A combine harvester has a threshing mechanism for threshing grain and cleaning apparatus for removing chaff from the threshed grain. The threshing mechanism includes a rotor and a plurality of concaves and the cleaning apparatus includes and upper chaffer and a lower sieve. A blower provides cleaning air to the combine harvester. The blower is situated in a blower housing having a first cut off plate separating high-velocity air coming from the blower and directing a first portion of the high-velocity air to a lower duct that provides an airstream to the upper chaffer and lower sieve. The blower housing also has a second cut off plate directing a second portion of the high-velocity air to an upper duct that provides an airstream under the concaves. A leading portion of the second cut off plate contains a rolled edge along the width of the upper duct.
