The air distribution device has a casing (1) round an air channel and a guide valve (2) to set the strength of the air flow (A). The valve has a wall (4) facing the casing cavity, parallel to the wall (7) of this cavity so that air can pass through the cavity wall and valve wall if the valve is turned so that the air channel is open through both walls. A flexible sealing element (16) is fitted between the valve wall and the casing wall. The valve wall can move in the axial direction of the turning axis to alter the pressure on the sealing element.
