Patent ID: 7866298

Claim:
A butterfly valve device comprising a butterfly valve made of a resin material, said butterfly valve being rotatably supported by a rotating shaft in a fluid path, wherein: when the butterfly valve is located at a mechanically full-closed position facing a peripheral lower surface of the semicircular portion with respect to a rotating shaft of the butterfly valve, a partial annular projection is adapted to radially inwardly extend towards an inner wall surface of a fluid path, the partial annular projection including a plane that contacts the peripheral lower surface of the valve to form a fluid seal; and a controllable-full-closed position is provided at a position which is opened from the mechanically full-closed position to a full-opened position, and wherein, at the controllable-full-closed position, flow amount of fluid is prescribed by the perimeter side of the butterfly valve and the inner circumference side of the fluid path.