Abstract: A pressure responsive flow divider valve for servo-powered steering devices comprises a flow control valve having three ports to divide the fluid flow delivered by a pump between a pair of partial volumes, one flowing to the steering valve and the other flowing to a further hydraulic load. When the steering device is not operated, the further load is primarily supplied with fluid, while the flow to the load is reduced, but the steering valve is fully supplied when the steering device is actuated. The valve comprises a valve member which is actuated in response to pressure to change the cross section of the throttle in the flow control valve so that the steering valve is supplied with a relatively small volume of fluid when the steering device is not operated, whereas the valve member is shifted by a pressure increase when the steering device is actuated to supply an increased fluid flow to the steering valve as required. The valve according to the invention allows to reduce energy to drive the pump.

Abstract: A servovalve includes a flow-control valve connectable between a source of fluid pressure and a load and having a spool displaceable between an open position permitting fluid flow between the load and the source and a closed position axially offset therefrom and blocking such flow. A pilot valve has an impact plate and a pair of nozzles operatively axially oppositely effective on the spool and oppositely flanking the plate. Thus when the plate is closer to one of the nozzles than to the other the spool is axially displaced into one of its positions and when the plate is closer to the other nozzle the spool is urged axially oppositely. A solenoid-type servomotor is connected to the impact plate to move same between the nozzles so that when it is close to one nozzle it blocks flow therefrom and allows pressure to build up on the corresponding end of the spool, while the other nozzle is opened to reduce pressure at the corresponding spool end.

Abstract: An apparatus for controlling the movement of a movable element as a working circuit (10) with a directional control valve (3) equipped to control devices (11, 12) which can be pressure activated in two directions. A control circuit (29) which can be connected to a fluid source (19) is used to activate the directional control valve for which the control circuit is connected to the two control devices and has an adjustable first choke (24) connected to one of the two control devices (12), a second choke (22) which is similarly adjustable and connectable to the same control device, and third and fourth adjustable chokes (27, 28) which are connectable to the other of the two control devices (11). The first and third chokes are connectable further to a storage tank (7) and the second and fourth chokes are further connectable to a pressure source. A proportioning pressure valve (45) can be connected to the other of the two control devices (11). The first and third chokes are connected to a pilot valve (38).

Abstract: A three chambered solenoid-actuated directional control valve in which a spool is reciprocally mounted for movement within a valve housing. The housing and spool define the three chambers with one adapted to be connected to a pump for supplying hydraulic fluid, the second adapted for connection to a first load and the third adapted to connection to a second load. A solenoid is reciprocally mounted for movement along the direction of the bore for actuating the spool with a rod fixedly mounted to the armature of the solenoid. At least one groove is formed between the outer surface of the armature and the inner bore of the valve housing for conducting flow of hydraulic fluid between a recess at the end of the solenoid adjacent the three chambers and the end remote therefrom. A throttle in the form of a single cross wall having either a groove or bore extending therethrough dampens movement of the armature to reduce pressure peaks during switching. Throttle grooves are also provided on the lands of the spool.

Abstract: A piston for a hydraulic piston machine in which a piston body receives a ball in a space defined at one end of thereof. A bearing dish supports the ball in the space with an O-ring engaging the recess to seal the bottom surface of the bearing dish. Preferably the bearing dish is formed with a steel support layer, a bronze layer cast onto the steel support layer, and a plastic layer supporting the ball.

Abstract: The invention refers to a pressure reducing valve including a pilot valve. The main piston of the pressure reducing valve allows to selectively connect a load port to either a port connected to a pressure source or to a port connected to the reservoir. The pilot valve is connected to a control pressure line and to the reservoir. The main piston controlled connection to the reservoir opens within the valve housing into a port connecting the pilot valve to the reservoir. This provides for a substantially simplified construction of the valve since there are only two operating ports and a reservoir port. Furthermore, the main piston is engaged by a spring which is capable of becoming activated such that dynamic stresses resulting from a change from high to low pressure values are avoided which vibrations are detrimental in generating pressure peaks as well as pressure breaks.

Abstract: A pressure-relief valve has a housing forming a chamber extending along an axis and a valve seat centered on the axis and subdividing the chamber into an outer high-pressure compartment and an inner low-pressure compartment. The seat defines generally the only fluid-communication path between the compartments. A pump and a load can be connected to the high-pressure compartment and a sump to the low-pressure compartment. A valve body is formed with a central radially outwardly open main groove, an outer face exposed in the high-pressure compartment, an inner face exposed in the low-pressure compartment, a radially outwardly open control groove offset axially inward from the main groove toward the inner face, and a diametrally throughgoing control bore at the main and control grooves.

Abstract: The electrode of an electric arc melting furnace is adjusted in height by a hydraulic cylinder having an operating chamber which is connected via a servo valve to a hydraulic pressure source or, respectively, to a reservoir. The servo valve is actuated by a control signal which is produced by a comparison of the actual value of the electric arc current and a predetermined desired current value. Additionally, the pressure in the operating chamber of the cylinder is measured and supplied to the control circuit as a feedback value. An important advantage deriving from the present invention is the ability to provide a control of the electrode motion by virtue of the measured pressure even before the electric arc is ignited and to steadily hydraulically support the electrode under any condition of operation. Accordingly, uncontrolled motions of the electrode are prevented which motions might result in an increased danger of breakage, in overcurrents or short-circuits.

Abstract: A hydrostatic machine, in particular of bent axis design comprises a clutch which is provided between the drive shaft and the pistons. The force necessary for clutch engagement is produced by hydraulic pressure forces which are either applied to the pistons or delivered by the pistons depending on whether the machine operates as a motor or as a pump. When the machine neither produces a moment nor receives a moment the clutch is automatically disengaged due to the reduction of the hydraulic pressure forces. According to the invention the clutch helps to prevent hydraulic losses of the machine while running idle and improves the overall efficiency.

Abstract: An apparatus for positioning an adjustable member as a function of a command signal and a control condition, especially for the positioning of a hoisting mechanism on a tractor or the like, comprises an operating circuit and a control circuit. The operating circuit has a bidirectional positionable valve with a valve side and first and second control devices for regulating flow of pressure medium from a supply tank to the adjustable member. The control circuit connects a control pressure medium source to the control devices at first and second junctions and includes adjustable throttles and a flow-regulating valve. A first adjustable throttle is connected between the supply tank and the first junction. The second adjustable throttle is connected between the control pressure medium source and the first junction and in series with the first adjustable throttle.

Abstract: The position control and force control of a device mounted to a tractor, in particular for controlling the depth penetration of a plough, is supplemented by a lowering speed-responsive control to limit the lowering speed to a predetermined maximum value in order to increase safety of operation. Activating and disabling the lowering speed signal takes place in response to operating a mode select switch provided for the position control and force control as well as in response to a high-speed actuation of the mounted device. Furthermore, the lifting and lowering function of the hydraulic jack of the mounted device may be locked to prevent undesired motions of the mounted device when the system is put in operation.

Abstract: In the spool member of a multi-way-valve leakage of pressure fluid from the inlet port to the operating ports and a corresponding pressure increase in a consumer are prevented by annular grooves and radial bores through which pressure fluid leaking from the inlet is discharged to the reservoir. The radial bores are provided in the spool member so that the land relief between the pressure inlet port and the operating port is achieved via the spool member, and the housing of the multi-way-valve may remain unchanged.

Abstract: A hydraulically unblockable non-return valve has a control piston (21), the control side of which can be connected with a control pressure medium source (35) and the other side of which can be connected with a supply container (33). In order to create a hydraulically unblockable non-return valve, in which the control side of the control piston does not need to be relieved of pressure, the other side of the control piston is perpetually connected with the supply container. Also provided is a throttle bore (27) which connects the two sides of the control piston with each other.

Abstract: A device for controlling a consumer, in particular a hydromotor includes a restrictor, preferably an electrohydraulic proportional directional control valve, and a control valve operating on the basis of a releasable non-return valve. The control valve is provided with an actuating cylinder-and-piston unit having control ports and a biasing spring for the piston. The control valve also has a connecting port which is connected with a connecting port of the restrictor. In order to substantially simplify the structural design of the device, a flow regulator is installed between the control port of the control valve and the connecting port of the restrictor which is connected with the consumer. The control sides of the flow regulator and the control valve are connected through a throttle with a supply container. The space of the cylinder-and-piston unit adjoining the control side of the control piston is connected with another connecting port of the control valve and with the restrictor.

Abstract: A hydrostatic machine having a fixed displacement volume which is connected to the operating chamber of a hydraulic cylinder which machine is mechanically coupled to a second hydrostatic machine having a variable displacement volume to control the force exerted by the hydraulic cylinder. When control liquid is displaced from the working chamber of the cylinder the first machine acting as a motor drives the second machine which displaces control liquid into an accumulator. Vice versa, liquid is taken from the accumulator and the second machine acting as a motor drives the first machine which feeds liquid into the working chamber. The pressure in the working chamber, or, respectively, the force exerted by the cylinder is maintained constant by a corresponding adjustment of the displacement volume of the second machine.

Abstract: The invention relates to pressure relief valves which spring bias is controlled by a proportional magnet. The force applied by the proportional magnet is increased by an additional hydraulic pressure force which acts on the spring. There is the advantage of decreasing the size of the proportional magnet and/or increasing the flow capacity of the valve.

Abstract: A pressure-reducing valve is secured to a proportional magnet by resiliently connecting the valve sleeve of the valve receiving the piston to the housing of the proportional magnet, thus avoiding possible deformations of the valve sleeve resulting from mounting. Furthermore, the operational safety of the valve is improved by abutments limiting the stroke of the valve piston and by a control edge which is additionally provided at the valve sleeve.

Abstract: A first front face of a main control spool of a main control valve is loaded with a constant pressure, whereas the opposite face is loaded with a controlled pressure to control the fluid passages to and from a hydraulic actuator. The control pressure is adjusted by means of a two-edge control of the pilot control spool of a pilot control valve which is actuated by a single proportional solenoid against the force of a spring. The advantages obtained thereby result in a substantial savings in manufacturing expenditure and a substantially improved control operation.

Abstract: The pressure response of a pressure control valve is adjusted by a solenoid valve of which the solenoid is connected to an electrical three point control device. A programmed signal and an actual signal derived from a transformer of the control pressure valve are fed to the input of the three point control device.

Abstract: A hydrostatic radial piston pump has a housing with a suction chamber, an eccentric, a pressure valve member spaced from the eccentric and having a convex support, and a movable structural unit arranged between the eccentric and the pressure valve member and including a cylinder with a supporting face and a sealing edge spring-biased against the support of the pressure valve member, and a piston with a piston shoe spring-biased against the eccentric, wherein the supporting face has a circumferential groove subdividing it into an outer and inner annular face portion, the outer annular face portion has at least one substantially radial groove communicating the annular groove with the suction chamber, and the ratio of the force of a biasing spring and the dimension of the supporting face does not exceed substantially 2.5 kp/cm.sup.2.