LIFT TRUCK ROTATOR WITH PRESSURE-RELIEVED VALVING

A rotator attachment for rotating a load handling mechanism on a lift truck includes a frame carrying an inner gear with external teeth and rotatable about a longitudinal axis of the truck. An outer gear surrounds the inner gear and has a greater number of internal teeth engaging the external teeth of the inner gear. A pair of double-acting hydraulic cylinders connected to the frame and outer gear are operated in sequence to drive the outer gear in a gyratory eccentric path with respect to such axis so as to rotate the inner gear and a connected load handling attachment about such axis. Control valving responsive to the position of the outer gear in its eccentric path is provided for operating the cylinders in the correct sequence for driving the outer gear. Relief valving is provided in conjunction with the control valving for preventing pressure-locking of the cylinders. The relief valving is responsive to excessive pressure in either side of either cylinder to relieve such excessive pressure through the control valving when the control valving is in a neutral position.