Abstract: A first cylinder chamber of a hydraulic cylinder is connected to a pair of variable displacement pumps of which the first one is connected to a reservoir and second one is connected to the second cylinder chamber. This allows to bias the piston by a hydraulic force acting on either side of the piston corresponding to the direction of motion. This is obtained by adjusting the delivery volume of both the pumps such that the volume supplied is larger than the volume drained. Metering the difference of both the delivery volumes results in the desired biasing counter-pressure.

Abstract: A hydraulic drive system comprising a prime mover (21), a hydraulic pump (22) driven by the prime mover, a plurality of hydraulic actuators (23-28) driven by hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (29-34) for controlling flow of the hydraulic fluid supplied to the actuators, and a plurality of pressure compensating valve (35-40) for controlling respective differential pressures across the respective flow control valves, in which each of the pressure compensating valves applies a control force (f-F.sub.c) in a valve opening direction for setting a target value of the differential pressure across the flow control valve. There are provided a first detector (60) for detecting the target rotational speed (N.sub.0) of the prime mover (21), and controllers (61, 62, 63) for controlling the control force on the basis of the target rotational speed detected by at least the first detector such that the control force (f-F.sub.

Abstract: A service valve circuit of a hydraulic excavator connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve. The service valve circuit comprises a confluence valve 17 for performing electromagnetic proportional flow rate control, disposed in a confluence circuit 16 in communication with the section between inflow circuits 3F and 3R of two variable pumps 2F and 2R, an electrical switch 21 for switching the confluence valve 17 on or off according to a required flow rate and a volume 22 for adjusting the quantity of flow after passing through a confluence valve 17 in a range of flow for a maximum of one to two pumps. Since the requirement of confluence with respect to a required quantity of flow for a special attachment e and the quantity of confluence are set in advance, there will be no excess or shortage of the quantity of confluence.

Abstract: A prioritizing method and arrangement for a hydraulic system including two independent hydraulic fluid supply units (4, 5) adapted to jointly and severally supply hydraulic fluid to at least two hydraulic components (2, 3). A cross-communication between the at lest two hydraulic components (2, 3) is controlled, with a flow of hydraulic fluid from one of the two hydraulic fluid supply units (5) being diverted to one of the at least two hydraulic components (3) to a substantial exclusion of the other of the at least two hydraulic components (2) in dependence upon an operating condition of the other of the two hydraulic fluid supplying units (5). A biasing force (F) acts upon the prioritizing arrangement so as to define an operating stage at which the respective hydraulic fluid supplying units (4, 5) exclusively supply hydraulic fluid to the respective ones of the at least two hydraulic units (2, 3).

Abstract: An oil hydraulic circuit for a hydraulic shovel with which a composite operation can be performed readily and smoothly without special skill in operation of the hydraulic shovel. The oil hydraulic circuit comprises a first actuator which can operate with pressure oil from a predetermined one or both of a pair of hydraulic directional control valve sets, a second actuator which operates only with pressure oil from the other hydraulic directional control valve set, a proportional changing over device interposed intermediately in a pipe line communicating the other hydraulic directional control valve set with a first actuator for adjusting the maximum meter-in opening value to the first actuator in response to a magnitude of a signal received at a signal receiving portion of the proportional changing over device, and a controller for arbitrarily adjusting the signal to be supplied to the signal receiving portion of the proportional changing over device.

Abstract: A control system having a flow-dividing selector valve mechanism (52) for changing the channels for causing a pressure fluid to flow from two main pumps (40), (50) into two control valve groups (60), (70) therethrough, and confluent selector valve mechanisms (80), (90) for causing the pressure fluid flowing into each group to flow into a working device control valve of the other group. The confluent selector valve mechanism (80) of the group wherein the working device control valve (62) has a need to compensate for the flow of fluid thereinto cancels the confluence function. The system has a mechanism for restricting the stroke of the spool of a working device control valve (160) to be subjected to varying loads to cause the fluid discharged from the actuator connected thereto to flow into the actuator again when the load is small. A sequence valve (170) operates the spool stroke restricting mechanism (190) by a pilot primary pressure.

Abstract: A hydraulic control circuit adequate to control a main hydraulic actuator and auxiliary hydraulic actuators. The main actuator drives farm machinery mounted to an agricultural tractor or the like. The auxiliary actuators drive farm attachments independent of said farm machinery. At least two hydraulic pumps and at least two sets of control valves are connected in series. The exit of one hydraulic pump is connected with the other hydraulic pump via a check valve. Said one hydraulic pump is connected with a tank via an openable valve upstream of the check valve. The upstream set of control valves is used to control the auxiliary hydraulic actuators needing more flow rate than the downstream set of control valves. The openable valve has an offset valve at its one end to determine the direction of flow. The openable valve is either opened or closed by the pressure admitted from the downstream side of the upstream set of control valves.

Abstract: A single hydraulic pump (6) is employed in a vehicle for supplementing fluid to a hydrostatic transmission (1) and for supplying fluid to a fluid-operated clutch (2) and to high pressure-actuated hydraulic actuators (3, 4, 5). Fluid discharge path (7) of the pump is connected to the hydrostatic transmission through a pressure-reducing valve (8). Fluid drain path (9) of the reducing valve is fashioned to a fluid supply path for the clutch. A second fluid supply path (11) is connected to the discharge path for supplying fluid to the hydraulic actuators and include a relief valve (12) or orifice (12A) for maintaining fluid pressure in the discharge path higher than the output pressure of the reducing valve. A high pressure relief valve (10) for establishing fluid pressure to be applied to the actuators is connected to the discharge path for minimizing a discharge pressure required to the pump.

Abstract: A hydraulic control system includes a pump, a hydraulic cylinder and a cylinder hydraulic circuit interconnecting the pump and the cylinder. The circuit includes a first hydraulic fluid line extending between the pump and the cylinder and a control valve located in the fluid line for controlling the communication of fluid between the pump and the cylinder. A second hydraulic fluid line is in fluid communication with the first line downstream from the control valve. A first relief valve is located in the second fluid line and a first shut off valve is also located in the second fluid line and interposed between the first relief valve and the first fluid line. The shut off valve is solenoid actuated to a closed position. A motor hydraulic circuit includes a third hydraulic fluid line and a solenoid actuated motor control valve for controlling the flow of fluid through the third fluid line. An interconnect system is provided for operating the first shut off valve and the motor control valve in unison.

Abstract: A charge flow distribution valve routes all charge pump flow into a main pump until the main pump has sufficient inlet pressure. The valve opens to a first stage which routes excess charge flow to lubrication circuits. At a slightly higher main pump inlet pressure, it also routes oil to an inlet of the charge pump.

Abstract: Apparatus is provided for delivering a controllable, variable flow of pressurized fluid. Conduits define a circulating fluid flow system, the flow system passing through a transducer for transferring energy as a mechanical input or output to or from pressurized fluid circulating in the system. At least first and second volumetric pumps are connected to conduits of the flow system in parallel relation to each other and in flow communication with the transducer. An operating shaft, preferably a single shaft, engages the first and second pumps. Valves and piping are provided for selectively shunting and isolating the first and second pumps from the fluid flow system. Thus, energy applied to the fluid flow system through either the shaft or transducer may be applied to the other of the shaft or transducer with variable pressure and flow velocity in the flow system, depending on whether one or both of the pumps are in operating mode with the flow system.

Abstract: A control circuit for a hydraulic actuator which allows the hydraulic actuator to be operated readily without much skill and at a suitable speed in accordance with a load applied thereto. The control circuit includes a change-over valve provided intermediately of a pilot pipe line communicating with a pilot oil chamber of a hydraulic change-over valve which belongs to one of a pair of hydraulic change-over valve sets of a hydraulic operating circuit for the hydraulic actuator. The change-over valve is normally urged to a position wherein the pilot oil chamber of the hydraulic change-over valve is communicated with a tank, but is changed over, when a hydraulic pressure higher than a predetermined value acts upon a pilot oil chamber of the change-over valve, to another position in which the pilot oil chamber of the hydraulic change-over valve is communicated with the pilot pipe line.

Abstract: A hydraulic lifting arrangement for a lift assembly on a materials-handling vehicle includes a working piston-cylinder device (17) for raising and lowering the lift assembly, a reversible pump assembly (40) for operating the piston-cylinder device, and an electric motor for driving the pump assembly. The piston-cylinder device (17) is a double-acting device and has two working chambers (28,29), which are connected to the pump assembly by connecting pipes (46,47). The pump assembly comprises a first and a second hydraulic pump (41,42) having fixed displacements. The pumps are so arranged in the system that together they supply hydraulic medium to and receive hydraulic medium from solely the first chamber (28) whereas only the pump motor (41) supplies and receives hydraulic medium to and from the second chamber (29).

Abstract: A cylinder unit is supplied with pressurized fluid from a hydraulic machine which is variable in speed and/or displacement. The machine may be operated as a pump and as a motor to increase the pressure or, respectively, to decrease the pressure so that the piston of the cylinder unit may be actuated in both directions and, furthermore, the brake energy is recovered by the machine when the piston is driven through an external load. This results in an increased efficiency of the control apparatus for the cylinder unit avoiding any problems arising from heat.

Abstract: A hydraulically-operated support device for semitrailers is disclosed comprising a hydraulic cylinder semitrailer support and a pump subassembly having three independently operable pumps for generating and controlling the hydraulic operating pressure. The hydraulic cylinder semitrailer support has an extending piston in an extending cylinder, in the bottom end of which is formed a load-raising cylinder for a load raising-piston. A first annular space is formed between the extending piston and the extending cylinder and a second annular space is formed between the load-raising piston and the load-raising cylinder. The annular spaces allow application of pressure in the retraction direction. The pump subassembly comprises an extending pump acting on the extending piston, a load-raising pump acting on the load-raising piston and a retracting pump acting on the annular spaces.

Abstract: Hydraulic circuit in an industrial vehicle, which comprises: a cargo-steering hydraulic circuit, flow rate of which is large and pressure of which is high; and a booster hydraulic circuit, flow rate of which is small and pressure of which is medium; the hydraulic circuits being independent from each other; the cargo-steering hydraulic circuit being communicated with a hydraulic pump, flow rate of which is large and pressure of which is high; and the booster hydraulic circuit being communicated with a hydraulic pump, flow rate of which is small and pressure of which is high.

Abstract: A hydraulic transmission, in particular for an automotive drive system including a combustion engine comprises at least a pair of hydrostatic pumps and at least a pair of hydrostatic motors each pump and/or motor having the same size or different size with a constant or adjustable through-put. Automatically actuated clutches are provided to connect the pumps to the engine and to connect the motors to a load. A variety of transmission ranges is obtained by activating selected ones of the individual pumps and motors by actuating corresponding clutches. Therefore, the combustion engine may be operated under conditions in which fuel comsumption is as low as possible.

Abstract: A multiple stage rotary fluid device enclosed within a housing containing a working hydraulic fluid. An axially extending shaft is adapted to be secured to a source of power at one end. Fluid within the housing is directed across a control valve to an initial pump stage driven by the shaft. Pressurized fluid from the initial pump stage is directed to a hydraulic motor having a rotor which is rotatably driven through a planetary gear arrangement within an accentric housing. The pump housing surrounding the motor and pump is driven in a direction opposite that of the main shaft through a bevel gear arrangement driven from the axial shaft. Fluid is discharged through peripheral exhaust ports and the reservoir.

Abstract: The present specification discloses a brake actuation system for a vehicle, which is applicable to both hydraulically or pneumatically operated/spring released brakes and spring operated/hydraulically or pneumatically released brakes. With such brakes it is often necessary to have secondary means for brake operation or release. Such braking systems thus have primary and secondary means for brake operation or release. The present invention provides a fail-safe system which can provide at least an indication of impending failure. The brake actuation system of the present invention comprises a cylinder within which two axially aligned pistons are axially slidable, the space between one end of the cylinder and one piston being connected to a primary power system and the space between said pistons being connected to a secondary power system.

Abstract: A hydraulic circuit for a large crane furnished with a counterweight carriage detachably connectable to the swivel unit of the crane.

Abstract: A common relief valve circuit for controlling or monitoring two or more pumps. The circuit includes two fixed displacement pumps with the pumps being connected to at least two valve bodies or sections that supply fluid to hydraulic cylinders for operating earth-working buckets or the like. A main relief valve is connected to the inlet of a first valve section, and a check valve is connected in a parallel cavity line in the first valve section. The check valve remains closed under conditions where a valve spool in the first valve section is shifted but a valve spool in the second valve section is not shifted or when a valve spool in the second valve section is shifted and a valve spool in the first valve section is not shifted.

Abstract: A control system for the boom and bucket operation system on a front end loader that includes an unloader valve responsive to pilot valve pressure to bypass hydraulic fluid pumped by an auxiliary pump to the reservoir while maintaining the primary pump supply to a loader valve which supplies pressure to the boom and bucket cylinders in response to the operation of pilot valves. The unloader valve bypasses the auxiliary pump flow when the pressure is below a predetermined value and when the pressure is above a second higher predetermined value.

Abstract: A hydraulic pressure system comprising a hydraulic pump, a hydraulic motor, a pair of main hydraulic pressure lines connecting the pump and the motor so as to form a closed loop or circuit, a booster line for supplying a hydraulic pressure from a booster pump to the low pressure side of the closed circuit, a pilot line for taking out a pilot pressure from the high pressure side of the circuit to operate an actuator for controlling the hydraulic pump and the hydraulic motor, and a boost pressure regulator for causing the pressure in the booster line to rise only when the differential pressure between the two main hydraulic pressure lines of the closed circuit becomes lower than a predetermined level.

Abstract: An arrangement for operating a diesel-hydraulic drive on a construction machine in limit-load control with a microprocessor controller in which the installed hydraulic power is greater than the rated output of the diesel engine. Upon thermal and/or diesel-engine overload the hydraulic power which can be taken off is reducible; in the case of non-output loading, after a selectably predetermined time the diesel engine can be switched to idling speed of rotation and hydraulic displacement pumps can be operated with minimum delivery oil quantity; and the adjustable hydraulic displacement pumps can be adjusted in accordance with selectably predeterminable output curves.

Abstract: A refrigerated mobile cargo container having side and rear platforms for loading and unloading cargo and hydraulic control valves for regulating the raising and lowering of the platforms. Fluid to the control valves can be supplied from either a primary pump system powered by the refrigeration unit prime mover or by a secondary pump system powered by a twelve volt power supply. Each pump system has its own fluid reservoir. Check valves are provided which prevent the fluid from one pump system from being passed into the other pump system.

Abstract: The invention contemplates hydraulic-lift mechanism which employs a power integrator in the connection between a charged hydraulic accumulator and the actuator for a vertically positionable load; the power integrator, additionally, has a prime-mover connection, and the pressurized charge of the accumulator is advisedly set to fully accommodate a preselected level of average load upon the actuator. The hydraulic circuit importantly includes check valves, with a pilot-operated check valve interposed between the power integrator and the accumulator and another pilot-operated check valve interposed between the power integrator and the load actuator. The pilot-operated check valves cooperate with other check valves to assure automatic transfer of hydraulic fluid under pressure from the accumulator to the load actuator, and vice versa, as may be determined by selected control of or via the power integrator.

Abstract: A pump supplies via in each case a directional valve with associated pressure balance fluid or pressure medium to a plurality of loads. When the pump power is not sufficient a proportional quantity reduction is achieved at all loads in that the control voltages of the control members for electrical actuation of the directional valves are supplied to a summation stage and the sum voltage is compared in a comparison stage with a limit value corresponding to the maximum pump displacement, whereupon when the limit value is exceeded a control signal is generated with which the stroke of the driven directional valves is reduced.

Abstract: A hydraulic drive system for a counterweight dolly in a counterbalance type crane having a crane body provided with a lower travelling structure an upper swivelling structure and the counterweight dolly connected to the rear portion of the upper swivelling structure through a connecting member, characterized by including a swivelling hydraulic motor for swivelling the upper swivelling structure of the crane body; a swivelling control valve for controlling the pressure of hydraulic oil to be fed to the swivelling hydraulic motor; a hydraulic circuit for swivelling operation which controls the amount of operation of the swivelling control valve; a hydraulic motor for the counterweight dolly which drives each wheel of the dolly; a dolly control valve for controlling the pressure of hydraulic oil to be fed to the hydraulic motor for the counterweight dolly; and a control circuit for actuating the dolly control valve in accordance with an operational pressure of the hydraulic circuit for swivelling operation and t

Abstract: A vibration roller comprises a power limiting device (20) engaging the travelling lever (3), the vibration roller having a prime mover (1), a hydrostatic pump for the travelling drive, which hydrostatic pump is driven by the prime mover and arranged to be controlled by a travelling lever (3), and a vibration drive driven by the prime mover. The power limiting device comprises a stepped piston (27) slidingly movable in a stepped bore (24). The fluid pressure in the travelling drive and in the vibration drive engage the steps thereof. The stepped piston (27) is movable into the setting range of the travelling lever (3), by the sum of the fluid pressures, such that the maximum deflection of the travelling lever is limited to values, at which the total power consumption of the vibration roller does not exceed the limiting power of the prime mover.

Abstract: The invention contemplates a hydraulically operated twin-cable suspension for a clamshell or the like load-handling device. In a preferred embodiment, a charged accumulator is effectively a counterweight and is the source of all hydraulic fluid needed for the full range of actuation of two traction cylinders, one for each of the respective cables. Two power integrators are employed: one is interposed between the accumulator and one of the traction cylinders, and the other is interposed between the accumulator and the other traction cylinder; hydraulic control interconnections between the respective integrator circuits enable load sharing by both cables and simplified single-lever control of plural clamshell functions, including (a) an automated closing dig into loadable material and (b) a quick opening for load discharge.

Abstract: A hydraulic power and control system for operating a reciprocating hydraulic mechanism including pump means connected to the hydraulic mechanism, a continuous torque hydraulic motor, a direction control driven by the motor to sequentially direct hydraulic power fluid to separate inlets of the mechanism, an escapement for restraining the motor at 180.degree. intervals of rotation for sequentially holding the direction control at two separate positions, one for supplying one inlet and the other for supplying the other inlet of the mechanism, and hydraulic limit valves for controlling the escapement when a reciprocating member of the mechanism reaches the end of each stroke. One embodiment has two constant volume hydraulic pumps connected with the hydraulic mechanism through a reversing valve assembly operated by a scotch yoke connected with the escapement.

Abstract: A hydraulic intensifier having a hydraulic motor driven from a low pressure source and operable to drive a low pressure pump for sucking oil from a reservoir and for delivering the oil as charge oil to a high pressure pump. The latter also is driven by the hydraulic motor and pressurizes the charge oil so as to deliver oil at high pressure to a hydraulic actuator. The intensifier is of a self-contained and modular construction and includes a case which defines the oil reservoir and which is closed by detachable end caps permitting the motor and the low pressure pump to be pulled out of one end of the case and permitting the high pressure pump to be pulled out of the other end of the case.

Abstract: A control having a primary work system, a secondary work system, a first fluid flow generating system, and a second fluid flow generating system is provided. A control signal delivering device is provided to deliver a control signal having a magnitude responsive to a relative location of a control valve between a first and second position of a control valve. A control signal receiving device receives the control signal and separately controls the flow rate deliverable from the first and second flow generating system in response to the magnitude of the control signal received. The control signal receiving device has a set point value which is representative of a preselected magnitude of the received control signal. The second fluid flow generating system is controlled to deliver fluid only in response to the magnitude of the received control signal having a value greater than preselected deliverable flow rate.

Abstract: A power assisted steering system of the type which includes a hydraulic reaction mechanism for controlling the hydraulic power assist in accordance with an increase or decrease of the vehicle speed. The system includes primary and secondary hydraulic pumps, the primary pump having the function of applying hydraulic pressure to the power cylinder and the secondary pump having the function of applying hydraulic pressure to the reaction mechanism in proportion to the vehicle speed. The secondary pump is unitedly assembled with the primary pump to be driven by the prime mover, and comprises a first control valve for controlling the quantity of fluid applied to the reaction mechanism for the secondary pump in a constant amount, and a second control valve for controlling the pressure of fluid controlled by the first control valve in accordance with the vehicle speed.

Abstract: A control drive is provided for the drive of a vehicle, whose steering is effected by a differential driving of the drive wheels of the two sides of the vehicle, where the drive wheels of each vehicle side are driven through a hydrostatic drive unit, whose final control element is connected with a servo piston capable of sliding in an operating cylinder and is acted upon from both sides, in which case the servo piston is acted upon from one side for controlling the travel speed and the control pressure determining the travel speed is reduced for effecting a turn on one side of the vehicle for large turning radii, and for smaller turning radii a pressure is additionally built up on the opposite side of the servo piston, the said pressure being derived from the control pressure determining the travel speed on the other side of the vehicle.

Abstract: A hydraulic circuit arrangement for controlling a plurality of actuators connected to a high pressure line of a main pump parallel to each other has a sequence valve interposed in a line bypassing from the high pressure line to a reservoir. In the bypass line a throttle is interposed between the sequence valve and the reservoir. A regulator for controlling the displacement of the main pump is connected to the bypass line between the sequence valve and the throttle at a pilot chamber thereof. An auxilially pump is connected to the high pressure line parallel with the sequence valve. A delivery line of the auxilially pump has a bypass line interposed with a relief valve. The main pump may be switched to unloaded condition for the stand-by condition of the actuators and to loaded condition for the operation condition of the actuators.

Abstract: An actuator control system is disclosed using fluid dispensing means to selectively add or remove fluid from a closed actuator system, whereby the movement of the actuator is volume rather than pressure responsive.

Abstract: A winch apparatus, such as draw works used for raising and lowering drill pipe into a borehole, in which motive power is provided by a hydraulic motor. A multi-stage rotary disk valve is interposed between the fluid supply pump and the hydraulic motor to provide a variable fluid flow rate and thereby to provide means for variably controlling the speed and direction of rotation of the draw works. A directional control disk is provided in the valve to provide reverse flow to prevent cavitation when the drill pipe is in free fall into the borehole, which drives the hydraulic motor in reverse. The directional control disk also controls the entry into the reverse flow of additional fluid provided by a high volume, low pressure auxiliary pump.

Abstract: A control drive is provided for the drive of a vehicle, whose steering is effected by a differential driving of the drive wheels of the two sides of the vehicle, where the drive wheels of each vehicle side are driven through a hydrostatic drive unit, whose final control element is connected with a servo piston capable of sliding in an operating cylinder and is acted upon from both sides, in which case the servo piston is acted upon from one side for controlling the travel speed and the control pressure determining the travel speed is reduced for effecting a turn on one side of the vehicle for large turning radii, and for smaller turning radii a pressure is additionally built up on the opposite side of the servo piston, the said pressure being derived from the control pressure determining the travel speed on the other side of the vehicle.

Abstract: A control system for a hydraulic vehicle having a pair of bidirectional travel motors driven by respective pumps via respective travel valves, and implement actuators, including a swing motor, driven by the pumps via two parallel connections of pilot-operated implement valves. For making possible the straight travel of the vehicle, either forwardly or rearwardly, while any of the implement actuators is being driven by either pump, a straight travel valve is provided for the on-off control of communication between the forward travel ports, and between the rearward travel ports, of the two travel motors. Normally held closed under spring pressure, the straight travel valve is pilot opened by a series connection of two straight travel control valves, which delivers pilot control fluid to the straight travel valve when the travel valves are both hand operated to set the two travel motors into rotation in the same direction.

Abstract: A control valve assembly having a plurality of control valves, each including a pair of logic valves, with each of the logic valves having a pump port, a work port and a pilot port. The control valve assembly has a housing, and a pair of hydraulic fluid passageways arranged in the housing in side-by-side relationship. Each pair of logic valves, constituting one of the control valves, are arranged in the housing in such a manner that they are located in opposed relationship to each other in a direction substantially perpendicular to a direction in which the hydraulic fluid passageways extend. The pump ports of the logic valves are in communication with the associated hydraulic fluid passageways. The work ports of the logic valves are oriented in a direction substantially perpendicular to both the direction in which the hydraulic fluid passgeways extend and the direction in which the pair of logic valves are arranged.

Abstract: A hydraulic circuitry for a backhoe in which a hydraulic motor for driving one of right and left crawlers and a hydraulic cylinder for vertically oscillating a working arm assembly are connected in parallel to each other to a first pump through a multiplex valve assembly having a first center bypass, and a hydraulic motor for driving the other crawler, a hydraulic motor for slewing a platform, a hydraulic cylinder for flexing and stretching the arm assembly, a cylinder for actuating a bucket and a cylinder for actuating a dozer are connected in parallel to one another to a second pump through a further multiplex valve assembly having a second center bypass. The invention provides a circuit to permit fluid pressure from the first pump to enter the circuit connected to the second pump to provide confluence therein, when the dozer actuating cylinder connected to the second pump, for example, is operated while the backhoe is running.

Abstract: A hydraulic drive system including at least one hydraulic actuator, two variable displacement hydraulic pumps each connected to the hydraulic actuator to form a closed circuit therewith and connected in parallel with each other, two prime movers each driving one of the hydraulic pumps, and directional control valves each arranged between the hydraulic actuators and one of the hydraulic pumps. The directional control valves are each operative to shut, when one of the prime movers associated therewith is shut down, the hydraulic pump connected to the shutdown prime mover off the other hydraulic pump and the hydraulic actuator, to thereby prevent the hydraulic pump from being rotated by the pressure fluid delivered by the other hydraulic pump.

Abstract: Pipe thrust-jacking apparatus includes a pressure ring 5 which is advanceable by a plurality of hydraulic rams 3. The rams are controlled by hydraulic control means having a plurality of hydraulic control valves 19. Each control valve is associated with a respective hydraulic ram, and is connected to a first input line and to a second input line. Each of the first input lines is connected to a respective hydraulic fluid feed line 9, and each of the second input lines 17 is connected to a common hydraulic fluid supply line 11 and to an auxiliary pump P2. The common supply line is connected to all of the feed lines. Means 12,15 are provided for selectively connecting each of the hydraulic control valves to its first input line and/or its second input line.

Abstract: A quick changeover hydraulic circuit for use in an auger drive mode or percussion hammer mode, controllable in each mode by the same flow regulator. The circuit comprises a first branch circuit which powers a first auxiliary hydraulic powered device and a hydraulic motor for drill steel rotation. A second branch circuit powers a hydraulic percussion motor for a drill steel hammer or a rotary hydraulic motor for an auger, only one of which is in the circuit at one time. An interbranch circuit comprises a priority flow divider which distributes flow. In a first mode with the percussion motor for the drill steel hammer connected into the second branch the flow is delivered to the steel rotation motor and the first auxiliary device. In a second mode with the auger motor connected into the second branch, combined flow from both branches is delivered to the auger motor.

Abstract: A civil machine having a flow-rate controller which applies a preset signal instead of a normal flow-rate signal to a variable type hydraulic pump when delivery pressure of the hydraulic pump exceeds a preset pressure value. The normal flow-rate signal corresponds to the position of an operating lever. The preset signal has a value of minimum flow rate to hold a working tool in a certain posture. With this control system, pressure loss and temperature rise in hydraulic operating oil as well as fuel consumption of the machine can be reduced and cycle time of the work can be improved.

Abstract: A control system for variable displacement hydraulic pumps for use in a hydraulically operated construction vehicle having a fixed displacement hydraulic pump, a plurality of reducing valves operatively interlocked with work implement control valve units of the vehicle disposed on the delivery sides of the variable displacement pumps, control sections for controlling respective flow rate of the variable displacement pumps and equipment for exerting delivery pressures of both the fixed and variable displacement pumps and output pressure of the reducing valve on the control units. The control system exhibits three control functions, i.e., flow control for varying the angle of the swash plate of the variable displacement pump in proportion to the manipulating position of the respective work implement controlling valve, constant torque control in proportion to the delivery pressures of the variable displacement pumps, and cut-off control for reducing relief losses.

Abstract: A combined power steering pump and vacuum pump assembly is disclosed wherein a vented reservoir is connected to receive the discharge of the vacuum pump as well as supply the fluid for circulation by and lubrication of the power steering pump. A sealing arrangement seals the vacuum pump from the power steering pump when the pumps are stopped but provides limited delivery of the fluid from the power steering pump to the vacuum pump when the pumps are running whereby the fluid in the power steering system is prevented from draining into the vacuum pump when stopped and is delivered thereto when running to lubricate same and is then delivered with the discharge air to the reservoir so that there is no loss of the fluid from the power steering system in lubricating the vacuum pump.

Abstract: The hydrostatic control system for an articulate loader provides an improved method for controlling the output of a hydrostatic drive unit for a front end loader, with cooperative connecting means disposed between a pair of axially aligned drive pumps to provide selective output of one or both pumps as dictated by operation of the control mechanism.

Abstract: In a hydrostatic transmission of the type in which a motor and a variable displacement pump are coupled within a casing, both the motor and the pump are of the radial displacement type and each includes two oppositely phased reaction surfaces, so as to enable improved dynamic balance and a simpler and more robust construction. An engine starting function may also be provided.