What are Three-eccentric Metal Hard Seal Butterfly Valves?

Three-eccentric metal hard seal butterfly valves are a kind of advanced butterfly valves. The valves use body and seat as connection. The sealing face of seat on the butterfly valves is made of bead welded stellite material having high temperature resistance and corrosion resistance. Multilayer soft fold sealing rings are installed on disc of valves. Compared with conventional butterfly valves, three-eccentric metal hard seal butterfly valves have the advantages of high temperature resistance, light operation, no friction during on-off. When closing valves, sealing can be compensated with torque of actuator growing, which highly improving the sealing performance of valves and extending service life.    
 
Although three-eccentric metal hard seal butterfly valves have the advantages that other types of butterfly valves cannot match, they still have some shortcomings. 
 
1. Because of multilayer soft fold sealing rings are fixed on the disc, the media cause positive wash to sealing face when the valves is normally open. Soft sealing tape inside metal interlayer will deform and wear after being washed for a long time, which has direct influence on sealing performance of butterfly valves.
2. Limited by structure, the valves are not suitable for the valves whose diameter bellows DN200. Because disc has too thick structure and high flow resistance. 
3. Due to principle of three-eccentric structure, the sealing between sealing face of disc and seat is realized by torque of actuator pressing disc to seat. When it is flow state, the higher pressure of media is, the stricter of extrusion on sealing is. When media in passageway back flowing, with the pressure of media growing, positive pressure per unit between disc and seat is lower than pressure of media. Sealing begins to leak.  
 
What are Three-eccentric Metal Hard Seal Butterfly Valves?
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