Abstract: The disclosure relates to plural, motor driven hydraulic pump circuits, including circuits having the pumps in at least one circuit operated in pairs with all pumps being driven by a single prime mover. A speed responsive control device unloads one pump in one circuit when engine speed drops below a predetermined value without regard to the source of the condition causing the slowdown. Also included is a crossover means for sensing the pressure in aother circuit for preventing reloading of the unloaded pump when speed rises above the predetermined value unless and until the pressure including the pressure sensed in the other circuit is below a predetermined pressure.

Abstract: The present invention is directed to a supply circuit for a hydraulic jack employing two pumps in which a valve is positioned in a pipe which is branched to the delivery pipe of the first pump and is controlled by two jacks supplied by the fluid delivered by the second pump. A constrictor is positioned in the supply system for one of the jacks and another constrictor is placed in the discharge system for the two jacks with the invention being particularly applicable to achieving a stable control circuit for the load relief of the first pump.

Abstract: A hydraulic pump arrangement and control circuit for supplying fluid at high volume and high pressure to a work circuit. The system utilizes a fixed displacement pump, a variable displacement pump with a compensator, and a relief valve at a pressure setting higher than the variable displacement pump's compensator setting.

Abstract: A hydrostatic vehicle drive system having a closed loop front wheel drive circuit and a closed loop rear wheel drive circuit with bi-directional pressure compensating crossover flow between the two closed loop circuits. Another hydrostatic circuit for driving auxiliary equipment also operates as a source of pressurized fluid for charging the wheel drive circuits. The auxiliary hydrostatic circuit includes priority flow to the auxiliary equipment and a flow control with pressure relief means to maintain a constant charging pressure and a predetermined fluid flow for operating the braking circuit as well as charging the wheel drive circuits.

Abstract: Flow sensing and control apparatus is provided to selectively combine the fluid output of an auxiliary pump with a hydraulic system. The apparatus includes a valve body having a primary pump passage therein through which fluid from one of a pair of primary pumps is conducted to its respective inlet of a control valve, an auxiliary pump passage interconnected between the auxiliary pump and the primary pump passage and a fluid receiving passage which is connected to the auxiliary pump passage. A pilot operated valve is disposed within the fluid receiving passage and operative in response to fluid flow through the primary pump passage for selectively controlling fluid to the fluid receiving passage so as to permit the combining of any available fluid from the auxiliary pump with that of the primary pump up to a predetermined minimum flow rate through the primary pump passage and for diverting any excess fluid from the auxiliary pump to the receiving passage above that necessary to maintain the minimum flow rate.