Abstract: A load sense hydraulic system includes a pilot operated on/off valve disposed within a signal line which communicates a dynamic load sense signal from a steering control valve to a pressure controller of a load sensing pump. Upon actuating a brake valve or applying a brake mechanism, a pressurized fluid signal downstream of a variable flow control orifice in the brake valve is directed to move the on/off valve to its closed position blocking the dynamic load sense signal from a load sense port to the pump controller. This causes the pump controller to stroke the load sensing pump to its high pressure stand-by position so that the brake valve always functions under high pressure operating conditions.

Abstract: A hydraulic control system for work vehicles including a control unit to control the steering wheels of a vehicle via a cylinder and a priority valve which by a first load-sensing system controls the pressure fluid flow to the control unit and to a subsequent proportional valve group. By a second load-sensing system the proportional valve group controls the pressure fluid flow to secondary hydraulic motors or work cylinders to control the work tools of the vehicle. The control system also includes an open-centre valve connection and a fixed displacement pump. The first load-sensing system is connected with a second load-sensing system, whereby drop-off of the pressure fluid flow to the control unit is avoided at simultaneous operation of the latter and of one or several of the proportional valves as is the case with known control systems. Hereby a control system is provided which is particularly agreeable to operate for the driver of the work vehicle.

Abstract: A fluid control system for powering vehicle accessories includes a pump for generating a supply flow of hydraulic fluid. The system also includes a fluid valve assembly having a housing which includes an inlet, a first outlet, a second outlet, and a third outlet defined therein. The inlet is in fluid communication with the supply flow of fluid. The fluid valve assembly provides (1) a first fluid path between the inlet and the first outlet, (2) a second fluid path between the inlet and the second outlet, and (3) a third fluid path between the inlet and the third outlet. The system also includes a fan motor for rotating an engine cooling fan. The fan motor is in fluid communication with the first outlet. Moreover, the system includes a steering control circuit which is in fluid communication with the second outlet. The system further includes a reservoir which is in fluid communication with the third outlet. A method of controlling fluid flow between a plurality of vehicle components is also disclosed.

Abstract: An unloader valve is connected to a pump and has first and second ends, a priority flow port communicating with the first end and being connected to a first conduit connected to a first hydraulic circuit, an excess flow port communicating with a tank, and a spring disposed at the second end biasing the unloader valve to a priority flow position with a force sufficient to maintain the pressure in the priority flow port above a predetermined minimum level. The unloader valve is biased toward an unloading position in opposition to the spring force by pressure generated force acting on the second end. A check valve is disposed between the first conduit and a second conduit connected to a second hydraulic circuit. A valve device controls the pressure at the second end of the unloader valve in response to pressure in the second conduit so that pressure in the second conduit is maintained above a second higher predetermined level.

Abstract: A hydraulic control apparatus having two groups and formed by combination of actuator circuits on large flow rate side (a boom cylinder circuit and an arm cylinder circuit) and actuator circuits on small flow rate side (a bucket cylinder circuit and a rotating motor circuit), for independent supply of hydraulic fluid. In these groups, a bucket preferential valve and a rotating preferential valve form bucket cylinder preferential and rotating motor preferential circuit constitutions.

Abstract: A controller 520 has a data portion 520c in which the relationship between a pump delivery pressure and a target opening area of a variable throttle 300a of a control valve 300 is set such that the target opening area is large when the pump delivery pressure is low, and small when the pump delivery pressure is high. An input portion 520a takes in a detection signal from a pump pressure sensor 700, a processing portion 520b reads the data from the data portion 520c and calculates a signal output to a solenoid proportional valve 590, and an output portion 520d converts the calculated signal into a command signal for the solenoid proportional valve 590 and outputs the command signal. Upon receiving the command signal from the controller 520, the solenoid proportional valve 590 produces a command pilot pressure for the control valve 300 corresponding to the input signal and controls the opening area of the variable throttle 300a.

Abstract: A method for the positionally correct placement of an operating equipment including a scoop tiltably disposed on a descending lift frame of a mobile machine including a wheeled loader. An automatic positioning device is actuated thereby activating a first magnetic valve utilizing a logical switching device cooperating with the automatic positioning device for switching a tilting piston of a control slide operatively connected to a tilting cylinder and to the lift frame into a position in which the control slide releases an oil flow to the tilting cylinder. The oil flow is delivered utilizing a controlled pump. A plurality of measurements is performed of a traveled distance of a piston rod of the tilting cylinder at predeterminable places during a continued extension of the piston rod thereby obtaining distance measurement values.

Abstract: An hydraulic line and valve assembly for supplying hydraulic pressure to an hydraulic auxiliary implement, the implement being adapted for attachment to a construction vehicle having an hydraulic power system, the implement having an hydraulic motor driven workpiece, and the implement having a plurality of hydraulic positioning means; the hydraulic line and valve assembly comprising an on demand priority flow control valve, a branched primary pressure line an end of which being fixedly attached to the on demand priority flow control valve, a plurality of position control valves, the position control valves being fixedly attached to the opposing branched ends of the primary pressure line, and a branched hydraulic load signaling line extending from the position control valves to the on demand priority flow control valve, the hydraulic load signaling line being capable of sending pressure signals to the on demand priority flow control valve causing said valve to divert hydraulic pressure to the position control

Abstract: A priority biased load sense hydraulic system for hydraulic excavators is provided. The hydraulic system includes first and second variable flow pumps which are coupled in load sense arrangement. The first pump is coupled to a first valve bank having a first valve section having a main spool and a compensator spool having an orifice therein, a second valve section having a main spool and a compensator spool having an orifice therein, and third and fourth valve sections each having a main spool and a compensator spool. The second pump is connected to a second valve bank. The second valve bank includes a first section having a main spool and a compensator spool having an orifice. A second valve section having a main spool and a compensator spool having an orifice and a third valve section. The compensator spools in the first and second valve banks serve to prioritize hydraulic fluid flow through the valve banks thereby affectively prioritizing the hydraulic functions receiving hydraulic fluid flow.

Abstract: A control system is typically used for controlling the implements of a machine. The control system includes a lift circuit and a tilt circuit. The control system includes a module which receives a signal from the lift circuit and the tilt circuit and selects a signal for controlling a valve to meter pump-to-cylinder fluid flow.

Abstract: A new creeper drive system has a hydraulic motor with first and second flow lines connected thereto. A directional valve apparatus is connected in the flow lines and the system has a flow control valve operable independently of the directional valve apparatus. The creeper drive system is particularly useful on a mobile construction machine. The machine hydraulic circuit needs but a single pump for powering the creeper drive motor and an auxiliary attachment motor and creeper direction and speed functions are independently adjustable.

Abstract: A fluid controller (17) is disclosed of the type including a relatively rotatable valve spool (95) and valve sleeve (97) which define a series of variable control orifices (71-76) during normal steering operations. Fluid flow to a control port (27) is controlled by a variable control orifice (74). During small steering corrections, at relatively small valve displacements, the present invention provides an additional variable control orifice (155), which opens before the control orifice (74) opens. A form of check valve (153) is in series with the additional orifice (155), and downstream thereof, to prevent reverse flow from the control port (27) through the controller. The invention is especially beneficial in controllers of the dynamic load signal type including a load signal drain orifice (76) which is open to the system reservoir (R) at the relatively small displacements.

Abstract: A control is proposed for dividing the output flow in hydraulic systems made available by at least one pump to a plurality of users according to the load pressure-independent principle in case of output flow undersupply of the users, wherein a compensator is connected downstream of each control slide valve provided with a predeterminable control cross section, with the compensator including a piston and actuating element and each user connected downstream of the compensator receiving a predeterminable portion of the output flow as a function of the degree of undersupply by the pistons of the compensators, with the piston being acted upon by different forces which bring about different opening pressures.

Abstract: A hydraulic circuit is disclosed for a tractor in which a steering circuit and an implement circuit are utilized to provide a high flow capability to the implement valve stack. A series of priority valves are operable to divert hydraulic flow from the steering circuit to the implement circuit under conditions where the steering mechanism is not being operated and the implement circuit pump is operating at full capacity. The first priority valve diverts the hydraulic flow from the steering circuit to a second priority valve that is controlled by a pressure differential valve that senses the implement circuit pump working at full displacement, whereupon the second priority valve directs the diverted hydraulic flow into the implement circuit. The first priority valve retains hydraulic flow within the steering circuit whenever the steering mechanism is being operated.

Abstract: A hydrostatic drive system including a pump (1) and consumers (6, 8) which can each be actuated by a directional control valve (5,7) is disclosed. Each directional control valve (5, 7) is assigned a pressure compensator (9, 10) which can be controlled by a signal difference formed from a load pressure signal and a delivered pressure signal. The load pressure signal is derived from the highest of the load pressures occurring downstream of the directional control valves (5, 7), and the delivered pressure signal is derived from the pressure upstream of the directional control valves (5, 7). To limit the driving force and driving moment of at least one of the consumers, the signal difference across the pressure compensator (9) of at least one consumer (6) can be influenced by a controllable pressure output signal of an infinitely variable pressure control valve in such a way as to adjustably limit through-flow across the pressure compensator.

Abstract: An electric forklift truck having a single motor which drives a pump which provides, via a priority valve, hydraulic fluid for both the working hydraulics and a steer unit on the truck. The motor is driven continuously at an idle speed in order to generate in the steer unit a dynamic load sensing signal to control the position of the priority valve. An optical sensor is associated with the steering column in order to provide an electric control signal to the motor controller to step up the speed of the motor in response to a steering demand.

Abstract: A variable priority device for a swing motor in heavy construction equipment including a variable orifice device installed in an arm cylinder-side parallel oil passage of an parallel oil passage for supplying oil pumped by a single pump to a swing motor and an arm cylinder, the variable orifice device serving to perform a switching operation between an orifice state and an orifice release state in response to a pilot pressure for moving the spool of a swing motor control switching valve.

Abstract: A load sensed variable output gear pump system including a pump within a housing, an inlet passage extending to a pump inlet and an outlet passage extending from a pump outlet. A secondary outlet passage is located in the housing and a bypass outlet passage is located in the housing and is connected to a reservoir. A load sensed passage is located in the housing and is connected to load pressure. First and second independent control devices are provided for controlling flow through the secondary outlet passage from the outlet passage.

Abstract: Cylinder head (81) of a hydraulic lift cylinder (39) includes a fluid input port (74) and first fluid output port (75) to be connected respectively to a pump (46) and to a power steering mechanism (40). These ports preferably open at one and the other side surfaces of the head. The head further includes a second fluid output port (83) and fluid inlet port (84) which open at a front surface of the head. These ports are connected through an inside of a cover member (49a, 50a; 201; 250a) detachably mounted on the front surface of head. The head includes therein a flow divider (47) which divides inflow of the input port into first and second flows directed respectively to the first and second output ports. Fluid returned into the inlet port is directed towards a first control valve assembly (48) for the lift cylinder.

Abstract: To excavate sticky soil such as clayey soil, left and right buckets of a clamshell bucket are slightly inclined, thereby reducing the force to pull the buckets from a hole. The clamshell bucket includes left and right buckets which are closable, thereby holding soil, and a hydraulic cylinder having a stroke reserve so as to be further extendible after the buckets are closed, whereby the closed buckets can be displaced sidewardly relative to the vertical.

Abstract: Disclosed is a hydraulic system for a machine having a pump, a steering circuit and first and second hydraulic implements, e.g., a hydraulic loader and a backhoe, powered by first and second valve sections, respectively. In the improvement, the system includes a priority valve receiving fluid from the pump and configured for movement between a first position and a second position. In the first position, the priority valve flows fluid to the steering circuit and to the second valve section and in the second position, the priority valve flows fluid to the both valve sections which are connected in series.

Abstract: A hydrostatic drive system having consumers (6, 8) connected to a demand regulated pump (1) and actuated by a directional control valve (5, 7) is disclosed. The consumers can be connected downstream of the control valves via return valves to a load-sensing line (12). To provide for load-independent allocation of the delivered flow when the consumers are simultaneously actuated, each directional control valve (5, 7) is assigned a pressure balance (9, 10) which can be controlled directly or indirectly by a signal difference formed from a load pressure signal and a delivered pressure signal.

Abstract: A hydraulic system suited for use with a backhoe apparatus and which is configured to automatically direct a priority flow of actuating fluid from an actuating fluid source to hydraulic motors used to swing the backhoe apparatus into a desired swing position independently of other backhoe operations and the corresponding loads thereof. The hydraulic system of the present invention includes a priority valve which is connected to the fluid source and has priority and secondary hydraulic circuitry extending therefrom. The priority valve is positioned under the influence of fluid pressure differentials applied against it. In response to operator desires to swing the backhoe apparatus from one position to another, the priority valve automatically directs a dedicated flow of actuating fluid through the priority circuit to the swing motors used to swing the backhoe apparatus into the desired swing position.

Abstract: A volume flow control for a hydraulic system of a vehicle has a pump for supplying a main consuming device and an auxiliary consuming device with a hydraulic medium. A valve having a main connection for connecting the pump to the main consuming device an auxiliary connection for connecting the pump to the auxiliary consuming device and is provided. The valve has a main piston with a throttle and an auxiliary piston positioned downstream of the throttle. The throttle is positioned within the auxiliary connection. The auxiliary connection is pressurized by the main piston. The auxiliary piston has a first end face, subjected to the operational pressure of the hydraulic medium, and a second end face, biased by at least one pressure spring and subjected to a reduced pressure of the hydraulic medium caused by the throttle.

Abstract: A hydraulic base-load motor (M1) drives a load with the working pressure generated at the motor rising with the load. When the working pressure reaches an upper limit pressure, a hydraulic stand-by motor (M2) is switched on. Since the pressure drops upon switching on the stand-by motor, the control device is designed such that, upon reaching a lower limit pressure, it deactivates the stand-by motor again, the lower limit pressure being less than half the upper limit pressure. This switching hysteresis prevents a repeated switching over of the stand-by motor.

Abstract: A Hydraulic control circuit and a hydraulic control apparatus therefor are disclosed to preferentially feed fluid in a controlled amount or below to a first circuit system and feed fluid in an excessive amount exceeding the controlled amount to a second circuit system, and change over a pressure generated to a pilot pressure. Changing-over of control valves which are provided in the second circuit system permits a pilot pressure to be generated in the circuit. When any trouble occurs in the control valves, fluid fed to the second circuit system is unloaded, to thereby eliminate a possibility that an actuator is unexpectedly actuated.

Abstract: A brake valve (45) is disclosed of the type which permits communication from a source (11) of pressurized fluid to a brake actuator (47) in response to manual movement of a valve spool (57) from a neutral position (FIG. 2) to a power brake position (FIG. 5). In the power brake position, the valve spool permits fluid communication between a work port (53), which communicates with a brake actuator, and a brake load signal chamber (87), the brake load signal controlling the fluid output of the source. As the valve spool moves toward a manual brake position (FIG. 6) communication between the work port and the brake load signal chamber is blocked. In the manual brake position, movement of the valve spool causes a large piston (63) to displace fluid from its piston bore (73) into a piston bore (75) in which is disposed a small piston (61), the small piston being operable in response to movement of the valve spool to build brake pressure in the work port (53).

Abstract: A hydraulic device is furnished for an automatic connection of the pressure means source, either preferably to the primary user or to the secondary user depending on the pressure in the circuit of the primary user. A switching valve can be actuated by way of a precontrol pilot valve for the generation of the connections. An additional restoring second part compression spring (33) with adjustable pretension acts on the precontrol pilot valve (19, 20, 21, 22, 27). A fluid-loadable auxiliary piston (32) serves for a switching-pressure support. The hydraulic device is suitable for applications in hydraulic circuits exhibiting different transport priorities to different ports.

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: A fluid controller (15) is provided of the type having a primary valve member (53) and a follow-up valve member (55). The controller includes a housing (41) defining main fluid ports (27,29) connected to a steering cylinder (19), and also defines auxiliary fluid ports (31,33), connected to an auxiliary fluid motor (21). The spool and sleeve cooperate with the housing to provide main control valving (35) controlling the flow of fluid to the steering cylinder in response to relative rotation of the spool and sleeve, and auxiliary control valving (35), controlling the flow to the auxiliary motor in response to axial motion of the sleeve, relative to the spool and housing. By performing both the main and auxiliary valving in the spool and sleeve, the main valving (35) is automatically given priority over the auxiliary valving (37), without the need for any expensive, complicated controls or interface between the two types of valving.

Abstract: A control mechanism for two consumers includes a flow divider valve (3) which is connected to a pump 2. From flow divider valve (3) springs a flow line (12) for the working flow (A) of a first adjustment device (10) such as a steering motor. Another flow line (13) of the flow divider valve (3) leads via an activation valve (14) to a second adjustment device (15). A pilot flow line (4) connected with the flow divider valve (3) via a measurement diaphragm (3A), is connected with a pilot valve (5). Pilot valve (5) can choke or entirely block the connection from the pilot flow line (4) to a nonreturn line (11) for the purpose of setting a pressure in flow line (12). For purposes of activation, pilot valve (5) is coupled with a steering valve (6) that controls flow line (12) so that both valves can be deflected together during one steering movement. A hydraulic steering unit is provided as the steering mechanism and it includes a rod-set connection from a manual steering wheel to the vehicle wheels.

Abstract: A hydraulic pressure-control device, specially for powershift transmissions of motor vehicles, comprises a fluid pump (1) and a main valve for regulating the pressure in at least one high-pressure consumer device (6), which is attached to a pressure pipe (3) between the fluid pump (1) and the main pressure valve. The main pressure valve is designed as pressure-relief valve. In the main pressure valve is integrated the operation of a second pressure-relief valve. Two different pressure limits can be adjusted in the pressure pipe (3) by a valve piston (21) through two compression springs (17, 18) connected in parallel of which one compression spring (18) is bound.

Abstract: A fluid controller (15) is provided of the type which controls the flow of fluid from a source (11) to a priority device (19) and an auxiliary device (21). The controller includes a valving arrangement (33) comprising a primary, rotatable spool valve (51), and a cooperating, relatively rotatable follow-up sleeve valve member (53). The spool and sleeve cooperate to define controller valving (35) while the sleeve and housing cooperate to define load sensing, priority flow control valving (37). In a preferred embodiment, the controller valving is defined by relative rotation between the spool and the sleeve, while the priority flow control valving is defined by relative axial movement between the sleeve and the housing. The axial position of the sleeve is controlled by fluid pressure in a pilot pressure chamber (95), and in a load signal chamber (103), the difference therebetween representing the pressure differential across a main variable flow control orifice (A1) defined by the controller valving (35).

Abstract: A hydrostatic steering device is provided with a pump connected with a reservoir, a steering valve, a controlled-volume pump that is capable of being activated by a steering wheel and with a steering cylinder. The steering mechanism has a variable working flow and a constant pilot flow, with the pilot stream flowing through a constant throttle and the pressure drop through the constant throttle serving as a control signal for the conveying flow in a pressure delivery line. The controlled-volume pump is coupled mechanically with an adjustment throttle through which the pilot flows. Between the constant throttle and the adjustment throttle lies a pressure compensator that is controlled by the adjustment throttle's differential pressure. To receive the load signal, a control line branches off between the constant throttle and the pressure compensator and leads to the pump or, in the case of a fixed displacement pump with a rear-position flow-dividing valve, to the flow-dividing valve.

Abstract: A vacuum supply system for a brake power assist unit of a motor vehicle with at least one additional vacuum consuming device is achieved by the installation of a valve, which can be switched as a function of existing vacuum level in a pipe leading from the vacuum generating device to the at least one additional consuming device. Switching of the valve causes a throttling of this pipe to be more extensive when the existing vacuum level is above a certain absolute pressure value.

Abstract: Load sensing hydraulic systems conserve energy by generating only the fluid flow demanded by the system and at a pressure only slightly greater than the highest load pressure of the system. Optimizing the operating characteristics of the system for certain applications also caused the variable displacement pump to go to its maximum displacement setting with the excess fluid generated thereby not doing any useful work. The load sensing hydraulic system includes a flow control valve connected to a directional control valve and has an operating position in which fluid exhausted from a hydraulic jack is transmitted therethrough to a tank. A signal valve is disposed in a control pressure signal line for controlling fluid flow therethrough from a supply conduit to one end of the flow control valve. When the signal valve is blocking fluid flow through the signal line, the flow control valve is in the above-noted operating position.

Abstract: Power fluid from a pump are provided through one power fluid branch conduit to an extend port for activating the smallest cylinder of a multi-stage packing cylinder and fluid is conducted through a second extend branch conduit to a second port which provides fluids to the larger cylinders of the packing cylinder. A normally closed sequence value is in the second branch conduit. When the pump first is activated, fluid goes through the first extend branch conduit to extend the smallest stage of the packing cylinder. When the smallest stage is fully extended or reaches resistance, the pressure in the pump output conduit rises. When this pressure reaches a preselected value, the sequence valve is opened and high pressure fluid is directed through the second branch conduit and second port to provide power fluid to the larger cylinders of the packing cylinder.

Abstract: A hydraulic system is provided for powering a steering unit, a trailer brake and an auxiliary power unit from a single pump. A control circuit ensures that the hydraulic trailer brake and/or the power steering unit on the vehicle will operate on a preferential basis over the auxiliary power unit. The hydraulic control circuit has two priority valves connected in series. The upstream priority valve has a priority position in which it makes the pump fluid available to a supply line for the common priority flow for the steering and braking apparatus and a non-priority position for powering the auxiliary power unit. The common priority flow is passed through the second or downstream priority valve for priority powering of the power steering circuit.

Abstract: A vacuum supply system for a brake power assist unit of a motor vehicle and at least one additional vacuum consuming device, is achieved by a parallel arrangement of two pipes leading from a vacuum generating device one to the brake power assist unit and one to the additional consuming device. Both pipes are equipped with flow control devices one of which is blockable by means of a check valve with an increased restoring or closing force for securing a vacuum supply priority for the brake power assist unit.

Abstract: A hydraulic valve is adapted to be connected between a pressurized supply line and first and second lines feeding respective first and second circuits with different functions, such as the steering and braking functions of an automobile vehicle. It comprises a first control member adapted to connect the supply line to the first feed line, a two-way distributor device for the second feed line and a second control member adapted to apply to the second feed line a pressure proportional to the force exerted by the user damped by virtue of a dashpot effect.

Abstract: The invention relates to a priority valve for a hydraulic installation having a main circuit and an auxiliary circuit. The priority valve has a slide member which primarily has a controlled throttle for dividing the supply fluid between the main and auxiliary circuits in accordance with the priority demands of the main circuit. The priority valve has a flow path leading to the auxiliary circuit which has throttle elements in series which provide pressure drops in steps to minimize cavitation when there is a rapid flow of fluid in the auxiliary circuit.

Abstract: A hydraulic control apparatus for a vehicle capable of being significantly simplified in structure and stabilizing its control characteristics. The apparatus includes a variable constriction provided in a first flow passage arranged between a steering pump and a steering cylinder and a steering spool for changing over the first flow passage and controlling the degree of opening of the variable constriction. The apparatus also includes a single flow control valve spool which changes over depending on a variation of pressure on an upstream side of the variable orifice and accomplishes an increase and a decrease in the degree of opening of a second flow passage arranged between a switch pump and an implement circuit corresponding to an increase and a decrease in pressure on the upstream side of the variable constriction.

Abstract: Valve device for controlling the delivery of pressurized fluid from a common pump to two hydrostatic working motors, one of which is subjected to a load dependent on the speed of the other motor. A volume flow regulator is disposed in the flow path between an inlet port of the valve device connected to the pump and an outlet port connected to the other working motor and varies the volume flow rate in this flow path in inverse proportion to the pressure in the inlet port to keep that pressure substantially constant.

Abstract: A bidirectional flow communication passageway is provided by the present invention in a multiple-circuit fluid pressure responsive system on a motor vehicle to allow a gradual reduction of pressure in a parking brake circuit which is a part of such system. The passageway is restricted to limit such bidirectional flow to a predetermined level. The pressure reduction permitted is sufficient to activate a parking brake valve in such parking brake circuit when a defect occurs in an operating service brake circuit which is also a part of such system.

Abstract: A bidirectional flow communication passageway is provided by the present invention in a multiple-circuit fluid pressure responsive system on a motor vehicle to allow a gradual reduction of pressure in a parking brake circuit which is a part of such system. The passageway is restricted to limit such bidirectional flow to a predetermined level. The pressure reduction permitted is sufficient to activate a parking brake valve in such parking brake circuit when a defect occurs in an operating service brake circuit which is also a part of such system.

Abstract: The present invention relates to, in combination, a vehicle utilizing a first hydraulic cylinder to operate lifting means and a second hydraulic cylinder to operate end effector means, each of the cylinders including a piston, the pistons when moved toward their "up" sides causing the lifting means and end defector means to move in a first direction and when moved toward their "down" sides causing the lifting means and means to move in a second direction, and a load self-leveling system for the vehicle, the system comprising a pair of fluid flow dividers interposed in flow lines between a source of hydraulic fluid under pressure and the first and second hydraulic cylinders, the flow dividers being structured to direct a greater flow of hydraulic fluid to the first cylinder and a lesser flow to the second cylinder, each of the flow dividers comprising adjustable spool valve means located in flow passages between the source of hydraulic fluid and the first and second hydraulic cylinders.

Abstract: A safety circuit which is essentially for supplyng hydraulic loads. Briefly stated, this circuit has a control pump which, via a priority valve, supplies hydraulic power to a power steering hydraulic circuit and at least one other load hydraulic circuit on a priority basis where the power steering receives the highest priority. Also provided is a control circuit which limits the intake pressure of the control pump and has a safety valve associated with it which is controlled by the intake vacuum of the control pump. This valve effects a reduction of the pump output when pressure in the suction line from the hydraulic fluid storage container drops below a minimum pressure.

Abstract: In the supply of priority and lower-ranking consumers the flow to the priority consumer must be maintained even when there is a leak in the hydraulic system of the lower-ranking consumers. For this purpose the priority consumer is connected via in each case a check valve to a pump and an auxiliary pump. If the pressure generated by the pump drops for example due to a leak a valve opening the pressure line to the discharge is shut-off and the priority consumer thereby supplied with fluid delivered by the auxiliary pump.

Abstract: A self-leveling series type hydraulic system including boom and bucket valves which separately control boom and bucket cylinders and a flow divider valve positioned in the exhaust flow path of the rod end of the boom cylinder. The flow divider valve splits the flow sending a portion of it to the cap end of the bucket cylinder so as to maintain the bucket in a level condition during raising of the boom with the remaining flow connected to one of the boom valve motor ports. An improved boom lower circuit which bypasses the flow divider valve as the boom is lowered to achieve a faster boom lower rate and the inclusion of an unloading valve in the bucket circuit which includes the dual function of preventing cavitation and relieving high pressure.

Abstract: A load self-leveling system for a vehicle utilizing hydraulic cylinders to operate a telescopic lifting boom and a material handling carriage. The system includes a pair of fluid flow dividers interposed between the source of hydraulic fluid under pressure and the hydraulic cylinders operating the boom and carriage. The flow dividers are structured to direct a greater flow of hydraulic fluid to the boom cylinder and a lesser flow to the carriage cylinder, the precise numeric proportions of flow division being engineered to best suit a particular vehicle, combined with the specific componentry of that vehicle. In addition to the flow dividers, the system includes reversible flow piloted check valves, override control including override relief valves to allow independent adjustments, and matched cylinder area ratios. A compact assembly housing various of the components comprising the system is disclosed.