Blower and a blower diffuser

A diffuser adapted for being mounted at the downstream side of a blower, the diffuser comprising a diffuser shroud being substantially circular symmetrical about an axis of symmetry and having an upstream side being attached at the exhaust end of a blower pipe and a downstream side opposite the upstream side, and where the diffuser shroud encircles a diffuser opening having a cross section perpendicular to the axis of symmetry that increases from the upstream side of the diffuser to the downstream side of the diffuser, and where a back draft damping butterfly valve is arranged in the diffuser opening, the butterfly valve comprising two doors both being attached to the diffuser shroud via a hinge arrangement adapted for allowing each of the two doors to rotate between a closed and an open position about a hinge axis extending between opposite sides of the diffuser shroud and where the doors are shaped so that they together substantially close the diffuser opening when they are in their closed position, wherein each hinge axis intersects the diffuser shroud at a position closer to the upstream side at one side than on the opposite side of the diffuser shroud, and wherein two points of intersection between each hinge axis and the diffuser shroud are disposed between the upstream side and the downstream side of the diffuser shroud.