An annular inflatable sealing member located in said housing, said annular inflatable sealing member made from an elastomer material,BUTTERFLY VALVES said annular inflatable sealing member having elastomer legs that lengthen and contract in response to pressurization and a self-cleaning elastomer sealing portion of sufficient thickness that moves radially inward and outward as a unit in response to pressurization of said inflatable sealing member, said elastomer sealing portion locally deformable to form a seal around a rotatable butterfly disk, said annular inflatable sealing member including annular means to hold said annular inflatable sealing member in position on said housing to form an air chamber between said housing and said annular inflatable sealing member; a rotatable butterfly disk mounted on a shaft extending through said annular inflatable sealing member,Butterfly Valves said butterfly disk having an exterior edge which, when in the closed condition and when the annular inflatable sealing member is in the uninflated condition, has a clearance therebetween; and means in said butterfly valve to prevent fluid from escaping around said shaft, Butterfly Valvesso that when fluid is introduced into the chamber to inflate the annular inflatable sealing member, it expands the inflatable sealing member to form a sealing and locking engagement with said butterfly disk.

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