Abstract: A vehicle stabilizer apparatus having a plurality of hydraulic stabilizer actuators with each actuator having an integral isolation valve effective to enable operation of a sequentially operable device such as a boom cylinder only after ground-engaging feet associated with the actuators have been brought into firm contact with the ground or other supporting surface. Each actuator is mounted for bodily movement between upper and lower positions on an associated vehicle supported mounting pin. The actuator is caused to move to its upper position when the associated ground-engaging foot engages the ground and through a plunger and plunger spring associated with the isolation valve the position of the actuator is sensed. The isolation valve is in a hydraulic circuit to prevent operation of the boom cylinder unless the actuator is in its upper position.

Abstract: According to the parent patent on inadequate power of the delivery pump the flow rate set at the directional control valves for the consumers is reduced in equal proportions in that electrical signals proportional to the flow rates 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 delivery flow. When the limit value is exceeded a control signal is generated with which the stroke of all the driven directional control valves can be jointly reduced. According to the application of addition the signal voltage supplied to the summation stages and corresponding to the respective flow rate can be obtained in a displacement pickup associated with each directional control valve or in a pressure pickup measuring the pilot pressure if the directional control valves are not controlled electrically but hydraulically.

Abstract: A pump supplies a plurality of consumers each via a directional control valve with pressure balance. When the pump delivery is not adequate, manifesting itself in a dropping of the pump pressure, the pressure balance of the consumer with the highest load pressure is displaced out of the end position of its regulating position into a further control position in which a control pressure line is connected via a throttle point to a discharge so that by means of the throttle point a control pressure is generated which is used for equiproportional reduction of the supply flow to the consumers. This is done either by reducing the stroke of the directional control valves or by acting on the pressure balances in the closure direction.

Abstract: A hydraulic drive system for one or more hydraulic motors, comprising a pump (1), a tank (25) for hydraulic fluid, one or more control valve sections (10, 11, 12) each being provided with a shunt passage and each being coupled to a respective hydraulic motor, a first shunt conduit (4) including the shunt passages of said control valve sections (10, 11, 12) connected in series for leading off of the tank (25) the temporarly surplus flow of hydraulic fluid from the pump (1), and a feed conduit (3) for connecting the control valve sections (10, 11, 12) in parallel to the pump (1).

Abstract: A hydraulic operating circuit for working members of earth-moving machines includes linear and rotary hydraulic actuators each of which is associated with a respective hydraulic distributor supplied from a principal supply and with a pressure compensator of the load-sensing type. A re-supply circuit is also associated with one or more of the rotary actuators for integrating the leakage and includes two anticavitation valves and a valve for boost-feeding the anticavitation valves from the principal supply.

Abstract: An earth-moving machine has an automatic device for minimizing the running speed of the main engine when no power is required by the hydraulic actuators. This device establishes a predetermined hydraulic fluid flow-rate in the servocontrol in the non-neutral position of the servocontrol itself. This flow-rate is indicated by an on-off flow-rate sensor inserted in the auxiliary hydraulic control circuit between the pump and the servocontrols, this sensor controlling the variation in the operating condition of the injection pump of the main engine by means of an electromagnet.

Abstract: A large industrial earthmoving machine having a hydraulic propulsion system comprising at least two hydraulic motors which are powered from a source of hydraulic fluid to drive a common load. Each motor of the hydraulic propulsion system is provided with two compensating valve assemblies. Each compensating valve assembly is provided with a compensating spool and a shuttle spool to provide accurate control of the hydraulic motors. In each pair of compensating valve assemblies, there is a forward compensating valve assembly and a backward valve assembly respectively controlling forward and backward movement of the hydraulic motor. Between the both forward compensating valve assemblies and the respective hydraulic motors, the compensating valve assemblies are fluidically coupled to one another by a small hydraulic communication line that better equalizes hydraulic fluid flow to the motors and prevents domination of one forward compensating valve assembly over the other.

Abstract: A hydraulic drive system for a construction machine in which a hydraulic circuit has at least one hydraulic pump, at least first and second hydraulic actuators driven by a hydraulic fluid discharged from the pump, and at least first and second directional control valves connected to the pump in parallel with each other for controlling flows of hydraulic fluid supplied from the pump to the first and second actuators, respectively, and a control unit is responsive to first and second operation signals for driving the first and second actuators, respectively, to produce first and second control signals for actuating the first and second valves and deliver such control signals thereto, respectively, each of the first and second valves having a degree of opening changed in accordance with a level of the corresponding one of the first and second control signals for controlling a flow rate of hydraulic fluid supplied to the corresponding one of the first and second actuators.

Abstract: A fluid control valve for controlling the flow of hydraulic fluid at a high pressure from a primary pump and the flow of the hydraulic fluid at a low charge pressure from a charge pump to cam-lobe type hydraulic motors which are used to assist in driving a vehicle. When energizing the motors, charge pressure is first delivered to the motors. Thereafter, all of the supply and return lines leading to the motors and to the primary pump and the charge pump are connected together to further increase the pressure delivered to the motors. Finally, the charge pressure line is disconnected and the supply and return lines leading to the motors are connected to the high pressure supply and return lines leading to the primary pump. When the supply and return lines leading to the motors are disconnected from the primary pump, the lines leading to the motors are drained into a reservoir. An accumulator is provided within the motors to absorb sudden pressure delivered thereto.

Abstract: A control system for terminating the power input to the picking units of a cotton harvester after a short delay by automatically causing a hydrostatic drive to return to neutral. A seat switch and a delay timer electrically connected to a solenoid valve on a servo control system of the hydrostatic pump deactivates the servo system and returns the pump swashplate to a neutral position to stop the unit movement when the operator leaves his seat. Another switch connected in parallel with the operator seat switch is activable when the unit drive is in neutral making the system effective only when the picking units are engaged. A service bypass circuit is provided which, when the hydrostatic lever is in a special low speed position and when the main ground drive of the transmission is in neutral, permits the units to be operated at a relatively slow speed by depressing a remotely located switch.

Abstract: A drive system having two hydrostatic gears (1, 2) driven by a common driving motor or by a plurality of driving motors having a fixed speed ratio, each having a pump (5, 6) and a hydraulic motor (7, 8) and in which the delivery or intake volume setting of the pumps (5, 6) and/or the hydraulic motors (7, 8) is performed by hydraulic servomechanisms (13, 14) of which the control pressures in the control pressure lines (23, 24) can be varied as desired either independently or together by means of pressure indicating valves (26) connected to each of the gears (1, 2) and supplied by an auxiliary source of pressure (9, 10) is arranged so that, at least on starting, the outputs of the gears (1, 2) are as nearly as possible equal.

Abstract: A pump supplies via in each case a directional valve a plurality of consumers with fluid, a pressure balance for load-independent division of the pump displacement being provided between each branch line branching off the pump delivery line and the directional valve. In a pressure regulating valve common to all pressure balances a control pressure is generated from the pressure difference between the pump pressure and the respective highest consumer pressure and is applied to all the pressure balances so that when the pump power is inadequate a proportional quantity reduction at all consumers is achieved.

Abstract: A hydrostatic drive with an adjustable pump and several consumers is provided in which one or several consumers simultaneously can be selectively connected with the pump, in which case the connection to a consumer can be effected by an arbitrarily actuable control valve having a throttling effect in the intermediate positions, where the loading of the adjusting element of the pump is controlled by a pump adjusting valve, which in turn is regulated by the pressure differential arising at the regulated control valve so that it is regulated to a constant pressure differential, where the highest prevailing pressure in a line between the regulated control valve and the regulated consumer is conveyed through a control pressure line to the control pressure chamber on the spring side of the pump adjusting valve and where a pressure limiting valve is connected to the pump delivery line and provided on the spring side with a control pressure chamber connected with the control pressure line (load-sensing signal line).

Abstract: Hydraulic control circuit for working members of earth-moving machines including linear and rotary hydraulic actuators associated with respective hydraulic distributors for the operation of respective working members. The rotary hydraulic actuators with their distributors are grouped in a circuit separate from the linear hydraulic actuators and are provided with braking valve means constituted by a single counterbalance valve connected in a common discharge line, the opening of which is controlled by a pilot pressure signal corresponding to the lowest supply pressure for the rotary actuators.

Abstract: A hydraulic or the like drive system which can include a variable-speed pump with at least one control element. The control element can be connected to a pump control piston arranged in a pump control cylinder, the position of which is determined by a control pressure. The drive system can further include a conveying conduit connected to the pump and a return conduit which leads to the respective reservoir, and can furthermore include control elements, with the conduit emanating from the pump are connected--by intervention of a respective branch line--several demand points which respectively can be connected to the conveying conduit by means of an in the respective branch line arranged, randomly movable valve. The valve has two auxiliary pistons arranged in the main piston of the valve and each auxiliary piston houses a reversing piston.

Abstract: An apparatus for controlling the fluid flow delivered to work elements of a work vehicle. In the operation of hydraulic work vehicles, when quick or multiple implement movement is required, the fluid pumps often are requested to surpass their capability in providing fluid flow to the work elements. A flow-limiting situation then occurs wherein some of the work elements are not receiving the requested flow and therefore cannot perform their requested functions. To solve this problem, the total available flow and the total requested flow from the pumps are monitored. If the total requested flow is not great enough to cause a flow-limiting situation, the operators demands are communicated to control valves which control fluid flow to the respective work elements. However, if the total requested flow is greater than the total available flow, the operators demand signals are "scaled down" in order to prevent a flow-limiting situation.

Abstract: In a method of and device for adjusting the feed movement of a drill rod for drilling a rock, the drill rod is rotated by a pressure-medium-operated rotary motor and fed in a drilling direction and in the opposite direction by a pressure-medium-operated feed motor. A pressure change on the pressure side of the rotary motor due to a change in the rotation resistance on the rotary motor acts oppositely on the pressure and outlet sides of the feed motor toward reversing the feed force of the feed motor, i.e. in inverse and direct dependence on the pressure change, respectively. The pressures on the pressure side and the outlet side of the feed motor are, therefore, controlled so that, when the pressure on one side increases because of the pressure change, the pressure on the other side decreases and vice versa.

Abstract: A pressure compensated hydraulic valve (2) is provided with a housing (4) having a reciprocal spool (6) for communicating hydraulic fluid to work ports (8,10). Pressure compensating means (58) is provided in the same housing with the valve and senses work port pressure by hydraulic fluid flow through the spool from the work port and creates a substantially fixed differential pressure across the spool by controlling the pressure after the flow has passed through the spool.

Abstract: An hydraulic control system is disclosed for energizing a load, such as the lift cylinder of an electric lift truck, with a minimum of power loss during the transition from zero to full energization, i.e. during the feathering range. An electric motor drives a positive displacement pump which supplies the flow requirements of different load circuits, one having a greater flow requirement than the other and requiring higher pump speed. A proportioning valve of the open center type provides full flow to the tank when the valve is closed and full flow to the load circuit having the greater flow requirement when the valve is open. A manually actuable lever actuates the valve through the feathering range with the pump motor in a low speed range and actuates a speed control switch to operate the motor in the high speed range when the valve is fully open.

Abstract: A hydraulic control arrangement for regulating a lifting device in an agricultural vehicle has a proportionally operating regulating directional valve which includes a blocking unit, a control slider controlling said blocking unit and connected with a throttling valve so that its throttle slider during lifting operates as a pressure compensation valve and during lowering as a pressure reducing valve, and a spring associated with the throttle slider is only insignificantly stronger than the regulating spring in an adjusting device of an adjusting pump, so that during actuation of the throttle slider depending upon the high load pressure of a parallel-operating second hydromotor, the pressure differential required for the lifting stream at the control slider and the pressure differential acting during lowering in the first control conduit remain substantially constant.

Abstract: The invention relates to a hydraulic system of the type in which a pump unit supplies pressurized fluid to a plurality of bidirectional servomotors. The system includes at least two modules each of which includes a bidirectional servomotor, a control valve and a compensating valve on the upstream side of the control valve. The pump unit includes a feedback loop having a throttle and a pump pressure regulator in series. Each of the modules has a sensing conduit connected to a common header which is operable to sense load pressure at the upstream side of the control valve for controlling the compensating valve in accordance with the load pressure. A pressure divider comparator valve is connected to the header and a point in the feedback loop between the throttle and the pump pressure regulator. The comparator valve is operable to compare the pressure at such point with the pressure in the header and to bleed pressurized fluid from that point to the tank to equalize the pressures.

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 high pressure hydraulic distributor with a pilot pressure generator, in which a device for reducing pressure is integrated into a distribution section of a compound high pressure hydraulic distributor. The displacement of the slide of the distributor of the section concerned modifies automatically the calibration of the pressure reducer and permits obtaining a reduced pressure which is a function of the displacement of the slide. This reduced pressure is utilized as the pilot pressure for the control means of the source of hydraulic fluid pressure which feeds the distributor.

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 circuit including at least first and second variable displacement volume type hydraulic pumps, at least first and second hydraulic actuators driven by the pumps, and valves for controlling hydraulic connections between the pumps and the actuators. The control system includes a device for deciding the order of priority of hydraulic connections between the first actuator and the first and second hydraulic pumps and the order of priority of hydraulic connections between the second pump and the first and second actuators. A first sensor is provided for sensing maximization of the displacement volume of the first pump, sensing that the displacement volume of the second pump has become substantially zero. A device decides target displacement volumes of the first and second pumps based on information supplied at least by the priority order deciding device and first and second sensor.

Abstract: A microprocessor (158) based control for a hydraulic pump motor (26) used to control the operation of a mast assembly (12) on a work vehicle (10). The speed of each function performed by the mast assembly (12) is programmable to one of a plurality of possible speeds. An additional function for performing lifting of the mast (12) produces incremental speed variations relative to incremental movement of a corresponding control lever (14). Each of the functions have a predetermined priority such that attempted operation of multiple functions results in a pump motor speed requested by the function of highest priority.

Abstract: A two-speed, pilot-operated selector valve which directs hydraulic fluid to two motor elements with a common output shaft to obtain a high-torque, low-speed mode, or to one motor element, while recirculating the second element in a loop, to obtain a low-torque, high-speed mode. The spool has a built-in logic mechanism which, while shifting from one position to the other, prevents any momentary condition where a motor discharge port is blocked or a fluid path exists that bypasses both motor elements.

Abstract: A hydraulic system is disclosed for energizing the power steering and various work handling hydraulic load circuits of a lift truck. A single positive displacement pump supplies the requirements of the plural load circuits and is driven by a changeable speed prime mover. Manually actuable selector means are operatively connected with the load circuits and speed control means are provided for the prime mover. A priority demand valve is connected between the pump and the respective load circuits. When only the power steering circuit is selected, the prime mover is operated in a low speed range and the priority demand valve supplies the required flow to the power steering circuit. When the lift circuit is selected, the prime mover is operated in a high speed range and the priority demand valve supplies the flow requirements to the power steering circuit and to the lift circuit.

Abstract: A single lever control facilitating engagement of the speed and range transmission of an agricultural tractor comprising a handle lever initially engaging range gears and subsequently variable speed transmission when moved in one direction and engaging reverse speed when moved in the opposite direction.

Abstract: There is disclosed a hydraulic circuit system for use in a swivel type excavator. The circuit system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulations of work implements and swivel means of the excavator, and control means operative to automatically adjust pump displacement to the output hosepower of a prime mover driving the pumps. The control means includes hydraulic pressure detector means, servo-control means respectively provided in the pumps, negative control valves for respectively controlling the servo-control means by the action of the pressure detector means, cut off valves respectively connected in series with the negative control valves, and summing valves respectively connected in series with some of the cut off valves so as to control pressurized fluid to be supplied into the servo-control means by the action of the fluid pressure delivered from the pumps.

Abstract: An electric hydraulic control device for controlling hydraulic cylinders of work tools in a construction vehicle, in which control valves of the hydraulic cylinders are controlled in two ways. For some work tools which need not be controlled smoothly and finely, the corresponding control valves are controlled directly by an electric signal outputted according to the position of the operation levers, and for other work tools which must be controlled smoothly and finely, the corresponding control valves are controlled through an electric servo mechanism which is operated by an electric signal representative of the amount by which the operation lever is manipulated. In addition, there is provided a detector for detecting as to whether the transmission lever is in the locked condition, and electric systems of all of the control valves are rendered inoperative when the transmission lever is in the locked condition.

Abstract: A tractor hydraulic control system of the kind comprising a power lift with a hydraulic actuator (12) and a main control valve (17) controlling the supply of fluid from a pump (19) to the actuator, the system including selector valve means (50) interconnected with the main control valve (17) and movable between a first position in which flow to and from the actuator (12) occurs via the selector valve means under the control of the main control valve and the associated system control mechanism (28) and a second position in which the actuator is hydraulically locked in a given position and an external services outlet (51) is placed in communication with the pump. Linkage means (60,61,62) operatively connects the selector valve means (50) and the system control mechanism (28) to condition the main control valve (17) to cause the pump (19) to supply fluid to the external service outlet (51) via the selector valve means on movement of the selector valve means to the second position.

Abstract: An open center, load sensing hydraulic system is disclosed which contains a primary work circuit and a secondary work circuit. A fixed displacement pump is fluidly connected between a reservoir and both the primary and secondary work circuits for supplying pressurized fluid thereto. The primary work circuit includes a control valve which regulates fluid flow from the pump to a primary hydraulic function and which includes a feedback mechanism connected thereto. The secondary work circuit includes a manually operable control valve for regulating fluid flow from the pump to a secondary hydraulic function. A priority valve is connected between the pump and both the primary and secondary work circuits and is movable to regulate the pressure to the primary work circuit.

Abstract: A closed center, load sensing hydraulic system is disclosed which contains a primary work circuit which has priority in flow demand over a secondary work circuit. The system includes a variable displacement pump fluidly connected between a reservoir and a control valve with the primary work circuit. The primary work circuit includes a control valve which regulates fluid flow from the pump to a primary hydraulic function and which includes a feedback mechanism connected thereto. The secondary work circuit also includes a manually operable control valve for regulating fluid flow from the pump to a secondary hydraulic function. A priority valve is connected between the pump and the secondary work circuit and movable between an open and a closed position to regulate the pressure of fluid discharged by the pump.

Abstract: An open center hydraulic system is disclosed which contains a primary work circuit and a secondary work circuit. A fixed displacement pump is fluidly connected between a reservoir and the primary and secondary work circuits for supplying pressurized fluid thereto. The primary work circuit includes a control valve which regulates fluid flow from the pump to a primary hydraulic function and which includes a feedback mechanism connected thereto. The secondary work circuit also includes a manually operable control valve for regulating fluid flow from the pump to a secondary hydraulic function. A priority valve is connected between the pump and the secondary work circuit and is movable between an open and a closed position to regulate the pressure of fluid discharged by the pump.

Abstract: A load sensing hydraulic system is disclosed which essentially eliminates kickback from a feedback mechanism contained in a manually operable control valve which in turn is fluidly connected to a hydraulic function. The system includes a power on demand pump fluidly connected between a reservoir and the control valve for supplying pressurized fluid to the hydraulic function. A load signal line is also connected between the control valve and the pump which serves to transmit pressure signals, which are generated by loads acting on the hydraulic function, to the pump for controlling the pressurized output thereof. A load signal control valve is positioned in the load signal line and is fluidly connected to the discharge side of the pump. The load signal control valve is capable of sensing pressure variations between the fluid discharged by the pump and the upstream fluid present in the load signal line.

Abstract: A control is provided for the drive of a motor vehicle with differential-speed steering and with a hydrostatic power transmission unit on each side of the vehicle, where the adjusting element of each of the two power transmission units is provided with a spring-loaded adjusting piston that can be acted upon by control pressure, in which case two pairs of control pressure pick-offs are provided, of which two are assigned to forward and backward movement and the other two are assigned to cornering, where a pressure-dependent switchable pilot valve is installed in the connecting line between a control pressure pick-off assigned to a cornering direction and the adjusting element of the assigned power transmission unit, the pilot valve connects this control pressure pick-off assigned to the cornering direction with a specific pressure chamber of the adjusting element of the power transmission unit on the side of the vehicle on the inside of the curve, so that through actuation of the control pressure pick-off dete

Abstract: A priority flow control system in which the priority feature is obtained by progressively lowering the pressure differential of nonpriority valves, once the maximum pump output is reached, so that all of the system valves always retain their compensated proportional flow feature.

Abstract: A direction flow control valve for control of positive and negative loads operated by a single pilot valve stage, which automatically maintains a relatively constant pressure differential across valve spool, while controlling positive and negative loads and which permits variation in the level of pressure differential in response to an external control signal, while this pressure differential is maintained constant at each controlled level.

Abstract: A hydraulic valve mechanism has a housing with first and second bores, a control valve element in the first bore, a pressure compensation valve in the second bore, and a non-return valve cooperating with motor parts, wherein control edges for direction control are arranged on the control valve element only at one side of throttle means, the non-return valve is also arranged in the second bore of the housing, and the longitudinal valve element of the pressure compensation valve also forms a closing member of the non-return valve.

Abstract: A hydrostatic drive system with an adjustable pump is provided with branch lines from a main delivery line to several consumers, an arbitrarily actuatable switch in each branch line, an adjustable parallel connecting restrictor in each branch line with an adjusting element loaded on one side by pressure from either the main delivery line or the branch line and on the other side by a spring and control pressure and a source of common control pressure furnishing the control pressure to the adjusting element through a check valve.

Abstract: The hydraulic system has an adjustable pump for delivering pressure fluid to a plurality of loads, multiway control valve assigned to respective loads and means for adjusting the flow of the pressure fluid to the working conditions of the loads, the adjusting device includes measuring throttles provided in the switching passages of respective control valves and a flow regulating device having a differential piston displaceable by the pressure difference at the outlet of the pump and at the outlet of the measuring throttle of the activated control valve. The differential piston controls a branched stream of high pressure fluid from the pump to control an actuator in the form of a cylinder and piston unit mechanically coupled to the adjusting member for the pump.

Abstract: A hydrostatic drive system having a closed loop front wheel drive circuit and a closed loop rear wheel drive circuit. A variable displacement pump in each of the circuits is cammed to vary the displacement delivered to dual displacement wheel motors to provide two speed ranges for the drive system. A servosystem uses hydraulic fluid to cam the displacement of the variable displacement pump and a hydraulic control to selectively engage each of the drive ranges.

Abstract: A control system for a hydraulically driven vehicle having a pair of closed loop each including a variable displacement hydraulic pump driven by an engine and a variable displacement hydraulic motor, the control system comprising a charge pump driven by the engine, a directional control valve for speed control and forward and reverse change-over of the vehicle connected with the charge pump, a pair of steering valves connected with the directional control valve, a pair of servo controls each operatively connected with the respective variable displacement hydraulic pumps for controlling the displacement volume thereof, another charge pump driven by the engine, and a manually operated selector valve connected with the another charge pump and the servo controls, the selector valve having formed therein a throttling position and a communication position and normally held in the throttling position and being interlocked with the operation of the steering valves, whereby the selector valve is changed-over to its co

Abstract: Load responsive system controls to vary output flow control of a system pump to control the pressure differential, acting across a control orifice positioned between system pump and a fluid motor. The system controls permit variation in the level of pressure differential in response to an external control signal, while this pressure differential is maintained constant at each controlled level.

Abstract: An improvement is disclosed in a hydraulic system (10) having a variable displacement pump (12) and being capable of delivering pressurized fluid from the pump (12) to selectively engage at least three work circuits (18) with a first (20) of the circuits (18) being normally operable up to a first pressure and a second (22) of the circuits (18) being normally operable up to a second and lower pressure. The improvement comprises circuitry (80, 92, 94, 98, 108, 120, 122, 124, 126) for selectively operating a third (24) of the circuits (18) at one of the first or second pressures or at an upstaged pressure which exceeds the first pressure and circuitry (128) for reducing the displacement of the pump (12) in response to the third circuit (24) being operated at the upstaged pressure. Such upstaged pressure is available in a controlled manner for working against particularly heavy loads. Thus, a third and higher operating level is added to a system which already operates at at least two pressure levels.

Abstract: In a load responsive fluid power and control system employing plurality of control valves with positive and negative load compensation, a pressurized exhaust system supplied with make-up fluid from pump discharge circuit by a pressure reducing valve and deactivating valve of the pressure reducing valve operable when the pessurized exhaust system is completely unloaded during control of positive load.

Abstract: A direction flow control valve for control of positive and negative loads equipped with a load responsive positive load control which automatically regulates valve inlet pressure to maintain a relatively constant pressure differential between inlet pressure and load pressure. The load responsive control of direction flow control valve blocks the pump flow to the motor while controlling negative load, providing the motor inlet with fluid from the motor exhaust.

Abstract: A direction flow control valve for control of positive and negative loads equipped with a load responsive positive load control which automatically regulates valve inlet pressure to maintain a relatively constant pressure differential between inlet pressure and load pressure. The load responsive control of direction flow control valve blocks the pump flow to the motor while controlling negative load, providing the motor inlet with fluid from the motor exhaust.

Abstract: A load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single fixed displacement pump equipped with a load responsive bypass valve or a variable displacement pump equipped with load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher by a constant pressure differential than the pressure required by largest load being controlled. The load responsive valve is of a four position regeneration type which in the regeneration position while connecting together both of the load chambers supplies irrespective of the pressure level an adjustable controlled flow into those chambers from the inlet chamber through a metering orifice.