US3628567A - Power control valve - Google Patents

Power control valve Download PDF

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Publication number
US3628567A
US3628567A US46109A US3628567DA US3628567A US 3628567 A US3628567 A US 3628567A US 46109 A US46109 A US 46109A US 3628567D A US3628567D A US 3628567DA US 3628567 A US3628567 A US 3628567A
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United States
Prior art keywords
valve
piston
cylinder
pressure
neutral position
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US46109A
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English (en)
Inventor
Alfred Bender
Horst A Hornig
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
TDK Micronas GmbH
ITT Inc
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Deutsche ITT Industries GmbH
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Publication of US3628567A publication Critical patent/US3628567A/en
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Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/0401—Valve members; Fluid interconnections therefor
    • F15B13/0402—Valve members; Fluid interconnections therefor for linearly sliding valves, e.g. spool valves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/8593—Systems
    • Y10T137/86493—Multi-way valve unit
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/8593—Systems
    • Y10T137/87169—Supply and exhaust
    • Y10T137/87177—With bypass
    • Y10T137/87185—Controlled by supply or exhaust valve
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/8593—Systems
    • Y10T137/87169—Supply and exhaust
    • Y10T137/87233—Biased exhaust valve
    • Y10T137/87241—Biased closed

Definitions

  • ABSTRACT A two-stage hydraulic valve system for controlling a double-acting load the system having a three-position first stage valve for supplying pressure-medium to pressure chambers on either end of a piston valve slide in a power control valve having twin lift valves for connecting the pressure source to the double-acting load.
  • the lift valves which are in the ends of the piston valve cylinder connect the load to the pressure chambers when the valves are opened, either by the movement of the piston valve slide against the lift valve, or by the increased pressure in the pressure chamber when the valve slide is at one end of its stroke and the pump pressure is applied to the'pressure chamber at the other end of the valve slide.
  • in the neutral position of the power valve there is free circulation of pressure medium from the source to the reservoir through a pressurizing valve.
  • One such system comprises a servocontrolled circulation valve which controls the circulation of pressure medium from a pump to a reservoir in the rest or neutral position of the system, two consumer valves which respond alternately according to a mutual servocontrol and a two-way twin check valve, the actuating member of which is applied by the pressure controlled by the consumer valves.
  • the double acting consumer is applied by the pressure medium flow, the latter being released in one direction or the other by the twin check valve.
  • the servocontrol of both the circulation valve and the consumer valves can be electric, mechanic, or hydraulie.
  • the pressure resulting from a pressure medium circulation which is interrupted by a directly controlled slide valve acts upon the actuating member of the twin check valve.
  • the slide itself is kept in a floating position inside the valve chamber during rest position. Since the pressure medium flows through the chamber of the slide valve, the actuation of said valve will require a cor respondingly great external force and consequently a larger electromagnet'if the actuation is made electrically, the electromagnet requiring not only much more space but also a relatively long time to be energized, the result being a greater response time of the total system.
  • the slide valve could be servocontrolled and the pressure medium circulating through the slide valve prestressed by a pressurizing valve.
  • the slide of the main valve is then controlled by actuation of the servocontrol valve, said slide interrupting the pressure medium circulation and deviating the pressure medium for the actuation of the twin check valve. This, however, would not sufficiently improve the total response time.
  • a two-stage hydraulic valve system for controlling a doubleacting load having a three-position first stage valve for supplying pressure medium to pressure chambers on either end of a piston valve slide in a power control valve having twin lift valves for connecting the pressure source to the doubleacting load.
  • the lift valves which are in the end of the piston valve cylinder, connect the load to the pressure chambers when the valves are opened, either by the movement of the piston valve slide against the lift valve, or by the increased pressure in the pressure chamber when the valve slide is at one end of its stroke and the pump pressure is applied to the pressure chamber at the other end of the valve slide.
  • In the neutral position of the power valve there is free circulation of pressure medium from the source to the reservoir through a pressurizing valve. This circulation is cut off when the valve is actuated and the full pump pressure applied to one of the pressure chambers by means of valving passages and ports in the cylinder and slide.
  • this invention provides a piston-type valve slidably arranged in the valve housing and controlling the connections between valve pressure chambers on either side of the piston and the pressure medium source, the high-pressure outlet and the return line; said valve piston or slide opening in its two end positions, the valve bodies of two oppositely disposed lift valves in the housing, said lift valves being arranged in the connection lines of the valve pressure chambers to the consumer connections.
  • the valve piston acting in both directions and providing actuating members for the seat valve bodies of the twin lift valve.
  • a pressurizing valve is arranged in one of the passageways.
  • Axial bores in the valve piston are provided for the flow to and from the consumer or load, which bores are connected to the reservoir via circular grooves in the piston and in the housing upon actuation of the valve slide.
  • the pressurizing valve is preferably arranged in the longitudinal bore connecting the radial bores of the valve slide.
  • the effective surfaces of the valve slide are provided with pins for the actuation of the seat valves of the twin lift valves, the seat valves closing the consumer or load connections.
  • the first stage pilot valve and the second stage power valve have three positions. Preferably both first stage valve and the valve slide piston of the twin lift valve are centered by helical springs and pressure-balanced in the neutral or zero position.
  • the first stage pilot valve provides five circular grooves of which the three grooves in the center are interconnected in the neutral position of the valve, the center groove being connected to the circular grooves of the second stage which are connected to the reservoir, whereas the other two circular grooves of the first stage servo-pilot valve are connected to the actuating pressure chambers located between the valve piston and the seat valves of the second stage valve.
  • one of the two outer circular grooves is connected to the adjacent circular groove which is connected to one of the pressure chambers of the second stage power and separated from the other grooves whereas the second outer circular groove is separated from the adjacent groove, which again is connected to the center groove.
  • First stage pilot valve is actuated either manually, hydropneumatically, mechanically, or electrically.
  • valves can be connected in series in such a way that the circulation lines of the various valves are hydraulically connected in series with only the last valve which is directly connected with the reservoir, having a pressurizing valve.
  • FIG. ll shows a valve system embodying the present inven tion.
  • FIG. 2 shows a cross section through Section A-A of the power valve shown in FIG. 1.
  • FIG. 3 shows an arrangement of three power valves of type shown in FIG. 1 connected in series.
  • FIG. 4 is a schematic representation of the valve system shown at FIG. 1.
  • FIGS. 1, 2 and 4 there is shown a two-stage pilot valve system comprising a three-position first stage pilot valve 70, a second stage power valve 72, and a load or consumer in the form of a double-acting power piston 74!.
  • a pump 15 supplies hydraulic liquid to power the system while the outlets from the valve system are connected to a reservoir 76.
  • the second stage power valve 72 has a valve slide or piston 3 arranged in the housing 78 and provides a diametrical bore 2 which is aligned with a circular groove or port 1 in the housing wall in the neutral or relaxed position shown. Groove 1 provides a direct connection to the pump of the system.
  • a diametrical bore 6 is preferably arranged in parallel to the bore 2, the bore 6 being aligned with the circular groove 7 in the housing, the groove 7 being connected to the reservoir 76.
  • There are two additional circular grooves 45, 48 in the housing which are connected to the reservoir, these grooves being closed by the valve piston or slide 3 in the neutral position.
  • the circular groove 48 will cover a circular groove 47 of the valve slide 3 whereby the circular groove 48 is connected to the pressure chamber 44 via the longitudinal bores 50 opening into the groove 47, the chamber 44 being located on the left surface of the valve slide as seen in FIG. 1.
  • the circular groove 45 of the housing will cover a circular groove 46 of the valve slide and is connected to the pressure chamber 43 located on the right surface of the slide 3 via the bores 49.
  • the diametrical bores 2 and 6 are interconnected via a blind bore 4, which is formed on the right face of the valve slide 3. and closed with a blind plug 5.
  • a seat valve body 9 is arranged in the connecting bore 4 between the bores 2 and 6, said seat valve body being held in the closed position shown by a spring 8 which rests against the surface of the blind plug 5.
  • the pressure medium flows to the reservoir from the pump via the circular groove 1, the radial bores 2, the longitudinal bore 4, a passage in the valve body 9, the radial bores 6 and the circular groove 7.
  • the seat valve body 9 prestressed by the spring 8, establishes the operating pressure for the system which can be used for control purposes.
  • valve slide 3 In order to ensure that the valve slide 3 assumes the neutral position shown in which diametrical bores 2 and 6 are aligned with grooves l and 7 respectively, the valve slide 3 is positioned with respect to the housing abutments 21 and 22 on both sides by means of the springs 17 and 18 and by the sleeve-type catches or spring retainers 19 and 20.
  • the centering springs 17 and 18 bear upon the respective catch 19, 20 on the one hand and on a guide bushing 52, 68 on the other hand, said bushing limiting the chamber 43 or 44 respectively in the housing and resting by its step against threaded end plugs 54, 66, the latter holding the guide bushing against the abutment 69, 70 of the housing.
  • the end plugs 54, 66 provide a cylindrical recess into which projects the stepped end of the respective guide bushing 52, 68.
  • a lift or seat valve body 56 or 62 respectively is disposed in a longitudinal bore in the guide bushings 52, 68, each of the mentioned valve bodies being held in the initial closed position against the valve seat 60 or 64 by a spring 57 or 63 respectively, which rests against the bottom of the cylindrical recess of the respective end plugs 54, 66, thereby keeping closed the passages 58 and 65 leading to the power piston 74.
  • axially extending pins 55, 73 are attached to both surfaces of the valve slide 3, said pins opening the respective seat valve when the valve slide is displaced.
  • the stroke of the seat valve body 56, 62 is limited by the end plugs 54, 66.
  • the first stage pilot valve 70 is a three-position slide valve to be actuated in either direction by two electromagnets 32, 33, or any other external force.
  • the valve is held in the center or neutral position shown by means of the springs 28, 29 which press the abutment discs 30 and 31 against the abutments 26 and 27.
  • the housing of the first stage valve is provided with five circular grooves, the end two of which 34 and 35 are connected via the lines 36 to the circular groove 1 of the second stage power valve, thereby providing a direct connection to the pressure medium source.
  • the groove 39 adjacent the circular groove 34 is connected via the line 41 to the chamber 43 at the right surface of the valve slide 3 whereas the groove 40 adjacent the circular groove 35 communicates with the chamber 44 via line 42.
  • the center circular groove 37 is connected with the reservoir via lines 38 and circular grooves 45 and 48 in the second stage valve.
  • the hydraulic communication of the circular grooves 34, 35, 37, 39, 40 is controlled in such a way that power is transmitted to the power valve.
  • the circular grooves 37, 39, 40 are interconnected and communicate with the pressure medium return whereas the circular grooves 34, 35 are connected to the pressure medium source. OPERATION Both the first stage pilot valve and the second stage pilot valve are pressure balanced in the neutral position.
  • Movement of the power valve slide 3 is effected hydraulically via the first stage valve control slide 25 which is brought into position I in which the valve slide 25 is moved to the right by energizing of the electromagnet 32 and into position ll in which the valve slide is moved to the left by energizing of the electromagnet 33.
  • the groove 34 and 39. as well as the grooves 37 and 40 are interconnected whereby the pump pressure or the prestressed pressure respectively, which is generated by the seat valve 9 during circulation, is conveyed through the connections 36 and 41, respectively, to the power valve pressure chamber 43 whereas the main power valve pressure chamber 44 communicates with the pressure medium return via the connections 38 and 42.
  • valve piston or slide 3 of the second stage power valve 72 is moved against the centering spring 17 by the force pressure created by the pump and valve 9 multiplied by the crosssectional area of the valve slide 3. Due to the surface or ratio of the surfaces on the valve slide 3 and the check valve body 62, the force acting upon the valve slide 3 will always prevail and move the valve slide 3, whereas the seat valve is kept closed by spring pressure and the pressure from the load or consumer. As the valve moves to the left, the circulation bores 2 and 6 withdraw with their pressure relief grooves from the area of the housing grooves 1 and 7 causing the pressure medium circulation to be interrupted and the pressurizing valve 9 to close.
  • the control piston groove 47 registers with the housing groove 48 which is also connected to the pressure medium return and then the control piston groove 46 registers with the housing groove 1 at the pressure medium source.
  • the pressurizing valve 9 After the pressurizing valve 9 has closed, the full pump pressure will reach the chamber 43 via the actuated servocontrol valve. Since the housing groove 1 positively overlaps the control piston groove 46, the same will happen via the eccentrically disposed axial bores 49.
  • the flow returns from the chamber 44 via the bores 50, which are symmetrically arranged towards the bores 49, the control piston groove 47 and the housing groove 48.
  • the pin 55 on the left side of the valve slide 3 presses against the front surface of the seat piston 56.
  • the seat piston 56 which is guided in the guide bushing 52 is kept in closed position by the compressing spring 57 which rests against the end plug 54, and by the force resulting from the consumer or load pressure the latter reaching the seat edge 60 or the reverse side of the seat piston 56 respectively via the bores 58 multiplied by the cross sectional area as limited by the circumference of the seat edge 60.
  • the resulting seat force must be exceeded by the force moving the valve slide 3.
  • the valve slide 3 opens the seat valve piston 56.
  • the pressure medium which had so far collected in the consumer behind the seat piston 56 flows via the bores 58, the seat bore above the seat edge 60, the chamber 44, the bores 50 and the groove 47 in the valve slide 3 and the housing groove 48, into the pressure medium return.
  • a pressure difference will align between the seat valves 56 and 62 since the other chamber of the consumer is connected to the hydraulic line behind the seat valve 62. If this pressure difference has dropped below the pressure in the chamber 43 and if the pressure in the chamber 43 is in a position to overcome the additional counteracting force of the spring 63, the seat valve 62 will lift off the seat edge 64. The hydraulic fluid which had so far flown from the pump into the chamber 43 now flows through the bore which is limited by the circumference of the seat edge M, the bores 65, and on the the load, the seat valve being further opened against the force of the spring 63 by the forces resulting from the flow of the pressure medium.
  • the force acting on the valve slide is always greater than that on the seat valve 62 so that the seat valve 62 cannot open unless the valve slide 3 first opens the seat valve 56.
  • the centering spring 23 which has been compressed, returns the first stage valve slide 25 to the neutral or zero position.
  • the chamber 43 is again connected to the return flow via the connection ll which results in a pressure drop in the mentioned chamber.
  • the spring 63 causes the seat valve 62 to close the consumer chamber on the seat sealing edge 64, said chamber being exposed to pressure.
  • the pressure in the consumer chamber supports the force of the spring 63 in the sense of a check valve. Since both chambers 43 and 44 are now connected to the return flow, the valve slide 3 is pressure balanced.
  • the centering spring which was compressed causes the valve slide 3 to return to the neutral or zero position as described before.
  • the seat valves 56 and 62 return to their initial positions, too.
  • FIG. 3 shows an arrangement for connecting three power valves l0, l1 and 12 in series.
  • the pressure inlet ll of the valve communicates with the pressure medium source 15.
  • the high-pressure outlet 13 of each of the valves connected in se ries communicates with the high-pressure inlet of the subsequent valve.
  • the high-pressure outlet of the last valve is connected to the return line and hence to the reservoir 16.
  • the pressurizing valve 9 is installed in the last valve 112 only whereby a prestressed pressure is forced upon the pressure medium flow by all valves together. A separate control has to be provided for each valve.
  • valve-slide 3 of one of the valves l0, ll, 12 is moved axially as described above, the circulation of the medium conveyed by the pump 15 is inter-' rupted and the consumers of the respective valves will be actuated.
  • a special advantage of the power valve is that there is a free pressure medium circulation in zero position which means that a valve, viz. the circulation valve and the servocontrol thereof, conforming to valve arrangements known in the art, can be omitted.
  • a valve viz. the circulation valve and the servocontrol thereof, conforming to valve arrangements known in the art, can be omitted.
  • a servo valve comprising; a housing having a closed cylinder therein with axially spaced supply and discharge ports in the cylinder wall, a double-acting piston in the cylinder forming a pair of pressure chambers one between each end of the piston and an end of the cylinder, a pair of normally closed lift valves one in each end of the cylinder, each valve connect ing one of the pressure chambers to a load passage, means on each end of the piston for opening one of the valves as the piston approaches the end of the cylinder, a pair of passages in the piston, each passage leading from one pressure chamber to an opening in the piston wall, the passage openings being axially spaced from each other, means for holding the piston in a neutral position intermediate the ends of the cylinder in which the passage openings in the piston are each positioned between a discharge port means which is nearer to the pressure chamber to which the passage is connected and a supply port means which is further from the pressure chamber, each passage opening being spaced the same distance from its supply port means and the same distance from its discharge
  • valve of claim ll wherein the mean on each end of the piston for opening the lift valve is an axially extending stud adapted to lift the valve before the piston abuts against the cylinder end wall.
  • valve of claim 2 including recirculating means comprising a passage in the piston connecting the supply port means to the discharge port means in the neutral position of the valve and a spring-loaded check valve in said passage.
  • valve of claim 3 wherein the means for holding the piston in the neutral position comprise compression springs in each pressure chamber acting between the end of the cylinder and the piston to bias the piston toward the neutral position and abutments in the cylinder for limiting the spring force on the piston in the neutral position.
  • a valve system comprising a plurality of valves as defined in claim 1 connected in series with the discharge port means of the preceding valve connected to the supply port means of the next valve.
  • valve of claim ll including recirculating means comprising a passage in the piston connecting the supply port means to the discharge port means in the neutral position of the valve and a spring-loaded check valve in said passage.
  • the valve of claim 1 wherein the mean for holding the piston in the neutral position comprise compression springs in each pressure chamber acting between the end of the cylinder and the piston to bias the piston toward the neutral position and abutments in the cylinder for limiting the spring force on the piston in the neutral position.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Multiple-Way Valves (AREA)
  • Fluid-Driven Valves (AREA)
  • Fluid-Pressure Circuits (AREA)
  • Compositions Of Oxide Ceramics (AREA)
US46109A 1969-06-14 1970-06-15 Power control valve Expired - Lifetime US3628567A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19691930387 DE1930387B2 (de) 1969-06-14 1969-06-14 Vorgesteuertes wegeventil, insbesondere fuer einen doppelwirkenden verbraucher

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US3628567A true US3628567A (en) 1971-12-21

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Application Number Title Priority Date Filing Date
US46109A Expired - Lifetime US3628567A (en) 1969-06-14 1970-06-15 Power control valve

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US (1) US3628567A (de)
DE (1) DE1930387B2 (de)
FR (1) FR2052597A5 (de)
GB (1) GB1249963A (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4072169A (en) * 1975-07-29 1978-02-07 Robert Bosch Gmbh Hydraulic control system
USRE29538E (en) * 1971-09-30 1978-02-14 Load responsive fluid control valve
US6079956A (en) * 1998-03-26 2000-06-27 Trench Plate Rental Co., Inc. Multi-stage hydraulic pump
US6158973A (en) * 1998-03-26 2000-12-12 Trench Plate Rental Co., Inc. Multi-stage manual hydraulic pump
US20050120873A1 (en) * 2003-12-09 2005-06-09 Government Of The Usa, As Represented By The Administrator Of The U.S. Epa Method and device for switching hydraulic fluid supplies, such as for a hydraulic pump/motor

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3709913C1 (en) * 1987-03-26 1988-05-05 Daimler Benz Ag Working piston with a stroke-dependent valve device for cutting off the working pressure of an actuator, in particular of a steering system of a vehicle
DE3709914C1 (en) * 1987-03-26 1988-05-11 Daimler Benz Ag Working piston of a double-acting pressure-medium actuator, in particular of a steering system of a vehicle, with two stroke-dependent cut-off valves

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3006372A (en) * 1959-04-22 1961-10-31 New York Air Brake Co Control valve with cavitation-minimizing replenishing circuit
US3145734A (en) * 1961-10-06 1964-08-25 Borg Warner Pressure compensated flow control valve
US3272085A (en) * 1963-11-19 1966-09-13 Parker Hannifin Corp Fluid system and valve assembly therefor
US3274902A (en) * 1965-10-22 1966-09-27 Deere & Co Hydraulic control system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3006372A (en) * 1959-04-22 1961-10-31 New York Air Brake Co Control valve with cavitation-minimizing replenishing circuit
US3145734A (en) * 1961-10-06 1964-08-25 Borg Warner Pressure compensated flow control valve
US3272085A (en) * 1963-11-19 1966-09-13 Parker Hannifin Corp Fluid system and valve assembly therefor
US3274902A (en) * 1965-10-22 1966-09-27 Deere & Co Hydraulic control system

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE29538E (en) * 1971-09-30 1978-02-14 Load responsive fluid control valve
US4072169A (en) * 1975-07-29 1978-02-07 Robert Bosch Gmbh Hydraulic control system
US6079956A (en) * 1998-03-26 2000-06-27 Trench Plate Rental Co., Inc. Multi-stage hydraulic pump
US6158973A (en) * 1998-03-26 2000-12-12 Trench Plate Rental Co., Inc. Multi-stage manual hydraulic pump
US20050120873A1 (en) * 2003-12-09 2005-06-09 Government Of The Usa, As Represented By The Administrator Of The U.S. Epa Method and device for switching hydraulic fluid supplies, such as for a hydraulic pump/motor
WO2005061905A1 (en) * 2003-12-09 2005-07-07 Government Of The United States Of America, As Represented By The Administrator Of The U.S. Environmental Protection Agency Method and device for switching hydraulic fluid supplies, such as for a hydraulic pump/motor
US6996982B2 (en) 2003-12-09 2006-02-14 The United States Of America As Represented By The Administrator Of The Environmental Protection Agency Method and device for switching hydraulic fluid supplies, such as for a hydraulic pump/motor

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Publication number Publication date
DE1930387B2 (de) 1973-03-22
GB1249963A (en) 1971-10-13
FR2052597A5 (de) 1971-04-09
DE1930387A1 (de) 1970-12-17
DE1930387C3 (de) 1973-10-11

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