US3127688A - Hydraulic circuit for control of earthmoving scraper bowls - Google Patents

Hydraulic circuit for control of earthmoving scraper bowls Download PDF

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Publication number
US3127688A
US3127688A US247056A US24705662A US3127688A US 3127688 A US3127688 A US 3127688A US 247056 A US247056 A US 247056A US 24705662 A US24705662 A US 24705662A US 3127688 A US3127688 A US 3127688A
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United States
Prior art keywords
valve
bowl
jack
fluid
circuit
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Expired - Lifetime
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US247056A
Inventor
Allyn J Hein
James E Scheidt
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Caterpillar Inc
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Caterpillar Tractor Co
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Publication date
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Priority to US247056A priority Critical patent/US3127688A/en
Priority claimed from FR954991A external-priority patent/FR1387905A/en
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Publication of US3127688A publication Critical patent/US3127688A/en
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Expired - Lifetime legal-status Critical Current

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    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02FDREDGING; SOIL-SHIFTING
    • E02F3/00Dredgers; Soil-shifting machines
    • E02F3/04Dredgers; Soil-shifting machines mechanically-driven
    • E02F3/64Buckets cars, i.e. having scraper bowls
    • E02F3/65Component parts, e.g. drives, control devices
    • E02F3/652Means to adjust the height of the scraper bowls, e.g. suspension means, tilt control, earth damping control
    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02FDREDGING; SOIL-SHIFTING
    • E02F3/00Dredgers; Soil-shifting machines
    • E02F3/04Dredgers; Soil-shifting machines mechanically-driven
    • E02F3/64Buckets cars, i.e. having scraper bowls
    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02FDREDGING; SOIL-SHIFTING
    • E02F3/00Dredgers; Soil-shifting machines
    • E02F3/04Dredgers; Soil-shifting machines mechanically-driven
    • E02F3/64Buckets cars, i.e. having scraper bowls
    • E02F3/6454Towed (i.e. pulled or pushed) scrapers
    • E02F3/6481Towed (i.e. pulled or pushed) scrapers with scraper bowls with an ejector having translational movement for dumping the soil
    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02FDREDGING; SOIL-SHIFTING
    • E02F3/00Dredgers; Soil-shifting machines
    • E02F3/04Dredgers; Soil-shifting machines mechanically-driven
    • E02F3/64Buckets cars, i.e. having scraper bowls
    • E02F3/65Component parts, e.g. drives, control devices
    • E02F3/651Hydraulic or pneumatic drives; Electric or electro-mechanical control devices
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00Details of servomotor systems ; Valves for servomotor systems
    • F15B13/01Locking-valves or other detent i.e. load-holding devices

Description

A ril 7, 1964 A. J. HElN ETAL HYDRAULIC CIRCUIT FOR CONTROL OF EARTHMOVING SCRAPER BOWLS 3 Sheets-Sheet 1 Filed Dec. 26, 1962 INVENTORS. ALLYN J. HEW JAMEs ESCHEHJT AT ORNEYS April 7, 1964 A. J. HElN ETAL HYDRAULIC CIRCUIT FOR CONTROL OF EARTI-IMOVING SCRAPER BOWLS 3 Sheets-Sheet 2 Filed Dec. 26, 1962 INVENTORS. ALLYN J. HE! N BY JAM ES E. SCH E. DT
A ORN-EYS A ril 7, 1964 A. J. HEIN ETAL 3,127,633
HYDRAULIC CIRCUIT FOR CONTROL OF EARTHMOVING SCRAPER BOWLS Filed Dec. 26, 1962 3 Sheets-Sheet 5 INVENTORS. ALLYN J. Ham BYJAMES EScHEwT 9 w 1 ATTORNEYS United States Patent M 3,127,688 HYDRAULIC CHRUUHT FOR CONTROL OF EARTHMUVENG RAPER BUWLS Allyn J. Hein and lames E. Ssheidt, Juliet, Ill., assignors to Caterpillar Tractor (10., Peoria, lll., a corporation of California Filed Dec. 26, 1962, Ser. No. 247,056 3 Claims. (ill. 3'7129) This invention relates to tractor drawn earthmoving scrapers wherein various elements and particularly the bowl of the scraper is adjusted by means of double acting hydraulic jacks and pertains specifically to means for preventing accidental quick lowering of the bowl.
' The hydraulic circuit of the present invention is an improvement on the circuit disclosed in the Allyn J. Hein et al. Patent No. 3,868,596 for Hydraulic Circuit for Actuation of an Earthmoving Scraper Bowl. The said Hein et al. patent discloses two valves in a bowl jack circuit including a load supporting check valve which prevents escape of fluid from the jack when it is supporting a load elevated with respect to the earth. This prevents the weight of the load from imposing high fluid pressures in the conduits and hoses which connect the jack supported on the scraper with the control valve supported on the tractor.
A second or quick drop valve is assocated w-tih each of the bowl lift jacks normally closing communication between the head end of the jack and the rod end of the jack but adapted to be opened to-permit such communication in order to effect quick lowering or dropping of the bowl from a raised position. This quick drop valve is held in its closed position by fluid pressure vented through a line communicating between the scraper and the control valve on the tractor. The line is, therefore, subject to breakage in operation and failure of the line would vent pressure holding the quick drop valve closed creating a hazardous condition because dropping of the bowl from a carry position while the tractor and scraper are traveling at high speed could cause a sudden stop that would throw the operator from his seat.
It is the object of the present invention to overcome the aforementioned disadvantages and hazard and to provide a circut for actuating a scraper bowl or the like including a quick drop valve adapted to be opened upon intentional venting of its closing pressure but incapable of being opened by accidental venting of such pressure as will occur upon leakage or failure of the vent line.
Further and more specific objects and advantages of the invention are set forth in the following specification wherein the invention is described in detail by reference to the accompanying drawings.
In the drawings:
FIG. 1 is a schematic view of the hydraulic circuit for a tractor-scraper combination which includes bowl, ejector and apron actuating jacks;
FIG. 2 is a schematic sectional view of one of the bowl lift jacks shown in FIG. 1 including the valve mecha nism associated therewith for accomplishing the objects of the present invention; and
FIG. 3 is a side elevation of a tractor-scraper combination illustrating the location of the several components of the hydraulic circuit which control the operation of adjustable elements of the scraper.
In FIG. 3, a conventional two-wheel scraper is illus- 3,1127,688 Patented Apr. 7, 1964 trated at 10 as drawn by a tractor 11 through a hitch or draft connection generally indicated at 12. The main body or bowl of the scraper may be raised and lowered about its pivotal connection with its wheels 13. Draft arms 14 pivoted to opposite sides of the scraper bowl as by connections, one of which is shown at 15, enable raising and lowering of the scraper bowl by means of a pair of jacks, one of which is shown at 16. A pivoted apron 17 is adapted to be raised and lowered for opening and closing the forward end of the bowl by means of a jack 18, lever 18b and link 18c and an ejector 19 is moved forwardly to discharge the contents of the bowl through its forward end by an ejector jack 2%), all in it well known manner. A control valve assembly 22 for controlling the flow of fluid to and from the several jacks is disposed on the tractor as are also control levers, one shown at 23 positioned adjacent the operators station.
The hydraulic circuits disclosed in FIG. 1 of the drawings are, generally speaking, the same as those disclosed in the above mentioned Hein et al. patent and will be briefly described herein to facilitate an understanding of the present invention.
The control valve assembly, generally indicated at 22 in FIG. 1, comprises a single housing suitably bored for the reception of three sliding type valve spools 16a, 18a and Zita for controlling jacks l6, l8 and 2% which actuate respectively the scraper bowl, apron and ejector. Each of the spools is formed at one end for connection to control levers, not shown, and is fitted at its opposite end with a centering spring assembly shown at 26, 21; and 36. The function of such assembly is well known and only that pertaining to the bowl lift control is shown in detail and will be hereinafter described.
A pump 35 delivers fluid under pressure from a reservoir 36 to an inlet passage 37 in the valve housing which is divided to direct fluid selectively toward either end of the valve spool 16a depending upon its position of adjustment. Similar inlet passages 38 and 39 communicate with each other and with the first pasage 37 so that with the valve spools in their neutral positions, as shown, there is a constant flow of fluid under pressure from the pump through the passageways 37, 38 and 39 and a discharge passage 40 and thence back to the reservoir through a return line 41. A relief valve 42 in the pressure line from the pump also has its'discharge side connected with the return line 41.
Each of the jacks or sets of jacks has what may be termed a high pressure and a lower pressure end because the work of moving an implement part in one direction as when it is being raised or moving earth is usually greater than that of moving it in the other direction. Movement of any one of the spools to the right connects it with the high pressure end of its associated jack. For example, the spool 16a upon movement toward the right opens communication with the inlet chamber 37 containing fluid under pressure from the pump and directs the fluid into a line 46 and through lines 46a to the rod ends of the jacks 16 for raising the bowl. Similarly movement of spools 18a to the right connects the inlet passage 38 thereof with a line 48 connecting with the head end of the jack 1-8 through a valve mechanism 64 and movement of spool 219a to the right directs fluid under pressure from inlet 3? through a line 50 to the head end of the ejector jack 20. The
construction of the valve mechanism 64 is not necessary to an understanding of the present invention.
The opposite or low pressure ends of the jaoks are all connected with a common manifold 52 which communicates with each of the three bores containing the valve spools and is opened by rightward movement of any spool into communication with a discharge manifold 53, also common to all three spools and communicating with the reservoir through the line 41. Consequently when fluid is directed under pressure to the high pressure side of any of the jacks, fluid on the low pressure side is returned to the reservoir. The common manifold 52 is connected with the jacks through a common line 54 with a branch 55 to the low pressure or head ends of the bowl jacks 1 6, a branch 56 to the rod end of the ejector jack 2t} and a branch 57 to the rod end of the apron jack through the valve mechanism 64'.
Movement of the jacks in the direction opposite to that described above is accomplished by movement of any one of the valve spools in the opposite direction or to the left which communicates high pressure through the actuated spool to the manifold 52 and thence to all of the jacks through line 54 and its branches 55, 56 and 57. The valve spool which has been actuated to the left also opens communication to a discharge passage 68 which is common to all or the spools and similar to the discharge passage 53. The discharge passage 60 permits return of fluid from the jack which has been actuated through the passage 46 and line 51 to the reservoir. Under the condition just described where a single valve spool is actuated and directs fluid to all three jacks, only the selected jack is moved because return flow from the other jacks is blocked by their respective spools which have remained in their neutral position.
Pressure in the conduits communicating between the bowl jacks 16 on the scraper and the control valve on the tractor is relieved while the bowl is held in a raised position so that the lines are protected against excessive pressure resulting from the dynamic action of the weight of the bowl and its contents when being transported over rough terrain. This is accomplished by a check valve 65, see FIG. 2, in a housing 66 associated one with each of the jacks 16. This check valve is urged toward its closed position by a spring 67 and is opened by pressure from the pump entering the rod end of the jack through the line 46 during raising of the bowl. With the check valve open, the fluid under pressure passes through the line 46a to the rod end of the jack. When the bowl is held in a raised position, the check valve is closed by the spring 67, the force of which is augmented by fluid pressure within the spring chamber entering through orifices 68 in the valve element.
Pressure in the spring chamber of the check valve 65 is reduced when it is desired to lower the bowl and this is accomplished through a line 72 communicating between the spring chamber and a passage 73 (see FIG. 1) which upon movement of the spool 16a. to the left for lowering the bowl, will communicate with a groove 74 in the spool 16a and through this groove with a second passage 75 in the valve housing, and a bleed line 76 communicating between the passage 75 and the reservoir. With fluid pressure thus reduced in the spring chamber 67, pressure in line 4611, due to weight of the bowl, becomes effective to open the check valve 65 and permit return of fluid from the rod end of jack 16 through the line 46 as previously described. This is accomplished by a pilot piston 78 with an end 79 engageable with the check valve when it is in its closed position. Pressure from the rod end of the jack is communicated through a passage 88 to the interior of the pilot piston 78 moving it to the right as viewed in FIG. 2 and opening the check valve against the closing force of spring 67.
To provide for dropping or lowering of the bowl at a rate in excess of that resulting from normal operation of the control valve for moving the bowl toward its lowered position, a quick drop valve 86 is contained in the housing 66. This valve closes communication between the head end and rod end of the jack by way of a line 55a, passage 88 and line 46a. When the valve 86 is opened, as by movement toward the right as viewed in FIG. 2, flow from the rod end to the head end of the jack permits rapid downward movement of the piston due to the weight of the bowl and its contents and without evacuating the head end of the jack. The check or quick drop valve is urged toward its closed position by a spring 8 9 acting against a pilot piston 96 slidable in the valve bore and abutting the valve as shown. The pressure of the spring 89 is augmented by fluid pressure communicated from the line 46 through a passage 91 in the valve housing and communicating with the spring chamber. The pilot piston prevents opening of the quick drop valve when the pressure in passage 88 is less than the pressure in line 46 and the spring chamber. When it is desired to permit the valve 86 to open under pressure of fluid in the line 46a, the pressure in the spring chamber is vented through a line 95. This line, as shown in FIG. 1, communicates with a passage 96 in the control valve housing adjacent the bleed passage 73 previously described and can be opened by movement of the spool 16a toward the left beyond its bowl lowering position. This further movement of the spool 16a. toward the left provides communication between the passage 96 and the passage 75 so that pressure in the chamber of spring 89 (FIG. 2) is relieved through the line 76 to the reservoir. Pressure for opening the valve 86 is admitted to its face through orifices 92 in a cup-shaped stop member and fluid flows through orifices 93 in the valve body. Meanwhile the spool 1611 having been moved to its bowl lowering position, the chamber of its spring 67 has been vented through the line 72 and pressure in pilot piston 78 has opened the check valve.
A spring 98 in the centering spring assembly 26 is used in addition to the conventional centering spring which is shown at 99. When the centering spring 99 is com pressed by movement of the spool to its bowl lowering position, a flange 1% on the spring seat engages an amin lus 101 which serves as a seat for the heavier spring 98 providing a stop which can be sensed by the operator. Further leftward movement of the spool is accomplished only by greater operator eflort sufficient to compress the spring 98.
It is to be understood that the check valves associated with the jacks 16 as well as the bleed lines associated with them are identicalfor both of the bowl jacks. In order to insure balanced pressure in the rod ends of the two jacks, the valve housings 66 are interconnected by a small line 105 which, as shown in FIG. 2, forms communication between the lines 46a which communicate with the rod ends of the jacks.
Due to the construction described above wherein the load supporting check valve is disposed intermediate the jack 16 and the quick drop valve, the load supporting valve serves in its normally closed condition to prevent flow of fluid from the rod end to the head end of the cylinder. Consequently leakage or breaking of the line which permits opening of the quick drop valve will not result in accidental dropping of the bowl.
We claim:
1. In combination with a tractor drawn earthmoving scraper having a bowl, a hydraulic circuit, means supplying fluid under pressure to said circuit, a double acting hydraulic jack in said circuit for raising and lowering the bowl, and means in said circuit including a control valve on the tractor for directing fluid to said jack, a fluid pas sage between the head and rod ends of the jack a quick drop valve in said passage preventing flow between the head end and rod end of said jack, means normally communicating fluid under pressure to said quick drop valve 3. The combination of claim 2 in which the control to hold it closed, means to vent said fluid to permit openvalve etfects opening of the quick drop valve and the load ing of the valve, and a load supporting check valve dissupporting check valve upon movement beyond a normal posed in the circuit between the cylinder and the quick bowl lowering position. drop valve to prevent accidental bowl drop upon leakage 5 of said venting means. References Cited in the file of this patent 2. The combination Of claim 1 in which the venting UNITED STATES PATENTS means 1s assoclated with the control valve on the tractor, 2,897,613 Davidson Aug. 4, 1959 and means to effect opening of the load supporting check valve upon actuation of the venting means. 10

Claims (1)

1. IN COMBINATION WITH A TRACTOR DRAWN EARTHMOVING SCRAPER HAVING A BOWL, A HYDRAULIC CIRCUIT, MEANS SUPPLYING FLUID UNDER PRESSURE TO SAID CIRCUIT, A DOUBLE ACTING HYDRAULIC JACK IN SAID CIRCUIT FOR RAISING AND LOWERING THE BOWL, AND MEANS IN SAID CIRCUIT INCLUDING A CONTROL VALVE ON THE TRACTOR FOR DIRECTING FLUID TO SAID JACK, A FLUID PASSAGE BETWEEN THE HEAD AND ROD ENDS OF THE JACK A QUICK DROP VALVE IN SAID PASSAGE PREVENTING FLOW BETWEEN THE HEAD END AND ROD END OF SAID JACK, MEANS NORMALLY COMMUNICATING FLUID UNDER PRESSURE TO SAID QUICK DROP VALVE TO HOLD IT CLOSED, MEANS TO VENT SAID FLUID TO PERMIT OPENING OF THE VALVE, AND A LOAD SUPPORTING CHECK VALVE DISPOSED IN THE CIRCUIT BETWEEN THE CYLINDER AND THE QUICK DROP VALVE TO PREVENT ACCIDENTAL BOWL DROP UPON LEAKAGE OF SAID VENTING MEANS.
US247056A 1962-12-26 1962-12-26 Hydraulic circuit for control of earthmoving scraper bowls Expired - Lifetime US3127688A (en)

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US247056A US3127688A (en) 1962-12-26 1962-12-26 Hydraulic circuit for control of earthmoving scraper bowls

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Application Number Priority Date Filing Date Title
US247056A US3127688A (en) 1962-12-26 1962-12-26 Hydraulic circuit for control of earthmoving scraper bowls
GB4339563A GB987078A (en) 1962-12-26 1963-11-04
FR954991A FR1387905A (en) 1962-12-26 1963-11-26 Hydraulic circuit for controlling a scraper bucket
DE19631484636 DE1484636A1 (en) 1962-12-26 1963-12-17 Device for preventing an unintentional rapid downward movement of the bucket of a bucket loader

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Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3360875A (en) * 1965-07-27 1968-01-02 Gen Motors Corp Two speed hoist for earth-moving vehicle
US3438308A (en) * 1966-09-12 1969-04-15 Cascade Corp Hoist ram control apparatus
US3469861A (en) * 1967-11-22 1969-09-30 Caterpillar Tractor Co Hydraulic control circuit for push-pull coupling of tandem machines
US3653132A (en) * 1969-08-28 1972-04-04 Caterpillar Tractor Co Automatic positioning systems for scraper elevators
US3728941A (en) * 1970-11-23 1973-04-24 Caterpillar Tractor Co Flow control valve
US3788401A (en) * 1972-07-17 1974-01-29 Caterpillar Tractor Co Hydraulic circuit with valve to provide semi-float control of a dozer blade
US3800670A (en) * 1969-10-21 1974-04-02 Caterpillar Tractor Co High pressure implement hydraulic circuit
US3906840A (en) * 1972-04-17 1975-09-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3943825A (en) * 1972-04-17 1976-03-16 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US3947981A (en) * 1974-12-09 1976-04-06 International Harvester Company Scraper bowl with hydraulic safety lock
US4000683A (en) * 1975-05-27 1977-01-04 Caterpillar Tractor Co. Hydraulic load lifting system
US4006667A (en) * 1972-04-17 1977-02-08 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US4088151A (en) * 1976-05-26 1978-05-09 Borg-Warner Corporation Cylinder locking apparatus
US4130049A (en) * 1977-04-07 1978-12-19 Caterpillar Tractor Co. Vent control for cylinder mounted load check valves
US4165675A (en) * 1977-04-07 1979-08-28 Caterpillar Tractor Co. Load check valve cylinder mounted
US4167892A (en) * 1977-04-07 1979-09-18 Caterpillar Tractor Co. Load check with mechanical venting means
US4278011A (en) * 1977-06-06 1981-07-14 J. I. Case Company Automatic hydraulic shut-off system
US4337689A (en) * 1979-06-22 1982-07-06 Sulzer Brothers Limited Safety system for a double acting servomotor
US20110132473A1 (en) * 2009-12-04 2011-06-09 Walvoil Fluid Power Corp. Hydraulic control valve assembly with monolithic body and single spool port lock

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7984576B2 (en) 2006-09-04 2011-07-26 Miller Uk Limited Coupler
GB2476915B (en) * 2007-06-13 2011-09-14 Miller Uk Ltd Coupler

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2897613A (en) * 1956-04-25 1959-08-04 Int Harvester Co Hydraulic carrying-lock for earth-working scrapers

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2897613A (en) * 1956-04-25 1959-08-04 Int Harvester Co Hydraulic carrying-lock for earth-working scrapers

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3360875A (en) * 1965-07-27 1968-01-02 Gen Motors Corp Two speed hoist for earth-moving vehicle
US3438308A (en) * 1966-09-12 1969-04-15 Cascade Corp Hoist ram control apparatus
US3469861A (en) * 1967-11-22 1969-09-30 Caterpillar Tractor Co Hydraulic control circuit for push-pull coupling of tandem machines
US3653132A (en) * 1969-08-28 1972-04-04 Caterpillar Tractor Co Automatic positioning systems for scraper elevators
US3800670A (en) * 1969-10-21 1974-04-02 Caterpillar Tractor Co High pressure implement hydraulic circuit
US3728941A (en) * 1970-11-23 1973-04-24 Caterpillar Tractor Co Flow control valve
US4006667A (en) * 1972-04-17 1977-02-08 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US3906840A (en) * 1972-04-17 1975-09-23 Caterpillar Tractor Co Hydraulic control system for load supporting hydraulic motors
US3943825A (en) * 1972-04-17 1976-03-16 Caterpillar Tractor Co. Hydraulic control system for load supporting hydraulic motors
US3788401A (en) * 1972-07-17 1974-01-29 Caterpillar Tractor Co Hydraulic circuit with valve to provide semi-float control of a dozer blade
US3947981A (en) * 1974-12-09 1976-04-06 International Harvester Company Scraper bowl with hydraulic safety lock
US4000683A (en) * 1975-05-27 1977-01-04 Caterpillar Tractor Co. Hydraulic load lifting system
US4088151A (en) * 1976-05-26 1978-05-09 Borg-Warner Corporation Cylinder locking apparatus
US4130049A (en) * 1977-04-07 1978-12-19 Caterpillar Tractor Co. Vent control for cylinder mounted load check valves
US4165675A (en) * 1977-04-07 1979-08-28 Caterpillar Tractor Co. Load check valve cylinder mounted
US4167892A (en) * 1977-04-07 1979-09-18 Caterpillar Tractor Co. Load check with mechanical venting means
US4278011A (en) * 1977-06-06 1981-07-14 J. I. Case Company Automatic hydraulic shut-off system
US4337689A (en) * 1979-06-22 1982-07-06 Sulzer Brothers Limited Safety system for a double acting servomotor
US20110132473A1 (en) * 2009-12-04 2011-06-09 Walvoil Fluid Power Corp. Hydraulic control valve assembly with monolithic body and single spool port lock
US8316757B2 (en) * 2009-12-04 2012-11-27 Walvoil Fluid Power Corp. Hydraulic control valve assembly with monolithic body and single spool port lock

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GB987078A (en) 1965-03-24
DE1484636A1 (en) 1969-10-23

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