In the chemical industry, often deflector wheel classifiers are employed for classifications with cut sizes <50 mum. It is known that different wheel geometries yield strongly differing cut sizes at the same centrifugal acceleration. Systematic trial were carried out to investigate the influence of the deflector wheel geometry of the potential vortex inside the wheel. the radial gas velocity and the load on the result of the separation. A strong influence of the spiral vortex depending on the wheel geometry was found. The results of a simulation with a commercially available flow simulation program coincided satisfactory with the experimental data. (C) 2004 Published by Elsevier B.V.