Abstract: A drive control system, which is suitable for use in a hydraulic machine, is equipped with an electric lever device having a manipulation lever and a potentiometer for generating an electrical manipulation signal corresponding to the degree of each manipulation of the lever, a control valve connected to a hydraulic circuit adapted to actuate a hydraulic actuator, and a controller unit equipped with a main controller for receiving the manipulation signal and computing a control signal for the control valve on the basis of the manipulation signal and an output device for generating an electrical actuation signal corresponding to the control signal.

Abstract: A valve for retaining a jack which retains a drive load. The braking valve includes a pressure reducing valve and safety valve, one of which ensures that the pressure in the chamber is retained, while the other modulates the pilot-control pressure P.sub.p. Thus, at each moment, the pilot-control pressure P.sub.p is adjusted to the value of the retaining pressure P.sub.l.

Abstract: A hydraulic servo system to control flow rate of working fluid to a hydraulic motor as a function of command includes a spool-type pilot valve with manual or electrohydraulic structure for positioning the pilot valve and control conduits connecting the pilot valve to a flow control valve having lands and chambers between the lands for directing flow to the hydraulic motor, the flow control valve having a cylindrical cavity at one end and being exposed to full system pressure at the other end, a shuttle valve coaxially positioned with respect to the flow control valve having an axial extension extending into the cylindrical cavity, a spring in the cavity which tends to urge the flow control valve in a direction to oppose the system pressure, with control passages connecting opposite sides of the shuttle valve with the flow control valve chambers causing the shuttle valve to select the higher pressure in the flow control valve chambers and causing the spool to seek a position providing the desired flow rate.

Abstract: An air-operated expansible chamber motor comprising a cylinder having first and second end heads, a piston reciprocable in the cylinder, a spool valve for controlling the supply to and exhaust of air from opposite ends of the cylinder, a relay valve mounted in one of the end heads for controlling the spool valve, a pilot valve in each end head having a stem engageable by the piston for controlling the relay valve via pressurization and exhaust of a pilot line, and a bleed for feedback of pressure air to the pilot line.

Abstract: A static hydraulic continuously variable transmission includes a cylinder block which is secured to an output shaft and comprises a pump cylinder of a hydraulic pump and a motor cylinder of a hydraulic motor, these cylinders being connected to each other, wherein, a number of pump cylinder bores and a number of motor cylinder bores are annularly arranged respectively in the pump cylinder and the motor cylinder and the transferring of a working oil between the group of the pump cylinder bores and the group of the motor cylinder bores is conducted through the medium of a pair of oil chambers which are concentrically provided around the output shaft communincation between these cylinder bores is controlled by a number of first and second dispensing valves extending between both the oil chambers and adapted to be reciprocally radially moved.

Abstract: A control system for an actuator used to position a control surface on an aircraft such as a horizontal stabilizer, including a source of pressurized fluid, a pressure control for establishing a predetermined pressure level that is substantially one-half source pressure, a blocker valve and at least one direction control valve for controlling the application of fluid pressures to the actuator. During idle periods, the blocker valve supplies substantially equal control pressures to the actuator so that the control system remains pressurized to substantially one-half source pressure. When the actuator is being energized, the direction control valve determines the direction of actuation and the blocker valve controls the fluid flow rate to and from the actuator to maintain a constant actuation rate regardless of load.

Abstract: A relay valve is operatively disposed between a pressurized air source and a work chamber of a brake booster. The relay valve has a pilot chamber so that the relay valve can feed the work chamber with a pressurized air, the pressure of which corresponding to that of a pressure applied to the pilot chamber. Electromagnetic valves are arranged to selectively connect the pilot chamber with the pressurized air source and the atmosphere. The valves are so controlled by an electronic control unit that the pilot chamber is supplied with pressurized air the pressure of which being determined in accordance with a brake pedal force applied from a brake pedal to an input means of the booster.

Abstract: An hydraulic system for operating double acting piston/cylinder assemblies and for effecting automatic transition from a regenerative mode of operation of a double acting piston/cylinder assembly to a non-regenerative mode of operation thereof. Pressure responsive valve means automatically converts the hydraulic system from one initially being a high-speed/low force operation to a high force/low speed operation.

Abstract: A control switching arrangement for a hydraulic power lift control system comprises a power lift control valve which is controlled via control lines in a low pressure section. The main hydraulic section is controlled by the said control valve via a check valve which is hydraulically openable, at least for carrying out lowering movement by the power lift. The check valve is opened via the said control valve itself, which furnishes the switching line a pressure generally equal to the circulation pressure of the main hydraulic section. Further, means are provided whereby, in the switching state corresponding to lowering movement of the power lift, the circulation pressure of the main hydraulic section can be increased. With this control system the low pressure control section is simplified, and energy losses in the control system are kept as low as possible.

Abstract: The hydraulic control is constructed for time-sharing of the pump which normally controls the turning mechanism, to operate other hydraulic equipment in conjunction with other pumps.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions, a pump system for supplying fluid, and a directional valve provided to which the fluid from the pump is supplied for controlling flow to and from the actuator. A pair of lines extends from the directional valve to the respective openings of the actuator. A controller alternately supplies a first fluid pilot pressure to pressure reducing valves associated with the directional valve for reducing the pressure from the pump system or any other source and supplying a second reduced pilot pressure to the directional valve for controlling the flow to and from the actuator. Preferably, the directional valve comprises a meter-in valve and a meter-out valve associated with each line to the actuator for controlling flow out of the actuator.

Abstract: The present invention is directed to a hybrid hydraulic system for a work vehicle having both an open center hydraulic circuit and a close center hydraulic circuit. An internal combustion engine drives a fixed displacement pump and a variable displacement pump. The fixed displacement pump provides hydraulic fluid to the open center circuit which directs hydraulic fluid to a steering circuit and the working circuit through a priority valve. The variable displacement pump provides hydraulic fluid to the close center circuit which directs hydraulic fluid to a braking circuit and a pressure reduction circuit. The pressure reduction circuit directs hydraulic fluid to a pilot control system, a clutch cutoff and a differential lock out. Both pumps receive hydraulic fluid from a common sump and a common suction line. The braking circuit comprises two independent braking circuits.

Abstract: In one form of the present invention, a plurality of serovalves are connected to a common manifold. The manifold transmits fluid pressure from the servovalves to a modulator piston which controls the fluid pressure applied to a hydraulic actuator piston. The servovalves are designed such that, if the fluid pressure provided by any one of them to the manifold falls below a threshold, then the servovalve disconnects itself from the manifold, allowing control of the modulator piston to be assumed by the remaining, functioning servovalves. The present invention can be used in control surface actuators of short takeoff and landing (STOL) aircraft.

Abstract: A load responsive control system using on a selective basis the energy derived from a negative type load for operation of system controllers, which may be of various types, including electro-hydraulic multi-stage controls, for use in positioning of the main control spools and in control of other system components.

Abstract: For connecting servohydraulic linear or rotation drives to a line with impressed pressure a valve means is provided which shuts off the pressure-carrying lines in leakage-free manner and connects the consumer line pressure-free to the tank. For a trial setting operation a fluid flow of reduced pressure and amount can be supplied to the consumers via an auxiliary means. The connection of the consumers is surge-free.

Abstract: A control system for a pneumatic actuator uses pressurized gases, such as air, as the actuating medium. Such gases and particularly air commonly contain moisture which condenses to form a liquid, such as water, which collects in a closed chamber of an expandable chamber assembly in the pneumatic actuator. In cold climates, the water freezes, preventing proper control of the pneumatic actuator. By providing a control system having a valve positioned elevationally higher or in close proximity to a pneumatic actuator and a tube which extends into the closed chamber of the expandable chamber assembly, water which is contained in the closed chamber is expelled from the elevationally lowest portion of the assembly when the valve is shifted to exhaust the air from the control system.

Abstract: The present invention incorporates a free swing system into the hydraulic flow system of a boom crane in order to permit an operator to control the boom crane during the centering operation, which occurs immediately before and during the hoisting of a load. The free-swing system is incorporated into the hydraulic flow system between the swing control valve and the hydraulic swing motor and operates by "bleeding-off" a portion of the hydraulic fluid being pumped to or by the hydraulic swing motor so as to greatly reduce or control the rotational speed of the hydraulic swing motor.

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

Abstract: A trigger for a fluid operated tool has a control with a pilot valve which when open pressurizes a chamber to cause a throttle valve to open. When closed, the pilot valve restricts fluid flow and reduces fluid pressure in the chamber, permitting the throttle valve to be closed. A continuously variable trigger control is also featured for varying the fluid flow rate to the tool.

Abstract: A pneumatic-hydraulic booster for vehicle includes a master cylinder part; a pneumatic cylinder part combined with the master cylinder part which includes a power piston slidable fitted to a cylindrical casing and an output rod fixed to the power piston, extending to the master cylinder part; a partition wall body fitted to the cylindrical casing; and a relay valve part arranged at the opposite side of the partition wall body from the power piston in the cylindrical casing. The relay valve supplies compressed air into an air pressure chamber formed between the partition wall body and the power piston and discharges the compressed air from the air pressure chamber to the atmosphere. When compressed air is suppplied into the air pressure chamber through the relay valve part the power piston and the output rod are moved forwards to generate hydraulic pressure in the master cylinder. The hydraulic pressure is applied to a wheel cylinder for braking.

Abstract: A pneumatic-hydraulic booster for vehicles includes a master cylinder part; a pneumatic cylinder part combined with the master cylinder part including a power piston slidably fitted to a cylindrical casing and an output rod fixed to the power piston, extending to the master cylinder part; a partition wall body fitted to the cylindrical casing; and a relay valve part being arranged at the opposite side of the partition wall body to the power piston in the cylindrical casing. The relay valve supplies compressed air into an air pressure chamber formed between the partition wall body and the power piston and discharges the compressed air from the air pressure chamber to the atmosphere. When compressed air is supplied into the air pressure chamber through the relay valve part, the power piston and the output rod are moved forwards to generate hydraulic pressure in the master cylinder part. The hydraulic pressure is applied to a wheel cylinder.

Abstract: A pressure relief system for the primary hydraulic system of a large industrial machine wherein the biasing force biasing one of the pressure relief valves is supplied by the pilot hydraulic control system of the machine. A two-position valve is used to selectively change the biasing force in response to a temperature indicator. The two-position valve couples and decouples the pressure relief valve to and from the pilot control system hydraulic pump and the pilot hydraulic system sump. If the pressure relief valve is in communication through the two-position valve with the pilot hydraulic fluid sump, the biasing force is reduced against the pressure relief valve and the pressure in the primary hydraulic system opens the pressure relief valve and directs hydraulic fluid to the primary hydraulic fluid sump.

Abstract: A poppet valve having novel seal means for use in a pneumatic fastener apparatus of the kind having a cylinder, a piston slidably mounted for reciprocal movement in the cylinder, a fastener-driving hammer attached to the cylinder, and means including the poppet valve for controlling the application of pressurized air to the piston so as to cause it to execute a work stroke. The seal means comprises an O-ring disposed in a circumferentially-extending groove formed in the outer surface of the poppet valve member and arranged to make a sealing engagement with an end edge surface of the cylinder. More than half of the cross-sectional area of the O-ring is disposed within the groove so that as the poppet valve is driven into closing relation with the cylinder, the O-ring seal is clamped between an annular circumferentially-extending surface of the poppet valve member and the annular end edge surface of the cylinder, thereby providing a secure seal along the full perimeter of the cylinder.

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

Abstract: A battery-operated electric-motor driven hydraulic-lift mechanism for a fork-lift vehicle employs a hydraulic accumulator which serves an intertia-free counterweight function, designedly to the degree that such counterweight action is a direct offset of a predetermined average-load condition, as seen by the hydraulic-lift actuator of the system. Electric-motor drive is utilized for up/down operation of the fork lift, only to the extend needed to displace hydraulic fluid into or out of the "counterweighted" actuator. In some cases, such displacement will call for expending energy to add to or substract from the counterweight action; in other cases, the necessary fluid displacement results in an energy return to the system, i.e., in restoring energy to the battery.

Abstract: A hydraulic valve assembly which can be used for controlling a motor or the like includes a first directional control member which selectively allows hydraulic fluid to flow from an associated hydraulic pump through a hydraulic fluid circuit to an associated reservoir and to an associated hydraulic motor. A second directional control member is connected to the fluid circuit for selectively allowing hydraulic fluid to flow directly to the associated reservoir as directed by the first member. A third directional control member is connected to the fluid circuit for selectively allowing hydraulic fluid to flow directly to the associated hydraulic motor as directed by the first member. A relief member is operatively connected with the fluid circuit for allowing hydraulic fluid to be relieved from the assembly to the associated reservoir.

Abstract: The invention relates to a 5/3-valve, which contains two separately controllable control members which are arranged coaxially with one another in the valve housing, are movable independently of one another and each bear two sealing surfaces which in the two end positions of the relevant control member engage with an appertaining valve seat of the valve housing. Such a 5/3-valve is distinguished by a very simple construction, compactness and a long working life.

Abstract: A pilot hydraulic system comprises a directional control valve having at least one pilot chamber for controlling the operation of a hydraulic actuator; and a pilot valve connected through a pilot line to the pilot chamber of the directional control valve for operation thereof. The pilot line includes a flow control valve which allows a free flow of hydraulic fluid from the pilot valve to the directional control valve while limiting a flow of hydraulic fluid from the directional control valve to the pilot valve.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A pilot operated spool type meter-in valve is provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator and a pilot operated meter-out valve is associated with each line of the actuator for controlling the flow out of the actuator when that line to the actuator does not have pressure fluid from the pump applied thereto.

Abstract: A base means (12) for directing fluid from a pneumatic control assembly to a number of pneumatic cylinders wherein the base means (12) is remotely mounted from the pneumatic cylinder and the pneumatic control assembly is mounted to the base means (12) and is in fluid communication with the base means (12) through base ports (38,40) which extend completely through the base means (12). The base means includes an upper and lower support surface (28,30), as well as side walls (31,32) and end walls (33,34) extending therebetween, and also includes communication ports (35,36) disposed on the faces of the walls. Flow passeges provide (44,46) fluid communication between the base ports (38,40) and the communication ports (35,36) and delivery means (48) extend between the communication ports (35,36) and cylinder ports located on either side of the piston in a pneumatic cylinder.

Abstract: A safety valve assembly for regulating the flow of a fluid under pressure to a fluid operated system e.g. a double acting cylinder element includes a housing with an inlet port, outlet ports and working ports and accommodating a pair of parallel valve spindles which are controllable by respective pilot valves so as to be shiftable between two valve positions. Each valve spindle is provided with a working piston, valve piston and a control piston which cooperates with a respective valve seat as defined by the housing. The control pistons of the valve spindles are successively disposed in a passageway extending between one of the working ports and one of the outlet ports.

Abstract: A pneumatic gun having an improved firing valve is disclosed wherein the firing valve is sealingly secured to the housing of the gun by a pair of rolling diaphragm seals. On the underside of the firing valve, there is a deflector having a downwardly curled outer edge operative to direct air flow into the top of the cylinder upon opening of the firing valve. The firing valve is so configured that exposure of multiple differential areas of the valve to a common high pressure results in the valve being biased toward a sealed position relative to the cylinder of the gun while in the unfired position.

Abstract: Automatic device for economizing compressed air comprises a means for ensuring the passage of driving fluid under pressure during most of the stroke of the moving element of a user apparatus. The device consists of a single-unit body having a first circuit connecting a fluid supply pipe to one chamber of the cylinder actuator. The first circuit is controlled by a valve moving with a piston subjected to the action of an elastic means and slidably mounted in the body. The piston is actuated by the presence or absence of a pressure signal, the body having a second circuit by-passing the first circuit and connecting a fluid exhaust pipe to the cylinder chamber.

Abstract: An apparatus for controlling the angular position of the booms of an earthwork vehicle such as a wheeled tractor loader includes a shock absorber, by which the hydraulic pressure to be applied to a cargo handling valve for changing the position of a valve spool therein is lowered so as to lessen the shocks which are felt when the booms come to a stop position.

Abstract: Apparatus for controlling operation of an aerial lift having a boom. A hydraulic fluid pump is connected to a hydraulic cylinder, and the control arrangement controls the supply of hydraulic fluid from the hydraulic fluid pump to the cylinder and controls the supply of hydraulic fluid pressure to a first pilot fluid port and to a second pilot fluid port of a pilot operated control valve to control operation of the pilot operated control valve. A first hydrulic fluid conduit operably connects the hydraulic fluid pump to a first pilot fluid port, and a second hydraulic fluid conduit operably connects the hydraulic fluid pump to a second pilot fluid port of said control valve. A control handle selectively vents hydraulic fluid from the first fluid conduit and the second fluid conduit to control fluid pressure at the pilot ports.

Abstract: The brake circuit apparatus for a hydraulic motor in a hydraulic circuit system having at least one main hydraulic pump, a hydraulic motor driven by a hydraulic fluid supplied from the main pump and having a rotary shaft, and a directional control valve actuated by an operation device for control of flow rate and flow direction of the hydraulic fluid supplied to the hydraulic motor from the main pump. The hydraulic motor is provided with a mechanical brake device having a brake release cylinder adapted to release the rotary shaft of the motor from the braking by the mechanical brake device by supply of a hydraulic fluid to the brake release cylinder. The apparatus further has an auxiliary hydraulic pump and a control circuit connected to the auxiliary pump, brake release cylinder and reservoir for control of fluid communication therebetween.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a pump system with load sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a manual or electrohydraulic controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the flow therefrom to the actuator to control direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator. A meter-out valve is associated with each line to the actuator for controlling flow out of the actuator. Each meter-out valve is operated by the pilot pressure from the controller.

Abstract: An actuator for moving a valve or other controlled part in correspondence with variations in an input signal and including a piston movable in opposite directions within a cylinder and having a smaller effective area exposed to fluid in a first chamber at one side of the piston than to fluid in a second chamber at the opposite side of the piston, a pressure fluid source delivering pressurized fluid to the first of these chambers and delivering pressurized fluid to the second chamber through a three way valve having a body containing inlet and outlet openings and a valve element movable relative thereto in a manner varying the pressure delivered to the second chamber of the cylinder.

Abstract: A control system for a hydraulic circuit having an on-off valve interposed between the control valve and the actuator for allowing and blocking a flow of hydraulic fluid therebetween in which the control valve and on-off valves are actuated and switched in accordance with an operation signal from an operation device. Pressure sensors are connected to hydraulic lines upstream and downstream of the on-off valves for detecting the pressures in these hydraulic lines, and control unit is operative to calculate, based on the pressures detected by the pressure sensors, a value which reduces the difference between thrusts applied to the actuator and output the calculated value to the control valve while the on-off valves are closed to thereby perform pressure matching control.

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

Abstract: A hydraulic circuit system for use in hydraulically operated vehicles having a bidirectionally rotatable hydraulic motor with a brake unit, a directional control valve for controlling a pressurized fluid supply to the motor, bypass circuits connected between a fluid supply circuit and a drain circuit, a shadow valve provided in the bypass circuits, and an ON-OFF changeover valve provided in the bypass circuits for allowing the bypass circuits to connect with and disconnect from the shadow valve. The system further includes a cavitation preventing circuit device connected through check valves between the bypass circuits and the shadow valve so as to allow the bypass circuits to communicate with each other in co-operation with the shadow valve.

Abstract: An emergency drain device for pneumatic cylinders which is integrated in an orientatable connection fixed directly to the cylinder body and comprises a valve which closes an orifice of the bolt of the connection, going to the atmosphere, when a control pressure is applied to the head of the bolt.This device is advantageously used in installations where a general isolating switch, controlled by the same control pressure, connects the general distribution line to the atmosphere, for example in the case of an emergency, when said pressure disappears.

Abstract: A fluid operated positioning apparatus includes a multi-position valve operated in response to differential pressure in a fluid control circuit. The control circuit includes two adjustable throttles in series, the junction between the throttles being connected to a control device at one end of the valve. Particular relationships for the throttles are disclosed. Other embodiments include additional throttles for improved control with low pressures.

Abstract: A hydraulic valve provides infinitesimally variable flow in both directions through the valve including a position of no flow. The valve can be operated either hydraulically or mechanically. It includes a housing with a bore therethrough, a sleeve slidably mounted inside the bore, and endplates enclosing the ends of the bore. Ports allow controlled passage of hydraulic fluid through the housing, the sleeve, and extensions from the endplates so that fluid from a hydraulic pump enters ports in the housing, flows controllably through the valve, out one of the endplates, through a use apparatus, back into the remaining endplate, and to a sump.

Abstract: A pneumatic servo valve comprising a piston in a cylinder. Both controlling surfaces of the piston are exposed to controlling air. The piston is provided with an axial drilling extending through it, which communicates via a radial groove with an inlet of controlling air. Both openings of the drilling are normally closed by spring actuated mushroom valves. Controlling chambers in the cylinder communicate through calibrated conduits in the piston with the radial groove, and can be put into communication with the surrounding atmosphere via outlets. The outlets are controlled by electromagnet valves. A microcomputer receives signals from correct and actual value indicators respectively, and administers opening and closing of the valves. When one of these is opened the connected controlling chamber is decompressed and the piston moves in the direction of the empty chamber. One of the mushroom valves follows the movement of the piston, while the other mushroom valve is prevented from moving by a valve seat.

Abstract: The times of response of a circuit-breaker control system to breaker-closing orders are reduced by means of a unit comprising a pressure reducer and a low-capacity compensating hydraulic accumulator, the unit being connected to the portions of the hydraulic control circuit which are alternately pressurized and depressurized. The hydraulic accumulator resupplies oil at reduced pressure to the portions of circuit in which there is a lack of oil or which are filled with emulsified oil as a result of depressurization operations.

Abstract: A valve arrangement for a compressed-air operated nailing apparatus with valve pistons operating without intersection in such a manner that the one valve piston cooperates with the working cylinder and is guided by the other working piston which is controlled by an auxiliary control valve, wherein the first auxiliary piston is also controlled at the same time, and wherein upon opening the valve arrangement the second valve piston is moved first into the opening position and the first valve pistion thereafter.

Abstract: A hydraulic system includes a pilot controlled, pressure operated, spool valve (2) which acts substantially as a by-pass valve when regulating supply of fluid to an actuator (8), and as an in-line valve when regulating the return flow of fluid from the actuator (8) to tank. Both these regulating functions are provided by means of a single main valve spool (31). A flow sensor (20) provides negative feedback to the pilot valve in both by-pass and in-line modes of operation of the main valve, which makes the operation of the system substantially independent of load, temperature, and pump flow. If it is essential that the actuator (8), once it has reached a desired level, remains at that level, the system may additionally incorporate a releasable non-return valve (7) in the service line (71) from the main valve (2) to the actuator (8).

Abstract: A fluid-pressure driving device including a driving cylinder for producing a driving force, a main control valve for controlling the direction of movement of the driving cylinder and a fluid under pressure, and a pilot valve for controllng the main control valve. The main control valve includes a valve member in the form of a hollow cylinder, and a valve body constituting a part of a cylinder body of the driving cylinder. The valve member of the hollow cylindrical configuration is slidably interposed between the valve body and a sleeve of the pilot valve.

Abstract: The present invention incorporates a free swing system into the hydraulic flow system of a boom crane in order to permit an operator to control the boom crane during the centering operation, which occurs immediately before and during the hoisting of a load. The free-swing system is incorporated into the hydraulic flow system between the swing control valve and the hydraulic swing motor and operates by "bleeding-off" a portion of the hydraulic fluid being pumped to or by the hydraulic swing motor so as to greatly reduce or control the rotational speed of the hydraulic swing motor.