterfly valve in the high temperature field. However, because its sealing principle is a position seal structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, and the sealing effect is caused by the elastic deformation caused by the butterfly plate squeezing the valve seat, so the requirement for the closed position is very high (especially the metal Seat), low pressure bearing capacity, which is why traditionally people think that the butterfly valve is not resistant to high pressure and large leakage.
Fourth, butterfly valve <br> <br> to high temperature, it must use the hard seal, but the leak is greater; for zero leakage, you must use a soft seal, but not high temperature. In order to overcome the contradiction of the double eccentric butterfly valve, the third eccentricity of the butterfly valve was performed. The structural feature is that the double-eccentric valve stem axis position is eccentric and the cone-shaped axis of the butterfly plate sealing surface is skewed to the body cylinder axis. That is, after the third eccentricity, the sealing profile of the butterfly plate is not In addition, the shape of the sealing surface is round and oval, and the shape of its sealing surface is therefore asymmetrical. One side is inclined to the centerline of the body and the other side is parallel to the centerline of the body.
The biggest feature of this third eccentricity is that it fundamentally changes the seal structure, no longer the position seal, but the torque seal, that is, not relying on the elastic deformation of the valve seat, but completely rely on the contact surface pressure of the valve seat to achieve sealing The effect, therefore, solves the problem of zero leakage of the metal seat in one stroke, and the contact pressure and the pressure of the medium are directly proportional to the high pressure and high temperature.
The classification of butterfly valves in the development process
A concentric structure wherein <br> <br> butterfly valve of the kind of stem axis, the center of the disc, the same position on the center of the body. The structure is simple and easy to manufacture. The common lining butterfly valve belongs to this category. The disadvantage is that the butterfly plate and the valve seat are always in the state of squeezing, scraping, large drag, and fast wear. In order to overcome the squeezing, scratching, and guaranteeing the sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but it is also subject to temperature restrictions in use, which is why it is conventionally considered that the butterfly valve is not resistant to high temperatures. the reason.