Abstract: A pneumatic classifier having a dispersion chamber with crushing function disposed between a material supply port and a classifying chamber so that the material is sufficiently crushed and dispersed before entering the classifying chamber.

Abstract: In a classifier having a rotary classifying impeller in a casing for discharging fine powder to the outside of the casing, a leakage prevention apparatus is provided for the classifier which has a rotary seal member mounted on the upper plate of the rotary classifying impeller at the boundary portion between the rotary classifying impeller and a fine powder discharge duct. The upper portion of the rotary seal member protrudes outwardly from an opening in the top plate of the casing to separate the reduced air pressure in the discharge duct perfectly from the high pressure in the raw material dispersion chamber which is radially outside of the seal member. Furthermore, the rotary seal member can be provided with a circular groove in a J-shaped sectional structure. The end portion of this rotary seal member can also be formed into a square shape, a rounded shape or an inclined acute shape.