Abstract: An adaptive multi-stage overload protection system for a crane provides an optimal response dependent upon the magnitude of the crane overload. The control system permits the crane operator to take remedial action for overloads of relatively low magnitude, but automatically reponds to dangerous overload conditions. Under extreme conditions, the hoist line is permitted topay out, but only if less drastic responses have not adequately or timely corrected the overload condition.

Abstract: The present invention incorporates a free swing system into the hydraulic flow system of a boom crane in order to permit an operator to control the boom crane during the centering operation, which occurs immediately before and during the hoisting of a load. The free-swing system is incorporated into the hydraulic flow system between the swing control valve and the hydraulic swing motor and operates by "bleeding-off" a portion of the hydraulic fluid being pumped to or by the hydraulic swing motor so as to greatly reduce or control the rotational speed of the hydraulic swing motor.

Abstract: The present invention incorporates a free swing system into the hydraulic flow system of a boom crane in order to permit an operator to control the boom crane during the centering operation, which occurs immediately before and during the hoisting of a load. The free-swing system is incorporated into the hydraulic flow system between the swing control valve and the hydraulic swing motor and operates by "bleeding-off" a portion of the hydraulic fluid being pumped to or by the hydraulic swing motor so as to greatly reduce or control the rotational speed of the hydraulic swing motor.

Abstract: A load recall valve has a mechanical memory which coordinates the releasing of the brake with the system pressure. The mechanical memory requires that the system pressure be at least equal to the system pressure just prior to when the brake was set. Setting of the brake prior to the load being taken off the system causes the memory to be activated. Setting of the brake after the load is taken off the system causes the stored memory portion to be erased.