Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator and a meter-out valve is associated with each line of the actuator for controlling the flow out of the actuator when that line to the actuator does not have pressure fluid from the pump applied thereto. Each meter-out valve is pilot operated by the pilot pressure from the controller.

Abstract: A combination shuttle and high pressure relief valve is provided within a hydrostatic drive or transmission system. The valve is constructed with a spool member in two sections. The sections include hooks that interact with one another to lock the spool sections together in one mode of operation, yet permitting the spool sections to act independently in another mode of operation. Complete fluid charging of the fluid system is ensured by dual flow circuitry between the system pump and motor, while a restrictor valve means is connected to the shuttle and pressure relief valve to provide continuous flow of fluid through a system filter.

Abstract: An apparatus for closing the guide vanes of a water turbine, for example, by means of a servo-motor controlled by a distributing valve responsive to the variation in the speed of the water turbine. The closing speed of the servo-motor is controlled to vary stepwisely by controlling the flow of the operating oil discharged from the servo-motor by a throttle control valve. The throttle transfer valve is controlled by first and second fluid actuators which are controlled by a first transfer valve operated by the closing operation of the servo-motor, a second transfer valve, and a time delay means.

Abstract: A hydraulic control arrangement for the lifting and lowering of loads is disclosed. The system is illustrated in an industrial truck and includes a multiple element control valve with timing circuitry to eliminate unwanted transient pressure surges during valve actuation. Series-parallel oil flow paths are provided for directing and controlling oil from the load lifting cylinder to the oil reservoir when the load is being lowered.

Abstract: A mixed loop hydrostatic transmission circuit for use principally with orbit, gear, vane and other non-piston type motors, which generate contaminants making them less suitable for applications using conventional closed loop hydrostatic transmission circuits. The mixed loop hydrostatic transmission drive retains the precise load control and high efficiency of a closed loop system, while introducing the benefits of contamination control of open loop hydrostatic transmission circuits. While maintaining the speed of the motor proportional to the output flow of the pump, both in positive and regenerative modes of operation, the full flow of fluid is diverted from the motor to the reservoir, while the full flow of fluid, required by the pump, is supplied directly from the system reservoir.

Abstract: A hydraulic safety circuit which keeps a hydraulic motor supplied with fluid during the interval when the motor coasts to a stop following shut off of its source of driving fluid. The circuit includes a conduit extending between the motor outlet and the motor inlet, with a check valve arrangement which shuts off normal fluid flow from the motor outlet to the fluid reservoir when the driving pump is shut off, and which instead diverts the fluid through the above noted conduit back to the motor inlet. This permits fluid to circulate through the motor as the motor coasts to a stop, preventing dry coasting and consequent possible burnout. The invention is particularly applicable to a wood chipper, where a heavy rotor (containing wood chipping blades) is connected to the motor and causes the motor to coast for an appreciable interval after the pump is shut off.