The uniqueness of the variable eccentric butterfly valve is that the valve stem shaft where the butterfly plate is introduced is a three-portion shaft structure. The three-portion shaft type valve stem has two shaft segments concentric, and the middle line of the focal shaft is veered off from the two finishes of the pivot by a middle distance, The butterfly plate is introduced on the transitional shaft area. A particularly eccentric design makes the butterfly plate a double eccentric shape when in the completely vacant position, and a single eccentric shape when the butterfly plate pivots to the shut position. Because of the impact of the eccentric shaft, when it is near shutting, the butterfly plate moves a distance into the sealing cone surface of the valve seat, and the butterfly plate coordinates with the sealing surface of the valve seat to accomplish dependable sealing execution.
Since the turn focal point of the butterfly plate (that is, the focal point of the valve shaft) and the sealing part of the butterfly plate is set eccentrically, the butterfly plate sealing surface progressively isolates from the valve seat sealing surface during the initial cycle of the butterfly valve. At the point when the butterfly plate pivots to 20°~25°, The sealing surface of the butterfly plate is isolated from the sealing surface of the valve seat. At the point when completely opened, a hole is shaped between the two sealing surfaces, with the goal that the general mechanical wear and expulsion between the two sealing surfaces of the butterfly valve are enormously diminished during the opening and shutting measure, consequently guaranteeing to seal of butterfly valves.