Example: Resolving product blockages and adhesions in silos. Electric external vibrators generate non-directional, circular vibrations. To drive chutes, screens, or vibrating tables, external vibrators are synchronized in pairs and operated in opposite directions to achieve a directional vibration. With an optional frequency converter, the vibration frequency and force can be adjusted and optimized for the specific process. Structure and operation: Electric external vibrators are motors with unbalanced weights mounted on both ends of their shafts. The unbalanced discs, and thus the working moment, centrifugal force, and amplitude of vibration, are adjustable.