The material is entered at the top of the classifier. Via a rotary valve, the material to be separated is transferred without pressure into the zigzag shaft of the classifier, in which it trickles down due to gravity and repeatedly bounces against the individual stages. A transport blower, which is used to discharge the fine or light material, generates a counterflow in the zigzag chute. The material must pass through this counterflow after each stage, separating the lighter material from the heavier material. The heavy material is discharged downward from the chute and pneumatically or mechanically fed to the downstream plant component. The selectivity can be controlled manually via an air control damper or electronically via an FI.