Abstract: A clean room is supplied with air at a controllable velocity from a blower with a variable damper mechanism. The ceiling of the clean room is comprised of a plurality of panels of particulate filter material Associated with at least some of the panels are air dampers comprised of first, second, and third adjacent perforated plates. The first plate is fixed and the second plate is mounted for translational movement relative to the first. The third plate is interposed between the first and second plates as a gasket to reduce air flow between the plates. By moving the second plate relative to the first, the perforations therein are selectably opened or occluded, permitting the air passing through each panel to be regulated. Air flow through the room as a whole is controlled by the variable air flow feature of the blower.

Abstract: A centrifugal fan in which the cone and wheel have a telescoping relationship to vary the rated capacity of the fan. The mechanism effects the relative movement manually, or by a servo arrangement responsive to system pressure. The telescoping relationship includes an anti-recirculation sleeve on the cone. The wheel and cone can be moved to effect engagement of the cone and the wheel back plate to cut off the fan, when in a parallel arrangement, and to arrest wheel movement, after the drive to the wheel has been stopped. In another aspect, the cone and wheel are bodily stationary and a separate movable flow control sleeve is positioned to control flow.