US Patent 7191485 Lawn waste sweeper with recirculating airstream

A vacuum sweeper includes a blower for pulling debris in a stream of air through a vacuum duct, past the blower, out a blower discharge duct and into a hopper. Debris settles to the bottom of the hopper and the air exits the hopper through a return air duct having a discharge opening. The discharge opening is positioned near a vacuum nozzle inlet of the vacuum duct such that dust and debris in the return air stream is pulled back into the vacuum duct. The air discharge opening and the return air duct are sized to be larger than the vacuum nozzle inlet. The speed of the air exiting the discharge opening is thereby reduced increasing the percentage of the return air pulled back through the vacuum nozzle inlet instead of being blown out of the vacuum chamber and into the atmosphere.