In the process of pneumatic separation we use as separating characteristics aerodynamic properties of particles, their critical velocity being the characteristic value. The investigations were carried out on a pneumatic separator whose design enabled a wide range of regulations of parameters. Based on the study results the essential fa- ctors that affected the course of the process were identified and the theoretical correlation between them, deciding about the efficacy of pneumatic separation, were determined. The main aim of the study was to analyse the separation process in an air stream of broken-up lupine seeds, chiefly involving theoretical considerations of movement and behaviour of mixture particles in a pneumatic canal. Investigations and observations gave ground for an attempt at determining a deriving a movement equation of particles in an unrestrained, uniform air stream. The equations obtained can be used for calculating the parameters of particle movement in pneumatic canals. The velocities of air stream, then, can be a few times higher than the critical velocity /convection/ of individual particles. While working out the above problems there were consi-dered, on the one hand possibilities of obtaining the greatest effectiveness of the separation process, and on the other, the smallest possible losses of valuable material in the discard-ed lot.