The cleaning of cereal seeds represent an essential operation of the conditioning chain.Taking into account all considerations, the experts attention has been drawn by the study of phenomena which influence upon the impurities separation process, aiming at a maximum reduction impurities. The paper presents the constructive and functional scheme of an gravitational separator driven by means of non balanced vibration generating systems known under the trade name of electrical motovibrators and also the constructive scheme of these, in view of theirs utilisation with best results for the drive of vibrating sieves. At the end of the paper are presented the advantages of using these types of acting systems for gravitational separators.