GB1394265A - Multi-stage hoist and control system therefor - Google Patents

Abstract

1394265 Telescopic hoists S W BUSHNELL JNR 17 Nov 1972 [17 Nov 1971] 53305/72 Heading B8H [Also in Division F1] A hoist platform 15, Fig. 1, is raised by telescopic cylinders 11, 12, 13 which are supplied with compressed gas through conduits 18, 22 sequentially so that the lower cylinder 11 is overpressurized to render it more rigid before the third cylinder is extended and pressurized. Fig. 1A shows a circuit for sequentially pressurizing cylinders 11, 12 by opening a valve 36 and then a valve 37 by depressing foot pedals 39 located on the load platform. When a valve is opened cylinder 12 is depressurized causing cylinder 13 to retract. At the bottom of its travel cylinder 13 opens a spring loaded valve 31 so that cylinder 11 is depressurized and cylinder 12 is retracted. Fig. 1B shows a circuit which has only one valve 50 for extending the cylinders. A restrictor 55 ensures that extension and pressurization take place sequentially. Fig. 1C shows an arrangement in which a valve 60 causes extension of cylinder 12 and pressurization of cylinder 11. When this is complete a high pressure sensor 63 opens a valve 64 to complete the raising of the platform. Fig. 2 shows an arrangement in which the spring loaded valve 31 is omitted. Figs. 2A-2F (not shown), illustrate control circuits with different degrees of automatic action during extension and retraction. Figs. 3 and 4 show embodiments with four cylinders and three supply conduits. Figs. 5 and 6, (not shown), illustrate arrangements with five cylinders and two conduits.