Abstract: In at least one bath of the system, tumbling barrels containing pieces to be treated are arranged with their respective longitudinal axes set parallel to or coinciding with the longitudinal axis of the bath and are free to move longitudinally along the bath, supported by idle wheels resting on the edges of the bath. At least one pusher in each bath is free to move for a length longitudinally and engages a frame of a barrel at a trailing position to push the said barrel and possible barrels in front of it in an advance direction. The system may comprise a spray wash in sequential stages.