US1870500A - Hydraulic press - Google Patents

Description

Aug. 9, 1932. w. ERNST ET Al.

HYDRAULIC PRESS 5 Shets-Sheet 1 Filed May 9, 1930 I I l l l l l .llllllll Snventors,

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Bg @n WLM Patented Aug. 9, 1932 fum-TED STATES PATENT OFFICE WALTER ERNST AN HOWARD F. MACMILLIN, F MOUNT GILEAD, OHIO, ASSIGN'ORS` TO HYDRAULIC PRESS MANUFACTURING COMPANY, 0F MOUNT GILEAD, OHIO HYDRAULIC PRESS Application led May 9, 1930. Serial No. 451,181.

Our invention relates to hydraulic presses and more particularly to improvements in hydraulic circuits for operating such presses.

In some types of hydraulic presses it is desirable that the platen or other work engaging element carried by the press ram be caused to advance rapidly towards the work and upon meeting the latter, to advance more slowly under high working pressure. v To this end it is usual to provide a large pressing cylinder for effecting the actual pressing or working movement of the platen and to also provide auxiliary hydraulically operated means for rapidly advancing the platen toward the work during the iirst part of the working stroke 'and for rapidly returning the platen to its initial position after the pressing stroke has been completed. Some presses of this type have been provided with booster cylinders and cooperating rams of relatively small diameter which Serve to advance the platen toward the work and with means aociatedA with the booster cylinders and responsive to the pressure therein for automatically effecting closed communication between the main cylinder and a source of high pressure when the platen encounters the work with consequent building up of pressure in the booster cylinders. In a well 3G known 'form of press this is eii'ected through the provision of a surge shifting valve which normally provides direct communication between a surge tank or reservoir and the main cylinder during the iirst part of a pressing stroke and which is responsive to built-up pressure in the booster cylinders for automaticallyl closing communication between the tank and the main cylinder when the platen encounters resistance to its downward movement.

In many cases it is desirable in the intercst of simplicity of construction of the press and of arrangement of the aociated hydraulic circuit, that the booster cylinders referred to be dispensed with and that the initial part of the pressing stroke of the platen or other work engaging element be accomplished under the iniiuence of gravity only, the main cylinder being arranged to communicate with a surge engages and is supported by the work even though the press is not provided with booster cylinders.

An object of the present invention is to provide a reversible flow hydraulic press operating circuit including means directly responsive to a decrease in pressure in a push back cylinder for automatically cutting ofi communication between a surge tank and a platen advancing cylinder prior to building up of pressure in the latter.

Another object is to provide a hydraulicv press of simplified construction including cylinder means having a main pressing chamber and one or more platen returning chambers, a cooperating press operating circuit so arranged that the platen will descend gravitationally during the first part of the pressing stroke, and means in said circuit for automatically eecting closed communication between the pressure source and the pressing cylinder when the platen encounters the work irrespective of the position of the platen and irrespective of the pressure in the main cylinder. Other objects of the invention will become apparent from a reading of the following description2 the appended claims and the several views illustrated in the drawings, in which Figure 1 is a view in front elevation of a press embodyingour invention;

Fig. 2 is a diagrammatic view showing the hydraulic circuit, certain arts of the press and certain valves being s own in section7 some parts being broken away and the location of certain pipes being somewhat different from that shown in Figure 1 in the interest of clear illustration of the invention;

Figure 3 is a View similar to Figure 2 but in whibh the invention is illustrated as bein embodied in a press of different mechanica construction;

Fi re 4 is a sectional view of a surge shiftlng valve showing the valve in a different position from that shown in-Figure 2;

Flgure 5 is a sectional view of a control valve, the valve being shown in a different position from that shown in Figure 2, and

Figure 6 is a fragmentary sectlonal view of a modified form of surge shifting valve.

In its general nature a press embodying our invention'comprises cylinder means including pressing and platen returning chambers, cooperatingrams mounted for recipro- A catory movements in said chambers and connected to a platen or like work engaging e-lement, a source of fluid pressure, means forming a hydraulic circuit with said pressing chamber, said platen returning chamber and said source, and valve means in said circuit responsive to a decrease in pressure in the platen returning chambers resulting from the platens meeting the work, for effecting closed communication between the source of pressure and the pressing chamber for thereby completing the pressing stroke under high pressure.

Referring now to the illustrative embodiments of the invention shown in the drawings, Figures 1 and 2 show a press of the downward (pressure type including a base A, a prem hea B connected to the base by strain rods C, and a reciprocatory platen D mounted for vertical sliding movements on the strain rods C. It is to be understood that although we have illustrated a press provided with a platen. adapted for performing pressing operations, the invention may be embodied. in` presses used tor punching, forging, shearing or other like operations and the term platen is intended to cover any tool, die, or other working element with which a press might be provided.

The platen D is reciprocated by means of a pressing ram 1 mounted for sliding movements in a main cylinder E, and platen returning rams 2 2 respectively mounted for sliding movements in platen returning cylinders F-F, the cylinders E and F--F, and the rams 1 and 2 2 thus respectively constituting cylinder means and ram means for reciprocating the platen. In the form shown in Figures 1 and 2, the cavity of the main cylinder E constitutes a pressing chamber 3 and the cavities of the platen returning cylinders constitute platen ieturning chambers 4--4. As will be later described in detail, means are provided foi placing the pressing chamber 3 in communication with a surge tank G whereupon gravitational descent of the platen toward the work is effected, for then cutting oil' communication' between the surge tank and the pressing chamber when the platen encounters the work, thereby completing the pressing stroke through the a plication of high pressure to the pressing c amber, and for subsequently reestablishing communication between the pressing chamber and the surge tank, and

simultaneously introducing iluid under pressure to the platen returning chambers for returning the platen to its upper position.

The press shown in Figure 3 is of slightly l different mechanical construction from that described above with reference to Figures 1 and 2 but hydraulically it is the same. In the form shown in Fig. 3 the platen returnin cylinders and rams considered as individua elements are dispensed with and a unitary y directions. In this form, the cavity of the main cylinder comprises a pressing chamber 3, being that part of the cavity above the raml, and a platen returning chamber 4, being that part of the cavity below the ram.

It will thus be observed that the two forms of press shown inFiguIes l and 2 and in Figure 3 both include the same essential hydraulic pressure chambers, and the descri tion whichv is to follow is therefore to be understood as referring to both embodiments vof the invention.

The hydraulic circuits of 4which each of the forms of press illustrated form a art, are identical. That part of each circuit shown which supplies and controls the application of high pressure fluid to the preing and to the platenreturning chambers includes the -pressing chamberv 3 (3" in Figure 3), the platen returning chamber 4 (4 in Figure 5), a surge tank G, a pump II, a control valve I and piping connecting the aforo-named elements and chambers to complete the circuit.

This piping includes a pump intake pipe 5, a pump discharge pipe 6, high pressure delivery pipes 7 and 8 respectively communieating with the pressing chamber and with the platen returning chambers, an exhaust pipe 9 communicating at one end with the surge tank G and at its other end with one end of the control valve I, and a branch exhaust pipe 10 communicating with the control valve at its other end. For a purpose to be later set forth, a throttle valve J of any conventional design, such as a'globe valve, mav be interposeddn the exhaust pipe.

' The arrangement of the aforenamed parts forming the hydraulic circuit is such that, on the downward stroke of the ram, fluid is drawn from the ram-returning chambers 4 and is delivered to the pressing chamber 3 by way of the pipe 8, the control valve I, the pipe 9, the surge tank, the pipe 5, the pump, the pipe 6, the control valve, and the pipe 7, in the order named. Conversely, during a returri stroke, iiuid is drawn from the pressing chamber 3 and is delivered to the ramreturning chambers 4 by way of the pipe 7, the control valve, the pipes and 9, the

surge tank, the pipe 5, the pump, the pipe 6,

the control valve, and the pipe 8. This ar rangement, providingV for an interchange of Huid between pressing and ram-returning chambers, constitutes a reversible flow hydraulic circuit.

The control valve I may be' any conventional type of four-way operating valve, but for the purposes of illustration, we have shown a valve of the balanced piston valve type comprising a valve casing 11 formed with a chamber 12, a piston valve 13 mounted for sliding movements therein, and including spaced heads 14 and 15 connected by a stem 16, and a stem 17 which is connected to the head and which extends through the lower end of the valve casing. The valve is operated by means of a hand lever 18 pivoted as at 19 on a lug 20 on the valve casing, the lever having pin and. slot connection as at 21 with the lower end of the stem 17. In the position of the valve 13 shown in Figure 1, fluid under pressure discharge through the pipe 6 enters the valve chamber between the heads 14 and 15 and thence iiows through the delivery pipe 7 .and into the pressing chamber, while atthe same time the -platen returning chambers 4 4 are in communication with the surge tank through the medium of the pipe 8, the valve chamber 12 below the valve head 15 and the exhaust pipe 9. When the piston valve 13 is moved to its lower position as shown in Figure 5, the discharge of the pump is directed to the platen returning chambers through the medium of the discharge pipefG, the valve chamber 12, and the pipe 8, and at thelsame time the pressing chamber communicates with the surge tank by means of the. pipe 7, the valve chamber 12 above the head 14, the branch exhaust pipe 10, and the exhaust pipe 9.

For effecting a prefilling o the pressing chamber and for thus permitting a gravitational descent of the platen during the initial part of its pressing stroke, there is provided a surge shifting valve K which includes a valve casing 22 formed with a chamber 23, and a piston valve 24 mounted for sliding movements in said chamber and having spaced heads 25 and 26 connected bya stem 27. The valve casing is provided with a port 28 which is adapted to afford communication between the valve chamber and the surge tank, and with an opening 29 in registry with an opening 30 :Tn the cylinder head which openings together afford communication between the pressing chamber 3 (3n in Figure 3) and the valve chamber 23.- lVhen the piston valve 24 is in the position shown in Figures 2 and 3, the surge tank communicates with the pressing chamber by means of the port 28, the valve chamber 23 and the openings 29 and 30, and when the piston valve is'moved' to the left to its Figure 5 position, the head 26 will cover the port 28 and thereby cut oii' communication between the surge tank and the pressing chamber. Vent openings 31and 32 respectively located at opposte ends of the valve chamber provide for free shifting of the piston valve.

The valve casing 22 is formed at its left hand end, as viewed in the drawings, withl a pressure chamber 33 within which is mounted for slidng movements a head 34 connected to the -head 25 of the piston valve by means of a rod 35, A pipe 36 affords constant communication between the chamber 33 and the platen returning chamber, so that the pressure in the platen returning chamber and, the chamber .33 acts on the head 34 to urge the piston valve 24 t-o-the right.

At its right handend the valve casing is provided with valve closing means comprising a pressure chamber 37 into which a plunger 38 connected to the head 26 of the valve projects. As shown in Figures 2 and 3, the chamber 37 isA connected to a source 39 of variable fluid pressure by means of a. pipe 40, and the pressure fluid thus supplied to the chamber 37 acts on the plunger 38 and urges the latterl and the valve 24 to its closed position. During the descent of the platen under the infiuence of gravity, the fluid contained in the platen returning chambers must be exhausted through the exhaust pipe 9 in order to accommodate the platen returning rams 2. This displacement of the iiuid Jfrom the platen returning chambers results in a building up of back pressure due to therestricted exhaust pipe, the restriction of which may, if desired, be varied by means of the valve J, and the back pressure thus built up acts upon the head 34 and maintains the piston valve 24 in its open position. lVhen the platen encounters the work its downward movement is temporarily arrested so that displacement of the iiuid in the platen returning chambers ceases, resulting in a drop in pressure in the returning chambers and in the chamber 33 of the surge shifting valve, at which time the pressure acting on the plunger 38 moves the surge shifting valve 34 to its Figure 4 position and communicationv between the surge tank and the main cylinder is cut oit, thereby effecting closed communication between the pump and the pressing chamber. The degree of dro in pressure inv the platen returning cham r necessary for effecting the shifting of the piston valve 24 to its closed position may be regulated and selectively fixed by adjusting the valve J, or by regulating pressure in the independent variable pressure source 39.

In the alternative form of surge valve,

shown in Figure 6, the pressure chamber 37 and the plunger 38 are dispensed with Land a sprin 41 interposed between the valve'head 26 an the adjacent end of the-valve casing 1s provided for moving the yalve from its open position to its closed position.

In order that the platen be brought to rest at the end of pressing and return strokes, means are provided for discontinuing the delivery of pressure fluid to the pressin and platen returning chambers at the end o each stroke. In the embodiment of the invention shown, this means comprises. a normally closed pressure actuated by-pass l valve 42 interposed in a pipe 43 connecting the delivery pipe 7 to the exhaust pipe 9, and a similar valve 44 interposed in a pipe 45 connecting the delivery pipe 8 to the exhaust i 9. P glahe operation of a press embodying the invention will be best understood from a description of a complete working cycle. Assuming the various parts to be in the positions shown in Figures l, 2 and 3, the pump will discharge pressure fluid into the discharge pipe 6, thence to the control valve chamber 12, and thence to the pressing chamber 3, (3 in Figure 3) by means of the delivery pipe 7. At this time the surge shifting valve will be in its open position and the surge tank will communicate .with the pressing chamber in the manner described above. The platen returning chamber 4 (4 in Figure 3) will communicate with the surge tank through the medium of the pi 8, the valve chamber 12 of the control va ve, and the exhaust pipe 9. The platen and associated rains will then descend under the iniuence of gravity, the rams 2 at this time displacing the fluid f rom the platen returning chambers and through the pipe 8 and exhaust pipe 9. The fluid 1n the returning chambers serves to cushion the downward travel of the platen, and the rate of descent of the latter may be governed by means of the valve J which serves to variably restrict the flow of fluid through the exhaust pipe 9. During the descent of the platen the back ressure built up-in the platen returning ciiambers will be transmitted to the chamber 33 of the surge shifting valve and will there act upon the head 34 to maintain the piston valve 24 in its open position against the pressure acting upon the plunger 38. When the platen encounters the work .and its descent is thereby temporarily arrested, the back pressure in the platen returning chambers will vanish and the remaining ressure will then bedue only to the static liead of the fluid in the surge tank, which is l.small since the chamber33 is itself disposed in the surge tank. The pressure acting upon the pln er 38 from the independent source 39 will t en move the valve 24 to its Figure 4 position,in which'pusition of the valve communication between the surge tank and the pressing chamber Wi' be cut oil, and discharge of the pump willthus be confined to the pressing chamber where the pressure will act upon the ram 1 to complete the pressing stroke. When the stroke is completed, and a predetermined pressure has bullt up 1n the pressing chamber, the by-pass valve 42 will open and fluid will be returned to the surge tank through the exhaust pipe 9. The piston valve 13 of the control valve I will then be moved down to its Figure 5 position so that the discharge of the ump will be directed to the platen returnlng chambers and the pressure thus created in the chamber 33 will act upon the head-,34 and 'will move the pist0n valve 24 to its open position. The pressure acting in the platen returning chambers will then lift the platen, and the luid remaining in the pressing chamber after the completion of the preceding pressing stroke will be expelled into the surge tank by way of the open surge valve and also by way of the pipe 7 the valve chamber 12 of the control va ve I, the branch exhaust pi e 10, and the exhaust pipe 9. When the p aten has been returned t-o its uppermost position it will enage the press head B and its movement will e arrested.- yPressure will then build up to a predetermined point in the returning cylinders, thus opening the by-pass valve 44, so that the pressure fluid will be returned to the surge tank and the platen will remain at rest. This will complete a cycle of operation of the platen, and .in order to cause the platen to perform another operation, the control valve will be again shifted to its Figure 2 position whereupon the operation just described will be repeated.

In order to simplify the disclosure and' to thus render the fundamental principles underlying the invention most apparent the invention has been described as embodied in a simple form of press and associated circuit in which a common source of` pressure serves for moving the platen in both directions, and in which the reversals of ow of pressure fluid are effected under manual control. It is apparent however, that the invention may be also embodied in presses and associated pressoperating circuits in which a plurality of pressure sources .are provided, and in which automatic control means for reversing the movement of the platen are provided. The invention is defined in the appended claims.

We claim as our invention: l

1. In a press, the combination of reciprocable ram means; cooperating cylinder means having a ram advancing chamber and a ram returning chamber; a surge tank; a reversible flow hvdraulic circuit connectedto the chambers of said cylinder means and providing for interchange of fluid between said chambers for operating the ram means in either direction; and a valve interposed between said tank and said .ram advancing chamber and normally affording communication therebetween and being directly responsive to a decrease in pressure in said ram returningchamber vduring performance of a pressing stroke and prior to building up of pressure in said ram advancing chamber for closing communication between said tank and said ra advancing chamber. v

2. In a press, the combination of reciprocable ram means; cooperating cylinder means having a ram advancing chamber and a ram returning chamber; a surge tank; a reversible ow h 'draulic circuit connected to the chamberso said cylinder means and providing for interchange of iiuid between said'chambers for operating the ram means -in either direction; and a valve interposed between saidl tank and said ram advancing chamber and normally aii'ordin communication Vtherebetween and V4being directly responsive to a predetermined selected decrease in pressure in said ram returning chamber during performance of a pressing stroke and prior to building up of pressure in said ramadvancing chamber for closing communication between said tank and said ram advancing chamber.

3. The combination with a hydraulic -press including a working element mounted for reciprocatory movements, cylinder means having a pressing chamber and a working element returning chamber, and ram means connected to said working element and arranged for reciprocatory movements in said chambers; of a surge tank; a source of iiuid pressure; means forming a reversible flow hy- 'draulic circuit with said surge tank, said source of pressure and the chambers of said cylinder means and providing for interchange of iiuid between said chambers for operating the working element in both directions; and a surge valve normally aording communication between said surge tank and said pressing chamber and being directly responsive to a decrease in pressure in said returning chamber during performance of a pressing stroke and prior to building up of pressure in said pressing chamber for closing communication between said surge tank and said pressing chamber.

4. The combination with a hydraulic press including a working element mounted for reciprocatory movements, cylinder means havingx pressing chamber and a working element-returning chamber, and ram means conf nected to said element and arranged for reciprocatory movements in said chambers; of a surge tank; a source of fluid pressure; means forming. a reversible flow hydraulic circuitwith said surge tank, said source of pressure and the chambers of said cylinder means and providing for interchange of iuid between said chambers for operating said working element in bothdirections; a surge valve interposed between'said surge tank and said pressing chamberand movable to two positions to respectively open and close communication between said tank and said urge sald valve to it closed position; and pressure responsive means associated with said valve and having hydraulic connection -with said returning chamber for'maintaining the valve in open position against the urge of said valve closing means during the initial part of a working stroke, said valve closing means bein operative for moving said valve to its close position when said element meets the work with consequent decrease in pressure in said ,returning chamber and prior to building up ofpressure in said pressing chamber.

5. The combination with a hydraulic ress including a working element mounte for,- -reciprocatory movements, cylinder means having a pressing chamber and a working element returning chamber, and ram means connected to said element and arranged for reciprocatory movements in said chambers; of

Va surge tank; a source of iluid pressure; means forming a reversible flow. hydraulic circuit with saidsurge tank, said sourceof pressure and the chambers of said cylinder means and providing for interchange of fluid `between`saidchambers for operating said element in both directions; a surge valve interposed between said surge tank and said pressingchamber and movable to two positions to respectively open and close communication betweensaid tank and said press- Ving chamber ;=p ressu're actuated valve closing means which urge'said valve to its closed position; and pressure responsive means associated with said: valve and havin hydraulic "connection with said returning c amber for maintaining the valve in open position against the urge of said valve closing meansduring the initial part of a working stroke, said valve closing means being operative for moving said valve to its closed position when said element meets the work with consequent decrease in pressure in said returning chamber and prior to building up of pressure in said pressing chamber.

6. The combination with a hydraulic press including a working element mounted for rec ing chamber for reciprocating said element; a

surge valve interposed between said surge tank and said pressing chamber and movable to two positions to respectively open and close communication between said tank and and pressure responsive means associated with said valve and having hydraulic connection with said returning cliamber tor maintaining the valvey in open position againstthe urge of said valve closing means during the initial part of a working stroke, said valve closing means bein" operative for moving said vvalve to its closed position when said element meets the work with consequent decrease in pressure in said returning chainber and prior to building up of pressure in said pressing chamber.

7. The combination with a hydraulic press including a working element mounted for reciprocatorvmovements, cylinder means hav- .ing a pressing chamber and a working element returning chamber, and ram means connected to said element and arranged for reciprocatory movements in said chambers; of a surge tank; a single source of Huid pressure; means forming a reversible ow hydraulic circuit with said surge tank; said source of pressure and-the chambers of said cylinder means for operating said element in4 both directions, said circuit including an exhaust pipe adapted tobe placed in communication with said returning chamber during a working stroke; means in said exhaust pipe for restricting the iow of fluid from said returning chamber; and a surge valve normally affording communication between said surge tank and said pressing chamber and being directly responsive to a decrease impressure in said returning chamber during `per formance of a pressing stroke and prior to building up of pressure in said pressing chamber for closin communication between said surge tank an said pressing chamber.

8. The combination with a hydraulic press including a working element mounted for reciprocatory movements, cylinder means having a pressing chamber and a working element returning chamber, and ram means c'oiinected to said elementand arranged for reciprocatory movements in said chambers; of a surge tank; a single source of fluid pressure means forming a reversible flow hydraulic circuit with said surge tank, said source of pressure, and the chambers of said cylinder means for operating said element, in Yboth directions, said circuit including an exhaust pipe adapted to be placed in communication with said returning chamber during a working stroke; means in said exhaust pi e for ad] ustably restricting the flow of Hui from said returning chamber; and a surge valve normally affording communication between said surge tank and said pressing chamber and being directly responsive to a decrease in pressure in said returning chamber during performance of a pressing stroke and rior to building up of pressure in said pressing chamber for closing communication beltween said surge tank and said pressing chamber. i

9. The combination with a hydraulic ress including a working element mounte for reciprocatory movements, cylinder means n having a pressing chamber and a working element returning chamber, and ram means connected to said element and arranged for reciprocatorymovements in said chambers; of a surge tank; a source of fluid pressure; means forming a reversible flow hydraulic c'rcuit with said surge tank, said source of pressure, and the chambers of said cylinder means and providing for interchange Wof iuid between said chambers, for o erating saidelement in both directions, sai circuit including an exhaust pipe adapted to be placed in communication with said returning chamber during a pressing stroke; means in said exhaust pipe for restricting the flow` 5 of fluid from said returning chamber; a surge valve interposed between said surge tank Iand Lsaid pressing chamber and movable to two positions to respectively open and close coinmunication between said tank and said pressing chamber, valve closing means which urge said valve to its closed position; and pressure responsive means associated with said valve and having hydraulic connection with said returning chamber for maintaining said gf; valve in open position against the urge of said valve closing means during the initial part of a working stroke, said valve closing means being operative for moving said valve to its closed position when saidvelement meets the 230 work with consequent decrease in pressure in said returning chamber and prior to building up of pressure in said pressing chamber.

10. The combination with a hydraulic ress including a working element mounte reciprocatory movements, cylinder means having a pressing chamber and a working element returning chamber, and ram means connected to said element and arranged for reciprocatory movements in said chambers; of a surge tank; a source of fluid pressure; means'forming a hydraulic circuit with said. surge tank, said source of pressure, and said pressing and returning chambers and including an exhaust pipe and control valve means operatively connected in said circuit and movable to two positions, in the ir'st of which said valve means aifords communication between said source of pressure and said pressing chamber and between said returning' fchamber and said exhaust pipe fOr effecting a working stroke, and in the second of which positions said valve means affords communication between said source of pressure and said returning chamber for eiecting a return stroke; a surge valve normally affording communication between said surge tank and said pressing chamber and being directly responsive to a decrease in pressure in said returning chamber during performance of a for Acal said returning chamber for eii'ecting a pressing stroke and prior to building up of pressure in said pressure chamber for closing communication between said surge tank and 'said pressing chamber.

11. The combination with a hydraulic ress including a working element mounte for reciprocatory movements,e cylinder means having a pressing chamber and a working element returning chamber, and ram means connected to said element and arranged for reciprocatory movements in said chambers; of a surge tank; a source of Huid pressure; means formino a hydraulic circuit with said surge tank, said source of pressure and said pressing and returning chambers and includmg an exhaust pipe and control valve means operatively connected in said circuit and movable to two positions, in the iirst of which said valve means affords communication between said source of pressure and said pressing chamber and between said returning chamber and said exhaust pipe for e'ecting a working stroke and in the second of which positions said valve means affords communication between said source of pressure and return stroke; a surve valve interposed between said surge tank and said pressing chamber and movable to two positions to respectively open and close communication between said tank and said pressing chamber; valve closing means which urge said valve to its closed position; and pressure responsive means associated with said valve and having hydraulic connection with said returning chamberV for maintaining said valve in open position against the urge of said valve closing means during 'the initial part of a working stroke, said valve closing means being operative for moving said valve to its closed position when said working element meets the work with consequent decrease in pressure in said returning chamber and prior to building up of pressure in said pressing chamber.

12. The combination with a hydraulic press including a working element mounted for reciprocatory movements, a pressing cylinder, a working element returning cylinder, and rams connected to said element and respectively arranged for reciprocatory movements in said-cylinders; of a surge tank; a source of fluid pressure; means forming a reversible flow hydraulic circuit with said surge tank, said sourceof pressure and saidcylinders and providing for interchange of fluid between said cylinders or operating the working element in both directions; a surge valve normally affording communication between said surge tank and said pressing cylinder and being directly responsive to a decrease in pressure in said returning cylinder during performance of a pressing stroke and prior to building up of pressure in said pressingchamber for closing communication between said surge tank and said pressing cylinder.

13. The combination with a. hydraulic press including a working element mounted for rec1procatory movements, a pressing cylinder, a working element returning cylinder, and rams connected to said element and respectively arranged for reciprocatory movements in said cylinders; of a surge tank; a source of iluid pressure; means forming a reversible iioiv hydraulic circuit with said surge tank, said source of pressure and said c linders and providing or interchange of uid between said cylinders for operating said working element in both directions; a surge valve interposed between said sur e tank and said pressing cylinder and mova le to two positions to respectively open and close communication between said tank and said pressin cylinder, valve closing means which urge sai valve to its closed position; and pressure responsive means associated with said valve and having hydraulic connection with said returning cylinder for maintainin the valve in open position against the urge og said valve closing means durin the initial part of a working stroke, sai valve closing means being operative for moving said valve to its closed position when said element meets the work with consequent decrease inpressure in said returning cylinder and prior to building up of pressure in said pressing chamber.

14. The combination with a hydraulic press including a working element mounted for reciprocatory movements, a pressing cylinder, a working element returning cylinder, and rams connected to said element and respectively arranged for reciprocatorymovements in said cylinders, of a surge tank; a source of fluid pressure; means forming a reversible iiow hydraulic-circuit with said surge tank, said source of pressure and said cylinders and providing for interchange of iiuid between said cylinders for operating said element in both directions, said circuit including an exhaust pipe adapted to be placed in communication with said returning cylinder during a. working stroke; means in said exhaust pipe for restricting the iiow of iiuid from said returning cylinder; and a surge valve normally affording communication between said surge i tank and said pressing cylinder and being directly responsive to a decrease in pressure in said returning cylinder during performance of a pressing stroke and prior to building up of pressure in said pressing chamber for closing communication between said surge tank and said pressing cylinder.

15. The combination with a hydraulic press including a working element mounted for reciprocatory movements, a hydraulic .cylinder having a cavity comprising pressing and working element returning chambers, and a double acting ram mounted in said cylinder for reciprocatory movements and bein connected to said element; of a' surge tan a source of fluid pressure; means to building up of pressure in said pressing chamber for closing communication between said surge tank and said pressing chamber.

16. The combination with a hydraulic press including a working element mounted for reciprocatory movements, a hydraulic cylinder having a cavity comprising pressing and working element returning chambers, and a double acting ram mounted in said cylinder for reciprocatory movements and being connected to said element; of a surge tank; a source of fluid pressure; means forming a reversible flow hydraulic circuit with said sur e tank, said source of pressure and the c ambers of said cylinder and providing for interchange of fluid between said chambers for operating said working element inboth directions; a surge valve interposed between said surge tank and said pressing chamber and movable to two positions to respectively open and close communication between said tank and said pressing chamber; valve closing means which urge said valve toits closed position; and pressure responsive means associated with said valve and havin hydraulic connection with said returning c amber for maintaining the valve in open osition against the urge of said valve closing means during the initial part of a working stroke, said valve closing means being operative for moving said valve to its'closed position when saidelement meets the work w1thconsequent decrease in pressure in said returning chamber and prior to building up of pressure in said pressing chamber.A

17. The combination with a hydraulic press including a working element mounted or reciprocatory movements, a hydraulic cylinder having a cavity comprising pressing and workin element returning chambers, and a dou le acting ram mounted in said cylinder for 'reciprocatory movements and being connected to said element; of a surge tank; a source of fluid pressure; means forming a reversible flow hydraulic circuit with said surge tank, said source of pressure and the chambers .of said cylinder and providing for interchange of fluid between said chambers for operating said element in both directions, said circuit including an exhaust pipe adapted to be placed in com-v munication with said returning chamber during a working stroke;means in said exhaust pipe for restricting the flow of fluid from said returning chamber; and a surge valve normallyaf'fording communication between said sur tank and said pressing chamber and being directl responsive to a decrease in pressure in sai returning chamber during performance of a pressing stroke and prior to building up of pressure in said pressing chamber for closing communication between said surge tank and 'said pressing chamber.

18. The combination with a hydraulic press including a Vworking element mounted for reciprocatory movements, cylinder means having a pressin chamber and a working element returning c amber, and ram means connected to said element and arranged for reciprocatory movements in said chambers ;of a surge tank; a source of fluid pressure; means forming a reversible flowv hydraulic circuit with said surge tank, said source of pressure and the cham ers of said cylinder means and providing for interchange of fluid between said chambers for operating said working element in both directions; a surge valve interposed between said sur e tank and said pressing chamber and Inova le to two positions to respectively open and close communication between said tank and said pressing chamber; adjustable valve closin means which urge said valve to itsclose position; and pressure responsive means associated with said valve and having hydraulic connection with said returning chamber or maintaining the valve in open position against the urge of said valve closing means during the initial part of a working stroke, said valve closing means being operative for moving said valve to its closed position when said element meets the work with consequent decrease in pressure in said returning chamber and prior -to building up of pressure in said pressing chamber.

19. The combination with a hydraulic ress including a .working element'mounted or reciprocatory movements, cylinder means having a pressing chamber and a working element returning chamber, and ram means conl nected to said element and arrangedfor reciprocatory movements in said chambers; of a surge tank; a source of fluid pressure; means forming a ,reversible flow hydraulic circuit with said sur e tank, said source of pressure and the cham ers of said cylinder means and providing for interchange of fluid between said chambers for operating said element in both directions; a surge valve interposed between said surge tank and said pressing chamber and movable to two positions torespectively open and close communication between said tank and said pressing chamber;

pressure actuated valve closing means associated with said valve; an independent source of variable fluid pressure having hydraulic I connection with said valve closing means, the pressure from said lndependent source urging said valve closin means and said valve to the closed position o the latter' and pressure responsive means associated wlth said valve and having hydraulic connection with said returning chamber for maintaining the valve in open position against the urge of said valve closing means during the initial part of a working stroke, said valve closing means being operative for movin said valve to its closed position when sai element meets the work with consequent decrease in pressure in said returning chamber and prior to building up of pressure in said pressin chamber.

20. In a press, the combination of reciprocable ram means; cooperating cylinder means having a ram advancing chamber and a ram returning chamber; a pump; hydraulic connections between said pump and said chambers; a reversing valve in said connections for directing Huid from said pump alternately to said chambers; and other valve means directl responsive to a decrease in pressure in sai ram returning chamber during performance of a pressing stroke and prior to building up of pressure in said ram advancing chamber for effecting closed communication between said pressure source means and said pressing chamber.

In testimony whereof, we have hereunto subscribed our names.

WALTER ERNST. HOWARD F. MAOMILLIN.

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