A robotic pool or tank cleaner is propelled by water jets, the direction of which is controlled by the direction of rotation of a horizontally mounted pump motor within the pool cleaner housing, having a propeller attached to either end of the motor drive shaft which projects from opposing ends of the motor body, each of the propellers being positioned in a water jet discharge conduit that terminates in discharge ports in opposing ends of the housing. Each discharge conduit has a pressure-sensitive flap valve downstream of the respective propellers. When the propellers rotate in one direction, the water is drawn through one or more openings in the base plate, passes through one or more filter assemblies associated with the pool cleaner and is discharged through one of the discharge ports as a water jet of sufficient force to propel the pool cleaner along the surface being cleaned.