Abstract: A centrifugal fan has blades the effective width of which are variable during fan operation through the actuation of modulation apparatus which rotates with the fan wheel and is driven thereby. The modulation apparatus isolates the blocked off and unused portions of the fan blades which prevents the interaction of the blocked off portion of the blades with air flowing through the fan housing in a manner which results in a highly efficient and extremely quiet fan.

Abstract: An inlet guide vane assembly for controlling air flow through a fan. A plurality of shafts are mounted extending radially inward of an inlet cone, and are affixed to a hub positioned at the center of the cone and concentric thereto. Rotatably mounted on each shaft is an adjustable inlet vane, having a crank arm extending from its root end. Cam follower bearings are used to rotatably mount a ring on the hub. The ring is connected to each of the crank arms by a link having a ball and socket joint at each end. Rotation of the ring thereby causes the inlet vanes to rotate about their supporting shafts without binding.