Abstract: Conventional vehicle lifts typically operate at a standard speed that is statically configured for the system, which may result in vehicles that are below the weight rating for the lift being raised at the standard speed while the lift motor is capable of safely raising at greater speeds. A set of lift controls may be configured to determine the load on the motor by a vehicle of an unknown weight during operation at a standard lift speed and use such information to determine a potential speed that the motor may raise the vehicle at while staying within safe operational levels for the motor. One or more of a magnitude of electrical power drawn, a pressure generated by a hydraulic lifting, or a sensed vehicle weight may be used to provide an indication of load on the motor and/or a higher potential speed.

Abstract: An actuator pressure intensifying assembly includes a mode valve and a gear motor assembly, the mode valve arranged to receive, at an input port, a supply pressure and to provide, at an output port, a control pressure to an actuator, the mode valve further configured to move, in response to the supply pressure exceeding a predetermined activation threshold, from a first mode in which the supply pressure flows directly from the input port to the output port in a first fluid flow path, and a second mode in which the supply pressure flows from the input port to the output port in a second fluid flow path which includes the gear motor assembly between the input port and the output port which intensifies the supply pressure such that the control pressure is higher than the supply pressure.

Abstract: A method of controlling a hydraulic control system of a material handling vehicle is provided. The method includes detecting an elevated height of a fork assembly, determining if the elevated height is above a first predetermined height threshold, and actuating a first low pressure control valve from a control valve closed position to a control valve open position to provide fluid communication from a supply passage to the first low pressure relief valve when the elevated height is above a first predetermined height threshold.

Abstract: Actuator systems and methods of operation are disclosed. The systems include a hydraulic actuator having a primary piston having a piston head arranged within a housing defining retract and extend chambers on opposite sides of the piston head. A control element is configured to control a supply of pressure to each of the retract and extend chambers. An actuator valve is coupled to the housing and includes a secondary piston that is biased into the retract chamber in an open flow state and when the primary piston is in a fully retracted state the piston head urges the secondary piston into a closed flow state. The actuator valve defines a flow chamber where, in an open flow state, fluid can be passed through the flow chamber and in a closed flow state the fluid is prevented from passing through the flow chamber.

Abstract: A valve device that changes the direction of flow of a hydraulic fluid supplied to and discharged from a cylinder mechanism to actuate the cylinder mechanism, the valve device including: a control valve including a main spool axially movable between different positions; a lock valve including a plunger and a pressure chamber; and a selector valve including a selector spool operable in conjunction with the main spool to axially move between different positions, the selector spool being located adjacent to the main spool and having an axis crossing an axis of the main spool.

Abstract: The subject matter of this specification can be embodied in, among other things, a method that includes actuating a closure member at a predetermined first velocity a predetermined first number of cycles between a first configuration and a second configuration, actuating the closure member at a predetermined second velocity a predetermined second number of cycles between the first and the second configuration, actuating the closure member at a predetermined third velocity a predetermined third number of cycles and the second configuration, actuating the closure member at a predetermined fourth velocity a predetermined fourth number of cycles and the second configuration, and actuating the closure member to the second configuration at a predetermined fifth velocity for a predetermined flushing period.

Abstract: In a hydraulic drive of a tool, a piston is adapted to be acted upon by a pump via a pressure limiting seat valve and a parallel switching seat valve of a valve arrangement. A restriction is provided in a pressure line upstream of the pressure limiting seat valve which is connected to a tank on the flow-off side. A drain line leads from a working chamber of the piston via the switching seat valve to the tank. A closing side is adapted to be acted upon by pressure and an opening side is adapted to be acted upon by a force generated when the pressure limiting seat valve responds. The pump is adapted to be switched off when the maximum operating pressure has been reached, so that the piston will execute a return stroke. A pressure-increasing restriction is provided on the flow-off side of the pressure limiting seat valve.

Abstract: A control system for a reciprocating device which includes a switching valve for directing fluid supply under pressure to one of two drive lines in an alternating manner, means for alternating the switching valve, and an exhaust circuit including and exhaust outlet, a first flow restrictor disposed between one drive line and the exhaust outlet, and a second flow restrictor disposed between the other drive line and the exhaust outlet. The system may include a selection valve for alternately connecting one of two drivelines to the exhaust outlet.

Abstract: To permit using hold-side pressure oil in a first hydraulic cylinder for the acceleration of a second hydraulic cylinder upon performing a combined operation of the first and second hydraulic cylinders, a hydraulic drive system is provided with a main hydraulic pump 21, a boom cylinder 6 and an arm cylinder 7, a directional control valve 23 for a boom and a directional control valve 24 for an arm, and a boom control device 25 and an arm control device 26. The hydraulic drive system is also provided with a pressure oil feed means for feeding pressure oil in a rod chamber 6b of the boom cylinder 6 to an upstream side of the directional control valve 24 for the arm when a bottom pressure of the arm cylinder 7 has increased to a high pressure equal to or higher than a predetermined pressure. This pressure oil feed means includes a flow combiner valve 44 arranged in a reservoir line 42 which can communicate to the rod chamber 6b of the boom cylinder 6.

Abstract: A hydraulic drive unit is provided with a boom cylinder, an arm cylinder, a communication line communicating a rod chamber of the boom cylinder and a bottom chamber of the arm cylinder with each other, and a switching valve arranged on the communication line for communicating or shutting off the communication line in accordance with a rod pressure of the boom cylinder. When an arm-crowding single operation is performed and by its digging counterforce, a rod pressure of the boom cylinder rises to a high pressure of at least a predetermined pressure, the switching valve is changed over from a shut-off position to a communicating position to feed pressure oil from the rod chamber to the bottom chamber. The boom cylinder is hence caused to automatically extend, thereby avoiding lifting of a hydraulic excavator body.

Abstract: A servo hydraulic flow control valve assembly includes an oil distribution board having a first manifold defined therein near an inlet end of the oil distribution board and a second manifold defined in the oil distribution board near an outlet end of the oil distribution board. A relief valve is secured on the oil distribution board, and includes a body positioned on the oil distribution board and a rated control device mounted to the body for selectively opening the first manifold. A servo control device is secured on the oil distribution board. The servo control device includes a controller rotatably received in the oil distribution board and having a passage defined to communicate with the second manifold. A control unit is secured on the oil distribution board for driving the controller to control the pressure and the flow rate in the second manifold.

Abstract: A hydraulic driving unit is provided with a directional control valve 23 and directional control valve 24 for controlling a boom cylinder 6 and arm cylinder 7, both of which are driven by pressure oil delivered from a main hydraulic pump, respectively, a boom control device 25 for selectively controlling the directional control valve 23 and an arm control device 26 for selectively controlling the directional control valve 24, and is mounted on a hydraulic excavator.

Abstract: The invention pertains to an electrohydraulic servo door drive for operating a door, a window, or the like, with a hold-open function, where a valve is installed in the hydraulic circuit to implement the hold-open function. To create an electrohydraulic servo door drive which requires less space and can be produced at lower cost, it is provided according to the invention that the valve is designed as a hydraulically controlled hold-open valve.

Abstract: For a valve arrangement of a pneumatically actuated, spring-loaded control cylinder, a non-return valve in pneumatic communication with the control cylinder piston chamber. At very low backpressures in the control cylinder piston chamber caused by leaks of the valve responsible for pressurization of the piston chamber, the chamber is vented by passage of a very small air stream via the non-return valve. In this way, leaks cannot cause a very slow pressure buildup in the control cylinder piston chamber, followed at some time by undesired shifting of the control cylinder. In contrast, in the case of normal pressure buildup, i.e., during switching of the pressurizing valve, the non-return valve is promptly closed and the pressure in the control cylinder piston chamber is not influenced.

Abstract: A hydraulic actuation arrangement including a double-action working cylinder whose working chambers are in communication via a mutually unseatable check valve with one side of a reversible pressure medium source, respectively, whereby each working chamber is connected to a pressure medium reservoir by a pressure-relief valve or pressurizing valve, and at least one working chamber is furthermore connected to the pressure medium reservoir via an additional pressurizing valve. When an additional pressurizing valve is provided with two different pressure threshold values, the manual force used in emergency operation is therefore clearly reduced after introduction of the manual movement whereby these force levels for both movement directions may be selected independently from the maximum system pressure.

Abstract: Active control system for a movable member, in particular a tailgate or door, includes a pump unit which is connected by at least one fluid connecting line to a piston-cylinder unit. The control system has an on-off valve through which the direction of motion of the piston-cylinder unit is controlled. A pressure-limiting valve is operable, in emergency conditions, to permit a displacement motion of the piston rod of the piston-cylinder unit by opening a connection to the working chamber of the piston-cylinder unit.

Abstract: A directional control valve system is provided in conjunction with a hydraulic actuator, using a meter-in flow control valve that is simple in structure to permit pressure fluid to be fed into a first and a second chamber of the hydraulic actuator. The directional control valve system includes a meter-in flow control valve 1 for establishing and blocking fluid communication of a pump port with an outlet port 12, a first and a second load checking valve 2 and 3 that is in fluid communication with the outlet port 12, and a meter-out flow control valve 4 for establishing fluid communication of one of a first and a second actuator port 72 and 74 at an output side of the first and second load checking valves 2 and 3 with a tank port 71, and has an arrangement that permits the first and second load checking valves 2 and 3 to be held in a closed state with pressure fluid.

Abstract: A meter-out flow control valve is provided that is compact and possesses a regenerative function. A poppet valve 70 for establishing and blocking fluid communication between a first actuator port 73-1 and a tank port 74 is urged by a spring 71 into a pressure contact with a seat 72. The poppet valve 70 is moved away from the seat 72 under pressure in a first pressure receiving chamber 80-1. A cylindrical valve 103 is fitted with the poppet valve 70 to provide a regenerative switching valve 101 that may establish and block fluid communication between the first actuator port 73-1 and a first regenerative port 100. A meter-out flow control valve having a poppet valve 70 and a cylindrical valve 103 fitted together is thus provided that is compact in form and yet capable of regenerating pressure fluid in a first actuator port 73-1 into a first regenerative port 100.

Abstract: A distributor for a hydraulic hoist which is controllable with regard to position and applied force, for tractors and agricultural machines, comprises a compact body having at least one inlet duct for a pressurized fluid, at least one discharge duct and at least one duct for connection to a hydraulic cylinder for lifting the hoist arms. Arranged in the body of the distributor are a valve for modulating the flow of pressurized fluid and for communicating with the connecting duct by way of a main internal duct and a valve unit for discharging the fluid coming from the hydraulic lifting cylinder. A slider is movable inside the cylindrical body in two opposite directions with respect to a neutral position and controls the modulating valve hydraulically, preferably with the interposition of a consent valve. The slider also controls the discharge valve unit and a variable choke member arranged in the main internal duct.

Abstract: Agricultural implement to be conveyed by a self propelled vehicle includes a structural frame and a substructure moveable between a raised position and a lowered position. The substructure has at least one ground engaging tool supported thereon so as to engage the ground when the substructure is moved to the lowered position. A fluid circuit is provided to control engagement of the tool with the ground. The fluid circuit includes a first check valve having a first side connectable to a source of pressurized fluid flow and a second side connected to a fluid cylinder. The fluid cylinder is operated between a retracted position and an extended position to move the substructure between the raised position and the lowered position, respectively. A second check valve is provided having a first side connected to drain and a second side connected to the fluid cylinder. A sensor assembly opens the second check valve when pressurized fluid flow is received by the first side of the first check valve.

Abstract: A dynamic pressure regulator cushion for use with a fluid power actuator to smoothly and linearly decelerate the piston at end of stroke. The dynamic pressure regulator cushion comprises a pressure sensor attached to a valve. A side of the pressure sensor tending to close the valve is exposed to driving pressure. A side of the pressure sensor tending to open the valve is exposed to fluid pressure in the cylinder ahead of the piston. An adjustable valve pre-loading is provided to maintain the fluid pressure in the cylinder ahead of the piston at a constant, pre-determined level above the driving pressure during the cushion stroke. This pre-set pressure differential across the piston serves to smoothly and linearly decelerate the piston to near zero at end of stroke. Two pressure sensor embodiments taught are a pressure sensor piston reciprocating within a plenum, and a diaphragm whose outer edge is attached to, and sealed to, an inside wall of a plenum.

Abstract: A pressure regulating valve is provided with a first valve for opening and closing a flow channel between a fluid pressure source and a reservoir, and a second valve for opening and closing a flow channel between an output chamber and the reservoir in order to regulate the pressure applied from the fluid pressure source in proportion to an input fluid pressure in an input chamber and to output the regulated pressure from the output chamber. A slidable valve body with one end subjected to an input pressure and the other end subjected to an output pressure, and a one-way valve for allowing communication only from the fluid pressure source to the output chamber are featured in that the movement of the valve body by a given quantity causes the first valve to close after the second valve is closed as the pressure in the input chamber rises.

Abstract: A pneumatic cylinder, especially for a spot-welding machine, has a sleeve valve mounted on the piston rod. The sleeve valve provides a venting valve for dumping pressure from a return chamber at the end of the forward stroke, and a progressive restrictor to close off a forward chamber and provide cushioning at the end of the return stroke.

Abstract: An engine for driving a piston arrangement for pumping water from an inlet to an outlet at a higher level is disclosed. The engine includes a hollow housing having an inlet and an outlet between which liquid passes, the housing at least partly enclosing a chamber through which the liquid flows from the inlet to the outlet. A movable wall is mounted in the housing and partly defines the chamber. A valve is provided to open and close the outlet so that when it closes, liquid in the chamber is suddenly decelerated producing an increase in pressure in the chamber to force the wall to move to a direction so as to increase the volume of the chamber. After an initial increase in the pressure, the water relaxes and the pressure decreases to such an extent that a spring will open the valve and the spring returns the wall to the position of decreased volume in the chamber. Thus, the wall is caused to reciprocate under the influence of pressure of the liquid increasing and decreasing as the valve is opened and shut.

Abstract: A hydraulic system for controlling the contract force of a hydraulic device. A proportional pressure relief valve acts as pilot valve for a main valve that controls the lowering process. The proportional pressure relief valve is provided with a solenoid whose voltage can be varied. A pressure sensing line is also applied to the same side of the valve as the solenoid for biassing the valve against a spring.

Abstract: A fluid unit, for example a piston/cylinder unit, is supplied with fluid via a cyclically opened or closed on/off valve. The vacuum peaks occurring on the outlet side of the on/off valve when it is closed and the inertia forces of the flowing fluid are used to supply additional fluid to the fluid unit via a non-return valve leading from a low-pressure connection or reservoir to the fluid unit.

Abstract: A power steering motor is operatively connectable with steerable vehicle wheels for steering the vehicle wheels. An actuatable power steering valve has a neutral position in which fluid flows through the steering valve to a fluid reservoir and an actuated position in which fluid flows through the steering valve to the steering motor. A main conduit conducts fluid from the outlet port of a pump to the steering valve. A return conduit conducts fluid from the steering valve to the reservoir when the steering valve is in its neutral position and in its actuated position. An orifice is located in the return conduit. A bypass valve bypasses fluid from the main conduit to the reservoir. The bypass valve is controlled in response to a pressure drop across the orifice located in the return conduit.

Abstract: A metering valve adapted to operate a seat on a side of an actuator port by means of a poppet section of a main poppet arranged in a valve casing to selectively communicate the actuator port to a tank passage. The main poppet is formed with a pressure chamber on a side thereof opposite to the poppet section. The pressure chamber has a pressure receiving area substantially equal to that of the seat. Also, the main poppet is formed with a through-hole constantly communicated to the actuator port and a pilot chamber to which pilot pressure for moving the main poppet in a direction of opening the seat is applied. Thus, the metering valve is capable of stably accomplishing its control irrespective of a variation of pressure on the side of the actuator port.

Abstract: A flow control device includes a control valve having a discharge line to be connected to a hydraulic motor, a supply line to be connected to a hydraulic pump, a first bleed-off control passage having a line connected to a tank, and a second bleed-off control passage having a line connected to the tank through a secondary control valve, a flow dividing valve provided in the supply line and having a first position for allowing a first desired flow of oil discharged from the hydraulic pump and a second position for allowing a second desired flow of the oil, and a selector valve operable for the secondary control valve and the flow dividing valve and having a first selection position for closing the secondary control valve and shifting the flow dividing valve to the first position and a second selection position for opening the secondary control valve and shifting the flow dividing valve to the second position.

Abstract: A power steering system includes a bypass valve for bypassing fluid from a main fluid conduit connected between an engine-driven, power steering pump and an actuatable, open-center, steering control valve which is actuated upon turning of a vehicle steering wheel. When the steering control valve is actuated, the demand for fluid through the steering control valve to a power steering motor increases. The fluid pressure in the main conduit varies as a function of the demand for fluid to the steering control valve. The bypass valve is urged toward an open condition by a fluid pressure signal. The bypass valve is urged toward a closed condition by a spring and by a fluid pressure which varies as a function of the demand for fluid to the steering control valve and as a function of an electrical signal which varies as a function of at least one vehicle operating parameter, such as vehicle speed.

Abstract: In a fluid control valve, a check valve is provided between the pump port and the first fluid chamber and allows the fluid to pass therethrough only in a direction from the pump port to the first fluid chamber, a down control valve is provided between the first fluid chamber and the second fluid chamber, an up control valve is provided between the first fluid chamber and the third fluid chamber, the fluid is allowed to flow from the pump port to the cylinder port through the check valve and through the down control valve when they are opened, and the fluid from the cylinder port to the tank port is allowed to flow through the down control valve, through the first fluid chamber and through the up control valve when they are opened. The fluid control valve can be obtained simple in structure and high in precision, and be allowed a reduction in cavitation and noise.

Abstract: A high pressure hydraulic flow control valve is formed with a spool which is capable of operating as a conventional spool to control the flow of fluid from an input port to an output port or to a return port. The spool also provides overload protection which will permit fluid to pass from the input port directly to the return port when an overload pressure condition exists in the fluid supply line. In alternative structure, the overload pressure release system may be incorporated into the valve which is used to control the return of fluid from the output port to the return passage. The high pressure hydraulic flow control valve is formed from a die-cast housing and has hardened seats mounted in access passages so as to bear against a seating shoulder. Preferably, a retaining sleeve is mounted in the access passage to bear against the hardened seat to retain it against the seating shoulder.

Abstract: A variable assist power steering gear mechanism for vehicles having primary and secondary steering valve portions, the primary portion controlling pressure in a power steering fluid motor, a steering pressure valve that controls the magnitude of the steering pressure as a function of vehicle speed, a steering torque sensor flow control valve that cooperates with the secondary steering valve portion to develop a steering torque signal, and an electronic signal processor for controlling the steering pressure valve in response to changes in the vehicle speed and the steering torque signal.

Abstract: A high pressure hydraulic flow control valve is formed with a spool which is capable of operating as a conventional spool to control the flow of fluid from an input port to an output port or to a return port. The spool also provides overload protection which will permit fluid to pass from the input port directly to the return port when an overload pressure condition exists in the fluid supply line. In alternative structure, the overload pressure release system may be incorporated into the valve which is used to control the return of fluid from the output port to the return passage. The high pressure hydraulic flow control valve is formed from a die-cast housing and has hardened seats mounted in access passages so as to bear against a seating shoulder. Preferably, a retaining sleeve is mounted in the access passage to bear against the hardened seat to retain it against the seating shoulder.

Abstract: A work cylinder having an internally-disposed, automatically-operated drain valve disposed in one or both ends of a housing having a cylinder bore formed therein. A reciprocally-movable piston divides the bore into first and second pressure chambers. A drain chamber formed in one or both ends has a movable plunger member disposed therein. A first passageway allows fluid from the pressure chamber to act on one surface of the plunger. A pilot valve is partially formed on a bottom portion of the plunger and opens when fluid pressure is exhausted from the adjacent pressure chamber. A bias spring acts on the plunger to prevent closing of the drain valve upon initial pressurization of the adjacent chamber. This initial pressurization assists in purging additional moisture from the chamber until a threshold level is exceeded to close the drain valve.

Abstract: A hydraulic elevator up direction control system is provided including a circulating valve connected between the supply and the return of a source that normally supplies pressure to the cylinder of an elevator controlled by a two position switchable setting valve that influences the pilot fluid pressure in the operating chamber of the circulating valve to control the size of opening of the circulating valve and thereby the volume of fluid passing through the circulating valve affecting inversely the volume of fluid passing through a check valve, to provide two distinctive intermediate up speeds of travel in addition to the nominal full speed of travel facilitating a fast, smooth and accurate ride of the elevator car as it approaches a stopping point relative to an upper floor of a building. A three speed down direction control system presents no problems of significance and is not dealt with.

Abstract: Valve arrangement in a line with pressure medium used as supply and return line, said valve arrangement being intended for controlling the flow through said line and comprising a valve body with a first and a second valve port which serve, alternately, as input and output, and a valve cone arranged in the valve body which connects in its open position the valve ports with each other, closes these in its closed position and is actuated by a holding force which is greater than the force acting on the pressure medium side of the valve cone and dependent on the medium pressure in the input port.

Abstract: A power steering system includes a bypass valve assembly which bypasses fluid from a main conduit connected with a power steering pump and motor. The bypass valve assembly is urged toward an open condition, bypassing fluid from the main conduit, with a force which varies as a function of the fluid pressure drop across an orifice in the main conduit. The bypass valve assembly is urged toward a closed condition by a spring. In addition a pressure responsive pilot valve assembly opens to communicate the fluid pressure in the main conduit to the bypass valve to urge the bypass valve assembly toward the closed condition. This decreases the rate at which fluid from the power steering pump is bypassed to thereby increase the amount of fluid available for actuation of the power steering motor.

Abstract: A valve for cooling a reversible hydraulic machine includes a valve piston in a connecting channel extending between supply and discharge passages. Pressure in these passages displaces the spring-centered piston from neutral position to an end position. A central reduced-diameter portion of the piston carries a spring-centered closing member which closes a discharge conduit leading to a leakage space when the piston is in its central position. When the piston is displaced out of the neutral position toward one of the end positions, pressure from one of the connecting passages which has the lower pressure prevailing therein is permitted to propagate through one of the spring-receiving spaces delimited by the closing member and through an annular throttling gap present between the closing member and the central portion of the piston into the other spring receiving space and from there into the discharge conduit and into the leakage space.

Abstract: A security screen having two rams to operate the screen which are located against the panel of the screen, the rams being connected at one of their ends substantially symmetrically relating to the center of the screen at or adjacent the top thereof and, at their other ends, substantially symmetrically relative to the screen to a structure beneath or beside the screen, the connections being such as to permit at least a degree of rotation of the rams relative to the panel and the structure, the arrangement being such that, as the rams are extended, the outward component of forces of the rams are substantially equal and opposite, the resultant being an upward component which can drive the screen upwardly rapidly.

Abstract: A signal valve (38) is connected to a supply conduit (16) connecting a pump (11) with a control valve (14) for transmitting an artificial load signal to a load signal chamber (34) of a pressure compensated unloader valve (27) when the control valve is at an operating position and the pressure in the supply conduit (16) is below a preselected value. This moves a valve member (31) of the unloader valve (27) to a blocking position causing essentially full pump flow to be directed to the hydraulic jack for decreasing the response time in situations wherein the hydraulic jack has cavitated and no positive load pressure signal is present.

Abstract: A hydraulic control device for a hydraulic motor having a working pressure line connecting a source of pressure with the motor and containing a non-return valve from which a bypass line branches off to communicate with the fluid reservoir or tank; a three-way flow controller is connected to the tank and is in communication with a two-way flow controller; characterized in that a single measuring orifice is common to several pressure balances with a single porportional magnet provided in the working pressure line.

Abstract: A valve arrangement for connecting a hydraulic machine, such as a pump or a motor, with a pressure accumulator in which a conventional manual shutoff valve is replaced by a leak-proof pressure controlled valve whose operating pressure signal is supplied by a shuttle valve from that one of two ports of the pressure controlled valve at which the higher pressure prevails at a given time. The pressure controlled valve is supplied with fluid under pressure by way of a leak-proof remote controlled slide valve.

Abstract: A control system for operating positive displacement hydraulic motors to minimize pressure peaks and stresses associated therewith upon starting the motor at full fluid flow includes a self-closing pilot operated valve which, upon initiation of fluid flow to the motor bypasses a majority of the flow to a return line circuit and progressively closes to force pressure fluid to accelerate the motor to a preselected operating speed. The self-closing valve includes a spool type closure member which is pilot actuated through a timing orifice to commence closing upon initiation of fluid flow therethrough from the pump discharge or supply line. The closure member is spring biased in the open position and automatically resets itself to the open position upon shutdown of the motor operating valve.

Abstract: A power steering apparatus is disclosed wherein improved steering characteristics are provided over a wide range of driving conditions. The system includes an oil pump for supplying pressurized oil from an oil tank to either a left or right cylinder chamber in a power cylinder and a flow control valve which returns part of the pressurized oil discharged from the oil pump to the tank. In accordance with the invention, at least one small orifice is provided communicating a pressurized oil feed line directed to one of the chambers in the power cylinder with a return line directed to the oil tank from the other one of the chambers in the power cylinder at the downstream side of the flow control valve.

Abstract: A hydraulic control system for an elevator or other similar reciprocating user is disclosed, which comprises an adjustable throttle valve and a control or bypass valve disposed in the fluid supply line between the pump and elevator. A pressure difference balance is provided for controlling the operation of the control valve, and the pressure difference balance has one end operatively connected to the pressure provided by the pump, and the other end operatively connected to the pressure in the user or load line. The control valve is thus adapted to maintain a desired pressure difference across the throttle valve which is independent of the load on the user. In addition, the zero setting of the pressure difference balance is adjustable, so as to permit the system to be equally operable in both the upward and downward movements of the elevator.

Abstract: A weight-balancing system for a farm implement, such as a disk harrow with foldable wings operated by wingfold cylinders, includes a selective control valve for controlling fluid communication to the head and rod ends of the wingfold cylinders. A pair of pressure-reducing/relieving valves permit individual adjustment of the pressures in both the head and rod ends to achieve the desired balance. In a preferred embodiment, a pilot-operated, two-position valve is connected between the rod ends and one of the pressure-responsive valves. The two-position valve is operated by pressure signals generated by a flow-responsive switching valve connected between the two-position valve and the selective control valve. The switching valve and the two-position valve cooperate to block the pressure-controlled outlet of the one pressure-responsive valve and the rod ends and to bypass return fluid flow from the rod ends to sump when the cylinders are being extended.

Abstract: Disclosed is a fan drive, in particular one for cooling installations of rail vehicles. The fan drive comprises a hydraulic motor and a control valve which regulates a bypass as a function of temperature, thus affecting the flow of a pressure medium driving the motor. The control valve comprises a control piston subjected to a control pressure in the direction of closing the bypass, and a counterbalancing pressure in the opposite direction from the source of the pressure medium. The control valve also comprises a control spring which biases the control piston in the direction of closing the valve, and a pilot valve which affects the control pressure. The pilot valve is actuated by an electromechanical servo component. The pilot valve is located in an insert which is arranged within the control piston. A central bore of the control piston is slidingly guided on the convex surface of the insert so as to form a seal.

Abstract: This invention relates to a hydraulic elevator wherein working oil is transferred from a tank to a jack or vice versa by means of a hydraulic pump which is driven by an electric motor, so as to cause the elevator to ascend and descend; characterized in that a hydraulic circuit is equipped with electronically-controlled variable flow solenoid valves which set flow rates of the working oil in accordance with a program for electronic control in correspondence with respective stages of stop, slow speed ascent, full speed ascent, slow speed descent and full speed descent of the elevator.

Abstract: A leak-detecting hydraulic system is disclosed for operation of a fluid actuator associated with a front-end loader, a backhoe, or a like implement on a material handling device. Notably, the system includes a leak-detection circuit which normally acts to prevent movement of the implement associated with the actuator by gravity in the event of a failure in one of the hydraulic fluid lines operatively connected with the actuator. Additionally, the system preferably includes a selectively operable float valve which permits fluid flow which bypasses the leak-detection circuit, thus desirably permitting operation of the implement associated with the actuator in a "floating" mode.