To obtain high-quality grain and seeds, it is necessary to clean the combine heap of weeds. Modern air-screen grain cleaners equipped with a screen cleaning systems, flat screens and a double-aspiration pneumatic system with pre-screen and post-screen cleaning channels are used. The fractional principle of post-harvest grain processing is promising. To create a universal grain cleaning machine to isolate the main fraction from the grain heap at the first stage of post-harvest processing, Voronezh State Agar University named after Emperor Peter I carried out theoretical and experimental studies, which made it possible to develop OZF-50, OZF-80 and SVS-30 separators. The machines have higher productivity, the original sieve design with an increased share of sorting sieves and an exclusive aspiration system. A number of new technical solutions have been used in the design of the separators, protected by patents of the Russian Federation. Theoretical prerequisites established the possibility of increasing the productivity 1.6-1.8 times according to GOST R 52325-2005. The total air consumption of the pneumatic system of grain cleaning machines can be reduced by 25-40%. Further improvement of separators requires a deeper study of the grain fractionation process, aerodynamic characteristics of aspiration systems, receiving and distribution devices, and establishment of close mutually beneficial relations between scientific institutions and agricultural engineering enterprises. This can contribute to the development of both domestic agricultural science and grain cleaning equipment production.