Abstract: A bleed circuit for a backhoe boom cylinder which minimizes cylinder pressure during over-center movement of the boom while permitting the maintenance of sufficient cylinder pressure during other boom operations. The boom cylinder is provided with a retract port, a head end port, and a small bleed port with a bleed line connecting the bleed and head end ports. As the boom cylinder crosses over-center, the fluid pressure in the retract side of the boom cylinder may be transmitted from the rod end to the head end of the cylinder thereby reducing cylinder pressure and improving the over-center controlability of the boom.

Abstract: A pressure-compensating hydraulic system is disclosed for preventing unauthorized use of an associated material handling implement. The system includes a variable displacement hydraulic fluid pump, and a load-sensing pressure-compensator for varying the output of the pump responsively to the pressurized fluid demands of the system. In order to prevent unauthorized use of the associated implement, the invention contemplates the provision of an override mechanism for negating the demand-responsive characteristics of the system. In this manner, a movable member of the implement, such as one of its stabilizers or its loader bucket, is positioned so as to immobilize the implement, with the member thus maintained in this position since the system will not respond to the demand for pressurized fluid to move the member from this immobilizing condition.

Abstract: A multiple compensating unloading valve circuit including multiple fixed displacement pumps and corresponding compensator unloading valves which are phased so that one pump supplies the fluid demand for the circuit until the demand exceeds that pump's capacity and then another pump adds to the flow to supplier larger flow demands. Thus, a primary pump delivers its output to satisfy low flow requirements while a secondary pump's output is vented to a reservoir. When the primary pump cannot supply the demand, the secondary pump automatically adds to the flow to satisfy larger demands. The compensator unloading valves are closed center and are operated in response to a differential pressure which is created between the primary pump's outlet pressure and the load pressure. The primary pump unloading valve has a differential pressure setting which is greater than the differential pressure setting for the secondary pump unloading valve.

Abstract: A multiple speed hoisting system has a first fluid circuit, with a maximum effective cross-sectional area for hoisting heavy loads at low speed, and a second fluid circuit, with a smaller effective cross-sectional area for hoisting lighter loads at higher speed. These circuits are separately actuated by a valve that is responsive to a regulating means for selectively positioning the valve. A pressure operated control, that is in flow communication with the second fluid circuit, automatically cancels the influence of the valve regulating means, in response to a predetermined pressure level in the second fluid circuit, and allows the valve to revert to a position actuating the first fluid circuit. Undesirable oscillations within the system between the pressure operated control and the valve regulating means are avoided.

Abstract: A multiple speed hoisting system has a first fluid circuit, with a maximum effective cross-sectional area for hoisting heavy loads at low speed, and a second fluid circuit, with a smaller effective cross-sectional area for hoisting lighter loads at higher speed. These circuits are separately actuated by a valve that is responsive to a regulating means for selectively positioning the valve. A pressure operated control, that is in flow communication with the second fluid circuit, automatically cancels the influence of the valve regulating means, in response to a predetermined pressure level in the second fluid circuit, and allows the valve to revert to a position actuating the first fluid circuit. Undesirable oscillations within the system between the pressure operated control and the valve regulating means are avoided.

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.

Abstract: There is disclosed a telescoping boom with first and second motors, each connected between adjacent boom sections to extend and retract one boom section with respect to the other. Each motor has a piston slidably received in a cylinder to define an extend chamber on one side of the piston and a retract chamber on the other side thereof. Each piston has a rod extending from the cylinder which has two passages therein, one communicating with the extend chamber and the other communicating with the retract chamber. A control valve has a first portion for control of the first motor and a second portion for control of the second motor. The hydraulic passage between the retract chamber of the second motor and the second valve portion includes the retract chamber of the first motor. The hydraulic passage between the extend chamber of the second motor and the second valve portion, and only that passage, passes over a reel between said members.