The device incorporates a rotary fan wheel (2) with a circular baseplate (6) and a central bearing (7) for the shaft (8) of the drive unit (3). The underside of the baseplate carries vertical blades extending radially from the centre to the edge as in a tangential blower. Alternate blades carry on the side turned away from the baseplate a chaff-cutter which projects in the direction of suction, so that the material drawn up from the ground is pre-comminuted and cannot become wedged in the small spaces between the blades.
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