Drum valve

The drum-type ventilation air valve (1) is especially suitable for use in a road vehicle air conditioning system (3). It has a moving valve body with two arcuate portions (5) with sealing surfaces (7,7') on their convex surfaces. The two arcuate surfaces meet at an obtuse angle (4) and there is a rib (6) on the outside of the angle. The rib engages fixed sealing surfaces (8,8'). The valve body performs a rotary motion inside a fixed housing (2) and can cover one of two apertures (9) in the housing.