Just like cyclones, these air classifiers use centrifugal force to separate particles at cutpoints ranging from 15 to 100 microns. First, the feed material is carried through the primary inlet flow. to separate the fines, drag forces are applied to the coarse p-articles and allow air to go through them. A second air stream flows from the bottom of the classifiers and through the materials. At this point, particles most similar with the cut point are returned to the machine while the most massive then falls to the bottom of the classifier and exits through an opening. The finest particles go through a spiral path toward the side outlets with the help of the air stream. Finally, the two air streams combine to make a cyclone which recovers the fine particles.