Extension device for telescopic booms of hydraulic cranes

摘要

The boom (7) of a truck-mounted crane comprises several telescopically slidable sections which are extended and collapsed by hydraulic jacks (13). Pressurized fluid is supplied to the jacks through extension and collapse transfer conduits (14, 15) bored or received inside the rods (18) of the jacks. The extension transfer conduits (14) are intercepted by valves (19) located on the heads of the jack pistons and mechanically operated by the bottoms of the cylinders of the jacks through tappets (21). The collapse transfer conduits (15) are provided with draining means comprising respective offtakes (17a) controlled by switches (24) that are mechanically operated by fingers (25) on the rods of the upstream-adjacent jacks, respectively. <IMAGE>