English: Physical and theoretical fundamentals of developing a pneumatic classification method for granular materials are aimed at the efficient use of the operating area of the classifier. This allows obtaining an effective impact of the air flow on a granular material for ensuring a significant increase of the separation quality. Consequently, the design of a device for pneumatic classification of granular materials by changing the form of the apparatus working volume as rhomb-shaped cross-sections is proposed. In this case, the increase of separation quality and the decrease of the hydraulic resistance, as well as specific productivity and efficiency of the pneumatic classification process, can be highly improved. To realize the abovementioned design, this new method of pneumatic classification of granular materials is proposed.