GB905565A - Multiple hoist apparatus - Google Patents

Abstract

905,565. Pulley hoists. MORGAN ENGINEERING CO. Oct. 6,1960, No. 34327/60. Class 78 (5). A hoist with variable mechanical advantage ratio includes a cable 12 reeved over an upper pulley block 22, a primary lower pulley block 26, at least one secondary lower pulley block 23, and locking means 19, 25 for releasably securing the pulley block 23 to the pulley block 21, yieldable stop means 36, 36a being provided for limiting upward movement of the pulley block 23 until overcome by force exerted upon it by the pulley block 26. Thus two different mechanical advantage ratios are obtainable according, respectively, as to whether the pulley block 23 is locked to, or released from, the pulley block 21. As shown, the cable 12 is in two sections, each of which is wound on a winding drum 11 and passes via a sheave on the pulley block 26 to sheaves on the pulley blocks 21 and 23 and finally to an anchorage 13 on a cross-bar 15 pivotally mounted at 16. The upper surface of the pulley block 26 is adapted to engage a corresponding lower surface of the pulley block 23 and is retained in this position as shown in Figs. 2 and 4 by means of arms 31, 31. The latter are pivotally mounted on the pulley block 23 and are apertured to engage lugs 34, 34, on the pulley block 26. Each arm 31 has a cam surface (Fig. 5, not shown) adapted to engage a leaf-spring 33 so that it is spring-loaded into both the retaining position shown in Fig. 4 and a retracted position (Fig. 3). The upper pulley block 23 has apertured lugs 25b which, when the hoist is sufficiently raised are adapted to be aligned with plungers 19 slidable in a block 18 rigid with the frame which carries the mounting of the winding drum 11. The plungers 19 are spring-pressed into an extended position and have cam-shaped ends so that they automatically engage with the holes in the lugs 25b when the pulley block 23 is raised to its limit of upper travel. In operation, when it is desired to immobilize the pulley block 23 and so work at a lower mechanical advantage and higher hoisting speed with the pulley block 26 only in operation, the arms 31, 31 are manually disengaged from the lugs 34, 34. The hoist is raised under noload conditions until the upper surface of the pulley block 26 engages stop-members 36, 36a. The latter are loaded by springs 38, 38a, which act through the stop-members 36, 36a, to hold the pulley block 26 while the pulley block 23 is further raised until the holes in the lugs 25b engage with the plungers 19. The hoist may then be lowered and the pulley block 26 alone will be in operation. The stop-member 36 also functions as a safety device to operate a switch 46 and stop the drive to the winding drum 11 when the load reaches its extreme limit of height. The springs 38 may be replaced by counterweights. The plungers 19 may be solenoid controlled.