GB1412666A - Cranes - Google Patents

Abstract

1412666 Controlling winches; cranes; grab buckets F E MOSLEY 20 Aug 1973 39253/73 Heading B8B [Also in Division F2] An hydraulic control for a cable drum 25 in a crane includes an hydraulic motor 31 supplied with pressurized fluid from a pump 87 through a reversing spool valve 99 which has a neutral position in which fluid passes therethrough to tank 94, a forward position in which fluid passes through the motor 31 to tank, a restricted reverse position in which the motor 31 is driven slowly in reverse and a full reverse position in which the pressure supply to the motor is sufficient to release a brake 45 in differential gearing between the motor 31 and drum 25 permitting free wheeling of the drum. The fluid ram released brake 45 is only operated when the motor reversing drive pressure is high enough to open a preset sequence valve 117, the brake being otherwise spring applied to lock the reaction member of the differential gearing, generating a high torque low speed drive for the drum. The crane shown includes a grab bucket 20 supported on a boom 10 pivoted to a platform 12 rotatable on a chassis 14, a dragline 40 being associated with the bucket 20. The bucket closing and hoisting cables 19, 18 and the dragline cable 40, are controlled by drums 30, 25 and 41, all operated as described above, the motors 37 and 39 for luffing the boom 10 and rotating the platform 12 have only forward, vertical and reverse selection on their spool valves, but in neutral the two lines to each motor communicate providing a coasting action, which in the case of the boom is automatically braked. The control levers for all the spool valves are mounted convenient to a single operator in a cab 151 on the platform 12 which also supports the pump prime mover 89 and fluid tank 94. Pressure limiting valves 149 prevent overloading the equipment by hoisting excessive loads. The grab bucket 20 comprises a pair of shells pivotal on a frame subject to pulley block action from the cable 19, the outer extremities of the shells being pivotally connected to rods pivotal at their remote ends to a frame supporting the said pulley block. In a further embodiment, the sequence valve 117 is omitted and the brake is released by back pressure built up on the line 113 due to a restriction 112 having a check controlled by-pass 111.