Abstract: A hydraulic circuit for a crane having both lift and boom hoist pumps driven by the same engine with appropriate control valves to independently control the lift hooks and the boom angle. An unloading valve is interposed in the boom hoise circuit and dumps the boom hoise pump directly to reservoir when the pressure in the left pump circuit becomes excessive. A boom limit valve, actuated as the boom reaches both upper and lower limits, also causes the unloading valve to dump the boom hoise pump to reservoir.

Abstract: A drum rotation indicator enables a crane operator to sense rotation of a drum, and thereby determine linear movement of a cable, that has one end wound about the drum. This indicator has a cam, that rotates with the drum, and a cam follower, that translates rotation of the cam into linear movement. A readout plunger is located conveniently for the operator's hand, and linear motion that is induced by the cam follower is transferred to the readout plunger by a medium that can be a mechanical linkage, a push-pull cable, or a hydraulic system. In a preferred embodiment of the invention, the cam follower disengages automatically from the cam after linear motion has been transferred to the readout plunger. The linear motion transferring medium also transfers motion from the readout plunger to the cam follower, which pivots into engagement with the cam. The cam has a serrated periphery, to give an instantaneous response, upon rotation of the drum, to engagement of the cam follower with the cam.