Abstract: A pressure holding apparatus incorporates a hydraulic pressure system having an engine-driven pressure source, a pressure holding valve, and a torque-transmitting mechanism. The torque-transmitting mechanism is selectively engaged and disengaged by fluid pressure from the engine-driven pressure source during normal powertrain operation. The torque-transmitting mechanism apply chamber is pressurized with the oil by the pressure holding valve when the engine operation is discontinued.

Abstract: The present invention relates to a variable flow control apparatus for an actuator of a heavy construction equipment capable of implementing constant flow of hydraulic fluid from a hydraulic pump to an actuator even when a pilot pressure capable of driving a seat valve openably and closably installed in a discharge flow path of the hydraulic pump exceeds a certain pressure level.

Abstract: The present invention relates to a control apparatus of a hydraulic valve for holding load in which a drain line of a holding valve adapted to preclude momentary drop of load in a hydraulic actuator is substituted with a path in the interior of a directional control valve, so that a pipe line of a drain side functioning as a hydraulic hose and exposed to the outside is not needed in the present invention. The control apparatus of a hydraulic valve for holding load comprises a drain line adapted to allow hydraulic fluid returned during a switching operation of the sub-spool to flow in a pilot line of the side of a drain corresponding to the opposite side of a pilot line adapted to pressurize the spool of the directional control valve.

Abstract: A fluid flow control valve assembly that can be actuated using an electrically operated or pneumatically operated flow control valve includes a valve body having a fluid supply passageway, a fluid exhaust passageway, and a fluid bypass passageway. A pilot operated relief valve is disposed in the fluid bypass passageway, wherein the pilot operated relief valve blocks the fluid bypass passageway to create a pressure upstream of the pilot operated relief valve to actuate a different pilot operated device having a pilot line in fluid communication with the fluid bypass passageway upstream of the pilot operated relief valve. Fluid flowing through a venturi nozzle in the fluid bypass passageway that intersects the fluid exhaust passageway lowers the pressure in the fluid exhaust passageway.

Abstract: Method and apparatus for isolating hydraulic devices in a stacked hydraulic circuit of modular design employing an isolator valve module which enables partial and/or complete isolation of components in a hydraulic system to be isolated for inspection, testing, maintenance or replacement, by selective operation of the isolator valves in the isolator valve module. The isolator valve module may be a sub-plate module supporting other modules or a plurality of stacks of modules or may be a “sandwich” type module sandwiched between a sub-plate and another module or between two sandwich-type modules.

Abstract: A fluid flow control valve assembly that can be actuated using an electrically operated or pneumatically operated flow control valve includes a valve body having a fluid supply passageway, a fluid exhaust passageway, and a fluid bypass passageway. A pilot operated relief valve is disposed in the fluid bypass passageway, wherein the pilot operated relief valve blocks the fluid bypass passageway to create a pressure upstream of the pilot operated relief valve to actuate a different pilot operated device having a pilot line in fluid communication with the fluid bypass passageway upstream of the pilot operated relief valve. Fluid flowing through a venturi nozzle in the fluid bypass passageway that intersects the fluid exhaust passageway lowers the pressure in the fluid exhaust passageway.

Abstract: The invention concerns a driving device, particularly a lifting device for a working vehicle, with a drive in the form of a hydraulic motor, the drive having a first connection and a second connection, a pump and a control valve arrangement between the drive and the pump. It is endeavoured to provide a simple way of extending the functionality of such lifting devices. For this purpose, the control valve arrangement can be switched from a first operating state, in which the motor is driven in a single-acting manner, to a second operating state, in which the motor is driven in a double-acting manner.

Abstract: In a fluid system, a source of pressurized fluid operably communicates with first and second actuators. First and second control valves control fluidly communicates with the first and second actuators. A first pressure compensating valve fluidly communicates with the first control valve and first actuator. A first signal conduit fluidly communicates with fluid flow being directed by the first control valve to the first pressure compensating valve and first actuator. A second pressure compensating valve fluidly communicates with the second control valve and second actuator. A second signal conduit fluid communicates with fluid flow being directed by the second control valve to the second pressure compensating valve and second actuator. A control signal pressure generated from a greater of a first signal pressure carried by the first signal conduit and a second signal pressure carried by the second signal conduit fluidly communicates with the first and second pressure compensating valves.

Abstract: A fluid system includes first and second control valves that control fluid communication with first and second actuators. The first control valve may combine fluid flow from a second end port of the first actuator with fluid flow from a pressurized fluid source when providing a supply of fluid to a first end port of the first actuator. The first and second control valves include first and second signal ports in fluid communication with the supply of fluid to the first and second actuators. A resolver outputs a resolved signal pressure equal to the greater of a first signal pressure output by the first signal port and a second signal pressure output by the second signal port. A compensator in fluid communication with the first control valve and the first actuator controls fluid flow from the first control valve to the first actuator based on the resolved signal pressure.

Abstract: A fluid operated actuator includes a shaft and a housing. The shaft is at least partially mounted in the housing for relative rotation between the shaft and the housing. The shaft includes a substantially central bore in which a first piston is mounted. The shaft also includes a fluid inlet that is connectable to supply of pressurised fluid and a fluid outlet. A conduit is provided for the flow of fluid between the inlet and the outlet. One end of the housing includes a chamber in which there is mounted a valve assembly comprising a second piston and a valve arranged to selectively open or close an inlet to the chamber. Fluid exiting the outlet opens the valve and exerts a force on the second piston, causing movement thereof in a first direction.

Abstract: An actuator is prevented from an abrupt descent by supplying a high-pressure hydraulic fluid drained upon the descent of the actuator to a path on a supply side of the actuator, provided is a main spool mounted in a path between a hydraulic pump and the actuator and controlling the drive of the actuator, a poppet mounted in a path between the main spool and the actuator and preventing the actuator from the descent, a spool mounted between a back-pressure and a feedback path of the poppet and communicating the back-pressure chamber with a path at an outlet of the main spool upon switching, and a fluid flow-reducing path communicating the back-pressure with the feedback path upon the switching of the spool and reducing hydraulic fluid drained from the actuator.

Abstract: A hydraulic drive system includes a hose rupture control valve unit 200 having a poppet valve member 5 serving as a main valve for opening and closing communication between a cylinder connection chamber 8 and a hose connection chamber 9, a spool valve member 6 disposed in pilot passages 15a, 15b connecting a back pressure chamber 10 and the hose connection chamber 9 of the poppet valve member 5. The spool valve member is operated by a pilot pressure supplied as an external signal and operates the poppet valve member 5, and a small relief valve 7 having the function of an overload relief valve. A check valve 39 is disposed in the pilot passage 15b for cutting off a flow of the hydraulic fluid from the hose connection chamber 9 to the back pressure chamber 10.

Abstract: A fluid system includes first and second control valves that control fluid communication with first and second actuators. The first control valve may combine fluid flow from a second end port of the first actuator with fluid flow from a pressurized fluid source when providing a supply of fluid to a first end port of the first actuator. The first and second control valves include first and second signal ports in fluid communication with the supply of fluid to the first and second actuators. A resolver outputs a resolved signal pressure equal to the greater of a first signal pressure output by the first signal port and a second signal pressure output by the second signal port. A compensator in fluid communication with the first control valve and the first actuator controls fluid flow from the first control valve to the first actuator based on the resolved signal pressure.

Abstract: A valve system is provided for the hydraulic work system of a work vehicle, in particular of an industrial truck, with a elevating drive system for raising and lowering a load and a tilting drive system, each of which can be actuated by a control valve, in particular by an electrically actuated control valve, the opening width of which determines the speed of movement of the user. The elevating drive system is realized in the form of a single-action hydraulic cylinder and a check valve in the form of a seat valve that can be opened toward the hydraulic cylinder is located in a hydraulic line leading from the control valve to the hydraulic cylinder. The tilting drive system is realized in the form of a double-action hydraulic cylinder. The valve system has an improved function with low energy losses.

Abstract: A preventative stop valve system for a wheeled trailer carrying hydraulic equipment is disclosed comprising a stop valve fitted for insertion in-line into the hydraulic line servicing the trailer equipment; the stop valve comprising a reciprocating piston moveable between open and closed positions. The stop valve is connected to the pressurized air line extending to the air brakes of the trailer. Actuation of the stop valve is controlled pneumatically by the setting and release of the air brakes of the trailer by the operator, utilizing conventional controls for the air brakes. A manual override mechanism is further provided for opening the stop valve manually in the event that the hydraulic equipment carried by the trailer must be utilized when pressurized air line to the trailers is disconnected.

Abstract: A safety circuit for protecting against an inadvertent operation activation of a pneumatic drive of an automatic assembling machine has at least one vertical cylinder (1) and one horizontal cylinder (2), each being controlled by one of first and second multi-way valves (3, 4) and fed by a primary pneumatic circuit. Two further pneumatic control circuits (8,9) are included in the automatic assembling machine that are automatically switch into and out of the primary pneumatic circuit, wherein the at least one vertical cylinder (1) and the at least one horizontal cylinder (2), after the “switching into”, either remains in its current position or moves to a rest position. Opened and closed switching of a pneumatic primary circuit is caused according to an activated mode-of-operation set by a system control (SPS) of the automatic assembling machine.

Abstract: An actuator is prevented from an abrupt descent by supplying a high-pressure hydraulic fluid drained upon the descent of the actuator to a path on a supply side of the actuator, provided is a main spool mounted in a path between a hydraulic pump and the actuator and controlling the drive of the actuator, a poppet mounted in a path between the main spool and the actuator and preventing the actuator from the descent, a spool mounted between a back-pressure and a feedback path of the poppet and communicating the back-pressure chamber with a path at an outlet of the main spool upon switching, and a fluid flow-reducing path communicating the back-pressure with the feedback path upon the switching of the spool and reducing hydraulic fluid drained from the actuator.

Abstract: A hydraulic drive unit is disclosed which can prevent the occurrence of cavitation at the time of turning OFF of a hydraulic motor without greatly modifying the circuit configuration and the entire system and which, as a result, can improve the deceleration feeling of the hydraulic motor and prevent the occurrence of a low noise.

Abstract: A hydraulic cylinder in which the cylinder head contains the main control valve for the cylinder. In one fluid path from the main control valve to an area located on one side of the cylinder's piston, fluid is directed through a transfer tube that extends through the center of the piston and terminates within a hollow ported section of the piston rod. The cylinder head can additionally include two electrically-actuated pilot valves and two pilot-operated check valves. The pilot-operated check valves are located in different passages that extend to areas located on opposite sides of the piston. The pilot-operated check valves include structure that, in combination with passages in the cylinder head, cause both pilot-operated check valves to open when pressurized fluid is being directed to one of the pilot-operated check valves by the main control valve. In the preferred embodiment, electrical wiring to the cylinder head travels through one of the fluid hoses connected to the cylinder.

Abstract: A tilt control device for a fork lift truck comprises a tilt spool for operating the tilt cylinder, a pilot operation type flow rate control valve connected to the hydraulic pump via the tilt spool and adapted to be switched between a fully opened position and a half opened position which are different in opening from each other in response to addition/deletion of a pilot pressure, a pilot operation type logic valve disposed between the rod side oil compartment of the tilt cylinder and the flow rate control valve and adapted to permit hydraulic oil to flow into the rod side oil compartment and to be operated so as to open/close relative to hydraulic oil flowing out of the rod side oil compartment in response to the addition/deletion of the pilot pressure, and an electromagnetic switching valve for controlling the addition/deletion of the pilot pressure to the flow rate control valve and the logic valve.

Abstract: A hydraulic drive unit is disclosed which can prevent the occurrence of cavitation at the time of turning OFF of a hydraulic motor without greatly modifying the circuit configuration and the entire system and which, as a result, can improve the deceleration feeling of the hydraulic motor and prevent the occurrence of a low noise.

Abstract: A hydraulic line slit 20 formed in a valve body 50 of a flow distribution valve 5-1, a control chamber 70, and a hydraulic line 31-1 are connected to a signal transmitting hydraulic line 9. A lap portion 32 is formed in the hydraulic line slit 20, the lap portion 32 having a check valve function with a lap amount X when the valve body 50 is in a cutoff position. A 2-position, 3-way valve 11 is disposed in the hydraulic line 31-1. The valve 11 connects the control chamber 70 of the flow distribution valve 5-1 to only the signal transmitting hydraulic line 9 when an external signal F is not applied, and to both the signal transmitting hydraulic line 9 and a lower-pressure detecting hydraulic line 35, which is connected an outlet passage 5b of a flow distribution valve 5-2 on the side of a hydraulic actuator 3-2, when the external signal F is applied.

Abstract: A main passage communicated to a pump passage or a tank passage by switching operation of a spool valve is provided with an operation check valve permitting communication only to a cylinder. A puppet in the operation check valve is provided with an orifice communicating the main passage with a pilot chamber of the operation check valve. The pilot chamber is communicated with the main passage through an electromagnetic on/off valve. Further, the pilot chamber in the operation check valve is communicated through a bypass passage with the main passage, and the bypass passage is provided with a manually operable opening/closing valve.

Abstract: A hydraulic cylinder in which the cylinder head contains the main control valve for the cylinder. In one fluid path from the main control valve to an area located on one side of the cylinder's piston, fluid is directed through a transfer tube that extends through the center of the piston and terminates within a hollow ported section of the piston rod. The cylinder head can additionally include two electrically-actuated pilot valves and two pilot-operated check valves. The pilot-operated check valves are located in different passages that extend to areas located on opposite sides of the piston. The pilot-operated check valves include structure that, in combination with passages in the cylinder head, cause both pilot-operated check valves to open when pressurized fluid is being directed to one of the pilot-operated check valves by the main control valve. In the preferred embodiment, electrical wiring to the cylinder head travels through one of the fluid hoses connected to the cylinder.

Abstract: A hydraulic valve having a main body in which is formed a pressurized-fluid inlet opening; a first conduit communicating hydraulically with a user device; a second conduit communicating hydraulically with the user device; and at least one spool for regulating pressurized fluid flow to and from the user device; the spool having a longitudinal axis, and the position of the spool being regulated by an actuating device; the hydraulic valve being characterized in that the actuating device has a guide member for preventing the spool from rotating about the axis; the actuating device also having a cable, e.g. a Bowden-type cable, for moving the spool in two opposite directions defined by the longitudinal axis.

Abstract: A control system is provided with a float condition to permit a double acting hydraulic cylinder to freely extend or retract in response to external forces acting on the hydraulic cylinder. The system includes a pair of pilot operated poppet valves disposed between the opposite sides of the hydraulic cylinder and a directional control valve. The pilot condition is obtained by opening a pair of pilot operated control valves to vent the control chambers of the poppet valves to a tank through a pair of float check valves. The float check valves are operative to prevent higher pressure fluid from being transmitted from the tank to the control chambers of the poppet valves when a negative pressure occurs in the side of the hydraulic cylinder that is connected to the control chamber.

Abstract: In a power steering device, a pump supplies a pressure fluid. A power cylinder has left and right chambers and is driven in accordance with a pressure difference between a pressure fluid supplied to the left chamber and that to the right chamber. A flow channel selector valve selectively switches a supply direction of the pressure fluid from the pump to the chambers of the power cylinder in response to steering operation of a steering wheel. Fluid paths connect the flow channel selector valve and the corresponding chambers of the power cylinder to each other. Variable restrictors are disposed in the fluid paths, respectively, to control flow rate of the pressure fluid from the power cylinder to the flow channel selector valve. Check valves are respectively connected to the fluid paths in parallel to the corresponding variable restrictors to prevent a flow of the pressure fluid from the power cylinder to the flow channel selector valve.

Abstract: A riding lawn mower is provided that has an engine, a device that requires control and a vacuum actuated control mechanism for controlling the device. The vacuum actuated control mechanism includes a vacuum actuator having first and second chambers separated by a movable membrane, first connecting means for operatively connecting the vacuum actuator to the device, vacuum means for providing a vacuum to the vacuum actuator, activating means for selectively activating the vacuum actuator and securing means for securing the vacuum actuator in place. The securing means also secures the device in place.

Abstract: A latching valve, useable in a multiplexed fluid control system, is switchable between two positions to control working output fluid flow to a corresponding actuator. The valve is latched by deriving a holding force from the working output flow. The latching valve may reside in one of the channels of the multiplexed fluid control system and eliminates the required modulations to hold position and reduces system wear of modulating and multiplexing components. The latching valve includes a working output port coupled with an associated actuator and a control chamber connected to a 3-way multiplexing valve to receive fluid signals. To provide a latching force, the valve includes bleed conduit that bleeds a controlled amount of fluid between the working output port and the control chamber to maintain the pressure in the control chamber. The last position of the latching valve is held until the next selective fluid signal from the modulating valve and multiplexer is received.

Abstract: An automatic depth control system is disclosed. The system includes a Console and remote Controller mounted in the tractor cab, power beyond Valving, and Depth Sensors, either ground contact or non-ground contact, mounted on the frame of the implement. The depth sensing system is provided to sense the actual penetration of an implement tool by determining the height of the implement frame above the ground. A circuit system is provided to receive the depth signal and to signal power beyond valving that will effect hydraulic corrections in order to maintain the select depth penetration. The Console includes an instrument panel having a toggle switch with AUTO, LOCK and MANUAL positions, an LED showing depth of tool penetration and a bargraph depicting variations from a desired depth and flashing lights on the bargraph to show depth corrections in process. The Console also includes a depth window in which no hydraulic correction would be made, a sensitivity switch, depth sensor switches and an UP/REPHASE switch.

Abstract: A hydraulically controllable valve for double-acting consumers that in the lowering mode drains off a flow of load volume from connection B to connection A in throttled fashion. To that end, the valve has a valve seat (5), which communicates with a sealing face (4) of a main piston (3). A pilot piston (8) is guided concentrically in the main piston (3) and communicates with a sealing face (7) to a pilot valve seat (6) in the main piston; the main piston (3) and the pilot piston (8) are held on the valve seat (5) and pilot valve seat (6), respectively, by the load pressure and/or by spring force. On the pressure-relieved side, the pilot piston (8) has a piston shank (9), guided in a seat bore, with a continuously decreasing throttling action and in particular throttle grooves (10), which form a throttle restriction.

Abstract: A pilot operated control valve has a housing defining an inlet and an outlet. A main valve poppet selectively engages a valve seat to control flow of fluid between the inlet and outlet. An aperture in the main valve poppet opens into a control chamber on a side of the main poppet remote from the valve seat. A pilot passage is formed in the main valve poppet with an inlet section between the inlet and the control chamber, and an outlet section between the aperture and the control chamber. A pilot poppet has a body that selectively seals communication between the control chamber and the aperture, and a pressure balancing stem attached to the body extends into the aperture. The pressure balancing stem having a recess which is acted upon by pressure in the outlet section and having an end which is acted upon by pressure in the inlet section. The pilot operated control valve also incorporates a compression check valve and/or a reverse flow check valve.

Abstract: A fluidic stiffness enhancing circuit for use with a fluid driven piston type actuator includes a fluid conduit arrangement that interconnects two variable volume chambers of the actuator upon occurrence of a loss of system pressure to at least one of the chambers. The fluid conduit arrangement incorporates an inertance device for controlling the rate of flow of fluid therethrough so as to control the pressures in the two chambers in response to external forces applied to the actuator piston and thereby the stiffness of the actuator.

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: The present invention provides a control apparatus for controlling movement of an implement. The implement is mounted to a subframe that in turn is joined to a frame portion of the vehicle. The subframe is moveable between the working position, where the implement is operable to perform work, and a second position. The implement has a hydraulic actuator for selectively moving a portion of the implement to perform work using controlled hydraulic fluid present in a hydraulic line connected to the hydraulic actuator. The control apparatus inhibits or allows hydraulic fluid flow in the hydraulic line as a function of the position of the subframe.

Abstract: A holding check control valve including a main valve, an assistant valve, a check valve installed in an actuator fluid passage provided at the main valve and provided with a spring chamber, the check valve being adapted to be switched between an opened state for opening the actuator fluid passage and a closed state for closing the actuator fluid passage in response to a pressure difference between the actuator fluid passage and the spring chamber so that the return oil in the actuator fluid passage is returned via a return fluid line provided at the main valve at the opened state, a pair of spaced seat members fixedly disposed in the assistant valve, a hydraulic chamber defined between the seat members, the hydraulic chamber communicating with the spring chamber of the check valve, a plunger extending through the seat members, the plunger being slidable along the seat members between a position closing the hydraulic chamber and a position opening the hydraulic chamber, a pressure setting spring for exerting i

Abstract: Roughness or jerkiness in a hydraulic swing circuit in an implement having a plurality of control circuits each having a work performing device (28), (30), (32) including a swing circuit having a hydraulic motor (32), which when under an aiding load may function as a pump, is avoided in a construction that includes a source (10) of hydraulic fluid under pressure and a plurality of control valves (22), (24), (26) for the circuits which are interconnected between the source (10) and the associated work performing device (28), (30), (32). The system includes a pair of hydraulic conduits (34), (36) extending from the control valve (26) for the swing circuit to the hydraulic motor (32). A pair of pilot operated, dual level pressure relief valves (56), (58) are connected oppositely across the conduits (34), (36) at a location between the control valve (26) for the swing circuit and the hydraulic motor (32).

Abstract: A safety circuit for a servo-hydraulic regulating system for the hydraulic control and actuation of load units, such as operating tools on utility vehicles and agricultural machines. The controlling of the load unit is effected via a proportional valve which is actuated in dependence upon a pair of output signals of a measuring bridge in such a way that, in the event of a balanced measuring bridge, it assumes a neutral setting in which the operating line running to the load unit or emanating from the load unit is blocked. In order to prevent the lifting gear from executing a regulating reaction if the measuring bridge is out of tune when the servo-hydraulic regulating system is switched on, a safety valve arrangement is provided in the operating line.

Abstract: Simultaneous operation efficiency in a case where a plurality of actuators are operated by one or a plurality of hydraulic pumps is improved. A delivery pressure passage (1a) of one hydraulic pump (1) and that (1a) of the other hydraulic pump (1) communicate with each other through a first short-circuit passage (39) via a pair of check valves (38, 38), and an unload valve (40) is provided in this first short-circuit passage (39). The load pressure introduction passages (6, 6) on the left and right hydraulic pumps (1, 1) communicate with each other through a second short-circuit passage (36) via a pair of check valves (35, 35), and a relief valve (37) is provided in this short-circuit passage (36).

Abstract: An operating valve device for supplying fluid under pressure to an actuator comprises: a first hole (3) and a second hole (4) for allowing fluid under pressure supplied by a pump (P) into an inlet port (2) connected with the pump to selectively flow into pressure chambers (B.sub.1, B.sub.

Abstract: An electrohydraulic regulating device, particularly for a motor vehicle rear axle steering assembly, includes an adjusting cylinder. An electrically actuated control valve controls a hydraulic fluid flow to the adjusting cylinder. At least one electrically actuated switching valve blocks or admits a hydraulic fluid flow. A control unit generates control signals for the control valve and the switching valve. A regulating circuit supplies a pulse-width-modulated regulating signal for regulating a mean current of the control valve. A pulse-width-modulated control signal controls a mean current of the switching valve. The same supply voltage is applied to the switching valve and to the control valve. A pulse-duty factor of the control signal for the switching valve is referred to a pulse-duty factor of an adjusting signal for the control valve.

Abstract: The invention relates to a method for, in a hydrostatic transmission having a preferably variable displacement hydraulic pump (P) feeding a number of hydraulic motors (M1, M2, M3, M4) provided in association with respective drive wheels, drive tracks or corresponding drive apparatus, mutually balancing the flow of hydraulic fluid through the different hydraulic motors (M1-M4) by individually controlling of the flow from and/or to the same, whereby the individual flows of hydraulic fluid through the respective hydraulic motors (M1-M4) are detected and compared across respective restrictions (14, 15) being variable dependent on the total flow but being of mutually equal size and whereby, for optimum control or balancing, the detected differences in flow through the different hydraulic motors are in themselves used directly for the balancing.

Abstract: A hydraulic control system in which the flow of hydraulic fluid to and from cylinders on either side of a piston is controlled by normally closed check valves that are opened whenever a control valve is not in its neutral state. Float check valves respectively in series with the check valves and the check valves are opened when the control valve is in a neutral state by pressure from one of the cylinders so as to permit the load to move freely in response to external forces applied to it. A normally closed check valve is provided in which load sense pressures drive it open and pressure from a cylinder is balanced out. A cross check valve is such that the ratio of the areas for driving it open to the area for keeping it shut are at least 35:1.

Abstract: A counterforce cylinder and piston exert an upward force on the vertically movable slide of a machine. The cylinder pressure line handles reverse flows during operations of the slide. A pilot-operated checkvalve (normally closed) is inserted in the cylinder line between a pressure source and the counterforce cylinder, and is held open during usual operation of the machine. An accumulator is branch-connected to the cylinder line, at a point between the checkvalve and counterforce cylinder. During machine operations, the accumulator stores pressurized fluid; at shutdown of power, the fast-acting checkvalve closes and reliably seals the cylinder line while the accumulator provides pressure to maintain the counterforce cylinder and slide in a substantially constant holding position for several days.

Abstract: A valve assembly is disclosed in two embodiments for selectively controlling pressurized fluid flow to operate a fluid operated working cylinder and piston. The valve assembly includes a valve body, groups of three bores operably paired in the body, biased plunger valves interposed in each of the bores, and a separate passage inter-connecting between each bore group on one side of the interposed valves. There is provided a pressure connection to a first one of the bores in each group on the other side of the interposed valves away from the passage and a first side cylinder connection to a second one of said bores in one of each pair of groups. The other cylinder connection is provided to a second one of the other one of each pair of groups of three bores while an exhaust connection is provided to a third one of the bores in each group.

Abstract: This invention provides a hydraulic circuit system capable of reducing the flow rate distribution error in supplying pressurized fluid from a single hydraulic pump into a plurality of hydraulic actuators, and also supplying pressurized fluid quickly. The circuit is simplified to reduce manufacturing costs.

Abstract: When a hydraulic circuit for driving actuators of a construction machine or the like includes a single hydraulic pump and a plurality of direction changeover valves connected to the hydraulic pump for controlling the respective actuators, operation of one of the direction changeover valves may result in undesirable change in the output oil pressure of the other direction changeover valves. The inventive hydraulic circuit includes means for driving a regulator of the hydraulic pump in response to any oil puressure change at the inlets of the direction changeover valves corresponding to the output oil pressure change, thereby compensating for the pressure change.

Abstract: Fluid regeneration circuits are useful for filling expanding sides of a hydraulic motor with fluid being exhausted from the other side. The components of the currently available regeneration circuits are disposed in or adjacent to the directional control valve such that the fluid used for regeneration must pass through relatively long motor conduits between the control valve and the hydraulic cylinder. The regeneration circuit of the present invention includes a load check valve which forces the fluid exhausted from the head end chamber of a hydraulic motor to pass through a poppet valve controllably opened by a control signal. A low pressure relief valve causes an increase in the fluid pressure of the exhausted fluid passing through the poppet valve such that when the pressure level exceeds the pressure level of the fluid in an expanding side rod end chamber of the hydraulic motor, the exhausted fluid passes through a regeneration check valve and fills the expanding rod end chamber.

Abstract: Hydraulic control systems are useful for controlling actuation of hydraulic motors. Some such systems use spool type valves while other systems use poppet type valves, both of which have their advantages and disadvantages. The present hydraulic control system is a hybrid system utilizing a combination of both a spool type control valve and poppet type control valves in a single work circuit. Specifically, a spool type control valve has an inlet port connected to a variable displacement pump and a pair of flow amplifying poppet type valves are serially disposed between a pair of motor ports of the spool type valve and a pair of actuating chambers of a double acting hydraulic motor. The spool type control valve is operative to control pump-to-motor flow while one of the poppet type valves is operative to control motor-to-tank flow.

Abstract: An extensible mechanism, in which a first hydraulic cylinder and piston has a fixed reference for movement in an extension direction and also in a retraction direction. A second hydraulic cylinder and piston is moveable in both of these directions. Hydraulic fluid actuates the first and second hydraulic units in series, whereby actuation in the extension direction sequentially moves the first and second hydraulic piston and actuation in the retraction direction reverses the sequential order of movement of the two hydraulic pistons.