Abstract: A butterfly valve having two interconnected synchronously movable discs spaced apart axially in the direction fluid flow. In order to ensure that fluid is not retained between the discs when the valve is closed there is at least one drainage outlet which communicatingly connects the space between the discs and the valve exterior.

Abstract: A flexible double toric sealing ring comprising two toric sealing ring sttures 2, 3 which ensure, respectively, a static seal and a dynamic seal. A counter ring is mounted radially on the second sealing ring structure and floats with it to allow self centering of the arrangement with respect to the valve seat. A sealing membrane 8 presents an elastically deformable structure 12 interconnecting the two sealing ring structures 2 and 3 while partially covering them. The two sealing ring structures 2, 3 are mounted on opposite sides of the middle section 11 of membrane 8. This double toric sealing ring can be advantageously applied to a butterfly valve.