BUTTERFLY VALVE

The invention relates to a butterfly valve comprising a butterfly closure member cooperating with a valve seat, which valve seat has a substantially annular seal that, with the closure member in the closed position, adheres by a given compression force in the direction transversal to the flow direction and/or to the axis of the valve seat against the head peripheral edge of the closure member and/or by a given compression force in the flow direction against a front peripheral band. The valve further comprises a diametral shaft rotatably supporting the closure member from a closed position wherein the closure member is placed transversely to the flow direction and/or to the axis of the valve seat to a maximum open position with the closure member rotated by 90° with respect to said closed position. The closure member has portions offset in an opposite direction with respect to a plane passing by the axis of rotation of the diametral plane.