US2617389A - Hydraulic press control system - Google Patents

Hydraulic press control system Download PDF

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US2617389A
US2617389A US120041A US12004149A US2617389A US 2617389 A US2617389 A US 2617389A US 120041 A US120041 A US 120041A US 12004149 A US12004149 A US 12004149A US 2617389 A US2617389 A US 2617389A
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valve
pressure
conduit
lever
press
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US120041A
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Jr Frederick E Munschauer
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Niagara Machine and Tool Works
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Niagara Machine and Tool Works
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B30PRESSES
    • B30BPRESSES IN GENERAL
    • B30B15/00Details of, or accessories for, presses; Auxiliary measures in connection with pressing
    • B30B15/16Control arrangements for fluid-driven presses
    • B30B15/22Control arrangements for fluid-driven presses controlling the degree of pressure applied by the ram during the pressing stroke

Description

NOV 11, 1952 F. E. MUNSCHAUR, JR 2,617,389
HYDRAULIC PRESS CONTRL SYSTEM Filed Oct. 7, 1949 l r 3 Sheets-Sheet l NOV 11, 1952 F. E. MuNscl-IAUER, JR' 2,617,389 l HYDRAULIC PRESS CONTROL SYSTEM Filed Oct. 7, 1949 3 Sheets-Sheet 2 N0v 11, 1952 F. E. MUNSCHAUER, JR 2,617,389
HYDRAULIC PRESS CONTROL SYSTEM Filed Oct. 7, 1949 3 Sheets-Sheet 3 W /i Il l o @w h nvenor M f /'7*ede/'/c/f E Manx/maagd.
@Z j /06 l @Mnl Maga,
Patented Nov. 11, 1952 UNITED STATES ATENT GFFICE.
Frederick E. Munschauer, Jr., Buialo, N. Y., as-
signor to Niagara Machine and Tool Works,
Buialo, N. Y.
Application October 7, 1949, Serial No. 120,041
1 Claim.
This invention relates to a hydraulic press or analogous machine and more particularly to novel arrangements for activating and controlling the operation of machines of this class.
In presses constructed according to the present invention, control means are provided whereby the eiective pressure applied to the work by the hydraulic ram of the press is under ready and accurate control of the operator, so that, during the actual pressing operation, he may selectively apply any pressure between predetermined minimum and maximum limits.
Further, the control means is so arranged that the hydraulic activating means supplies fluid at relatively low pressure but in substantial volume when a working stroke of the press is initiated. In this initial phase of a working stroke the operator controls the rate or volume of liquid supplied to the hydraulic cylinder and thus readily and directly controls the speed at which the ram approaches the work. When a predetermined degree of resistance is encountered, as when the ram or a punch or 'the like held thereby meets the work or a die or other tool on the bed oi the press, the high volume fluid supply means is automatically neutralized and pressure against the work at the aforesaid predetermined relatively low pressure continues until the operator further adjusts the control means to increase the applied pressure to any desired degree within the capacity of the apparatus.
In a preferred form of the apparatus of the present invention a single manually movable control device is provided which the' operator moves to eiect three distinct phases of press operation, namely, the approach of the ram to the work, the actual application of working pressure, and the return of the ram to its idle position, generally in a raised position above the bed of the press.
In the form of apparatus shown herein by way of example two iluid pressure generating pumps are utilized, both driven from a single power source. One of these pumps displaces liquid in relatively large volume at moderate pressure and the other is designed to develop high unit pressures, its volumetric capacity being relatively low.
In this way the driving motor of the press is utilized to the limit of its effectiveness in the various phases of press operation to the end that a driving motor of relatively low power output provides abundant energy for efficient operation. The sequence in which the two pumps become eiective is entirely automatic, the operator of the press concerning himself solely with the function- .ing of the press ram in approaching the work, in
applying working pressure t'o the work, and in returning the ram to idle position.
Numerous advantages inherent in apparatus arranged according to the principles of the present invention will occur to those skilled in the art to which it pertains from a study of the following specification and the accompanying drawings. However, it is to be understood that the embodiment thus described and illustrated in detail is by way of example only and that numerous mechanical and hydraulic variations may be made without departing from the underlying principles of the invention, the spirit and scope of which is limited only as dened in the appended claims.
In the drawings:
Fig. 1 is a general side elevational View of one form of press having operating and control means according to the principles of the present invention and with portions thereof broken away for added illustration;
Fig. 2 is a detail view of the manual control lever for the machine of Fig. l, viewed from the front;
Fig. 3 is a schematic layout of the hydraulic circuits and units which power and control the operation of the movable ram of the press;
Fig. 4 is an enlarged and more detailed view, partly in cross-section of a four-way valve and remote pressure relief valve which ultimately control the operation of the press ram, these units being shown in their operative hydraulic circuit connected relation in Fig. 3;
Fig. 5 is a detailed cross-sectional view of a sequence valve which performs the main pressure regulating function in the higher pressure range;
Fig. 6 is a detailed cross-sectional view of an unloading valve for neutralizing the large-volume, low-pressure pump in the higher pressure range; and
Fig. 7 is a detailed cross-sectional View of a foot valve which prevents the ram from settling when it is at rest in its upper idle position.
Throughout the several gures of the drawing like characters of reference denote like parts, and reference will first be had to the general side elevation view, Fig. l, which shows a press frame lil having a work or die receiving bed ll, and a a vertically reciprocable ram l2. A rock shaft I3 extends fore and aft of the press frame and has a manually operable lever I4 at its front end and an oppositely directed rock arm l5 at its rear end. A lever or rocker arm I6 is pivoted to the press frame as shown in the upper righthand portion of Fig. l, and a vertical link Il' connects one arm of lever i6 with the outer end of rock arm I5. A generally vertically disposed link I8 extends downwardly from the other end of lever I6, and the manner in which Vertical movement of link I8 effects control of the movements and effective pressures of ram I2 will presently appear.
Reference will now be had to the schematic layout, Fig. 3, which shows the various hydraulic circuits and control devices which cooperate to provide the novel control arrangement for hydraulic presses which forms the subject of the present application.
Referring to Fig. 3, the numeral designates a hydraulic press cylinder, and a piston element 2| therein has a depending piston rod 22 which connects with the usual hydraulic press ram, such as is indicated at I2 in Fig. l.
A common operating motor 24 has opposed drive shafts 25 and 26 which are flexibly connected to a pair of hydraulic pumps 21 and 28. Pump 21 is of large volumetric capacity, developing relatively low pressures, while pump 28 has a relatively small volumetric capacity and develops very high pressures. In one practical application of the principles of the present invention, merely by way of example, pump 28 has a maximum output pressure of 2,000 pounds per square inch.
It is common in hydraulic press construction to mount the several control valves and the pump or pumps in a tank which contains the hydraulic medium supply, so that all of these devices, excepting the electrical motor, are continuously submerged. This same procedure is contemplated in the case of the present invention, but for convenience of understanding the various control devices are shown in Fig. 3 as having tank, reservoir or drain connections. In the case of pumps 21 and 28 their intake ports are shown to have theoretical tank connections at 3| and 32, respectively.
The various control units will now be enumerated generally and their construction and cooperation with each other will then be described in greater detail. Referring to Fig. 3, the numeral 34 designates an unloading valve for large pump 21, and the numeral 35 designates a check valve which permits free fluid flow away from the output side of pump 21 but prevents retrograde ilow. The numeral 36 designates a conventional, manually-operated four-way valve for controlling fluid flow to cylinder 20 above and below piston 2|.
The numeral 31 designates a pressure regulating valve which is disposed generally in the output line from the small high pressure pump 28, and operation of the regulating valve is controlled in the rst instance by a remote, manually-operated relief valve 38.
Fluid pressure flow from pump 21 to four-way valve 36 is by means of a conduit 40 from pump 21 to unloading valve 34, a conduit 4| from the latter to check valve 35 and a conduit 42 from the check valve to an intake port 43 of four-way valve 36, the latter being shown in detail in Fig. 4.
Output pressure from small pump 28 goes to pressure regulating valve 36 by way of a conduit 45, and thence, by way of a conduit 46, to a connection with conduit 42, whereby they jointly lead to the supply port 43 of four-way valve 36.
In Fig. 3 the numeral 48 designates a foot valve, which is merely a special check valve which keeps the ram of the press from settling due to the leakage past four-way valve 36 when the latter is in neutral position. Four-way valve 35 has one of its output passages 50 connected to the top of cylinder 20 by means of a conduit 5|, and the other output passage 52 of four-way valve 36 connects to the foot valve 48 by means of a conduit 53 and thence to the bottom of cylinder 2U by means of a conduit 54.
When four-way valve 36 is in the position illustrated in Fig. 4 valve heads 55 and 56 block both outlet ports and 52 and the valve is in neutral position. A conduit 58 drains back to the tank or reservoir and connects with a pair of discharge ports 68 and 6|. If valve heads 55 and 56 are jointly lowered, supply passage 42 is connected with the top of cylinder 20 by means of port 50 and conduit 5| and the bottom of cylinder 20 is permitted to drain by way of the port 52 of fourway valve 56 and drain passage 6I leading to the tank connection 58. Obviously, if valve heads and 56 are jointly raised from their illustrated neutral position the pressure and drain connections tc cylinder 20 are reversed.
Referring at this point to foot valve 48, it will be noted that this valve contains two parallel passages designated and 66. Passage 65 is provided with a check valve 61 which is biased by means of an adjustable compression coil spring 68. Accordingly, lluid flow from the bottom of the cylinder through conduits 54 and 53 can only be achieved by unseating check valve 66 which requires an adjustable degree of pressure sufficient to prevent the ram from settling of its own weight, but not so great as to prevent unseating of check valve 66 when positive pressure is applied to the top of piston 2 I.
When valve heads 55 and 56 are moved upwardly from their illustrated position in Fig. 4, the bottom portion of cylinder 20 is connected with the pressure supply conduit 42, and the top of cylinder 20 is connected with drain conduit 53. In this phase of operation, again referring to foot valve 48, a check valve 10, which prevents flow through passage 66 from conduit 54 to 53, permits free passage of fluid through passage 66 from conduit 53 to conduit 54. It will thus be noted that foot valve 48 provides substantially no resistance to iluid flow into the bottom of cylinder 20 but imposes a controlled degree of resistance to fluid flow therefrom.
Reference will now be had to the pressure regulating valve 31 and remote relief valve 38, which are shown in greater detail in Figs. 5 and 4, respectively. Remote relief valve 38 has a chamber 13 which connects a iluid inlet port 14 and a passage 15 which leads freely to the fluid tank or reservoir. Inlet port 14 is normally closed from chamber 13 by a valve 16 which is urged to closed position by operation of a compression coil spring 11, whose initial pressure, as illustrated in full lines in Fig. 4, is sufficient to cause the valve to remain closed until pressure in inlet port 14 reaches approximately 200 pounds per square inch, by Way of example. The bottom end of spring 11 seats against a disc 18, which is fixed to an axially slidable bar 19. Manual pressure may be exerted temporarily against bar 19 to further compress spring 11 and thus temporarily increase in a selectively variable manner the unit pressure required in port 14 to unseat valve 16 and thus relieve pressure in inlet port 14 through chamber 13 and drain passage 15.
Referring to pressure regulating valve 31, the main fluid passage therethrough is designated 88 and connects at opposite ends with conduits 45 a1nd 4S, which lead from the output side of Smau `5 pump 28 to the pressure supply passage 42. Regulating valve 31 further has a relief or drain pas.- sage 8|, which is normally closed by an axially movable valve 82.
The body of regulating valve 31 has a bore 84 extending transversely from the main fluid passage 80 and valve 82 has a cylindrical enlargement 85 which is axially slidable in bore 84. A very light compression coil spring 86 acts against cylindrical enlargement 85 to bias Valve 82 slightly to a downward closed position as illustrated in Fig. 4.
A passage 81 leads from the upper end of bore 84 and connects with inlet port 14 of remote relief valve 38 as by means of a conduit 88. A passage 90 leads from passage 81 to a chamber 9| which houses a pressure relief valve 92 and a compression coil spring S3 which acts against valve 92. The bias of spring 93 may be varied by means of an adjusting screw 94, the pressure of spring 93 on valve 92 being proportional to and determining the maximum pressure which may be transmitted to cylinder 20 by operation of the small capacity, high pressure pump 28 when the ram of the press is meeting sufficient resistance to develop maximum pressure. A conduit 96 leading from chamber 93 provides a drain passage for liquid which passes valve 92 when the latter is unseated to relieve pressure. A relatively small bore 98 extends through cylindrical enlargement 85 of valve 82.
The construction of unloading valve 34 will now be described, reference being had particularly to Fig. 6. This valve is provided with a bore in which a valve velement |0| is axially slidable, valve lill having a pair of valve heads |02 and |03. Liquid from the output conduit 40 of large pump 21 is delivered t0 bore |00 between the valve heads |02 and |03 and normally passes from bore |80 by way of conduit 4I which leads to check valve 35. The lower end of valve |0| comprises a relatively small diameter piston |84 which is axially movable in a chamber |05 which connects freely with the main fluid passage 80 of regulating valve 31 as by means of conduit |08, see Figs. 3, 5, and 6.
The fluid pressure in chamber |05, which is normally the same as that obtaining in passage 80 of regulating valve 31, is counteracted, up to predetermined limits, by a compression coil spring IIO which acts against the opposite end of valve I 0I and Whose pressure is adjustable by means of an adjusting screw I Four-way valve 36 and the remote relief valve 38 are both operated by means of a single control arm I I5 in a manner which is best illustrated in Fig. 4. The left-hand end of arm I|5 is pvotally connected to the lower end of link I8 which has previously been described. The manner in which link I8 is moved up and down by manipulation of the remotely located hand lever I4 and the lever and linkage connection therebetween has also been described previously herein.
Referring to Fig. 4, a lever H5 is pivoted to a fixed part of the machine as at I I1 and has pivotal connection with the outer end of rod 19 of remote relief valve 38, as at I|8. An extension spring |20 connects at one end with lever I|6, and its opposite end is connected to a fixed part of the machine as at I2 I. The outer end of lever l I E is pivotally connected to control arm I I5, and the latter has an intermediate pivotal connection |24 with the outer end of valve rod |25 which carries the valve heads 55 and 56 of four-way valve 36.
lIn the full-line position illustrated in Fig. 4, rod 19 vof remoterelief valve 38 is fully withdrawn and is: held in such position by extension spring |20, andvalve rod |25 of four-way valve 36 is in the neutral position illustrated. If lever II5 be moved upwardly to the position indicated at A in Fig. 4, the rod |25 of four-way valve 36 will be moved to connect the lower end of cylinder 20 with pressure supply passage 42, and piston 2| will move upwardly. Since the resistance to this movement is relatively low, the movement will be accomplished rapidly,y mainly by fluid from large capacity pump 21, the pressures generated being not high enough to cause unloading of pump'21 by operation of unloading valve 34.
If lever II5 be moved downwardly to the position illustrated at B in Fig. 4, a reverse operation takes place until the` ram of the press encounters material resistance, as by meeting the work in the press. At this point the pressure in conduits 40.. 4|, and 42 rises through continued operation of both pumps 21 and 28 until the presvsure in chamber |05 of the unloading valve is suilicient to move the valve heads |02 and |83 upwardly to a point where the latter blocks further communication between conduits 40 and 4|, and valve |02 also moves upwardly to uncover a passage |28 of unloading valve 34, which is a drain passage. 'Ihe position of valve heads |02 and |03 in Fig. 6 is an intermediate position. The setting of spring ||0 may be assumed to be such as to unload pump 21 by operation of valve 34 when the pressure in conduit 42 reaches 175 pounds per square inch. This pressure is assumed herev merely for illustrative reasons and for comparison with pressures developed in the remote relief valve 38.
Assuming that lever II5 is not moved downwardly beyond the position indicated at B in Fig. 4, the rod or stem 19 of remote relief valve 38 will not be operated, and that valve will be in the condition illustrated in Fig, 4. At this point, valve rod |25 of four-way valve 36 is fully withdrawn, but the force of extension spring |20 is still operating to maintain rod 19 in its withdrawn position.
Immediately upon unloading of large pump 21 and because of the continued resistance to movement of piston 2| in cylinder 20, pressure in co-nduit 42 will tend to continue to rise by continued operation of high pressure low capacity pump 28. .Such a tendency to increase pressure in passage causes enlargement 85 to move upwardly, since spring 86 is merely a light biasing spring and orice 98 through enlargement 85 is too small to permit rapid equalization of pressure above and below enlargement 85. This opens valve 82 in an amount and for a time suicient to regulate the pressure in passage 80.
Asl the increased pressure tendency in passage 88 continues, fluid through orifice 88 gradually increases the pressure above enlargement 85 and this, through the equalizing action of enlargement 85 and valve 82 produces a corresponding increase in pressure in passage 80. This continues until the pressure in conduit 88, and consequently in the intake port 14 of remote relief valve 38, reaches the initial pressure setting of spring 11 against valve 16, whereupon the latter unseats and liquid drains through chamber 13 and passage 15. This unbalances the pressure at the top and bottom of enlargement 85 and unseats valve 82 to establish pressure in passage 80 equal to that established in conduit 88 by operation of spring 11 and valve 16. Valve 15 thus serves as a pressure limiting valve for conduit 88 and the space above enlargement 85, and the pressure in main passage 80 of the regulating valve 31 is thus fixed at a. maximum determined by the initial tension setting of spring 11, for instance 200 pounds per square inch, as long as lever I I does not move downwardly beyond the position indicated at B in Fig. 4.
In movements of lever II5 from the neutral position to the positions indicated at A and B in Fig. 4, the speed of movement of piston 2| is proportionate to the degree of displacement of lever I I5 from the neutral position since such degree of displacement is reilected in the degree to which ports 58 and 52 of the four-way valve 36 are exposed. This provides a very natural and convenient control of ram movement on the part of the operator during downward approaching movement of the ram and also during upward return movement.
As lever I I5 is moved beyond the position indicated at B in Fig. 4, toward the limit position indicated at C, rod I of the four-way valve 36 has been fully withdrawn, and thus further movement of lever I I5 moves lever II6 upwardly against the resistance of spring |20, pivot |24 now serving as a xed fulcrum for lever I|5, and rod or stem 18 of remote relief valve 38 is moved upwardly as viewed in Fig. 4. This causes collar 18 to apply greater pressure to spring 11 and thereby to valve 16.
This increased pressure is proportionate to the degree of displacement of lever I I5 from position B toward position C in Fig. 4, and permits the pressure in conduit 81 and above enlargement 85 to increase by fluid fiow upwardly through orice S8. It will be remembered that the pressure potential of small pump 28 is such that it constantly tends to increase the pressure in passage'I) up to the maximum output pressure of the pump. In this manner the pressure in passage 80 is manually controlled by movement of lever |I5 be tween positions B and C, and pressure thus applied to the top of cylinder 20 is limited only by the full capacity of pump 28 or the relieving operation of valve 92, which occurs only at a maximum press-capacity setting, for instance 2,000 pounds per square inch.
Here again the control of the degree of pressure by the operator in the range from position B'to position C is extremely natural and simple for the operator and he may guide his movements of lever I4 by reference to a pressure gauge which may be located conveniently and which is indicated schematically at |30 in Fig. 3. Safety is promoted by the fact that working pressures can only be developed in the range from B to C and if the operator releases the manual lever I4 the control arm I I5 will automatically be moved back to the lower pressure position B by operation of spring- |20.
A further safety arrangement for insuring neutralization of the controls when the press ram reaches predetermined upper and lower limit positions will now be described, and in that connection reference is had to Fig. l. Rock shaft I 3 has xed thereto an arm I3| which extends to the left from rock shaft I3, as viewed from the front of the press, and pivotally engages at its outer end a vertically extending rod |32. The upper end of rod |32 extends slidably through a guide |33, which may be a xed part of the press frame. Rod |32 has adjustably fixed thereto an upper stop collar and a lower stop collar |35. A bracket |38 is fixed to ram I2 and has a rearwardly extending arm portion I 39 which extends through a slot I 40 in the press frame and alongside of rod |32.
If the operator should keep the control lever I4 in a raising position for too long a time, the bracket |38 will move upwardly with ram I2 until it strikes collar |24, whereupon it will raise rod |32, move rock shaft I3 in a clockwise direction as viewed from the front of the press, and move the control linkage to neutral position. Conversely, if the operator tends to permit the ram to move downwardly beyond its safe limit of operation, bracket |38 strikes collar I 35, lowering rod |32, thus again moving the control linkage to neutral position.
What is claimed is:
In a hydraulic press or similar machine comprising a cylinder and a ram piston reciprocable therein, a source of hydraulic pressure and conduit means for communicating said pressure to the cylinder to act against said ram piston, reversing valve means having a neutral position for blocking said conduit means and two operative limit positions for selectively applying the pressure from said source to either end of the cylinder, a relief valve acting upon the conduit means and normally establishing a predetermined minimum pressure therein, said relief valve having movable means for variably increasing said predetermined minimum pressure setting, a manual control lever having a yieldably movable fulcrum, means connecting said reversing valve means with said control lever whereby movement of the lever in opposite directions on said yieldable fulcrum moves the reversing valve means to either of its limit positions, and means engageable between said yieldable fulcrum and said relief valve movable means whereby movement of said lever beyond the point where the reversing valve connecting means has reached its limit position in one direction moves said yieldable fulcrum to act upon said relief valve movable means to communicate to said cylinder selectively variable pressures in excess of said predetermined minimum.
FREDERICK E. MUNSCHAUER, Jn.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,982,711 Vickers Dec. 4, 1934 2,192,839 Orcutt Mar. 5, 1940 2,218,818 Harrington Oct. 22, 1940 2,243,364 Trautman May 27, 1941 2,318,851 Griith May 11, 1943 2,365,282 Lester et al Dec. 19, 1944 2,527,943 Lee Oct. 31, 1950
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2745500A (en) * 1952-02-28 1956-05-15 Gen Motors Corp Propeller control for controlling blade pitch in governed speed, feathering, and negative pitch regimes
US2782802A (en) * 1951-05-12 1957-02-26 Monarch Machine Tool Co Hydraulic control system
US2789541A (en) * 1953-01-26 1957-04-23 Projectile & Engineering Compa Hydraulic actuating system for injection molding machine
US2789542A (en) * 1953-09-23 1957-04-23 New York Air Brake Co Hydraulic motor control system
US2848874A (en) * 1953-12-14 1958-08-26 Electraulic Presses Ltd Control valves for hydraulic presses
US2993505A (en) * 1953-06-06 1961-07-25 Electraulic Presses Ltd Relief valve

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1982711A (en) * 1931-10-19 1934-12-04 Harry F Vickers Combined rapid traverse and slow traverse hydraulic system
US2192839A (en) * 1937-02-25 1940-03-05 Gear Grinding Co Ltd Valve mechanism for controlling fluid operated machine tools
US2218818A (en) * 1937-12-04 1940-10-22 Vickers Inc Hydraulic die spotting press
US2243364A (en) * 1939-10-19 1941-05-27 Bendix Aviat Corp Liquid pressure remote control system
US2318851A (en) * 1938-01-26 1943-05-11 Vickers Inc Power transmission for machine tools
US2365282A (en) * 1940-06-15 1944-12-19 Lester Engineering Co Pressure casting machine injection pressure control
US2527943A (en) * 1944-04-10 1950-10-31 Jeffrey Mfg Co Hydraulic valve and system

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1982711A (en) * 1931-10-19 1934-12-04 Harry F Vickers Combined rapid traverse and slow traverse hydraulic system
US2192839A (en) * 1937-02-25 1940-03-05 Gear Grinding Co Ltd Valve mechanism for controlling fluid operated machine tools
US2218818A (en) * 1937-12-04 1940-10-22 Vickers Inc Hydraulic die spotting press
US2318851A (en) * 1938-01-26 1943-05-11 Vickers Inc Power transmission for machine tools
US2243364A (en) * 1939-10-19 1941-05-27 Bendix Aviat Corp Liquid pressure remote control system
US2365282A (en) * 1940-06-15 1944-12-19 Lester Engineering Co Pressure casting machine injection pressure control
US2527943A (en) * 1944-04-10 1950-10-31 Jeffrey Mfg Co Hydraulic valve and system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2782802A (en) * 1951-05-12 1957-02-26 Monarch Machine Tool Co Hydraulic control system
US2745500A (en) * 1952-02-28 1956-05-15 Gen Motors Corp Propeller control for controlling blade pitch in governed speed, feathering, and negative pitch regimes
US2789541A (en) * 1953-01-26 1957-04-23 Projectile & Engineering Compa Hydraulic actuating system for injection molding machine
US2993505A (en) * 1953-06-06 1961-07-25 Electraulic Presses Ltd Relief valve
US2789542A (en) * 1953-09-23 1957-04-23 New York Air Brake Co Hydraulic motor control system
US2848874A (en) * 1953-12-14 1958-08-26 Electraulic Presses Ltd Control valves for hydraulic presses

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