Abstract: A control is provided for a drill head that is mounted on a drill mast. Hydraulic motors raise and lower the drill head and a hydraulically releasable brake holds the drill head in position on the mast. The control has a hoist line that connects the hydraulic motors to a source of hydraulic fluid under pressure. A brake release line is connected to the brake and a brake release valve normally connects the brake release to a tank. The brake release valve is electrically actuated to connect the brake release line to a source of hydraulic fluid under pressure to release the brake. A programmable logic controller with a memory storage controls the actuation of the brake release valve. A pressure transducer is connected to the hoist line and to the controller for providing a signal to the controller representative of the hoist line pressure and this signal is storable in the memory.

Abstract: A closed loop hydraulic swing circuit is provided with crossover auxiliary actuating connections between the pump control lines and the system relief valves to cause the relief valves to open at lower than maximum system pressure in an unloading action that limits braking when a coasting load is causing the motor to return more fluid than the pump can accept.

Abstract: A marine crane includes a high speed winch having a hydraulic heave compensating system that automatically controls the crane winch to compensate for the vertical movement of a load during offloading operations. The heave compensating system includes a reversing valve for overriding manual control and for directing control pressure to stroke the pump of a hydrostatic winch drive into its raise mode of operation, and a compensating valve that regulates the displacement of the pump permitting it to develop and maintain only a predetermined pressure in the high pressure main fluid line. The heave compensating system preferably includes a lift control system for automatically hoisting a heaving load only at or near the crest or trough of a wave.

Abstract: A control is disclosed for inhibiting the tilting of an earth drilling machine that is supported on hydraulic jacks. A hydraulic downfeed motor for the drill string is operated by a control that has pressure responsive switches connected to the hydraulic jacks, and in the event the drilling machine starts to rise upwardly during drilling one of the pressure responsive switches will operate to shut off fluid pressure to the downfeed motor and to entrap fluid within the motor. The entrapment of fluid in the motor maintains a drilling pressure that permits drilling to continue with a drilling force that will not allow the machine to rise upwardly on the supporting jacks.