US2328258A - Apparatus for controlling the slide movement in long-bed hydraulic presses - Google Patents

Description

E. C NON Aug. 31, 1943. 2,328,258

- APPARATUS FOR CONTROLLING THE SLIDE MOVEMENT IN LONG-BED HYDRAULIC PRESSES.

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. E'cA APPARATUS FOR CONTROLLING THE SLIDE MOVEMENT IN LONG-BED HYDRAULIC PRESSES 7 Filed Sept. 26,- 1942 3 Sheets-Sheet 3 ATTORNEY UNITED STATES PATENT OFFICE APPARATUS FOR CONTROLLING THE SLIDE MQVSEDIIIENT IN LONG-BED HYDRAULIC P E S S Earl-Cannon, Rockville Centre, N. Y., asslgnor to E. W. Bliss Company, New York, N. Y., a corporation of Delaware Application September 26, 1942, Serial No. 459,854

' 9 Claims. (Cl. 100 -71) Thisinvention relates to a method and apparatus for controlling the slide movement in longbed hydraulic presses.

Experience has shown that, for many purposes, hydraulic presses are preferable over mechanical presses. This preference arises, among other considerations, from the readiness with which a hydraulic press may be adjusted to vary either the length of its advance stroke or the pressure which said stroke may cause to be imposed upon the material or blank being pressed (hereinafter referred to as a blank").

It is often desirable, however, to provide a press in which the press bed and slide are relatively long as compared to their respective widths. Such parts, for example, may be two or more times as long as they ar wide. In mechanical presses having such long slides, the opposite ends of the latter are commonly connected to and operated by similar crank arrangements.v In some such presses one crank is employed at each end of the slide and in others a pair of cranks is employed at each end thereof. In any event, the mentioned crank arrangements are usually so designed that the press slide is constrained, by its actuating means, to remain substantially parallel with the bed of the press during its advance stroke, even though the shape of the die or dies or the natureof the material being processed is'such that the pressing reaction is centered at a point substantially to one side or the other of the center of the slide. While possessing the advantages just mentioned, with respect to parallelism of the slide and bed, such long-bed-mechanical presses, neveretheless, lack the facility for ready adjustment of the advance'stroke which, as hereto,- fore remarked, may easily be providd in hydraulic presses.

Difficulties have been experienced, however, in providing a long-bed hydraulic press adapted for handling relatively high pressures an having commercially practicable means for maintaining substantial parallelism between the press slide and bed; If, for example, a. single hydraulic ram is employed at the center of a long press slide, any inequality in the resistance opposing the advance of the slide, toward opposite ends thereof, induces or strongly tends to induce, tilting or cocking of the slide during the working portion of its advance stroke. The mentioned inequality may arise, among other conditions, from differences in the vertical dimensions of the die toward opposite ends of the slide or from variations in the thickness of the blank. Eflorts have been made to obviate this difliculty, in longbed hydraulic presses, by providing two r more rams along the length of the slide and by providing separate pumping systems, theoretically identical, for charging liquid into the several advance stroke chambers operating said rams. It has been found practically impossible, however, to attain uniform functioning of such separate pumping systems during the advance stroke of a press, largely because of different slippages encountered in pumps in such systems under the unequal'pressures to which they are subjected. Attempts, heretofore made, to effect compensation for such non-uniform operation, directly in the said pumping systems, have occasioned a sacrifice in efliciency inasmuch as such compensation necessarily involved operating one or both pumping systems below full capacity. Hence, theoretically identical pumping systems, as heretofore employed, have failed to accomplish the desired objectives efliciently.

It may be considered that a hydraulic press could be constructed in which the slide guides, the slide housing, and possibly other parts of the press could be made large and strong enough to maintain the desired parallelism by sheer force. Such an expedient would render the hydraulic press so much larger than mechanical presses for similar purposes, that the hydraulic press would be commercially unacceptable. In addition to the objectionable size of such a. press, the wear on the various working parts would b excessive and frequent adjustments and replacement or worn parts would'be necessary.

It should be understoo that the term longbed, when employed in this specification with reference to hydraulic presses, refers to any hydraulic press wherein the present invention may be employed advantageously to maintain, substantially, the mentioned parallelism of the slide and bed of the press.

An important object .of the present invention is the provision of improved means for so controlling the distribution of liquid to ram advance chambers actuating a plurality of rams in a longbed hydraulic press that the press slide, during its advance stroke, is maintained in substantial parallelism relatively to the press bed.

Another object of this invention is the provision of a long-bed hydraulic press, the functioning of which compares favorably with thefunctioning of a mechanical press designed for a similar purpose, while ,at the same time yielding the mentioned of the length or of the press.

advantages of ease of adjustment pressure of the advance strokev The foregoing and other objects are accomplished according to this invention, generally, by providing, in a long-bed hydraulic press, two or more rams, arranged substantially symmetrically along the length of the press slide, for operating the latter; by providing separate substantially identical pumping systems for operating each of said rams or for operating rams or groups of rams adapted to apply Working force to the slide toward opposite endsthe'reof by providing means for compensating for differences in the volume of liquid pumped to the mentioned rams; an by providing means, controlled by relatively slight differences in advance movement invention and without limiting the invention thereto, several embodiments thereof are shown in the accompanying drawings, in which:

Figure 1 is a perspective view of a preferred embodiment of the present invention (hereinafter referred to as the first embodiment) and of a long-bed press on which it may be employed.

Fig. 2 is a detail view, partly in section and partly in elevation, of a screw and nut assembly which is employed in the said first embodiment as a means, responsive to difierences of advance movements of opposite sides of the press slide, for actuating a pump adjusting device. 1

Fig. 3 is a sectional view of the mentioned screw and nut assembly, the section being on the line 3-3 of Fig. 2.

Fig. 4 is a diagram illustrating the operation of the said first embodiment of the invention.

Fig. 5 is a perspective view, similar in character to Fig. 1, of another embodiment of the invention (hereinafter referred to as the "second embodiment) and Fig. 6 is a detail view, partly in section and partly in elevation, of a differential assembly which is employed in the said second embodiment as a. means, responsive to differences of advance movements of opposite sides of the press slide, forv actuating a pump adjusting device.

Further improved means for attaining the ob- I jects of the present invention are described and illustrated in my application for patent filed relationship. Tie rod nuts I! preferably are provided at the upper and lower ends (the latter are not visible in the drawings) of the said tie rods.

The slide is is reciprocated in a well- -understood manner, by rams [8a and IN), fixed symmetrically upon the slide, toward opposite ends thereof. These rams, as best understood from Fig. 4, may be enlarged at their upper ends to form ram pistons I90, I91) and may be urged downwardly on their advance strokes by liquid n remain substantially at rest.

ra es introduced into advance chambers 29a, b, and upwardly on their return strokes by liquid introduced, into return chambers Zla, Zlb. The said through pipe 24a. and pumps said liquid through pipe 25a into a distributing slide valve 260. which. depending upon the position of a piston 21a therewithin, directs the liquid either through a pipe 28a to the ram advance chamber 20a to move' the ram |8a do'wnwardly or through a pipe 29a to the ram return chamber 2Ia. to move the said ram upwardly, or, through a pipe 30a, back to the tank 23, when it is desired that the ram The mentioned liquid distribution, yielding the said ram movements, is controlled largely by the provision on the piston 21a of three enlarged portions or spools 3la, 32a and 33a and intervening neck portions 34a and 35a.

When it is desired to advance thev ram I 8a (1. e., move it downwardly) to advance the slide I6 toward the bed I I and a die and blank thereon, the piston 21a is shifted, by any suitable means, to its extreme left position as shown in Fig. 4, whereupon liquid entering the valve 26a, through pipe 25a, passes around neck portion 34a, of the said piston, into pipe 280., and thence to the ram advance chamber 20a, thereby forcing the ram l8a downwardly while liquid is exhausted from the ram return chamber 2|a through pipe 29c into the valve 26a, wherein'the exhaust liquid passes around neck 35a of said piston to pipe 30a which carries it to the tank 23. By shifting the piston 21a, to its extreme right position, the flow of liquid is reversed with respect to the said ram chambers thereby causing the'ram l8a to pursue its upward or return movement.

When it is desired to arrest the movement of the ram l8a, the piston 21a, may be moved to its mid-position, in which the several mentioned spools on said piston close off all liquid communication between the pump 22a and the ram chambers 20a and 2m. However, the liquid, continuing'to be discharged by the pump 22a passes from pipe 250. into interior lateral passage 36a in the spool- 32a, thence through longitudinal passage 3112 into lateral passages 38a, 39a in the spools 3 la and 33a, whence said liquid passes into pipe 300. which carries it to the tank 23.

In view of the similarity of the pumpin systems for actuating the two rams, the foregoing description is intended to suflice for both. For this reason, the similar parts of the pumping systems are given reference characters, in the drawings and hereinafter in the specification, differing only in their suifixes, the sufllx a being applied to parts of the pumping system related to ram I81; and the suflix b being applied to parts of the pumping system related to ram-18b. Both valves 26a and 26b function alike and may be constrained to function in unison by having their respective pistons tied together by extension rods 40a and 40b which preferably are adjustably coupled by a turnbuckle 4|. The said pistons may be shifted within their respective valves by any suitable means to control the reciprocation of the press slide. Such means, for example, may be operated manually, electrically, by compressed a'ir, or by hydraulic pressure.

As illustrated in the accompanying drawings,

a an electric solenoid 42 may suitablybe connected as by a pin 43 to an end extension 44 of the piston 21a. The said solenoid is adapted, when energized, to move the pistons 21a and 21b to their left positions,as shown in the drawings, to cause downward movement of the press slide l6. Another solenoid 45 may be similarly connected to the piston 21b for moving both, pistons to their right positions to cause upward movement of the press slide. The two said solenoids, of

course, are connected in suitable electric circuits for controlling the operation of the press.

The pistons 21a,

for example, may employ springs ,or air or hydraulic pressure. As illustrated in the accompanying drawings, a spring centering device is employed comprising a coil spring 46 which is positioned about the extension rod 40a and is compressed between washers 41 which, normally, are held against the end of said spring by collars 48 formed on or fixed on the rod 40a. A cagelike frame 49 is fixed upon some fixed part of the press or other suitable fixed support in such position, adjacent the rod 40a, that the latter passes through holes 50 in the ends of said frame, large enoughto freely pass the said collars but small enough to confine the washers 41 within the said frame. Thus, when the pistons 21a and 21b are held in their left positions, as illustrated in the drawings, by the energized solenoid 42, the

spring 46 is exerting compression upon the right washer 41 and the right collar 48 which, when the said solenoid is de-energized, will cause the .said pistons to move to their mid-positions. A

similar, but opposite action of the centering device results when the saidpistons are held in their right position by the solenoid 45 and the latter is then de-energized.

Although the pumping systems for operating the rams I80, and lb, as thus far described in 21b may beheld yieldably in their mid-positions by any suitable means which,

detail, may be substantially identical in design,

it willbe appreciated that, where resistance to the advance of the slide is not uniformly distributed thereover, the different slippages in the two pumps, slight leakages, and possibly other factors, would cause the side or end of the press slide encountering the least resistance to advance ahead of the other side thereof and this uneven advance or cooking of the slide, in many instances, would becomejmore pronounced. as the slide progressed towardthe end of its advance stroke. This highly undesirable functioning of the press may be substantially obviated by com pensating means new to be described in detail.

An important feature of this invention is the provision of automatically controllable means for substantially equalizing the supply of liquid to the hydraulic chambers of the several rams which actuate the press slide. vide such means comprising a compensator pump 5|, connected by a pipe 52 to the pipe 28a, which carries the liquid supply to ram advance chamber 20a, and connected by a pipe 53 to the pipe It is preferred to procylinders 54 formed ina rotor 55suitably driven continuously by a motor (not shown). The inner ends of said cylinders open into an axial bore in the rotor 55 and each of said cylinders, as the said rotor revolves, communicates alternately with ports 56, which are in liquid communication with the pipe 53, and with ports 51, which are in liquid communication with the pipe 52 Pistons 58 are accurately fitted for reciprocation within and toward the .outer ends of the cylinders 54 andare yieldably urged outwardly by springs or other suitable means (not shown) against a confining ring 59 which is so mounted within the frame of the compensator pump as to I be capable of sliding movement laterally of the eter of the ring 59, of course, is materially greater than the diameter of the rotor 55 in order to permit the mentioned sliding movement of the ring. The said sliding movement may be effected by means of a turnbuckle-link 60, suitably connected between the pipe 59 and a lever 6| which may be actuated by means hereinafter described. If desired, thering 59 may be mounted so as to be free to rotate, whereby to minimize the friction between its inner surface and the pistons 58 which work thereon, by mounting said ring within a frame 62 and by connecting the link to said frame. l

The means by which the lever 6| 'is actuated to control the sliding movement of the ring 59 and, the resulting operation of the compensator pump, comprises a pair of vertically disposed racks 63' (see Fig. 1), secured at their lower ends to the slide l6 toward opposite ends thereof. The

ets 67, which gears drive pinions 68, keyed upon the outer ends of the shafts 651 and 651-. The two mentioned shafts are supported within brackets 69 fixed upon the crown I3. The bearings provided for said shafts in the mentioned brackets should be such as to prevent any material longitudinal movement of the shafts.

A screw 10, as best understood from Fig. 2, is fixed upon the inner end of shaft 651 against any possible movement relatively to the latter, as by a pin H, and additionally, if desired, by a key 12. An elongated nut 13 is slidably mounted upon ,the inner end of shaft 651- as by a spline 14and when the apparatus is assembled, the nut I3 and thescrew'lO are partly screwed together in halves having opposed end flanges 11 held to- 28b which carries the liquid supply to ram advance chamber 20b.

The compensator pump 5| may be of the type, known as the Hele-Shaw type, which, as shown in Fig. 4, has a plurality of radially arranged gether by bolts 18. The ring 16, of course, is constrained to follow any longitudinal movement of'the nut 13 and such longitudinal movement may be transmitted to the lever 6| by forming the lower end of the latter as a yoke 19 and pivotally securing the lower ends of said yoke to the ring ,16 by studs passing through suitable bearings in said lower ends'of the yoke and screwed into opposite sides of said ring.

The lever 6| preferably is pivoted, at an intermediate point 8|, upon a bracket 82 fixed upon the crown l9 of the press. The relative lengths of the arms of the lever 6|, as shown in Figs;

1 and 4, are not intended to be controlling, for it should be obvious that the said lengths, in practlce, will be determined with reference to the magnitude of sliding movement to be imparted to the ring 59 and to the various other mechani cal factors in the structure which give rise to such movement.

The racks 53 preferably are split longitudinally as indicated at 63a and the two parts of each rack are capable .of relative longitudinal adjustment through the medium of suitable adjusting screws 93 carried by brackets 84 fixed upon the slide 15. By suitable adjustment of the screws 89, the parts of the racks 63 may be slightly shifted longitudinally relatively to each other whereby to eliminate all material lost motion between the teeth of said racks and the teeth of the step-up gears 56.

ratus are so assembled that, when the-slide l6 and the bed. I I are perfectly parallel, the screw '10 and the nut 13 are in such relative longitudinal positions that the ring 59 is held in concentric position with respect to the rotor 55 of the compensator pump. When the ring is in the mentioned concentric position the pistons 58, during the continuous rotation of said rotor, follow the concentricity of the said ring and, hence,

do not slide within their respective cylinders 54,

and, as a result, the compensator pump, although being driven by its operating motor, yields no pumping action whatever. If, during the descent of the slide 18, the latter remains in parallelism with the bed of the press, and, hence, requires no compensating corrections, the ring 59 remains in concentric position and the compensator pump continues inactive in so far as pumping is concerned.

On the other hand, if the ram in its descent, encounters greater resistance toward its right end, caused, for example, by an irregularly shaped die, the liquid slippage in the pump 22b, in the face of such greater resistance, becomes greater than the slippage in the pump 22:; and, hence, more liquid is charged into cylinder 200, than into cylinder MD. This inequality in liquid distribution causes the left side of the slide to tend to descend somewhat in advance of the right side thereof. However, immediately upon the inception of such uneven descent and before the cooking of the i press slide becomes objectionable in any practical sense, the shaft 652 and the screw ill thereon rotate ahead of shaft 651 and the nut 13 thereon,

causing the said nut to screw somewhat furtheronto the said screw. The resultant movement of the nut I3 toward the left actuates the lever and shifts the ring 59 toward the right to the eccentric position indicated in Fig. 4.

When the ring 59 is in the mentioned eccentric position shown in Fig. 4, and assuming that the rotor 55 is continuously driven in a counter-clockwise direction as indicated by the arrow, the pistons 58, during the lower half of their circular travel within the ring 59, are moving outwardly within their respective cylinders 54 and, hence, are drawing liquid into said cylinders, through the ports 51, fromthe pipes 52 and 28a. The

liquid thus drawn into said cylinders, is dis-,

charged therefrom through the ports 56 into the In practice, the parts of the described ap papipes 53 and 28b, during the upper half of the circular travel of said pistons within the ring 59 by reason of the fact that,-during that period,

. the pistons are being forced inwardly within their respective cylinders 54 by the said ring.

It should be understood, from the preceding paragraph that the described action of the compensator pump 5| operates to draw liquid from the pipe 28a, supplying liquid to chamber 29a, and transfer it to pipe 29b, supplying chamber 201). This transfer of liquid continues until it compensates for the inequalities in liquid delivery caused by the unequal distribution of the resistance opposing the descent of the slide and until the parallelism of the slide and bed of the press is restored; When "said parallelism is restored, the nut 13 will have been restored to its normal setting and the vring 59 will resume its concentric position, thus discontinuing the pumping action of the compensator pump.

The degree of eccentricity imparted to the ring 5.9 and the rate of flow of the compensating liquid through the compensator pump is substantially proportional to the degree of the cocking of the press slide so that the compensating means described are automatically adjusted to effectively oppose and correct any objectionable cocking of the press slide. The described compensating means preferably may be so designed as to correct even slight cooking of the slide and to prevent such cooking from going beyond permissible limits at any time.

Although the compensating pumping action of the Pump 5| has been described only as it operates to correct downward movement of the left side of the slide in advance of the right side thereof, it should be clear that if the said right side moves ahead of the left side, an opposite coaction of the screw Ill and the nut 13 occurs, so that the ring 59 is shifted to an eccentric position toward the left of the rotor 55. When the said ring is in the latter position the flow of liquid through said pump is from the liquid supply of chamber 20b to the liquid supply of chamber 20a and thus yields the desired compensation in a manner opposite to that already detailed.

The second embodiment of the invention, illustrated in Figs. 5 and 6, differs from the first embodiment principally in. that the racks 63 are arranged so that the teeth on one of said racks face toward the front of the press while the teeth on the other rack fac toward the rear of the press whereby said racks, through the step-up gears 66,drive the shafts 551 and 551' in opposite directions rather than in like directions; and in that a differential mechanism 95 is employed between said shafts instead of thedescribed screw and nut arrangement.

The differential mechanism, as best seen in Fig. 6, comprisesbevel gears '85! and 951', keyed respectively upon the inner ends of shafts 651 and r and meshing with bevel differential gears 81 which are mounted within a cage 88 upon studs 99. The cage 88 preferably is so mounted within suitablebearings in brackets '69 as to be capable of pivotal movement coaxially of the shafts 551 and 651. An arm 90, fixed upon or formed integrally with the cage 88, extends upwardly from the latter and to the upper end of this arm is connected a turnbuckle-link to the compensator pump with the ring 59 of the latter in its concentric or neutral adjustment and the press slid l8 and bed II in parallelism, a uniform downward movement of the slide I 6 causes the shafts 651 and EST to move in similar degrees but in opposite directions, so that the rotation imparted to the differential gears 81 by the bevel gear 861, tending to turn the cage 88 in one direction, is exactly counteracted by the rotation imparted by the bevel gear 86r to said differential gears, tending to turn.

said cage in its opposite direction; It, hence, results that while the slide iiiv moves downwardly in parallelism with the bed H, the cage 88 and the arm 90 remain at rest, leaving the com- Densator pump in its non-pumping adjustment.

On the other hand, if one end of the slide l6 moves downwardly ahead of the other end thereof, one ofthe shafts 651 and 651' turns to a greater degree than the other, thus, through the difi'erential gears 81, imparting a rotative movement to the cage'88 which carries the arm 90 with it to move the ring 59 toward whichever eccentric position will yield the proper pumping action of the compensator pump. It is to be understood, of course, that the compensating action of the said pump is similar in both embodiments described herein.

The location of the compensator pump is not critical and has only been indicated diagrammatically in Fig. 4. It may, if desired, be mounted upon the crown of the press or other fixed supporting structure and any suitable linkage may be employed for connecting the nut and screw mechanism or thedifierential mechanism to the said pump.

The apparatus illustrated in the accompanying drawings and described in this specification may, of course, be varied in many respects or may be applied to various types of presses without, however, departing from the spirit of the invention as defined in the accompanying claims.

What I claim is! 1. Apparatus for controlling the slide movement in a long-bed hydraulic press having two or more symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a compensator pump. connected between ram advance chambers at opposite sides of the press slide and having flow regulating means for reversing the direction of flow of liquid through said pump and for con-'- trolling the volume of such flow, and pumpadjusting means, controlled by the advance movement of th 'press slide and adapted to coact with said flow regulating means to so adjust the said pump that the latter operates to transfer liquid, during the advance movement of said slide, in the proper direction and in suitable volume between the said ram advance chambers to eifect the advance of the pres slide in substantial parallelism with the press bed.

2. Apparatus for controlling the slide movement in a long-bed hydraulic press having two or more symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a compensator pump, connected between ram advance chambers at opposite sides of the press slide and having flow regulating means for reversing the direction of flow of-liquid through said pump and for controlling the volume of such flow, a pair of movable members coacting with the press slide at opposite sides thereof and with said flow regulating means whereby to control th operation of the latter in relation to advance movement of said slide.

' 3. Apparatus for controlling the slide movement in a. long-bed hydraulic press having two or more symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a compensator pump, connected between ram advance chambers at opposite sides of the press slide and having flow regulating means for reversing the direction of flow of liquid through said pump and for controlling the volume of such flow, a pair of rotatable shafts, driving means at each of opposite sides of the press slide, controlled by the movement of the latter and adapted to coact with and separately drive said shafts, during the advance movement of said slide, to degrees which correspond or differ in accordance with the parallelismor non-parallelism of the press slide, a pair of coacting members, constrained to rotate separately with the said pair of shafts, and motion transmitting means operatively arranged between said pair of coacting members and the fiow regulating means of the said pump, the said motion transmitting means being adapted to coact with the said pair of coacting members to derive movement from rotation of the latter to unlike degrees and to transmit such derived movement to the said flow regulating means whereby to so control the direction and volume of flow of liquid through said pump as to substantially compensate for non-uniform advance movement of the press slide.

4. Apparatus according to claim 3, further characterized in that the driving means for driving the said pair of rotatable shafts comprises, at each side of the press, a rack, and a pinion, fixed upon one of said shafts and adapted to be driven by said rack, the said rack and pinion being carried, one upon the slide of the press and the other upon a fixed part thereof. 5. Apparatus according to claim 3, further characterized in that the driving means for driving the said pair of rotatable shafts comprises, at each side of the press, a rack, carried upon the slide of the press, and a pinion, fixed upon one of said shafts and adapted to be driven by said rack, the said pinion and its related shaft being mounted upon a fixed part of the press.

6. Apparatus according to claim 3, further characterized in that the said pair of coacting members comprises a screw member carried on one of said shafts and a nut member carried on the other of said shafts and having a threaded portion adapted to work upon the threaded portion of said screw member, both said screw member and said nut member being fixed against rotative movement relative to their said related shafts and one only of the two last-mentioned members being slidable longitudinally with respect to its related shaft, whereby any relative rotative movement of the two said shafts operates to slidably move said slidable member to actuate the motion transmitting means and the flow regulating means of said pump.

7. Apparatus according to claim 3, further characterized in that the said motion transmitting means comprises a lever operatively connected between said pair of coacting members and the flow regulating means of the said pump.

8. Apparatus according to claim 3, further characterized in that the said pair of coacting members comprises gears in a differential assem-- bly, and in having a differential cage adapted for rotation in response to differences in the the parallelism of the a lever, adapted for operation in response to rotation of said cage and connected to the flow 2. degrees of 'rotative movement or said gears, and

and means for transferring liquid, during the advance movement of the said slide, from the said primary liquid supply. of a ram advance chamber located toward one side 0]. the press to the primary liquid supply or a ram advance chamber located toward the opposite side of the press, to an extent substantially sumcient to compensate for inequalities in the .volumes or said primary liquid supplies arising from un- 10 equal resistance to the advance of the press slide.

EARL CANNON.

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