GB1192879A - An Extensible and Retractable Boom Construction - Google Patents

Abstract

1,192,879. Jib cranes. JEFFREY GALION Inc. 11 Nov., 1968 [5 Dec., 1967], No. 53415/68. Heading B8B. [Also in Divisions F1 and F2] Jib boom.-A crane boom 10, Fig. 1, with a counterweight 18 is supported on a turntable 12 and may be luffed by a lift cylinder 15. The boom 10 includes three telescopic sections 20, 30, 31, and double-acting hydraulic cylinders 32, 38 are respectively connected between the sections 20, 30 and the sections 30, 31. Hydraulic circuit.-Fig. 2 shows the hydraulic control system for the cylinders 32, 38. Fluid is supplied under pressure from a pump 50 to a manual valve 51 shown centred by return springs to return the fluid to tank 52. Operation of the valve 51 connects the fluid supply via a line 53 to a pressure compensated flow divider valve PC55 which proportionately divides the supply of fluid into two lines 56, 57. When the line 53 functions as a return line the flow divide valve 55 proportionately combines the return flow from lines 56, 57. The rates of extension and retraction of the second and third boom sections 30, 31 are commensurate with the predetermined proportional rates of flow of the pressure fluid thus supplied to, or received from, the cylinders 32, 38. The cylinders 32, 38 respectively have check valves 58, 61 and pilotoperated relief valves 65, 67. Relief valves 68, 69 allow both cylinders 32, 38 to complete their strokes should one or the other bottom first. Flow divider valve.-Fig. 3 shows the pressure compensated flow divider valve PC55, the left hand side being identical to the right hand side and comprising a spool 77 slidably received in a fixed sleeve 75 and loaded to the right by a spring 78. The spool 77 has orifices 79 communicating to valve port 72 to which line 53 is connected. Additionally the spool 77 has orifices 80 communicating with orifices 81 in the sleeve 75. The spools 77, 87 have claws 92, 93 engaged to link the spools mechanically. Spring 94 acts against the spools 77, 87 in opposite directions. As illustrated the flow divider valve 55 divides (or combines) the hydraulic fluid equally between (or from) the lines 56, 57. If the flow should, for example, tend to increase towards the line 56 the flow induced pressure drop across the spool 77 shifts it to the left, as shown restricting the flow through the orifices 80, 81 until equal rates of flow are again achieved. Similarly for the spool 87 and when the valve 55 is combining fluid from the lines 56, 57. As described the second and third boom sections 30, 31 are extended and retracted at the same time and at the same rates of movement. For boom sections of different lengths from each other the sections can be extended and retracted at the same time and at different rates proportional to their respective lengths.