The feed material enters the classifier with the main air flow which can be a highly cost-effective process option if integrated into a system with direct pneumatic feed. The classifying wheel is driven by a belt drive and a three-phase asynchronous motor. The classifying wheel speed can be steplessly adjusted by means of a frequency converter. By altering the classifying wheel speed, the particle size can be easily adjusted even during operation. Fine particles whose size is below the set cut point are transported through the rotor blades along with the classifying air, are then discharged via the fines discharge in the main air flow, and finally collected in a suitable filter. Coarse particles are rejected by the classifying wheel and are discharged via the coarse material discharge. Before being discharged, the coarse material is rinsed intensively in a spiral flow taken from the secondary air stream to remove any last fines, i.e. this final classi-fication step improves the precision of cut and increases the fines yield.