Control system for a load handling attachment on an industrial truck

986,656. Hydraulic control systems for lift truck attachments. YALE & TOWNE Inc. Feb. 28, 1964 [March 14, 1963], No. 8342/64. Drawings to Specification. Heading B8H. An electro-hydraulic control system for a rotating, side-shifting clamp attachment on the lifting carriage of a lift truck comprises a pair of hydraulic lines extending from a source of fluid pressure and through a main directional control valve on the truck body, Fig. 3 (not shown), to two solenoid valves on the lifting carriage controlling the hydraulic rams for rotating, side-shifting and operating the clamp arms of the attachment. The arrangement is such that on moving a hand lever controlling the main control valve fluid passes through the solenoid valves to the clamp rams which are extended or retracted according to the direction of movement of the hand lever. The solenoid valves are actuated by push-buttons on the hand lever which is connected to a switch whereby operation of the push-buttons is rendered ineffective unless the hand lever is in its neutral position so that rotation or side shift of the attachment cannot be effected during operation of the clamp. On pressing one of the push-buttons with the handle in the neutral position, a circuit to the appropriate solenoid valve is set up and on subsequently moving the handle in the desired direction the switch actuated thereby sets up a holding circuit and pressing of the other push-button is rendered ineffective. In a second embodiment, Fig. 4 (not shown), a pair of solenoid valves is provided to control the rams for effecting the three operations, each pair being actuated by a push-button on the hand lever, the arrangement being such that during one of the three operations, the push-buttons corresponding to the other operations are rendered ineffective.