US2300162A

US2300162A - Hydraulic press

Info

Publication number: US2300162A
Application number: US207733A
Authority: US
Inventors: John H Maude
Original assignee: Dominion Engineering Works Ltd
Current assignee: Dominion Engineering Works Ltd
Priority date: 1938-05-13
Filing date: 1938-05-13
Publication date: 1942-10-27
Anticipated expiration: 1959-10-27

Description

Oct. 27 1942. J. H. MAUDE HYDRAULIC PRESS Filed vMay l5, 1938 7 Sheets-Sheet l INVEN TOR.' JOHNHMAUDE ATTO RNEY A Oct. 27, 1942. J. H. MAUDE 2,300,162 v HYDRAULIC PRESS Filed 'May 13, 1938 7 Sheets-Sheet 2 FIG. INVENTOR JOHNMMAUDE ATTORNEY oct. 27, 1942, Y J. H. MAUDEV 2,300,162

HYDRAULIC PREss Filed May 13, 19:58 -7 sheets-sheet s A1,21 37W 38W 38 INVENTOR JOHN .I-LMAU DE ATTORNEY 061:. 27, 1942. L MAUDE Y 2,300,162

'HYDRAULIC PRESS Filed May 13, 19:58 fr sheets-sheet 4 lf-w.: vm'l 80769 83 4 359 FIGE' INVENTOR JoH N.H.MAU DE ATTORNEY' J. H. MAUDE HYDRAULIC PRESS Oct. 27, 1942.

Filed lay 13, 1938 7 Sheets-Sheet 5 LA wm W 0d. 27, 1942. J. MAUDE 2,300,162

HYDRAULIC PRESS v y VFiled lay 13, 1938 l 7 Sheets-Sheet 6 6 nl 12|( i FICE@ INVENTOR/ f g JOHNHMAUDE ATTORNEY oct. 27, 1942. J, H, MAUDE l HYDRAULIC PRSS Filed nay 1:5. 1958 '7 Sheets-Sheet 7 79 man w w m m mm. 1 y m m@ 6l annu H M m .M 1. .nu u

.86 INVENTQR JOHNJ'LMAUDE y. gmw

mais

A ATTORNEY lfnemal oa. 27, 1942A nrnaamc mass John H. Mande, Verdun, Quebec, Canada, assigner to Dominion Engineering Works Limited, Lachine, Quebec, Canada Application May 13, 1938, Serial No. 207,733

10 Claims.

4 This invention relates to hydraulic presses and has particular reference to presses equipped with hydraulic cushioning rams serving to createiluid resistance to oppose the downward movement of the lower work supporting platen during a working stroke of the upper platen and to raise said lower platen to starting position during returnA of the upper platen. More particularly, the invention relates to` improved means for controlling the flow of pressure fluid to and from the pressing and/or cushioning cylinders of the press and to which high pressure fluid is supplied during the pressing operation. This enables the. maxiis adaptable to various kinds oi' presses whether mum fluid pressure applied to the upper platen s during the pressing operation to be conveniently varied within wide limits and is accomplished.

j plied to the rams to raise the lower platen to starting position, is discharged to a suitable tank.

Another4 characteristic feature of the resist` ance-control a'sembly is the provision of a selector valve which enables the maximum fluid resistance offered to downward movement of the lower platen to be varied within wide limits for any particular setting of the pressure relief valve.

A further feature of the invention resides in the provision of a fluid pressure control system in which the pressing, push back, and cushioning cylinders of the press are supplied with high pressure fluid from a common source and through (ci. 26T- 1) Other characteristic features and advantages of they invention, as well as the novel details of the particular embodiment selected for illustration will be apparent from the tollowingdetailed description taken in connection with the accompanying drawings, in which- Figure 1 is a diagrammatic view of the component parts of a press showingone embodiment of the present invention.

but showing certain `parts in different positions.

Figure 4 is an enlarged vertical sectional view of thelpressure control valve which is connected between the pressing cylinders and the main reversing valve as shown in the preceding iigures.

Figures 5 and 6 are enlarged detail views showing different operating-positions of the selector or isolating valve forming part of the assembly appearing in Figure 4.

Figure 'l is a vertical sectional view of one of the prefill valves associated with the pressing cylinders.

Figure 8 is a diagrammatic view illustrating certain modifications of the uid supply and exhaust connections to the uid resistance-control assembly associated with the lower platen.

Figure 9 is a view similar to Figure 8 but showing a further modification in which the uid resistance-control assembly associated with the lower platen is contained in a hydraulic circuit which is entirely independent of the hydraulic circuit provided in connection with the pressing and push back cylinders of the upper platen.

Figure 10 is a vertical sectional view-of the preferred type oi' pressure control valve provided between the pressing cylinders and the main reversing valve.'V p

Figure 11 is' a sectional view showing more or less diagrammatically certain modifications of 4o the fluid resistance control assembly associated `the agency yof a common reversing valve con- V nected between said source and cylinders` with the cushioning rams.

Figure 12 is a sectional View taken substantially along the line I2-I2 of Fig. 11. In this view certain parts appearing in Fig. 11 are omitted.

Referring to the diagrammatic illustrations appearing in Figs. 1 to 3 inclusive, the upper press platen and the lower or cushioning platen are respectively indicated at 5 and 6. 'I'he upper platen is operated by main central ram 1 working in cylinder 8 and two auxiliary side rams 9 working in cylinders I0. The lower platen is carried by three cushioning rams II, I2 and I3 working,

respectively, in cushioning cylinders I4, I5 and I6.

Platen 5 is equipped with a conventional top 5 drawing tool A. The cooperating bottom tool B Figures 2 and 3 are views similar to Figure l is shown mounted on the bolster plate C.v The work D is shown resting on a draw ring E which operates in the space between the tool B anda surrounding guide ring F fastened to plate C. Draw ring E is supported from platen 6 by cushion pins G working inthe guide openings H of plate C. During the pressing operation the work D is gripped between tool A and draw ring E and drawn downwardly around the bottom tool B.

Fluid is supplied to the lower ends of cylinders.

I and exhausted therefrom through line I1. This line is connected to port I8 of main controlvalve casing I9. It is also connected to ports 29,

`into Patent No. 2,246,379, dated June 17, 1941,

or in any other suitable manner.

Prefill valve casings

23, 24 and 25 are respectively provided, above the

valve seats

29, 30 and 3|, with ports 68. 69 and 10. These ports are line-connected to

tank

5,6 as indicated at 1 I.

rIThe--downward or working stroke of platen 5 commences when main control valve 64 is shifted to the positin shown in Figures l and 2. This permits fluid, previously supplied to the lower 'ends ofA cylinders I0, to be forced back, through line I1 and main control-valve ports I8 and 55a,

to exhaust line 51 leading to tank 56. y As rams 2I and 22 of the

prefill valve casings

23, 24 and. f

25 through which fluid passes into and out of the-upper ends of cylinders 8 and I6. As hereinafter described the

preflll valves

26, 21 and 28 are biased to close against the

seats

29, 39 and 3l. I

The cylinder spacesserved by line I1 are hereinafter referred to asthe push back cylinders to distinguish them from the cylinder spaces termed the pressing cylinders. It is feasible to operate the platen 5 on its return stroke by push back rams which are entirely separate from the sabove the

rams

1 and 9 which are hereinafter pressing rams employed for operating the platen during the working or pressing stroke. Consequently, the terms pressing and push back cylinders as employed in the present description and claims are intended to cover this arrangement as well as the arrangement actually shown in the present drawings.

A port 33 in the upper end of cylinder 8 opens. into the lower portion of valve casing 23.

Similar ports

34 and 35 in the upper ends of cylinders I0 open Vinto the lower portions of the

valve casings

24 and 25.

. A port 31, provided in valve casing 23 below valve seat 29, is connected, by line 38, to port 39 provided 'in casing 40 of an automatic pressureopening of a pressure operated check valve 5I which remains closd until a definite pressure is established in passage 41. When this occurs the pressure in bypass 52, communicating with passage 41, acts against plungerl 53 to open valve 5I so that port 39 is then connected, through passage 41 and line 48, tomain'valve port 49.

The ends of main .control valve casing I9 are provided with exhaust ports 5B and 55a connected to an overhead filling or supply tank 56 by a common return or exhaust pipe 61 provided with a4 stop valve 58.

Valve casing I3 is also provided with a pressure supply port I9a connected, by pipe 59. to the pressure side of pump 60. 'I'he suction :side oipump 66 is connected to tank 56 by pipe 6I provided with stop valve 62.

V'Sli'iie main control valve 54. operating in valve casing I9, is provided with an annular port 65 and an operating rod 66. The rod 66 may be operated through the agency of the control mech- 1 and 9 move downwardly the initial suction created in the upper ends of cylinders 8 and I0 is sufficient to immediately open the

prell valves

26, 21 and 28. The cylinder spaces above the descending rams are thus immediately filled by fluid supplied from tank 56 through the line connections 1 I. At this time fluid also iiows from pump 60 into the upper ends of cylinders I9 but not into the upper end of cylinder 8. The fiow from pump 60 to cylinders I0 is through line 59; main valve ports I9a, 65 and 49, line 48, passage 41 and port 45 of pressure control relief valve 4l, and line 44. Until platen 5 contacts the work there is no pressure in passage 41, bypass 52 y and cylinders I9 and 8, so that the Vpump discharge merely augments the ow. As soon as from the overhead tank, so that this light press` ing occurs at arapid rate. As the work rev'sistance increases, the pressure developed by the pump also increases, until it reaches a predetermined amount. when fluid in passage 52 opens valve 5I so that a portion of the pump fluid now ows through line 38 through port 31 to immediately close the lprefill valve 26 against its seat 29 and to act against ram 1 in cylinder 9, and provide additional pressure needed for the pressing operation.

When the pressing" operation is completed. platen 5 is returned to starting position by shift ing main control valve 64 to the position shown in Figure 3. Fluid is now pumped to the lower ends of cylinders I0 through line 59, main valve ports I9a, '65 'and I8, and line I1. Fluid, previously supplied to the upper ends of'cylinders 8 and I9, is returned directly to tank 56 through the preiill valve connections 1I, the

preiill valves

26, 21 and 28 being held open by the pressure in line I1 acting against the valve plungers 26a, 21a and In this position of valve 64 a portion of the yfluid previously supplied to the upper ends of cylinders IIJ may be returned to tank 56 through

preiill valve ports

42 and 43, line 44, port 45 and passage 41 of valve 4I. line 48,

ports

49 and 55 o1' main control valve I9 and line 51. At this time it is immaterial whether valve 5I is open or closed. Ii itis closed, all the iluid previously supplied to cylinder 8 will be returned directly to tank 56 through port 68 and connections 1I.

If itis open, a portion oi the iiuid from cylinder 8 may be returned to tank 56 through port 31,

` line 88. passage 41 of valve 4|, line 48, ports termediate valve port 83 of bore 82.

49 and 55 of main control valve I9 and line 51.

with reference to the iower maten s, it wm be noted that the lower ends of cushion cylinders I4 and |8 are connected by a common line 15 to port 16 of a cushion or resistance-control valve assembly 11. The remaining cushion cylinder 5 is connected by line 18 to port 19 of valve assembly 11. -As shown more particularly in Fig. 4,

ports

18 and 19 open into

annular valve ports

80 and 8| formed in the wall of a horizontal valve-bore 82 providedin valve casing 11a.

.Bore 82 is also provided with annular'valve port 83 located between

ports

80 and 8|. The two last mentioned valve ports are connected by passages 84 and 85 to opposite ends of a horizontal valve bore 88 located between the lower valve bore 82 and an upper horizontal valve bore 81. A vertical bore 88 intersects bores 81 and 88 and communicates, at its lower end, with the in- The upper end of bore 88 is connected to branch |1a (Figs. 1 to 3) of the previously mentioned iiuid line |1. A check valve 90 in the upper end of bore 88 is biased by spring 9| to close against a downwardly facing valve seat 92. This check valve opens automatically to admit pressure iiuid to bore 88 when pump pressure is established in line I1 during a return stroke of platen 5. When line I1 is connected to exhaust line 51 during a working stroke of platen 5'valve 90 closes under the influence of spring 9| to prevent reverse ilow from bore 88 to line |1.

A cylindrical isolating or selector valve 94 is slidably mounted in bore 82. This valve is provided with an external annular port 95 and an internal longitudinal passage 96, the latter being open to bore 82 at opposite ends of the valve. Mechanical shifting of valve 94 to different operating positions, hereinafter referred to, may be accomplished through the agency of any suitable valve shifting mechanism such, for example, as the rack and pinion mechanism generally indicated at 9T. l t

Valve 94 is also provided with a stem 99 extending outwardly througli a packing gland |004 closing one end of bore 82. The remaining end oi' bore 82 is connected to exhaust line 51 as indicated at 82a.

seat |04 by one end of a valve closing spring |05. l

Valves 83 and |09 are provided with longi-' from end ports |02 and |08'to intermediate ports ||2.

The `upper valve bore 81 is connected toexhaust line 51 by a passage ||5 which serves as a pressure relief passage; for the vertical bore 88. Communication between passage ||5 and bore 88 is controlled by an adjustable resistance-control valve ||8 operating in 'that portion of bore 81 which lies at the left of vertical bore 88. 'I'he right hand end I1 of valve 8 is normally closed against the seat |8 by a spring ||9. One end of spring 9 is seated in a socket formed in the left hand end ofthe valve. The other end-of said spring is seated in an opposing socket formed in a threadedvplug |20 closing the left hand end of bore 81. The right hand end of valve I8 is provided with a stem |23 extending across the vertical bore 88. The free end of this stem terminates in a cylindrical lenlargement |25 working in that portion of bore 81 which lies at the right of vertical bore 88. 'I'he cylindrical stem enlargement |25 is provided with a socket accommodating one endv of a pressure applying spring |21. The other end of spring |21 bears against the inner 4end of an adjusting screw |28 which is threaded through a packing gland |29 closing the" right hand end of bore 81. An operating wheel |30 is provided at the outer end of screw |28.

The area of the seat engaging portion of valve I6 is slightly greater than the opposing area of the valve stem at the inner end of the enlargement |25. This ,slight preponderance of pressure areas exposed to the pressure in the vertical bore 88 enables the valve springs ||9 and |21 to be made somewhat smaller than would otherwise be feasible. It is preferred that the opposing springs ||9 and |21 have diierent periodicities in order to damp out oscillations. The design and assembly of the component parts of this resistance control valve is preferably such that, with the hand wheel 30 screwed back to give zero pressure in the right hand spring |21, the left hand spring |9 alone gives a valve closing pressure of approximately the maximum desired fluid resistance pressure in the system. By turning the hand wheel in the proper direction compression is applied to spring |21 which, by opposing the valve closing pressure of the main spring 9, reduces the'eilective spring load on valve ||8 to give a reduction in relief. In other words the valve closing pressure ofspring ||9 may be balanced to any desired extent by increasing the opposing pressure offered by the spring |21, Y

In describing the functioning of the complete resistance-control valve assembly 11 it will be assumed that platen 5 is making a return stroke with main control valve 84 and valve 94 of the resistance-control lassembly 11 positioned as' shown in Fig. 3. In this position of valve 94 he three cushion cylinders |4, I5 and I8 are connected through

lines

15 and 18 and

valve ports

18, 19, 95 and 83 t0 vertical bore 88 which'. in turn, is connected to branch |1a of line i1. Cansequently,` the opening of check valve by the pump pressure established in line |1 permits ilu'd to ilow from this line to the lower ends ci the three cushion cylinders where the fluid acts against the rams I2 and i3 to raise the platen 8.

During the downward or pressing stroke ci' platen 5, lne |1 is connected to exhaust line 5l as previously described. Thispermits valve to close so that the uid previously admitted to bore 88 is trapped against return fiow to th'e Yblocked cylinders.

and I3 'therefore recede against a predetermined iiuid resistance which is regulated by the setting of the main relief valve IIG. When this fluid pressure resisting downward movement'of the platen 6 exceeds a predetermined value (determined by the effective valve closing spring load on valve I I6) it becomes effective to move valve I I6 away from its seat I I8 (see Fig, 2) thereby placing vertical bore 88 in communication with relief passage II and relief line 51. This permits the duid trapped in the cushion cylinders I4, I5 and I6, lines 15 and 18' and vertical bore 88, to be forced back to the tank 56 through line 51. From the opening or" valve IIE to th'e completion of the downward stroke of platen 6 the fluid resistance opposed'to the downward movement of the cushioning rams Il, I2 and i3 remains at an approximately constant value;

Maximum available resistance to downward movement of platen S (for any setting of valve IIB) is obtained when valve 94 is positioned as shown in Fig. 3 to connect all three of the cushion cylinders to the vertical bore 88. is desired to oppose less than the maximum nuid resistance to downward movement of'platen 5, this may be accomplished by shifting valve 99 either to the left or toth'e rightfrom theposition shown in Fig. 3. If valve 94 is shifted to the left, as shown in Fig. 5, the central cushioning cylinder I5 is isolated vfrom vertical bore 88 and is connected \to exhaust line 51 through the central passage 96 of valve 94. In this position of valve 94 fluid resistance, as controlled by valve IIB, is opposed only to the rams Il and' I3 duringdescent of the platen .6. If valve 94 is shifted to the right, as shown in Fig. 6, the cushioning cylinders I4 and I6 are isolated from vertical bore 88 and connected directly to exhaust line 51 through the left hand end of bore 82. In this case descent of the platen 6 is retarded, through the agency of valve I IGV, solely by Athe fluid resistance opposed to the central ram I2.

The operator may accidentally leave valve 94 inv an intermediate position in which the left hand end of the valve overlies port 16 and blocks communication between this port and exhaust passage ,51 or in anoth'er intermediate position in which the right hand end of valve 94 overlies port 19 in such manner as to block communication between this port and thev exhaust passage 96 of the valve. In either of these cases undesired intensification of pressure is liable to occur in the cylinder or cylinders which are thus blocked from communication with the exhaust .line. Th'e check valves' |03 and |09 are provided to prevent this intensification of pressure in the l If the iiuid pressure in central cylinder I5 is being used to resist'descent of the lower platen 6 and valve 94 is inadvertentline I1. The lower platen 6 and its rams II, I-2` When it line 18,

ports

19 and 8|, passage 85, check valve |09, port 88, relief valve `I I6, exhaust passage I I5 and exhaust line 51.

By varying the fluid resistance opposing downward movement of platenr 6 I am able to provide a variable vicing grip" around the edges of the Work plate C which are gripped between the tool A and the draw ring E. For any setting of resistance control valve IIB the vicing grip, insofar as it is determined by the fluid resistance opposing downward movement of platen 6, remains substantially rconstant from the opening of valve IIS-to the end of the pressing stroke. The intensity of the vicing grip" is varied through stepless variation from maximum to minimum by means of the adjustable resistance control valve I I6 in conjunction with the positioning of selector valve 94. The maximum vicing grip is obtained when the valve is positioned as shown in Figs. 3 and 4 to connect all three cushioning cylinders to exhaust line 51 by way of vertical bore 88 and rnain relief valve IIS. The minimum vicing grip is obtained when valve 9i! is positioned, as shown in Fig. 6, so that cylinders I4 and I6 are connected directly to exhaust line 51 through the left hand end of bore 82 while the remaining cylinder I5 is connected to said exhaust line by way .of vertical bore 88 and relief valve |95. The in- In this ngure port 22, which connects to tankl 56, is shown opening into one side of valve casing 25. When valve 28 is moved downwardly away ly left in a position blocking communication be- Y tween ports 16 and the exhaust line 51, the pressure developed in cylinders I4 and I6 will act through valve ports 16and`80, passage 84, and port |02 to open check valve |93. The opening of this valve permits the fluid in cylinders I4 and I6 and line 15 to escape into vertical bore 88 and from thence through the valve-controlled passage II5 into the exhaust line 51. If fluid pressure in cylinders I4 and I6 is being utilized to resist downward movement of platen 6 and valve 94 is inadvertently left in a position blocking communication between line 18 and exh'aust passage 96 of valve 94, the resulting intensificafrom seat 3|, port 22 is connected to port |32 which, inturn, is connected (by suitable piping not shown) to port 35 of the right hand cylinder I0 (Fig. 1). The high pressure port 43 in Fig. 1 is the same as the port 43 shown in Fig. 1. Valve 28 is guided during its opening and closing-movements by wings or vanes 28' working in the seat member 3|. This valve is also provided with a depending spring casing |33 containing the valve closing spring |36. The upper end of this spring bears against the lcentral portion of the valve while the lower end rests on a movable valve seat |35 working in the lower portion of the spring casing. The valve seat |35 is engaged by the upper end of a spring adjusting screw |34 having its lower end threaded through a gland nut |31 in this figure, valve opening plunger 53 is moved upwardly against the resistance of a spring |40 and is provided with a stem 53a which engages and opens the valve 5I against the resistance of valve closing spring 5Ia. Valve 5I is provided with a guide 58h working in a vertical guideway |4|. A screw |42 is threadedly engaged in the upper portion of guideway |4| and is provided, at its upper end, with a hand wheel |42a. By turnin'g the hand wheel in the proper direction, screw |42 may be forced downwardly against valve 5| to prevent the latter being lifted from its seat by pressure developed in bypass 52. When valve 5| is held closed by screw |42 no pump pressure is established in cylinder 8 during the pressing stroke of the platen 5. This is of advantage in certain cases where it may be desirable to apply pressure only to the rams 5 during the working stroke of platen 5. Provision is also made for disrupting communication between the cylinders I and the pressure side of pump 50 during the working stroke of platen and connecting the pressure side of said pump only to the cylinder 5. This is accomplished by closing the shut-oir valve 45 to disrupt communication between port 45 and passage 41 and backing oil? the screw |42 to permit valve 5| to open when the required pump pressure is established in passage 41 and bypass 52.

Further possible modifications ofthe iluid supply and exhaust connections to resistance-control valve assembly 11 are illustrated more or less diagrammatically in Figs. 8 and 9. y

As shown by full lines in Fig. 8, intake bore 88 and exhaust connection 82a of resistance-control valve assembly 11 may be respectively connected to branches 51a and 51h of line 57. In this case the fluid in tank 55 is maintained under pressure` by means oi air pressure supplied through line 55a. In this particular instance the platen 5 is raised during the return stroke of platen 5 by fluid supplied to cylinders |4, I5 and l5 through line '51 and branch 51a. During the pressing stroke of-platen 5 this iluid is forced back to line 51 through branch 51h.

According to another modiilcation the exhaust connection 82a of the resistance-control valve replaced by line |55 and separate tank |55.

When the cushion cylinders are supplied from an accumulator tank as in Fig. 9, the resistancecontrol valve assembly is modiiied as shown in Figs. l1 and 12. 'I'he principal change involved. here is the substitution of screw type shut-on arrangement shown in Figs. l1 and l2 is essentially the same as that shown in Fig. 4.

Having thusdescribed my invention, what I claim is:

1. In a hydraulic press, a plurality of cylinders, rams operating in said cylinders and carrying the lower press platen and a resistance-control valve assembly including a main iiuid passage connected to the lower ends of said cylinders, a high pressure line through which huid is delivered through said passage lto said cylinders to raise the platen to starting position, a check valve arranged to prevent reverse ow from said main passage to said high pressure line, a pressure relief passage opening into said main passage, a spring loaded pressure regulating valve normally closing oir communication between said 'main passage and said relief passage, said valve opening automatically to provide a relief connection for said cylinders when the cushioning pressure therein rises to a predetermined value during assembly 11 may be connected to the sump tank |45. In this case there will be no communication between exhaust connection 82a and exhaust line 51 but the latter will be connected to port 88 as indicated at 51a.

In all the previously described instances the pressing, push back, and cushioning cylinders form part of a single, self-contained hydraulic l control circuit. This, however. is not essential since the iluid circuit of the cushion cylinders i4, I5 and |5 may be made entirely independent of the iluid circuit of the pressing and push back cylinders. One example of the latter arrangement is illustrated in Fig. 9. In this case the bore 88 and exhaust connection 82a of the resistance-control valve assembly 11 are`respectively connected to branches |55a and |551 of a line |55 leading to a pressure tank |55 which is separate from the tank 55. Air pressure is maintained in tank |55 by means of compressed air supplied through line |51. Pressure in tank |51 may be maintained at a desired value by means of an adjustable relief valve |58 or by other suitable means. The operation of the circulating system disclosed in Fig- 9 is substantially the same as that described in connection with Fig. 8, except that,

the actual pressing operation, and selector valveA means adapted to be selectively positioned to maintain communication between the main fluid passage and all of said cylinders throughout the entire pressing cycle or to disrupt communication between the main fluid passage and one or more of said cylinders while maintaining communication between said main passage and the remaining cylinder or cylindersthroughout thel entire pressing cycle.

2. In a hydraulic press, a plurality of cylinders, rams operating in said cylinders and carrying the lower press platen and a resistance-control valve assembly including a main fluid passage connected to the lower ends of said cylinders, a high pressure line through which uid is delivered through said passage to said cylinders to raise the platen to starting position, a check valve arranged to prevent reverse flow from said main passage to said high pressure line, a pressure relief passage opening into said main passage, a spring loaded pressure regulating valve normally closing oil communication between said Y main passage and said relief passage, said valve opening automatically to provide a relief connection for said cylinders when the cushioning pres*- sure therein rises to a predetermined value during the actual pressing operation, and manually controlled selector valve means adapted to be selectively positioned to control the iiow of uid from said main passage to the lower ends of said cylinders, said selector valve means being selectively shiftable to a position maintaining comn munication between said main passage and all of said cylinders throughout the entire pressing cycle or to a second position isolating one or morein the former case, the line 51 and tank 55 are of said cylinders from said main passage while maintaining communication between said main passage and the remaining cylinder or cylinders throughout the pressing cycle and means for vplacing the cylinders thus isolated in communication with a pressure relief passage.

3; A resistance control valve assembly of the character described comprising a valve casing provided with almain passage, a supply line through which fluid is supplied to said passage, a check valve arranged to prevent reverse iiow from said passage to said supply line, selector valve means controlling communication between said passage and a plurality of ports provided in said casing, said selector valve means being operable to disrupt communicationl between said passage and one or more of said ports while sage and the remaining port or ports, a pressure relief passage opening into said main passage at a point between the check valve and the selector valve means and a pressure relief valve controlling the relief of pressure from s aid main passage by way of said reliefV passage.

4. A resistance control valve assembly as set forth in claim 3 in which each of said ports is connected to the main passage by an auxiliary pressure relief passage by-passing said selector Valve means, said auxiliary passage being controlled by a check valve which opens to permit flow of iluid toward said main passage but closes to prevent reverse iiow.

5. A resistance control valve assembly as set -forth in claim 3, including means for establish- Y ing a pressure relief connection between a p ressure relief passage and the port or ports which are' cut oif or isolated from said main passage by the port closing action of said selector valve means.

6. A resistance control valve assembly of the character described comprising a valve casing provided with. a main passage, a supply line through which fluid is supplied to said passage, a check valve arranged to prevent reverse iiow from said passage to said supply line, valve means operable to selectively establish and dismaintaining communication between said pasrupt communication between said passage and A provided with a seat engaging portion normally engaged with a valve seatl in said bore to close off communication between said main passage and a pressure relief passage communicating with said bore. a valve closing spring acting against one end of said pressure regulating valve to hold the same seated against the pressure developed in said main passage until such pressure reaches a predeterminedv value, a second weaker spring acting against the opposite end of said pressure regulating valve in such manner as to oppose the pressure of the valve closing spring and adjustable means for varying the compression of the weaker spring to thereby regulate the effective spring load imposed on the pressure regulating valve by the valve closing spring.

'7. A valve assembly as set forth in claim 6 characterized in that the opposing springs acting against the pressure regulating valve have different perlodicities in order to damp out oscillations.

8. In a hydraulic press, a plurality of cushioning cylinders, rams operating in said cylinders and carrying the lower press platen and a resistance control valve assembly comprising a valve casing provided with a main passage, a supply line through which fluid is supplied to said passage, a check valve arranged to prevent4 reverse ow from said passage to said supply line, selector valve means adapted to be selectively positioned for controlling communication between said passage and aI plurality'of ports provided in said casing, said selector valve means being selectively positionable to maintain communication between said passage and all of said ports throughout the entire pressing 'cycle or to disrupt communication between said passage and one or more of said ports throughout the pressing cycle while maintaining communication between said passage an'd the remaining port or ports. a pressure relief passage opening into said main passage at a point between the check valve and the selector valve means, a pressure relief valve controlling the relief of pressure from said main passage by way of said relief passage and -a fluid line connecting each of said cushioning cylinders to one of said ports.

9. A hydraulic press as set forth in claim 8 comprising three cushioning cylinders, two of which are connected to a single one of said ports while a third cylinder is connected to another of said ports.

l0. A hydraulic press as set forth in claim 2 in which the last mentioned pressure relief passage communicates with the first mentioned pressure relief passage which opens .into the main passage.

JOHN H. MAUDE.