Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of one or more implements includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes an underspeed valve responsive to a deviation in the speed of the prime mover from any of a wide range of selected speeds to transmit a fluid pressure signal to servocontrol means for adjusting the displacement of the pumps. The underspeed control means includes an infinitely variable orifice connected by way of lost motion linkage to the engine throttle control for adjusting the underspeed valves to respond to a deviation of an infinite range of engine speeds.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of an implement includes a control system operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes underspeed valve means responsive to a deviation in the speed of the prime mover from a predetermined normal speed and a selectable second speed to transmit a fluid pressure signal to a servocontrol means for adjusting the displacement of the pumps. The control system includes a valve for selectively conditioning the control system to cause the underspeed valve to respond to a deviation of the selected engine speed and an indicator for indicating the conditioning of the control system.