Abstract: A particle classifier includes a generally cylindrical, air and fine particle permeable cage having a closed top and open bottom mounted to a central drive shaft. A casing surrounds the cage and defines a volute air passage about the cage with an air separation zone between the volute and the cage. A generally tangential air inlet is provided in the casing volute and a material inlet is provided in the upper end of the casing. A stationary chamber is positioned below the cage for the air and fine material which enter the cage. From the chamber, the air and fine material is directed to cyclone separators in which the air is separated from the particles. A hopper is positioned below the chamber for collecting coarser material which fails to enter the cage. The size of the volute can be adjusted by a vertical partition within the casing. The partition allows flexibility in setting the air velocity.