Abstract: The invention disclosed herein relates to an apparatus for automatically cleaning surfaces submerged within a liquid, such as the walls and floors of swimming pools. The apparatus comprises two suction passages in suction communication with a cleaning head that is releasably engageable with the surface to be cleaned and means, such as a flapper valve, for automatically transferring the flow of liquid from one passage to the other. By this means, as the flow of liquid in a passage is halted, the kinetic energy of the liquid is transferred to the apparatus, causing it to be displaced along the surface. The apparatus thus migrates randomly across the surface, cleaning it.