Abstract: A seal arrangement for a gear machine includes a thrust plate for reducing the cross face leakage of fluid from a high pressure side to a low pressure side of a gear machine. A first groove and a second groove are formed in the thrust plate for receiving a first seal assembly and a second seal assembly, respectively. The first groove generally defines the numeral "8" with lateral sides spaced from one another and includes a top segment and a bottom segment. Each of the segments has an extension at each of its ends. The second groove generally defines a geometric form located between the lateral sides of the first groove and has its center spaced generally equidistant between the top and bottom segments. The first groove and the first seal assembly are arranged to form four chambers. Three of these chambers confine pressurized fluid therein for each direction of rotation of the machine, thereby urging the plate toward localized sealing engagement with the gears of the machine.

Abstract: The improved rotary valve includes a body and a valving block having a valve interface with at least two work ports. A rotatable valve plate is received in the body and has a working face with a land which is in sliding contact with the valve interface. A rotatable stem is received in the valve body and is coupled to the valve plate for causing rotational movement of the plate. The stem has an axial passage in fluid communication with the pressure region of the valve and has at least one metering orifice for intersecting the inlet conductor of the valve and controllably flowing fluid into the pressure region. In one embodiment, used with open center systems, each of the work ports is in fluid communication with the pressure region and the discharge region when the valve plate is in the neutral position.

Abstract: An apparatus for disabling an obstructed lift mechanism having at least two hydraulic cylinders for controllably lifting and lowering a load includes a pair of valves, each arranged for sensing the differential pressure between a first sensing line and a second sensing line. The first valve is movable to a position for preventing the flow of hydraulic fluid from a first cylinder when the pressure in the second sensing line exceeds that in the first sensing line by a first predetermined value. The second value is movable to a position for preventing the flow of hydraulic fluid from the first cylinder when the pressure in the first sensing line exceeds that in the second sensing line by a second predetermined value. If the flow of hydraulic fluid from the first cylinder is prevented by the movement of either the first valve or the second valve, the operator is required to lift the load slightly to remove the obstruction.

Abstract: A variable displacement pump 1 includes a housing 2 having an inlet port 3 and an outlet port 4. The pump 1 is an axial piston pump having a swash plate 5 which is actuated to different angular positions by an actuating member 7. The torque limit of the pump 1 is controlled by a horsepower control valve 19 and a speed responsive control valve 35, which change the torque limit of the pump 1 in response to changes in the position of the actuating member 7 and in response to changes in the speed of the engine 33. In this manner, the torque limit of the pump 1 for any position of the actuating member 7 closely approximates the maximum available output torque of the engine 33.

Abstract: Two variable displacement pumps each having a horsepower (or torque) control valve, a pressure limiting valve, and a displacement feedback valve are interconnected to provide fluid flow paths from the high pressure zone of one pump to the low pressure zone of the other pump via the horsepower control valve and the displacement feedback valve of the respective pumps and vice versa. When one pump is utilizing less than one-half of the available engine torque as at deadhead operation or low displacement operation wherein its pressure limiting valve determines the maximum delivery pressure or wherein the pump is in standby operation, its displacement feedback valve will correspondingly increase the back pressure of the horsepower control valve of the other pump so that the latter may utilize the torque deficiency of the former to bring the total torque utilization of both pumps to the engine torque limit.

Abstract: A variable displacement pump control assembly as for an axial piston pump having a swash plate actuating piston characterized in that the control assembly is embodied in the pump housing to provide a pressure compensated pump, or to provide a pressure compensated pump having an auxiliary modulator to control the pressure applied to the swash plate actuating piston to maintain a predetermined pressure drop across a variable area metering orifice embodied as in a directional control valve for a fluid motor, or to provide a pressure compensated pump having a horsepower modulator with or without the auxiliary modulator, said horsepower modulator providing desired control of horsepower in relation to pump delivery pressure and displacement.