An aerator includes a duct (50) defining a chamber in which a portion of the inner surface defines a spherical segment, a profiled body (60) with a holding device (62), and a ring (52) having an outer surface defining a portion of a sphere having the same radius as the spherical segment of the chamber and bearing the profiled body (60) in the duct (50) while allowing the rotational movement thereof relative to the duct (50) and the translation movement thereof relative to the find (22), wherein the profiled body (60) can assume a closing position when in contact with the duct. The profiled body (60) is provided with a member (70) for limiting the translation stroke when the translation axis of the body (60) is very inclined. Application in automotive vehicles.