Patent ID: 7037404

Claim:
Apparatus for controlling the amount of perforated surface area though which air can be drawn by suction through perforations extending through a surface of a hollow cylindrical drum having an inner surface, the cylindrical drum being closed at opposite ends to prevent air flow into the drum through the opposite ends, a circumference and an axis of revolution, comprising: a circumferentially moveable cylindrically curved element disposed inside the hollow cylindrical drum and having an axis of rotation contiguous with the axis of the hollow cylindrical drum and having a length less than a length of a cylindrical volume inside the hollow cylindrical drum, the curved element conforming to the inner surface of the perforated cylindrical drum and having an outermost radius of curvature about equal to a radius of curvature of the inner surface of the hollow perforated cylindrical drum, whereby circumferential positioning of the curved element controls the amount of perforated surface area; and axially moveable baffle plates disposed inside the drum to control a width of a portion of the perforated surface between the baffle plates through which air can be drawn, each baffle plate having a radius of curvature less than the radius of curvature of the inner surface of the perforated cylindrical drum.