Structure characteristics of the double eccentric butterfly valve is that the valve stem axis is deviated from the valve seat sealing surface center, the pipeline center and valve center. the effect of the double eccentric is that when it makes valve open, butterfly plate can quickly break away from the seat, greatly eliminating unnecessary excessive compression of the butterfly plate and valve seat and eliminating the phenomenon such as scratches, and reducing the opening torque and the wear ration, thus the serving life of the seat are improved. At the same time, the double eccentric butterfly valve are adopted the metal seat structure, enhancing the applicable temperature of butterfly valve. But because its seal principle position belongs to position seal structure, namely the butterfly plate and valve seat sealing surface is with line contact, the sealing effects is caused by elastic deformation which is formed by butterfly plate extruding seat. Therefore, the requirement for closing position is very high (especially metal seated). The main problem of the valve is that it has low bearing capacity, the butterfly plate or valve sealing surface friction phenomenon is very serious
For the triple eccentric butterfly valve, beside the double eccentric stem axis is eccentric, combined with the center line of the conical seal face is of deflection angle relative to a valve centerline, thus the third eccentric is the formed. This kind of valve sealing line circumference is increased with the increase of the eccentric angle. When the seat is abraded or damaged, it only need to change the valve closing position in close direction, thus the sealing effect is realized, which increases the eccentric angle and the valve seat elastic compression. The running between the butterfly plate and the seat when a valve is opened and closed eliminates the seat damage. And the adoption of the floating seat can ensure that after the closed valve position changed, there is a best sealing form between the valve plate and valve seat.
The third eccentric can make the seat and valve plate getting rid of the valve when the valve is in operation. The butterfly plate and valve seat contacts only in the sealing second. So It greatly reduces friction between the seat and plate when the valve is opened and closed, and reducing wear and prolonging the service life. Due to its sealing is realized depending on the seat and plate sealing ring extrusion. The sealing pressure ratio can be added by the valve stem torque. If the valve structure design is reasonable, very high sealing effect can be achieved. The reasonable design of the third eccentric can rule out the possibility of valve stuck, thus improving the reliability of operation. Compared with general butterfly valve, triple eccentric butterfly valve is usually adopts metal hard seal seat, thus making it high temperature resistant. In the valve plate surrounding, the overlapping cascade multi-level seal are embed, which is formed by stainless steel sheet and graphite sheet. The sealing has metal sealing and elastic soft seal dual advantages, solving the leaking problem. Triple eccentric butterfly valve as a kind of high performance valve. With its unique structural features and performance advantages, it has become preferred regulator in the market.