Abstract: A hydraulic fluid circuit system is provided for use in a vehicle and having a priority and a second fluid circuit therein. A variable displacement pump is the primary fluid source for the priority circuit, and a fixed displacement pump is the primary fluid source for the second fluid circuit. A demand valve responsive to differential fluid pressure between the priority circuit and the output of the variable displacement pump selectively switches increasing amounts of output from the fixed displacement pump into the priority circuit in proportion to the output of the variable displacement pump. The demand valve includes a three positioned spool valve. The priority circuit may include a hydraulic steering system, and the second fluid circuit may include an implement or accessory circuit.

Abstract: In a pressure compensated steering valve, the effect of an input steering signal is cancelled by connecting the spool valve actuator to the reservoir. A shiftable spool valve is acted upon by end cap actuators, which are in turn controlled by a hand pump that is operated by a steering wheel. The spool valve is provided with internal passageways which place the pressurized end cap actuator in restricted fluid communication with the reservoir in order to cancel the effect of the input steering signal at a predetermined rate.

Abstract: Fluid control valve apparatus is provided having a directional control valve for metering passage of fluid from a supply passage to a feeder passage for first actuator. A pressure compensating valve is provided for regulating flow through the directional control valve and for delivering excess fluid to a compensating valve output port for power operation of a second actuator. A main relief valve is connected to the first actuator feeder passage downstream from a metering portion of the directional control valve for sensing a first actuator stall condition. The main relief valve, when actuated, delivers fluid to a tank from a supply passage, through the metering portion of the directional control valve, and a relief passage including the main relief valve upon sensing an overload condition. The rate of flow through the relief passage is subject to limitation only by the metering portion of the direction control valve.

Abstract: A hydraulic control circuit for the steering system of an articulated vehicle is provided having a first pump means for delivering fluid under pressure and directional control valve means in fluid communication with the first pump means for controlling the direction of flow of the pressurized fluid. A second pump means, responsive to a steering input signal, develops an output indicative of a desired change in vehicle direction. An actuator means is connected to the directional control valve means for controlling the position of the directional control valve means, and said actuator means is in fluid communication with the second pump means so as to receive the output therefrom. A feedback means is placed in fluid communication with the actuator means for developing a feedback signal to counteract the effect of the second pump output, and a means is placed in fluid communication with the feedback means for varying the feedback signal to thereby vary the rate of counteracting the second pump output.