1. Because the multi-layer soft and hard overlapping sealing ring is fixed on the valve plate, when the valve plate is normally open, the medium forms a positive scouring on the sealing surface, and the soft sealing belt in the sandwich of the metal sheet is washed, which directly affects the sealing performance.

2. Limited by structural conditions, the structure is not suitable to do diameter DN200 below the valve, the reason is that the overall structure of the valve plate is too thick, the flow resistance is large.

3. Because of the principle of three eccentric structure, the sealing between the sealing surface of the valve plate and the seat is made by the torque of the transmission device to press the valve plate to the seat. In the positive flow state, the higher the medium pressure, the tighter the seal extrusion. When the flow channel medium countercurrent with the increase of medium pressure between the valve plate and seat unit positive pressure is less than the medium pressure, the seal begins to leak. The high performance three eccentric hard seal butterfly valve is characterized in that the seat sealing ring is composed of multiple layers of stainless steel on both sides of the soft T-ring.