Abstract: A positive shut-off air outlet comprises a nozzle having an internal surface with a spherical radius of curvature, a disc mounted within the nozzle having an external surface with a spherical radius of curvature adapted to interface with the internal surface of the nozzle, and a plurality of axle pins disposed in the external surface of the disc preferably extending beyond the external surface of the nozzle. A seal may also be provided encircling the nozzle in a space between the nozzle and a ball housing in which the nozzle is rotatably mounted at a point where the axle pins extend. The seal is adapted to rotate with the nozzle inside the ball housing. The disc is mounted for rotation and longitudinal movement within the nozzle between open positions permitting air flow and a closed position preventing air flow. The axle pins are received within axle openings disposed in the surface of the nozzle.