This series flanged butterfly valve are improved products on the basis of absorbed the advanced products from abroad, the seal structure accord with the standard require of American Water Supply Association. Designed according to the theory of waterpower transition process. It adopts eccentric disc and adjustable seat seal structure. It applied in various liquid gas pipes power lines. The products resorts its excellent seal capability, particular adjustable seal secure and low flow resistance, high throttle function and so many integration characteristic. Widely applicable in municipal works plumbing, power station, water station, environment protect water disposal industrial and drinking water control etc systems to flow-control and cut-off function.