Patent ID: 8562704

Claim:
A filter system for a mobile surface maintenance machine comprising: a hopper connected to a wheeled chassis and adapted to receive debris from a sweeping brush, said hopper being lifted away from a ground surface during a hopper dumping procedure; and a filter box carrying at least one filter and a vacuum fan impeller rotating about an axis of rotation and being externally provided relative to the hopper, said filter box being in air communication with the hopper so as to support a vacuum-based airflow through the hopper and said at least one filter when the hopper is lowered into an operational configuration, wherein the filter box defines an axially-expanding expansion chamber surrounding a radial perimeter of the vacuum fan impeller, with said expansion chamber having a cross-sectional area which increases as the expansion chamber proceeds around the vacuum fan impeller, with said filter box containing debris removed by said filter and having an opening through which said debris is selectively passed through and collected upon a surface of the hopper, and a movable seal positioned at the opening and sealing the opening when the vacuum fan impeller is rotating, with said movable seal being subsequently opened so as to permit said debris to pass out of the filter box and be collected upon the hopper surface.