GB1310454A - Cranes having telescopic booms - Google Patents

Abstract

1310454 Telescopic jib cranes J I CASE CO 10 May 1971 [10 July 1970] 14035/71 Heading B8B [Also in Division F1] A crane has a telescopic boom with first, second, and third sections, (30), (32), (34), Fig. 3 (not shown), pivoted by the first section (30) for luffing on a slewing turntable. A first ram 40 is attached by its cylinder 46 to the second section (32) and by its piston-rod 42 to the first section (30). A second ram 50 is attached by its cylinder 52 to the second section (32) and by its piston-rod to the third section (34). A pump 112 supplies fluid under pressure from a reservoir 110 for extending and retracting the boom under the control of a valve 114. In order to extend the boom the pressure fluid is routed through a conduit 116, a pressureresponsive relief valve 140, a passage 79 through the ram 40 (formed by tube 62 in the piston-rod 42 and tube 74 in the cylinder 46) and conduits 86, 88 to a flow divider 84. The fluid then passes through conduits 90, 94 and 92, 96 to the cylinders 46, 52 below their respective pistons. The other ends of the cylinders 46, 52 are connected by a conduit 100 and the fluid can pass through radial holes 80 in the pistonrod outer member 60 to an annular passage between the outer member 60 and the tube 62 to a conduit 118 leading back to the valve 114 and, for extension of the boom, to the reservoir 110. A second pressure-responsive relief valve 140 is positioned in the conduit 96. The flow divider 84 itself incorporates first and second pressure-responsive valves 120, 122 and if the elements of either of the rams 40, 50 are restrained, the fluid is directed first to extend the unrestrained ram and then to extend the other ram, thus synchronizing the rams 40, 50 at the ends of their respective strokes. During retraction of the rams 40, 50 by reversing the valve 114 the fluid divider 84 acts to recombine the flow from the two rams 40, 50.