Problems Exist on Hard Seal Butterfly Valve

With large programs being put into construction, valves are widely used in power, petroleum, chemical industry, urban supply and drain water system. Particularly, butterfly valves have large usage. So customers are facing with more and more problems when using butterfly valves. 
The followings are the problems that exist on hard seal butterfly valve:
1. Multi-level soft and hard folded sealing rings are fixed on the disc. So, when disc is opened, media form positive washing on sealing face. Soft sealing tape in interlayer of metal disc has direct influence on sealing performance, after being washed. 
2. Limited by structure, hard seal butterfly valve is not suitable for being used as valve whose diameter bellows DN200. Because the whole structure of disc is too thick and the valve has large flow resistance. 
3. Due to three eccentric center, sealing between sealing face of disc and seat is realized by torque on actuator pressing disc to seat. When media flow forward, the higher media pressure is higher, the tighter sealing pressure is. When media flow backward, with media pressure increasing, unit positive pressure between disc and seat is lower than media pressure. Sealing begins to leak out. 
At present, China has not established relevant specialized standards for flanges of hard seal butterfly valve. Based on current standard, under the situation that specified standard dimension of flange does not change, bore adopts socket welding. Bores of flanges are the same as nominal dimension, for increasing effective sealing face and providing convenience for installation. It also ensures that valve can be used normally. What the customers should notice that dedicated flanges must be used for pairing when using elastic hard seal butterfly valve, especially pipe flanges which are matched with pressure ring surface of body. 
Problems Exist on Hard Seal Butterfly Valve
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