Abstract: A hydraulic station in a hydraulic system of a wind turbine includes a tank for storing working fluid, first and second pumps fluidly connected to the tank, first and second flow paths extending from the respective first and second pumps to a hydraulic circuit, and first and second relief valves in fluid communication with the respective first and second flow paths. The first pump and first relief valve are controlled based on maintaining pressure of the working fluid in the hydraulic circuit between a first minimum limit and first maximum limit. If the pressure falls below the first minimum limit, the second pump and second relief valve are controlled in addition to the first pump and first relief valve, with the control then based on a second maximum limit and second minimum limit.

Abstract: A dual pump hydraulic system is provided for a vehicle driven by an internal combustion engine. The system includes a first circuit with a first high pressure pump supplying hydraulic fluid to the first subsystem at a higher pressure. The system also includes a second circuit with a second lower pressure pump supplying hydraulic fluid to the second subsystem at a second pressure. A first valve controls communication between the first pump and the second circuit. A second valve is operable to communicate the second pump with the first circuit when pressure in the first circuit is less than a second threshold pressure or when commanded by a control unit. A check valve prevents fluid flow from the first circuit back into to the second valve.

Abstract: A machine having a hydraulic power management system. The machine includes an internal combustion engine driving first and second fixed displacement pumps to produce a combined flow of pressurized fluid. Main and auxiliary implements are operable in response to a flow of pressurized fluid, and a control valve selectively directs the combined flow to the main and auxiliary implements. A power management system is operable to stop the flow of pressurized fluid to the main implement from the second pump when the pressure of the combined flow exceeds a pressure indicative of the impending engine stall. A means for providing the combined flow to the auxiliary implement without regard to the pressure of the combined flow is also provided, and may take the form of a power management override or bypass mechanism.

Abstract: A stabilizer system and method that can provide high speed, relatively low force extension and retraction of a stabilizer leg during a first portion of a stroke, and low speed, relatively high force extension and retraction during a second portion of the stroke. Accordingly, the stabilizer system and method takes less time to deploy than conventional stabilizer systems but without sacrificing performance.

Abstract: A working machine control device is provided which can surely determine whether working equipment attached to a working machine is in an operation state. The working machine control device is configured to control a vibration generating device that is supplied with pressure oil from a hydraulic pump to generate vibration to operate working equipment attached to a working machine. The working machine control device includes a controller that is configured to obtain frequency characteristic of the pump pressure based on a pump pressure value that is detected by a pressure sensing section, and to determine whether said working equipment is in an operation state or not based on said frequency characteristic.

Abstract: A hydraulic system comprising: a first pump, in fluid communication with a first valve; a second pump, in fluid communication with a second valve; an auxiliary passage, in fluid communication with the first valve and the second valve; and a supplemental apparatus, in fluid communication via a supplemental passage with the second valve and the auxiliary passage, wherein the supplemental apparatus comprises a relief valve.

Abstract: A hydraulic circuit for heavy equipment is provided, which can prevent signal pressure exceeding a predetermined pressure from being formed in a pilot signal path provided in a switching valve to sense whether the switching valve has been shifted in a hydraulic system that minimizes the discharge flow rate of a hydraulic pump when a working device such as a boom is not driven.

Abstract: A first group is supplied with hydraulic power from a first hydraulic pump. In the first group, an arm control valve is disposed at the most downstream position. A throttle is provided at the entrance of the arm control valve. Thus, a circuit is configured to give priority to boom raising or bucket excavation. During a combined operation, according to the operation amount of boom pulling or bucket excavation, a controller decreases the upper limit of the discharge amount of the first hydraulic pump determined by the operation amount of arm pulling and increases the recycling rate of oil to the expansion side of an arm cylinder.

Abstract: A hydraulic pressure supply unit has two exits that are alternately pressurized, a reversible pumping unit including at least two pumps, reversible electric motor that drives all pumps jointly, if necessary with mutually de-locking check valves before the exits, and a supply for hydraulic medium. One pump is a low-pressure pump and one pump is a high-pressure pump, and the pressurized exits of both pumps are placed against the same exit of the pressure supply unit. Both exits of the high-pressure pump can be separated from the low-pressure pump via check valves, and each pump is connected to the supply for hydraulic medium via its own shuttle valve.

Abstract: A hydraulic system including a multi-flow hydraulic pressure supply unit, especially a dual-flow hydraulic pressure supply unit, such as a pump, by which a volumetric flow of pressurized fluid is supplied to a hydraulic-fluid-operated device. A valve arrangement is provided either for switching between the individual pump flows or for interconnecting the individual pump flows.

Abstract: A powertrain includes a first pump and a second pump. A conduit defines a passageway for providing hydraulic pressure from the first pump or the second pump to a transmission. A valve assembly is configured to selectively supply hydraulic pressure to the passageway solely from the first pump, solely from the second pump, and from both the first and second pumps. The valve assembly thus enables the first and second pump to augment one another, thereby enabling the size of at least one of the pumps to be smaller than would otherwise be possible without the valve assembly.

Abstract: A hydraulic system is provided for an engine driven vehicle. The hydraulic system includes a higher pressure engine driven pump for supplying pressurized fluid to a higher pressure circuit via a first supply line. The system also includes a lower pressure engine driven pump for supplying lower pressure fluid to a lower pressure circuit via a second supply line. The system also includes a pressure responsive relief valve. The relief valve has a sensing port connected to the first supply line, an inlet connected to the first supply line, and an outlet connected to the second circuit via the second supply line. The relief valve opens when a demand of the higher pressure circuit is satisfied. A cut-off valve controls communication between the high pressure circuit and a reservoir, and a control unit controls the cut-off valve as a function of operation of the high pressure circuit.

Abstract: A hydraulic system including a multi-flow hydraulic pressure supply unit, especially a dual-flow hydraulic pressure supply unit, such as a pump, by which a volumetric flow of pressurized fluid is supplied to a hydraulic-fluid-operated device. A valve arrangement is provided either for switching between the individual pump flows or for interconnecting the individual pump flows.

Abstract: A fluid pump control device for wheel loaders includes an engine for driving an axle through a transmission, a main pump, a variable-displacement steering pump with a pump regulator, an auxiliary pump, an electronic proportional control valve provided on a discharge quantity control signal line leading to the pump regulator for variably controlling a pilot pressure conveyed the pump regulator, a hydraulic load detector for detecting a real hydraulic load (Px), an engine revolution detector for detecting the number of revolution (N1) of the engine, a transmission revolution detector for detecting the number of output shaft revolution (N2) of the transmission. A controller is adapted to control the electronic proportional control valve and hence the fluid discharge quantity of the steering pump, based on the real hydraulic load (Px), the number of revolution (N1) of the engine and the number of output shaft revolution (N2) of the transmission.

Abstract: A hydraulic control device includes first and second pumps, a swing control spool, a boom first-speed control spool, a boom second-speed control spool, a swing motor, a boom cylinder, a pilot control valve, and a confluence line for merging the hydraulic flow from the boom second-speed control spool with that from the boom first-speed control spool. Provided on the confluence line is a swing priority valve having an orifice for variably reducing the hydraulic flow supplied to the boom cylinder through the confluence line. A swing priority control line is provided to interconnect a pressure receiving part of the swing priority valve and a swing control pilot pressure signal line of the pilot control valve in such a manner that an aperture area of the variable orifice of the swing priority valve is reduced in proportion to the magnitude of a swing control pilot pressure of the pilot control valve.

Abstract: A hybrid hydraulic system for a work vehicle is provided that includes a first fixed displacement hydraulic pump whose outlet is connected to a priority valve. The priority valve, in turn, directs the pump's flow to a first group of closed center backhoe valves on a primary circuit and a second group of open center loader valves on a secondary circuit. A second hydraulic pump is provided with independent load sensing capability to supplement fluid flow provided by the first pump.

Abstract: A hydraulic control system for a hydraulic excavator of the present invention comprises a boom control valve in a first oil path for providing pressure oil from a first hydraulic pump with a boom cylinder according to operation of a boom operating means, an arm control valve in a second oil path for providing pressure oil from a second hydraulic pump with an arm cylinder according to operation of an arm operating means, a confluence switching valve having a confluence position for joining the paths and a confluence stop position for stopping the confluence, a flow control valve for returning pressure oil in the first oil path to a tank, and a control means for controlling the valves, so as to switch the confluence switching valve to the confluence position and close the flow control valve when the arm operating means is operated independently and so as to switch the confluence switching valve to the confluence stop position and open the flow control valve when both of the operating means are operated simultan

Abstract: A steering system for a work machine having a hydrostatic transmission is disclosed. The steering system has a primary source of pressurized fluid and a steering control valve. The steering system also has a first fluid passageway fluidly connecting the primary source of pressurized fluid to the steering control valve and a second fluid passageway fluidly connecting the hydrostatic transmission to the steering control valve.

Abstract: A tandem pump assembly of the type including a housing (H), disposed in which is a first pump (11), driven by an input shaft (19), and a second pump (33), also driven by the input shaft (19). The assembly is characterized by the tandem pump assembly including pressure override valve means (71,73) associated with only the first pump (11), and operable, in response to a fluid pressure at a fluid outlet port (35) in excess of a pressure override setting (79), to communicate pressurized fluid to a first fluid pressure responsive means (31), in a manner tending to decrease the displacement of the first pump (11) without effecting the displacement of the second pump (33), until said fluid pressure is substantially equal to the pressure override selling (79), even if it is necessary for the first pump (11) to go over-center from its initial displacement.

Abstract: A hydraulic system for a vehicle has a hydraulic, load carrying assembly which has a movable structural element and a hydraulic device for actuating the structural element. The hydraulic system has a primary circuit having a servo device, a stationary hydraulic pump, a directional valve, and the hydraulic device, which are arranged in order to operate the assembly. The hydraulic system has a supplementary circuit, being connected to the primary circuit and including a variable hydraulic pump which is arranged in order to supply an adjustable addition of hydraulic oil to the hydraulic device, and a proportional valve being arranged between the variable hydraulic pump and the hydraulic device in order to regulate the flow of hydraulic oil to the hydraulic device as a function of a received flow signal.

Abstract: A system for a hydraulically driven vehicle includes an engine having multiple, selectively operating cylinder-pump banks producing fluid flow at an outlet, a pump/motor having a variable flow rate including an inlet for driving the wheels, a hydraulic line having a line pressure and connecting the outlet and the inlet, sensors producing signal representing line pressure, pump/motor speed, pump/motor displacement, and a controller for determining a target hydraulic system parameter, determining, based at least in part on the flow rate of the pump/motor and a flow rate produced by each engine cylinder bank, a number of operating cylinder-pump banks that is required to produce the target hydraulic system parameter, and in response to determining the required number of operating cylinder-pump banks, adjusting an engine operating parameter of a cylinder-pump bank such that the required number of cylinder-pump banks operate.

Abstract: A load sensing hydraulic system includes two pumps, at least one hydraulic fluid consumer, and a pressure balance circuit. In the case of no demand from the consumer, hydraulic fluid flows from the pumps through the pressure balance circuit and to tank. In the case of demand from the consumer for hydraulic fluid at a flow rate less than or equal to the flow rate provided by the first pump, hydraulic fluid from the first pump flows to the consumer, and hydraulic fluid from the second pump flows to the tank. In the case of a demand from the consumer for hydraulic fluid at a flow rate greater than the capacity of the first pump, hydraulic fluid from both pumps flow to the consumer.

Abstract: In a hydraulic system that has first and second pumps, a pressure compensation circuit is provided to unload the output of the second pump when its operation is not required. The unloading reduces the power demanded of the engine that drives the pumps thus conserving energy. The first pump is directly connected to a supply line and a back flow check valve couples the second pump to the supply line. When pressure in the supply line is significantly greater than the load pressure of the actuators powered by the hydraulic fluid a bypass compensator valve opens to provide a path between the outlet of the second pump and the tank line. This action unloads the second pump and reduces its demand for engine power.

Abstract: A hydraulic transfer valve system has a main valve selectively placing one of a primary and secondary hydraulic system in communication with a hydraulic load. A pilot valve provides a toggling action between the primary and secondary systems with respect to pressure changes in such systems.

Abstract: Hydraulic oil supplied from pumps (12),(13) to an attachment actuator (60) is controlled by attachment control valves (27),(28). Hydraulic oil supplied from pumps (12),(13) to other actuators (52),(54),(56),(58) is controlled by other control valves (21) through (26). Control conditions for operating the attachment actuator (60) alone and control conditions for operating the attachment actuator (60) simultaneously with any of the other actuators (52),(54),(56),(58) are discriminated by the pilot pressure sensors (32),(34),(36),(38). Control characteristics of the attachment control valves (27),(28) are controlled by a controller (43) based on the discriminated control conditions.

Abstract: According to the invention, traveling bypass cut-off valves are disposed in center bypass passages respectively which are located between traveling direction control valves and working direction control valves disposed downstream of the valves, wherein, when at least a traveling motor and any of working actuators are operated simultaneously, the traveling bypass cut-off valves are switched from neutral position to another position. Thereby, when travel and work by working actuators are performed simultaneously, interference between pressure oil fed to traveling motors and pressure oil fed to the working actuators is to be prevented.

Abstract: Provided are hydraulic pumps 1,2, a control valve group 15a connected to the pump 1 and including a bypass on/off valve 7, a control valve group 15b connected to the pump 2 and including a reserve-actuator-controlling, directional control valve 11, a communication line 13 communicating a most upstream side of the control valve group 15a with a supply line 11a to the reserve-actuator-controlling, directional control valve 11, a merge control valve 14 for communicating or cutting off the communication line 13, an interlocked control means for changing over the merge control valve 14 to an open position and the bypass on/off valve 7 to a closed position in association with a change-over operation of the reserve-actuator-controlling, directional control valve 11, and a selective control valve 28 capable of taking one of a state, in which the operation to change over the merge control valve 14 by the interlocked control means is feasible, and another state in which the operation to change over the merge control va

Abstract: In a rotary servo valve (1) provided with at least two kinds of pump port (33, 39) for high and low pressures, a spool (11) that is free to rotate and free to reciprocate linearly is installed into a spool guide hole (7) of the valve main body (9), a servo motor (15) that rotates and drives the spool and a linear type actuator (13) that reciprocatedly travels are disposed, and the pump ports are selectively changed over by the reciprocation of the spool, and cylinder ports are selectively changed over by the rotation and at the same time the flow rate is controlled.

Abstract: A hydraulic system is provided for a vehicle having front, middle and rear portions. The hydraulic system includes a main pump located in the front portion, and a secondary pump located in the front portion which supplies fluid to an inlet of the main pump and to lube circuits. High pressure hydraulic functions are located in the middle and rear portions and receive high pressure fluid from the main pump. A hydraulic filter is located in the front portion and is connected to an outlet of the secondary pump for filtering fluid communicated to the inlet of the main pump. A relief valve is located in the front vehicle portion and is connected between the outlet of the secondary pump and the hydraulic filter. An inlet suction screen is located in the rear portion and is connected between a sump and the inlet of the main pump. An oil cooler is located in the front vehicle portion and is connected between the hydraulic filter and an inlet of the main pump.

Abstract: An off road machine is provided with a hydraulic system for operating drive motors for propelling the machine, as well as operating actuators for machine functions. The hydraulic system utilizes three pumps, with the pumps connected to a single high pressure relief valve. Additionally, two of the pumps normally are used for driving traction motors for the machine, and when a valve is operated the third pump flow is provided to both of the drive motors for the vehicle to increase the speed of machine movement. Additionally, a dump valve is used for insuring that the flow from the pump will be diverted to tank unless an operator ready signal is present.

Abstract: A control system and method for detecting and inhibiting an impending full saturation condition in a hydraulic system of a work machine wherein the hydraulic system includes a hydraulic pump for supplying fluid under pressure to the hydraulic system and a plurality of control valves for controllably passing fluid from the pump to a plurality of work elements, the present control system including an electronic controller coupled to both an operator input device actuatable to control the operation of the work elements and a plurality of control valves for controlling the fluid flow to the work elements, the controller being operable to determine the actual margin pressure of the hydraulic pump in response to comparing the pump pressure to the pressure of the heaviest loaded work element requested by an operator through the actuation of the operator input device and to compare the actual margin pressure to the established margin pressure for the pump.

Abstract: A fluid-operated circuit for setting the top dead center and the bottom dead center of the punch actuation cylinder in punching machines comprises a first copying distributor which distributes pressurized fluid, which has a spool at one end and can be connected in output to the upper section of the chamber in which the actuation cylinder slides and in input to a first pump for feeding low-pressure fluid and to at least one first fast-acting electric valve element; the spool can be pushed into position by contact by a corresponding setting element with continuous micrometric movement.

Abstract: A system allows pumps to run in parallel and preventing back flow through a non-operational pump. The system includes a first pump in parallel with a second pump. The system further includes a check valve in fluid communication with the first pump for preventing flow through the first pump when the first pump is not operating. The system further includes a sensing valve in fluid communication with the first pump and the second pump. The system also includes a load sharing valve in fluid communication with the check valve, the sensing valve, and the second pump for controlling a system flow, wherein the system flow is provided by the first pump when the second pump is not operating, and wherein the system flow is provided by the second pump when the first pump is not operating, and wherein the system flow includes a portion of flow from both the first and second pumps when both pumps are operational.

Abstract: A hydraulic drive system for a supersized hydraulic working machine such as a hydraulic excavator includes hydraulic pumps connected to main lines through a delivery line and a supply line. Branch portions from the main line include flow control valves for allowing a hydraulic fluid to flow from the hydraulic pumps toward hydraulic cylinders. A hydraulic reservoir is connected to the main lines through a reservoir line and a drain line. Other branch portions for the drain line include flow control valves for allowing a hydraulic fluid to flow from the hydraulic cylinders toward the hydraulic reservoir. A line branched for the delivery line includes a bypass valve for supplying the hydraulic fluid delivered from the hydraulic pumps to the supply line at a desired flow rate and returning the remaining hydraulic fluid to the hydraulic reservoir.

Abstract: A pressurized hydraulic fluid supply apparatus capable of merging or separating a plurality of hydraulic pump lines according to the driving states of a plurality of actuators. The pressurized hydraulic fluid supply apparatus has a merge/separation valve 40 that merges or separates the hydraulic fluids delivered under pressure by the first hydraulic pump 1 and the second hydraulic pump 11. The merge/separation valve 40 is set to a flow separation state upon driving of the second hydraulic actuator 16 and is preferentially shifted to a flow merging state when the third hydraulic actuator 21 is driven. Hence, even when a manually driven operation valve is used, the merge/separation valve 40 is automatically switched between the flow separation state and the flow merging state according to the operation of the operation valve. This apparatus prevents an unintended flow rate difference between the first and second actuators from being produced upon driving of the third actuator.

Abstract: A construction machine comprising two hydraulic pumps; right and left traveling motors for causing the construction machine to travel; work machine actuators for actuating a work machine of the construction machine; a control valve which makes control so that a hydraulic oil discharged from the two hydraulic pumps is fed to at least either the right and left traveling motors or the work machine actuators and so that when both traveling operation and work machine operation are performed simultaneously, the hydraulic oil discharged from one of the two hydraulic pumps is fed to the traveling motors and the hydraulic oil from the other hydraulic pump is fed to the work machine actuators, the control valve providing communication between the two hydraulic pumps through a pump communication path; a drive signal detecting device which detects drive signals with respect to the two hydraulic pumps when the traveling operation and the work machine operation are performed simultaneously; and a controller which controls

Abstract: A ganged pumping apparatus includes first and second variable displacement open circuit pumps, each having a load sensing control and a servo actuator together for changing the fluid displacement of each pump respectively. The load sensing controls being adjusted so that the setting of the control on the second pump is lower than the setting of the control on the first pump. The servo actuator of the first pump having over-center capability, allowing the first pump to operate with negative fluid displacement, and the servo actuator of the second pump having a stop to limit minimum displacement to non-negative or zero displacement. A single pressure compensating pilot valve disposed in the first pump provides the pressure compensation function of both pumps. A pilot signal line interconnects the pressure compensating pilot valve, the load sensing controls, and a load such that the flow output of the pumps is combinable into a single output and functions as a single large displacement pump.

Abstract: A system and method is provided for rapidly reconfiguring a jet aircraft from a cargo or passenger configuration into a parabolic flight configuration. In the parabolic flight configuration, a zero-gravity condition is created in the aircraft cabin to simulate a weightless atmosphere which can be provided as entertainment to paying customers. Various aspects of the invention include a hydraulic system design change which prevents loss of hydraulic function during a zero-gravity condition and a strap-down accelerometer which provides a visual indication of the parabolic flight condition. Additional interior modifications include removable padding areas, a dual-purpose interior gill liner, modified oxygen systems, handrail attachment fixtures, modified emergency lighting systems, and a palletized floor assembly.

Abstract: A hydraulic pump control system is shown that can control the absorbing torque of a hydraulic pump with respect to the engine power for driving the hydraulic pump in a well-balanced manner, and reduce a deviation of an actual revolution number from a target revolution number of the engine. A torque of hydraulic pumps during operation is estimated from a pump pressure and first and second line pressures. Based on the estimated torque, an output torque of the hydraulic pumps is controlled so that an error between a target revolution number and an actual revolution number of the engine becomes null.

Abstract: Continuously variable transmission, in particular for a motor vehicle, provided with a primary pulley mounted on a primary shaft, a secondary pulley mounted on a secondary shaft, and a drive belt running over both pulleys, each pulley formed by two sheaves, one of which is movable axially relative to the other under the influence of a hydraulic cylinder, for setting the transmission ratio, a pumping unit with at least two pumps for delivering hydraulic medium to the hydraulic cylinders, and a control unit for controlling the pump delivery depending on the operating conditions of the transmission, includes a pumping unit with at least two pumps, the first of which serves as a booster pump for the second pump connected in series, and a switch valve, under the control of the control unit, fitted so that the two pumps can be switched over from series connection to parallel connection if the volume flow of the medium required by the transmission is greater than the available volume flow in the series connection.

Abstract: In a hydraulic cylinder actuation system for a crane having a conventionally charged main hydraulic pump, a supplemental pump or "charge boost" pump is provided. To efficiently achieve fast actuation speeds of the cylinder, the charge boost pump provides supplemental charge flow in response to a need in the system. The charge boost pump is driven independently from the main pump or may be driven by the main pump if the main pump is equipped with drive thru capability to provide a variable output and preferably includes a load sensing means for controlling the output.

Abstract: Description of a system of a thermodynamic steam pump for water propulsion, its heating, disinfection and sterilization, or propulsion of other liquids, characterized by use of water steam pressure as the propelling media of a liquid mass directly, without intermediate equipment to convert the energy, which is composed of a pressure tank, an electric input valve, steam under pressure provided by an external source and means for introduction by gravity of the liquid mass to be impulsed, with electromechanical elements to control level and flow, including a heat exchanger where recycled steam is forced through a tube panel which over heats the liquid thus eliminating the existing microbes and bacteria or just taking advantage of said heat exchanger to pre-heat and fluidify heavy crude oils or other viscous liquids with no expense of additional energy. This same thermo-hydro-dynamic system installed in a surface vessel (ship) can act as propulsor of the same by the action and reaction principle. (Jet propulsion.

Abstract: A fluid joining device for construction vehicles is disclosed. The device has a bypass line control valve which is mounted to a second center bypass line of the second pump. The bypass line control valve normally opens the second center bypass line but selectively closes the second center bypass line in response to a pilot pressure. A second pilot line control valve is mounted to a second pilot line and controls the second pilot line in response to an outside signal. The second pilot line extends from the first pilot line control valve and selectively drives the first pilot line control valve. The device selectively performs the fluid joining function in accordance with operational conditions of the actuators, thus smoothly operating the actuators and improving operational effect of the construction vehicle.

Abstract: Pump ports 9p, 10p, 11p, 13p of boom, arm, bucket and first travel directional control valves 9-11, 13 are connected to first and second hydraulic pumps 1a, 1b through feeder lines 93a, 93b; 103a, 103b; 113a, 113b; 133a, 133b. Auxiliary valves 91a, 91b; 101a, 101b; 111a, 101b; 131a, 131b controlled respectively by proportional solenoid valves 31a, 31b; 32a, 32b; 33a, 33b; 34a, 34b are disposed in those feeder lines. The auxiliary valves each have a function as a reverse-flow preventing function and a variable resisting function including a flow cutoff function, whereby a joining circuit and a preference circuit can be realized in the closed center circuit with a simple structure and further, a preference degree and metering characteristics can be set independently of each other during the combined operation of plural actuators.

Abstract: Hydraulic control circuit for working components, in particular in earth-moving machines, said machines comprising a front group provided with actuators controlled by first hydraulic distributors (1,2) and a rear excavator group provided with actuators controlled by second hydraulic distributors (3-8), in said rear excavator group there being present a main arm actuated by a main actuator (13) controlled by a main distributor (3) located upstream of the remaining second distributors (4-8). The main actuator (13) supplies in series the remaining second distributors (4-8) when the pressure downstream thereof is less than a predetermined value and instead discharges the fluid under pressure when said pressure downstream thereof reaches or exceeds said predetermined value. In the front group there is also provided an additional distributor (A-B) which sends the fluid under pressure immediately downstream of the main distributor (3) of the rear excavator group via a bypass line (23).

Abstract: An apparatus for controlling the lifting operation comprising an operation mode selection switch which is selectively set to an ordinary operation mode or to a lifting operation mode and a hydraulic circuit isolating means. The hydraulic circuit isolating means isolates the hydraulic circuit into a running drive hydraulic circuit which feeds the pressurized fluid of one of the variable-capacity hydraulic pumps to the actuators of the running apparatuses when the operation mode selection switch is set to the lifting operation mode and a hydraulic circuit for driving the apparatus on the side of the turning body, which feeds the pressurized fluid of the other variable-capacity hydraulic pump to the actuators other than those of the running apparatuses.

Abstract: In a displacement control system for a variable displacement type hydraulic pump for supplying a discharge pressurized fluid of the variable displacement type hydraulic pump to an actuator via a direction control valve and then controlling a displacement of said variable displacement type hydraulic pump for maintaining a pressure difference between a discharge pressure of said variable displacement type hydraulic pump 1 and a load pressure at a portion between a direction control valve and an actuator, wherein an inlet side pressure of said direction control valve is detected as said discharge pressure.

Abstract: Hydraulically actuated grapple tongs mounted to a log skidder are useful, for example, in gripping a bunch of logs that are being dragged from one site to another. Maintaining a grip on the logs during the dragging operation with known hydraulic systems generates heat within the hydraulic systems. The subject hydraulic system includes first and second variable displacement load sensing pumps commonly connected to a control valve which controls fluid flow to an actuator. A load pressure signal is directed through a first signal line to a displacement controller of the first pump and to a pressure responsive valve normally resiliently biased to a position at which the first signal line is communicated to a displacement controller of the second pump. When the load pressure signal in the first signal line exceeds a predetermined value, the valve is moved to a position blocking communication of the load signal to the displacement controller of the second pump.

Abstract: The invention relates to a valve system for supplying fluid from a pair of fluid pressure sources to a load. A feed valve is provided which feeds--when required--a partial flow of the second fluid pressure source into the feed line of the load which is connected to the first fluid pressure source through a directional control valve. The feed valve comprises a pressure-compensating valve to control the volume of the partial flow and a switching valve to automatically open the pressure-compensating valve when required.

Abstract: The invention relates to a control system for automatically regulating the displacement setting of a plurality of variable-displacement hydrostatic pumps that are connected in parallel, each via a respective working pressure line, to a common consumer line and are each connected to a respective adjusting device that can be acted on by an adjusting pressure, each of said adjusting device having associated with it a pilot valve that is acted on towards a regulating position, against a counter-pressure, by a first control pressure corresponding to the pressure in the working pressure line of the respective pump and by a second control pressure corresponding to the displacement setting of the associated pump, and which in the control position regulates the setting pressure acting on the adjusting device to reduce the displacement of the associated pump.