as a lever to move damper portion 38 between an open and closed position relative to aperture 34 the air valving means 36 is hingedly supported on a bracket 42 fig2 and 3 which is attached to the barrier 12 adjacent the aperture 34 by any suitable means the bracket 42 has ears or curved projections 44 which are received in cooperating openings 46 and around receiving portions 47 located on the vertically disposed edge of damper portion 38 to provide an effective hinge arrangement for rotating the air valve means 36 relative to barrier 12 the air valving means 36 and more specifically the damper portion 38 is maintained in a closed position over aperture 34 by a biasing spring 48 spring 48 is of the torsion variety and has its coiled body portion arranged on a support member 50 formed on damper portion 36 and is in substantially axial alignment with projection 44 and portions 47 one free end of the spring 48 bears against stationary bracket 42 with the other end bearing against damper portion 38 as shown in fig1 and 3 of the drawings the air valving means 36 is hinged intermediate the damper 38 and operating portions 39 with the damper 38 biased normally closed as seen in fig1 it is then apparent that movement of the operating portion 39 toward barrier 12 will pivot air.