US1691667A - Punch press - Google Patents

Description

Nov. 13, 192s. 1,691,667

O. G. NILSON PUNCH PRESS Filed April 12. 1926 2 sheets-sheet 1 O. G. NILSON Nov. 13, 1928.

PUNCH PRESS Filed April 12. 1926 2 sheets-sheet 2 Patented Nov. i3, 1928.

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PUNCH 'Panes Application filed April 15B, 1926. Serial No. 101,457.

various weights or thicknesses of material,

the attainment of which uniformity has been one of the 'er present problems in this art, especially in connection with the drawing of shells, cups, etc. outl of fiat material or metal sheets.

Another object ofthis invention is to over- Y come, without more or less expensive, involved and com `alicated machiner the so called backlash or pressure against the punch during the up or return stroke of the press after each drawing oper-ation, which backlash is always present when the force co-operating with the engine power for the a compressible fluid, springs, rubber, or othe flexible material storing` up power to be released and operative during` the return, or release, stroke of the press, and primarily; for the referred to uniform grip upon the work, or material to be dra-wn or stamped into a new forni.

In all mechanisms of this type vit is highly desirable to maintain a uniform resistance against the pressure pad, or the well known dra w-ring, during the whole working operation, or drawing` or punching operation of the press when the press is under agreat strain. ln drawing metal shells the best resu are obtainable only by the nearest to uniform pressure applied to the blank throughout the entire movement which reshapes said blank, and a very important object of this invention is to attain this uniformity in a hig er degree, y j

This invention, further, makes provision for visually registering the degrees of resistance during operations, and tov make it possible to preserve the desired registry for future ope 'a ns, or return operations, on like material. VSuch preservation would consist of recording on paper, or in a suitable book, the indicator readings which have proved correct for the various classes of work such obviating the vufnial repetitions of creeppress is experimental adjustments, loss 0f time, spoilation of material, etc. Y`

Owing to their vertical dimensions portions of draw presses are necessarily lowered into'pits where adjustments are more or less inconveniently made and observed, and a still further 'object of this invention is "to enable original adjustments and variations thereof at a gage or registering' device operated by the press above the normal floor level, or above said pit, or at the operators working height. appear in the subjoined detail description, and, referring to the drawings, which show a punch press embodying my improvements.-

Figure l shows the press in elevationpart# ly broken away and insect-ion. Y y l Figure 2 is a greatly enlargedview showing a vertical section of the storage,l tank orA receiving cylmder'shown in the smaller sc-ale iin Figure l, with pipe connections broken away or omitted. y f

is a similarly enlarged viewvof the Vby-pass control portion of the press broken away and in vertical section.

' Figure 4 is substantially an enlarged view of Figure l showing the parts lin a changed position Ywith more parts broken away to show interior parts.

Inv the several views illustrating the present unirse srarss maar o,l-fricE-A onor e. ivrLsoN, or carcasa, rttnvorsgessroivon To Pnnss onsnron co., a con.

roar-irren or rtnruors. i

Other objects and advantages'willl resistance, 1n conjunction with hereinafter referred to other parts, for the vusual daw ring-9,v The cylinders Zand 3 communicate` with a storage tank or receiving cylinder l0 Y15,16 and 17, the first of whichTlQ-taps the main conduit section l1 while the last, or l?,

enters the top of a cylinder 18 connected with o5 through a capacious conduit shown in two seclil the section 12 and having therein a coiled spring 19 which surrounds astem having on its upper end a piston 20 while 1ts lower end bears against the closed lower end-21-.oi1 a cylindricalmember telescoping the cylinder 18. The end 21 constitutes a valvewhich is normally closed and controls a by-pass 22'in the main conduit section 12 in which is a i'lap valve 23 which closes the low of oil in the direction of the receiving cylinder 10, and imposes upon such flow the work of overcoming the resistance of the spring 19. Above a piston 10 inthe chamber 10 is a spill chamber 24 that is provided with a side opening 25, the latter being partly occupied by the outlet end of a pipe 26 branching oii' from the small pipes circuit 14k to 17 and provided with a valve 27. Above the piston 2O in the cylinder 18 is an oil tra-p chamber 28 which is in communication with the conduit section 11 through .said circuit of small pipes, or on the pressure pad pistons side of said conduit, and in said circuit a globe valve 29 is arranged between a pressure gauge 30 at its top and its pit portion. During the first down stroke of the pistons 32-32 in the pressure pad cylinders 2 and 3, which movement should be made very slowly, the globe valve 29 is held open to allow the same pressure per square inch to Vbe exerted 0n top of the spring-resisted piston l 2O as is exerted on the exposed part of the 'similarly spring-controlled by-pass valve 21. As the piston 20 has the larger area it is impossible for the by-pass valve 21 to open until the liquid forced out of the pressure pad cylinders 2 and 3 is backed up against the piston 21 with sufficient force to overcome the spring 19. When a predetermined pressure is registered by the pressure gauge 30 the globe valve 29 is closed and the liquid between the piston 20 and the globe valve 29 is entrapped in the pipes 16 and 17 and oil trap 28, whereby a constant pressure is maintained on the by-pass valve 21. In order to effect a slight initial pressure on the spring 19 to insure a tight seating of the by-pass valve 21 before liquid is forced into the chamber 28 a set-screw 31 is provided in the top of the chamber 28 to be adjusted. against the valve 2O to give proper ten- -sion to the spring 19. An outlet for the entrapped liquid into the spill chamber 24 is provided in the pipe 26 normally closed by the globe valve 27, and if the predetermined pressure on the by-pass valve 21 should prove to be vhigher' than desirable the tension on the spring19 can be relieved by opening the valve 27 and draining ofi' 'the required amount of liquid into the spill chamber 24, or Vdraining off sufiiciently to bring the gauge 30 registration to the desired pressure.

Through the pistonA 10 are two openings which are controlled by valves 33 and 34 which open and close in opposite directions.

The valve 33 is a normally open float valve and floated to its closed position by the rise of the oil in the receiving cylinder 10. The valve 3 4 is a species of safety valvewhich is opened by an excess of liquid over predetermined pressure in the cylinder 10, such excess being speciiically provided for to insure complete operation. On the valve 33 is a stem 35 which carries on its upper end a disk 36'that supports the valve in its opened or lowered position. The excess liquid temporarily entrapped in the spill chamber is permitted to return to the space below the piston 10 through a lateralv passage 37 therethrough, which is in communication with the bore 38 for the stem of the valve 33 and' extends, as showmbeyondthe periphery of the disk 36.

The valve 34 is provided with an opening 39 through the piston 10 and is seated from above. The latter valve has a stem 40 within a coiled spring 41 which bears against an adjustable plug 42 and the valve and holds the latter normally closed` The lug-42has threaded engagement with a bore 43 in the top of a valve-supporting bracket 44 secured to the upper side of the piston 10. The plug 42 is therefore adjustable against the spring to vary its pressurer upon the valve 34 and its resistance to pressure of oil or iiuid-45-in the chamber 10.

' The purpose of having a surplus' amount 0f liquid in the receiving chamber 1()l is to insure at all times that the pistons 32 and 32 in the pressure pad cylinders 2 and 3 are brought home, by the pistonlO continuing its downward stroke a short distance after the pressure pad pistons 32 and 32 have comeV to a rest. The spring pressure on the valve 34 is set to correspond with the liquid pressure per square inch necessary to lift the pressure pad pistons home. f

The spill chamber 24 is connected with a large conduit 46 whichleads into the main conduit section 11 and is provided with a valve 47. lVhen for certain purposes it is v desirable to drain the pressure pad cylinder or cylinders of oil (changing piston packings, cylinder packing or making repairs) the valve 47 is opened when the weight of the pressure pad and pistons forces the liquid through this passa 46 into the spill chamber 24 until the pistons 32 andf32 rest respectively on the bottoms of the cylinders 2 and ln the :female die-memliicr, or punch, 48 operating on the blank or material placedon the male die member and draw ring 9 is a recess 49 which ycontainsa movable plate 50 againts which bears a pair of coiled springs 51 and 52. This plate 5() serves to push out the inished stamping from the punch 48 when the ram of the press is lifted off the plate orwork-53.r Through the tops of the cylinders 2 and 3 slidably pass pipes 54 and 55 that are anchored in and pass through the pistons 32 vand 32 have stop cocks on their upper ends. By opening the latter While iilling the system with oil through the opening 25, or otherwise, air in the system permitted to escape and when the liquid is flowing through these cocks, or the system is iilled,said cocks are closed and the machine ready for operation. On the up stroke of the `on which is a crank 59 that is pivoted to a connecting link 60. The latter is pivoted to the upper' end, or at 61, to a piston rod 62 which reciprocates in a bearing 63 on a bracket arm 64 secured at 65 (Fig. l) to the frame 56 of the press. The lower end of the rod 62 vis bolted to the piston l0 at 66. rllie usual cranks-67 and 68-of the press have their throw in opposite direction to that of the crank 59. Hence the piston l0 is operated positively by the press in both directions while the, pistons 32 and 32 are operated in one direction (upwardly) hydraulically. The work knock out plate is suspended in its normal position of Fig. l on a bolt 69 having a head movable up and down in a counterbore 7l of the bolt hole in the punch, which counterbore provides a rest or ledge 7 2 for .said bolt head when in normal position.

The positions of the parts in Figure 4 are at the ends of a punching or drawing operation, or when the blank 53 h as been formed.

In this position it will be. noticed that there is a considerable space in the receiving tank lO between the liquid 45 contained therein, and the piston 10 .so that there will be an absence in this invention of the usual intensified compression which has heretofore'caused the so called backlashy noise and wear and tear upon machinery, to partly relieve which has caused the invention of various kindsof machinery for this onel purpose only. As the cranks 67 and 68, arranged at right angles to the crank 59. begin their upward swing` from the Figure 4 position, there is no compressed force operating against the pressure pad 6 the piston 10" starts to descend. Notuntil the )iston 10 reaches the licuid the l i downward swing of the crank 59 will its force operate against the pressure pad G, and then,v only gently and gradually. yet with absobacklash use of it. By the time the pistonV reaches the liquid 45 the upward movement of the ram, or upper portion of right hand portion of Figure 4, is beyond the backlash period of upward movement of punch or ram. In other words, the piston l0 upon its return in the container l0 will not strike the top of the liquid 45 therein at the moment of its return, but willbe delayed in contacting and forcing the column of liquid against the pistons 32 and 32 until after the ram and die 48 have returned partially to their normal or up positions.

The referred to usual storing up of force that causes said backlash also progressively increases the resistance to the rainor punch, and another object attained bythe present4 improvement is to obviate suoli constantly increasing strain and to make the strain no greater at thefend than' at the beginning of the drawing or punching movement.y rlhis is accomplished by clearing the path for the upwardly moving liquid 45 through the piston connections with the crank 59 while the punch or die is moving downwardly and f against the work or'blank. v

The above described means for saving wear and tear of machinery and eliminating its noise, also obviates the common danger from explosions or violent eruptions where compressed air, compressed rubber or springs are employed to store up the forces thatlift the pressure pad, draw `ring and work ofthe vpunching or drawing opera- LUI' pad resistance means of similar whether same be liquid, compressed air or gas. Y

I claim as myinvention-A- l. In combination, a punch press, a pressure pad moved in one direction 'by said press, separatemeans directly operated by the power which operates said press, for restoring said pressure pad to normalposition, and means whereby the direct action of the restoring' means itself will delay the operation of the said restoring means until the press has moved partly away from said pressure pad. p' 2. In combination, a punch press, a resisting pressure pad operated in one direction by. said press, hydraulic resistance means opposing the movement of the pad by the press, means making said resistance uniform throughout the movement of said pad, rnechanical means positively operatingupon said resist-ance means to gradually and uniformly restore said pad to normal position when said press moves away from it, and

- means delaying the action of said mechanical means upon the resistance means during theinitial movement of the mechanical means against the hydraulic resistance means.

3. In combination, a punch press ram, a

ypressure pad operated by said ram, hydraulic resistance meansvvhich resists the movement of said pressure pad by said ram, mechanical means operating directly upon the resistance means after the :ram has operated against said pressure pad, restore the latter to its normal position, and means rendering the operation of the said mechanical means upon piston means opposing said press movement,

a receiving chamber, a conduit between the latter and said cylinder `and piston means through Which fluid may be'inoved back and forth, an auxiliary conduit and chamber into which said fluid may be conducted and held to temporarily free other paits of the system from said fluid to enable repairs of the latter, andmeans for controlling at Will the said auxiliary conduit.

5. In combination, a punch press, a pressure Vpad operated in' oneV direction by said press, a'piston and a cylinder therefore connected withsaid pressure pad to resist its movement under pressure of said press, a conduit leading from said piston cylinder into a receivingrcylinder, the receiving cylinder, a piston in the latter arranged to move oppositely to the iirst mentioned piston, an adjustable pressure regulating device interposed in said conduit, and means automatically registering the degree of pressure to Which-said pressure regulating device has been adjusted.

6. In combination, a punch press i'am, aA

pressure pad, hydraulic means embodying a column of liquid for resisting'the move-v ment of the said pad in one direction, mechanical means operable directly upon said column of Vliquid for restoring said pad, `and meansadapting said mechanical means for an Vinitial movement ivitli respect'tor Ythe said column of liquid before creating a pressure thereupon to restore the said fpad, thereby permitting the said ram toY commence its return movement independently of and'in advance ofsaid pad. y

7. In combination, a puncli press ram, a pressurepad, hydraulic means embodying a column ot' liquid. for resisting tlie movement of the said pad in one direction, mechanical means operable directly upoirsaid column oft Vliquid for restoring saidr pad, means adapt-- ing said Vii'ieclianical meansA for an initial movementwith respect to tlie'said column of liquid before creating a pressure thereupon to restore the `said pad, thereby permitting the said rain to commence its ret-urn inove'- lment independently of and in advance ot'v said pad, and means for varying at will the resistance pressure of the said column of liquid upon the said pad.

8. A punch press embodying a pressure pad, a plunger resisting the movement of said pad in one direction, a container, a liquid column operating upon the plunger to resist its movement iii one direction and for returning tlie plunger to its normal position, said liquid column having communication with the container, means operable under a predetermined pressure upon the liquid for controlling the flow of lthe liquidv into the container, and a piston in the containerY and operable upon its movement to force the liquid from ythe container and against the plunger, saidpiston having an initial movement independently of the liquid and before operating upon the liquid to torce it from the container. l

9. A punch press embodying a pressur pad, a plunger resisting the movement of saidv pad in one direction, a container, a liquid column operating upon the plunger' to resist its movement in one direction and for return- 'Y `ing the plunger vto its normal position, said Y liquid column having communication with pad, a plunger resisting the movement` of said pad in one direction, a container, a liquid column operating upon the plunger to resist its movement in one direction and for returning the plunger to its normal position, said liquid column having communication with the con- ,tainer, means operable under a predetermined pressure upon the liquid for controlling the flow lof thefliquid into the container, a piston in the container and operable upon its movement to force the liquid from tlie container and against the piston, said piston having an initial movement independently ot' the liquid and before operating upon the liquidjto'force' it i'rom the container, a by pass for the liquid y around the first recited means and into the said container, and means for controlling at will the said by pass. Y v

l1. In combination, a punch press ram, a pressure pad, hydraulicv means embodying a column of liquid for resisting the movement of the said pad in one direction, a container for receiving the liquid,ffluid pressure conlln trolled means disposed between said pad and container for controlling said column, a piston movable in the container for forcing the liquidV against the pressurepad to return the pad, and a by pass for the said liquid column around Vthe said fluid pressure controlled means.

12. In combination, a punch press ram, a pressure pad, hydraulic meansn embodying a column of `liquid for resisting the movement of the said pad in one direction, a container for receiving the liquid, fluid pressure controlled means disposed between said pad and container for controlling said column, a. piston operatively connected with a movable part of the press land movable in the container for forcing the liquid against the pressure pad toreturn ythe pad, and a by pass for the said liquid column around'the said fluid pressure controlled means.

13. In combination a sheet metal working press embodying a power shaft, a ram operable by said shaft, a pressure pad, hydraulic means for resisting the movement of the pad in one direction, a container, a liquid column having communication with said container, means for causing said column'to exert a resistance pressure upon said pad, and a plunger reciprocable in the container, said plunger being responsive'in its movement to the operation of said shaft, said plunger operating during its movement in one direction to force the liquid against.' the said pad to return the pad to a normal position, said liquid being 'free from the active pressureof the plunger during a. portion of its movement in the last recited direction whereby the operation of the liquid to restore the pressure pad willbe delayed until after the ram of the press has f started to raise. e

14. In combination a sheet metal working press embodying a power shaft, a ram'operable by said shaft, a pressure pad, hydraulic means for resisting the movement ofthe pad in one direction, a container,a liquid column having communication with said container, means for causing said column togexert aresistancepressure uponsaid pad, aplunger recipro'cable in the container, said plunger being responsive' in itsmovementto the operation of ysaid shaft, said plunger operating during its movement in one direction to force the liquid against the said pad to return the pad to a` normal'positionysaid liquidfbeing free from the active pressure of the plunger during a portion of its movement inthe last recited ldirection` whereby the Voperation of the liquid to restore the pressure pad will -be delayeduntil after the ram of the presshas started to raise, a by pass leading fromisaid column to the container and around the said resistance pressure creating means, and means for controlling at will the said bypass.

15. Invcombinatio'n a powerpress including a power shaft, a pair of co-acting dies, a die position, said liquid column being free from the action of the' plunger during a portion only of its active stroke whereby the operation of the restoring means will be delayed until after the ram of the press has returned partly to its normal position.

16. In combination a power Apress including a power shaft, a pair of (3o-acting dies, a die cushioning apparatus embodying cylinder and piston members, one of saidmembers operating upon a blank holder, a container communicating with said cylinder and providing fora liquid column lmovable'under-the action of one of said members, means for resisting fthe said -movement lof said column,

means for-controlling and varying at willlthe said resisting means, and a plunger movable 1n the container and operating lduring its active stroke upon the liquid column to force the latter-against the last said member to restorethe latterAt'oa normal position, said liquid column'beingfreev-frQm-the action of the plungerduring Aa portion only'fof its active stroke wherebyfthe/operation ofthe restoring -means will fbe delaye'duntil after the ram of the press has returned partly to its normal position. i

' 17.` In combina-tion `a power press including a-power shaft, a pair of (3o-'acting dies, a die cushioning apparatus embodying cylinder and pistonmembers, one of said members operating upon a'rlolankV holder, a 4container communicating with saidcylinder and providing for arliquidcolumn'movable underthe action of one of saidmembers, means for resisting the said movement of said column, a plunger movable in the container ando-perat- .mg during its active stroke upon the liquid column to force the' latter against the last said member to restore tlielatter to anormal position, said liquid lcolumn being freefro-m the action of the plunger during .ap'ortion only of its Aactive stroke whereby the operation of the restoring means will be delayed until after the` ram of the press has returned partly toits normal position, a bypass leading from said'fliq'uidcolumn to the container land around the said resistance creating means, and means for Vcontrolling,at will the said by pass. e' i i 18. Incombination a' power press including a power shaft, a pair of co-actingdies, adie cushioning apparatus embodying cylinder and piston members, one of said members oplerating upon a blank holder, a container communicating with said cylinder and providing for a liquid column movable under the action of one of said members, a plunger movable in the container and operable upon the liquid column to move it againstthe last said member to restore the latter, means for controlling the first recited movement of said liquid column to create a resistance pressure of' the column to the said member operating thereupon, and means for varying at will the said resistance pressure. 19. In combination a power press including a power shaft, a` pair of co-acting dies, a die cushioning apparatus embodying cylinder and piston members, one yof said members operating upon a blankholder, a container communicating with said cylinder and providing for a liquid column movable under the action of one of said members, a. plunger movable in the container and operable upon the liquid column to move it against the last said member to restore the latter, an operative connection between the plunger and said shaft, means for controlling the first recited movement of said liquid column to create a resistance pressure of the column to the said member operating thereupon, and means for varying at will the said resistance pressure.

20.-In combination'a power press including a power shaft, a pairof co-acting dies, a die cushioning apparatus embodying cylinder and piston members, one of said members operating upon a blank holder,a container communicating with said cylinder and providing for a liquid column movable under the action of one of said members, a plunger movable in the container and operable upon the i liquid column to move it against the last said member to restore the latter, and means whereby a portion only of said liquid column may be employed to create a resistance to the first recited movement of the liquid column by the said member operating thereupon, independently of said liquid column.

21. In combination a power press includ ing a power shaft, a pair of co-actingv dies, a die cushioning apparatus embodying cylinder and piston members, one of said membersv operatingr upon a blank holder, a container communicating with said cylinder and providing for a liquid column movable under the action of one of said members, a plunger movable inthe container and operable upon theliquid column to move it against the last said member to restore the latter, mea-ns Vwhereby a portion only of said liquid column maybel employed to create a resistance to the first recited movement lof the liquid column by thesaid member operating thereupon, in-

dependently of said liquid column, and v means for varying atwill the fluid controlled resistance creating means. Y

22. In combination a power press includ ing a power shaft, av pair of `co-acting dies, a

Y viding for a liquid column movable under the action of one of' said members, a valve in said communicatiommeans for confining a porf tion only of the liquid of said column independent of the column, under a predetermined pressure to operate 'upon said valve, a piston in the container, and means for positively moving the piston in the container aga-inst the column of liquid vto restore the said work holder, while the fluid pressure upon the said valve remains constant.

23.`In ycombination a power press including a power shaft', aY pair ofco-acting diesa die cushioning apparatus embodying cylinder and piston members, one of said members operating upon a work holder, a container communicating with said cylinder and providing for a liquid column movable under the action of one of said members, a valve in said communication, means for confining a-por tion only of the liquid of said column independent of the column under a predetermined pressure to operate upon said valve, the last said means embodying means whereby the first recited action of the said member of the cushioning apparatusupon the column of liquid will separate a portion of the liquid from the column and createa predetermined resistance pressureuupon such separated portion, a piston in the container, and means for positively moving the piston in the container against the column of liquid to restore the said work holder, while the fluid pressure upon the said valve remains active. Y

24. In combination a power press including a power shaft, a pair of co-acting dies,'a

die cushioning apparatus embodying'cylinder and piston members, one of said members operating upon a workholder, a container communicating with said cylinder andproviding for a liquid column movable under the action of one of said members, a valve in said communication, Vmeans for confining a portion only of the liquid of said column independent of the column, under a predetermined pressure to operate upon said'valve, a piston in the container, means for positively moving the piston in the container against the column of' liquid to restore the said ywork holder, while the fluid pressure upon the said valve remains active, and means whereby the operation of the plungerv in said container llo upon the column of liquid to restore the work j rection of liquid passing therethrough, a by pass for return of liquid in the last said direction, a. valve normally closing said by pass, and means for trapping and coniining a portion only of the said liquid to establish and maintain a. predetermined and independent liquid pressure upon the said by pass valve for yieldingly holding the latter closed.

Q6. A die cushion operating mechanism embodying a. cushion piston cylinder, a liquid container having communication with said cylinder through a conduit, a valve closing said conduit against movement in one direction of liquid passing therethrough, a by pass for returnl ol liquid in the last said direction, a valve normally closing said by pass, moans for trapping and confining a portion only ot' the said liquid to establish and maintain a predetermined and independent liquid pressure upon the said by pass valve for yieldingly holding the latter closed, and means for controlling at will the liquid pressure upon the said by pass valve.

27. In combination a power press including a power shaft, a die cushion operating mechanism including a cushion piston lcylinder, a liquid container'having communication with said cylinder through a conduit, a valve closing said conduit against movement in one direction of liquid passing therethrough, a by pass for return of liquid in the last said direction, a valve normally closing said by pass, means for causing a portion only of the liquid to establish and maintain a predetermined liquid pressure upon said by pass valve for yieldingly holding the latter closed, a pis Y ton in the container, and means for delaying the action of the last said piston upon the liquid column until the press ram has returned partially to its normal position.

28. In combination a power press includ ing a power shaft, a die cushion operating mechanism including a cushion piston cylinder, a liquid container having con'nnunication with said cylinder through a conduit, a valve closing said conduit against movement in one direction of liquid passing therethrough, a by pass for return ofvliquid in the last said direction, a valve normally closing said by pass, means for causing a portion only of the liquid to establish and maintain a Y predetermined liquid pressure upon said b-y kpass valve for yieldingly holding the latter closed, a piston in the container, means for delaying the 'action of the last said piston upon the liquid column until the press ram has returned partially to the normal position, a. by pass leading from the said communication to the container and around the said by pass, and means for controlling at will the 'last said by pass. n y' 29. In combination a. power press including a power shaft, a. die cushion operating mechanism including a cushion piston cylinder, a liquid container having communication with said cylinder through a conduit, a valveV closing said conduit against movement in one Y direction of liquid passingtherethrough, a by pass for return of liquid in the last said di-' rection, a valve normally closing said by pass,- means for causing a portion only of the liquidk to establish and maintain a predetermined liquid pressure Iupon said by pass valve for yieldingly holding the latter closed, a piston in the container, means for delaying the action of the last said piston upon the liquid lcolumn until the press ram has re-y turned partially to its normal position, and means for varying at will the said predetermined liquid pressure upon the said by pass valve.

In testimony whereof I have aiiixedmy signature. Y

Y OLOF G. NILSGN.

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