US2070720A

US2070720A - Hydraulic press operating circuits and valves therefor

Info

Publication number: US2070720A
Application number: US581985A
Authority: US
Inventors: Ernst Walter
Original assignee: HYDRAULIC PRESS CORP Inc
Current assignee: HYDRAULIC PRESS Corp Inc
Priority date: 1931-12-18
Filing date: 1931-12-18
Publication date: 1937-02-16
Anticipated expiration: 1954-02-16

Description

Feb. 16, 1937. w.,ERNs'r "HYDRAULIC PRESSOPERATING CIRCUITS `AND VALVES THEREFOR Fled Dec. 18, 1331 2 Sheets- Sheet 1 I :invento Wlzzfep'rma,

II-feb. 16,1931.'

Filed Dec. 18. 19:51 2 Sheds-sheet 2 V la Gttomegs,

. Patented Feb. 16, 1937 UNITED STATES PATENT oFFlcE HYDRAULIC PRESS OPERATING CIRCUITS AND VALVES THEREFOR tion of Delaware Application December 18, 1931, Serial No. 581,985

15 Claims.

This invention relates to hydraulic press-operating circuits and to valve mechanism therefor. More particularly the invention relates to hydraulic press-operating circuits in which the fluid flow is controlled by main control valve means the operation of which is in turn controlled by means of pilot valve mechanism.

Press-operating circuits of this general kind have been known heretofore and have been found especially adaptable for use where the nature of the installation and the kind of operations to be performed by the press render impractical or difficult the direct actuation of the control valve without the use of an auxiliary or pilot valve. An object of the present invention is to provide an improved arrangement of press, press-operating circuit, and associated valve mechanism of the general character referred to which is more simple than prior arrangements and vhich, at thev same time, is adapted for e'icient operation under varying working conditions.

A more specic object is to provide such an arrangement in which the pilot valve is automatically operated by the buil-ding up of pressure inthe press-operating circuit, thus dispensing with the necessity of using a separate pilot circuit as has been common heretofore.

Another object is to provide an improved construction of control valve and pilot -valve mechanism. Other objects will become apparent from a reading of the following description, the appended claims, and the accompanying drawings.

In the drawings, Figure 1 includes a view in front elevation of a press, a somewhat diagrammatic showing of an associated hydraulic pressoperating circuit, and a vertical sectional view of the valve mechanism drawn on an enlarged scale, and

Figure 2 embodies a showing similar to that of Figure 1 but illustrating a modification of the invention.

'Ihe invention may be embodied in press-operating circuits employed in connection with various kinds of hydraulic presses, but for the purposes of illustration I have shown in the drawings a press A of the downward pressure type including a base I, a press head 2 connected to the. base by means of strain rods 3, and a platen 4 mounted on the strain rods for reciprocation towards and away from the base I. A cylinder 5 is carried by the press head, and mounted in this cylinder is a double-acting ram 6 connected to the platen by means of an extension or rod 1. That part of the cylinder cavity above the ram 6 constitutes a ram-advancing or pressing Chamber 8, and the part of the cylinder cavity below the ram 6 constitutes a ram-returning or pull-back chamber 9.

In operation, fluid under pressure is introduced into the ram-advancing chamber 8 for moving the platen downwardly on a pressing stroke, and,

after such stroke has been completed, fluid is introduced into the ram-returning chamber 9 to move the ram and platen upwardly on a return stroke.

For furnishing fluid under pressure to the ramadvancing and the ram-returning chambers. I have provided a pump B which may be of any suitable kind and means forming a hydraulic press-operating circuit withthe pump and

chambers

8 and 9 of the press cylinder 5, this means including a reservoir C, a valve mechanism D, and suitable connecting piping. 'I'his piping includes a pump suction pipe I0 connected between the intake side of the pump and the tank C, a pump discharge pipe II connected between the outlet side of the pump and the valve mechanism D, a delivery pipe I2 connected between the valve mechanism D and the ram-advancing chamber 8 of the press cylinder, a delivery pipe I3 connected between the valve mechanism and thevram-returning chamber 9 of the press cylinder, and an exhaust pipe I4 connected between the valve mechanism D and the tank C. A pump discharge return pipe I5 is connected between the pipe II and the tank C, and a valve I6 is Ainterposed in this pipe for controlling the flow of fluid therethrough and provides means for diverting the pump discharge from the valve mechanism D and consequently from the press at any time.

The valve mechanism generally designated D includes a casing I1 formed with a control valve chamber I B and a pilot valve chamber I9, the latter being the middle part of a long bore I9a extending through the casing parallel to the control valve chamber. The opposite ends of the control valve chamber are in constant communication through the medium of a cored passage 20, and the latter is in turn in constant communication with the exhaust pipe I4 by means of a second cored passage 2| oneend of which opens into the cored passage 20 and the other end of which opens into the bore I9a. The pipe I4 communicates with the cored passage 2| intermediate its ends.

Referring now to that part of the valve mechanism which controls the flow of iluid `to and from the press, the pump delivery pipe II communicates with the control valve chamber I8 approximately midway of the length thereof, the

pipe l2 communicates with an annular enlarged part 22 at one end of the control valve chamber, and the pipe I3 communicates with an annular enlarged part 23 at the opposite end of said 5 chamber.

Mounted in the control valve chamber is a pressure-responsive control valve element 24 comprising spaced

heads

25 and 26 connected by an 'intervening reduced portion 21, and a stem 28 extending outwardly from the head 25 and passing through packing 29 held in place by means of a gland nut 30. An enlargement 3l on the stem 28 is adapted to abut against the adjacent end wall of the valve chamber for limiting l5 movement of the valve element 24 to the left.

In operation, when the valve 24 is in the position shown in Figure 1, fluid delivered by the pump B will ilow through the pipe II, that part of the control valve chamber I8 included between the heads and 26, and then through the pipe I2 into the pressing chamber 8, thereby driving the ram 6 downwardly. At this time fluid contained in the ram-returning chamber 9 will flow outwardly therefrom through the pipe I3, that part of the valve chamber I8 included between the head 26 and the adjacent or right hand end of the valve chamber, the cored passages 20 and 2I, and the pipe I4 to the tank C. When the ram is in its lower position and the valve 24 has been moved to the right in a manner to be later described, the head 25 will be disposed in a position to? the right of the enlarged annular part 22 of the'control valve chamber and the head 26 will'be disposed to the right of the enlarged annular part 23. Fluid delivered by the pump B will then enter through the pipe I I, that part of the control valve chamber included between the

valve heads

25 and 26, the pipe I3, and thence to the ram-returning chamber 9, thereby driving the ram upwardly. During the ascent of the ram, fluid contained in the pressing chamber 8 of the press cylinder will ow outwardly through the pipe I2, that part of the control valve chamber included between the head 25 and the adjacent or left hand end of the valve chamber, the cored passages 20 and 2I, the exhaust pipe I4, and thence to the tank C.

In accordance with the invention, the control valve 24 is arranged to be actuated by a device 50 which is responsive to the pressure in the pressoperating circuit, the application of such pressure to this device being controlled by a pilot valve which may likewise be operated by the pressure existing in the press-operating circuit, no separate source of pressure being provided for actuating the main control valve or the pilot valve. In the illustrative embodiment of the invention, the valve casing I1 is formed with a pressure cylinder 32 disposed to the right of and in alignment with the valve chamber I8, and a piston 33 connected to the valve 24 by means of a stern 34 is slidably mounted in the cylinder. Hydraulic connections or

ducts

35 and 36 are formed in the valve casing for admitting fluid under pressure to the opposite ends of the pressure cylinder 32 for actuating the piston 33 and the control valve 24. Fluid under pressure is admitted from the press-operating circuit to the pilot valve chamber I9 by means of a branch pipe 31 connected to the pump discharge pipe II and communicating with the pilotvalve chamber. The admission of pressure fluid through the

ducts

35 and 36 is controlled by a pressure-responsive pilot valve 38 which is mounted for free sliding move- 75 ments in the pilot valve chamber I9,

. sition.

The pilot valve is preferably of the spool type and comprises

heads

39 and 46 connected by a reduced portion 4 I, a stem 42 extending outwardly from the head 39, and a stern 43 on theopposite end of the valve extending outwardly from the head 40.

In operation, when the pilot valve 38 is in the position shown in Figure l, iluid from the discharge pipe II of the press-operating circuit will flow through the branch pipe 31, that part of the pilot valve chamber included between the

heads

39 and 49 of the pilot valve, and the duct 36 into the right hand end of the pressure cylinder 32, thus acting upon the outer end of the piston 33 and moving the valve to its Figure 1 po- During this movement of the piston 33 from a position to the right of that shown in Figure 1 toward the left, fluid contained in the left hand end of the pressure cylinder 32 will flow outwardly through the duct 35, that part of the pilot valve chamber on the left of the valve head 39, an opening 43a in the valve casing, the cored passages 20 and 2I, the exhaust pipe I4, and thence to the tank C. When the pilot valve has been moved to the left in a manner to be later described, the head 39 will be disposed to the left of the duct 35, and the head 40 will be disposed to lthe left of the duct 36. Fluid will then flow from the discharge pipe I I of the pressoperating circuit through the pipe 31, that part of the pilot valve chamber included between the heads of the pilot valve, and the duct 35 into the left hand end of the pressure cylinder 32, thereby moving the piston 33 and the control valve 24 toward the right. During this movement of the piston 33 fluid contained in the right hand end of the pressure cylinder 32 will ow outwardly through the duct 36, that part of the pilot valve chamber on the right of the valve head 49, the cored passage 2I, the exhaust pipe I4, and thence to the tank C.

In accordance with the invention, the pilot valve is adapted to be actuated in at least one direction by means oi a device responsive to the pressure in the press-operating circuit. In the embodiment illustrated in Figure 1 the valve mechanism D is provided with a pressure-responsive device or piston 44 mounted for sliding movements in the right hand end of thebore I9a., and being formed with a stem 45 which extends inwardly toward and in alignment with the stern 43 of the pilot valve. A second stem 46 extends outwardly from the piston 44 through a closure 41, and a spring 48 interposed between this closure and a washer 49 held in place on the end of the stem by means of a nut 50 serves to urge the piston device 44 outwardly so that normally the stern 45 is spaced from and out of contact with the stem 43 of the pilot valve. A branch pipe 5I is connected at one of its ends with the pipe I2 leading to the ram-advancing chamber and at its other end communicates with a pressure chamber 52 between the piston 44 and the closure 41.

Another pressure-responsive device or piston 53 is mounted for sliding movements in the bore I9a and is provided with a stem 54 extending inwardly toward and in alignment with the stem 42 of the pilot valve. A second stem 55 extends outwardly from the piston element 53 through a closure 56, and a spring 51 interposed between the closure and a washer 58 held in place on the outer end of the stem 55 by means of a nut 59 serves to urge the piston 53 to the left, Aso that the stem 54 is normally spaced from and out of contact with the stem 42. A branch pipe 6U is connected at one of its ends with the pipe I3 of the press-operating circuit, and at its .other end communicates with a pressure chamber 6I between the piston 53 and the adjacent closure 56. The

springs

48 and 51 normally maintain the associated pistons 44 and 53 out of contact with the pilot valve, and the latter, being of the spool valve type, is therefore maintained in position by virtue of its being pressure-balanced, as will be apparent.

In operation, when the platen 4 has engaged the work during the pressing stroke, pressure will build up in the ram-advancing chamber 8 on the upper side of the ram. This pressure acting through the branch pipe 5I and in the pressure chamber 52 will move the piston 44 inwardly against the urge of the spring 48. During this movement the stem 45 will contact with the stem 43 of the pilot valve and move the latter to the left so as to admit fluid under pressure through the pipe 31, the pilot valve chamber, and the duct 35 into the left hand end of the pressure cylinder 32, thereby moving the piston 33 and the control valve 24 to the right so as to cause a return stroke of the ram to be performed in the manner already described. When the ram has approached the end of the return stroke, the plat en 4 will engage the cylinder so as to prevent further upward movement of the ram. This will result in a building up of pressure in the ram-returning chamber 9 and a consequent building up of pressure in the pipe I3, the branch pipe 60, and the pressure chamber 6I, thus causing the piston 53 to be moved to the right so as to bring the stem 54 into engagement with the stem 42 of the pilot valve and to move the latter from the left toward the right to its Figure 1 position. This will cause fluid from the pressoperating circuit to be delivered to the right hand end of the pressure cylinder 32, where it will act upon the piston 33 to move the control valve 24 to the left and to effect the start of another pressing stroke. By means of the pressure-responsive pistons 44 and 53 located atopposite ends of the pilot valve, the press will automatically perform an indeterminate number of pressing and return strokes, the reversals at the ends of such strokes being effected by building up pressure in the ram-advancingchamber 8 and in the ram-returning chamber 9.

In some cases it is desirable that the press ram be brought to rest automatically at the end of each return stroke instead of being reversed and started automatically upon another pressing stroke. In accordance with a further feature of the invention, I provide means for adapting the press for such operation when desired, this means including a by-pass valve E mounted on the press head and interposed between a branch pipe 62 connected at one of its ends to the pipe 60 which leads to the ram-returning chamber 9, and connected at its other end by a branch pipe 63 with the exhaust pipe I 4 which leads to the tank C. The valve E comprises a casing 64 and a piston valve element 65 mounted for' sliding movements therein. The valve element includes spaced heads 66 and 61 connected by a reduced portion 68 and a stem 69 extending downwardly through the lower end of the valve casing and through lugs 10 and 1I on the press platen and press base respectively. A spring 12 interposed between the lug 1I and a collar 13 on the lower end of the A stem 69 constantly urges the valve 65 downwardlimited by engagement of the head 61 with the lower end of the valve casing. A collar 1 4 is secured to the stem 68 in adjusted position and is adapted to be engaged by means of the lug 10 on the press platen when the latter approaches the end of a return stroke for raising the stem 68 and the valve 65, which, as will be later described, has the effect of by-passin'g the pump discharge to the tank and bringing the platen and the valve 65 to rest in their Figure 1 positions. In order to move the valve 65 still further upwardly to start the press on a. downward stroke in a manner to be described, I have provided a footoperated treadle 15 pivotally mounted upon a bracket 16 and having a rounded head 11 adapted to engage the lower end of the stem 69 for lifting the latter and the valve 65.

The branch pipe 62 and the branch pipe 63 communicate with the interior of the valve casing 64 at spaced points as indicated in Figure 1. When the valve 65 is in the Figure 1 position, each -of the

pipes

62 and 63 communicates with the valve casing between the heads 6B and 61. When the valve 65 is moved downwardly from its Figure l position, the head 66 will cut ofi communication between the branch pipe 63 and the valve chamber, and when the valve 65 is moved upwardly from its Figure 1 position the head 61 will cut off communication between the branch pipe 62 and the valve chamber.

In order that the cooperation of all of the parts of the press and press-operating circuit may be clearly understood, a complete operating cycle will be briey described.

It will be assumed that it is desired that the press operate under fully automatic control, that is, in such a way that the platen will perform an indeterminate number of pressing and return strokes. The collar 14 on the stem 69 will be rst moved to the dotted line position shown in Figure 1 so as not to be engaged by the lug 10 when the platen approaches the end of a return stroke. The pump will then be started and iiuid discharged thereby will ow through the pipe II, the control valve chamber I8`, and the pipe I2 into the ram-advancing chamber 8, thus moving the ram downwardly. At this time fluid contained in the ram-returning chamber 9 will ow outwardly through the pipe I3, the control valve chamber I8, the cored passages 20 and 2|, the pipe I4, and thence to the tank C. When the platen encounters the work and pressure builds up in the ram-advancing chamber 8, this pressure, acting through the branch pipe 5I and in the pressure chamber 52, will move the piston 44 to the left, thereby shifting the pilot valve 38 to a position in which pressure fluid from the lpipe II will act through the branch pipe 31, the pilot valve chamber I9, and the duct 35, thereby moving the piston 33 and the control valve 24 to the right. l Fluid delivered through the pipe II will lthen flow into the control valve chamber and thence through the pipe I3 into the ramreturning chamber in the manner heretofore described so as to move the ram and platen upwardly. At this time fluid contained in the ramadvancing chamber will flow outwardly'through thepipe I2, the control valve chamber I8, the cored passages 20 and 2|, the exhaust pipe I4, and thence to the tank C. During the ascent of the ram, the pressure in the ram-advancing chamber 8 and consequently in the pressure chamber 52 will drop, so that the spring 48 will return the piston 44 to its right hand position wherein the stem 45 is spaced from and out of contact with the stem 43 of the pilot valve. When the ramreaches the end of a return stroke, the platen 4 will engage the cylinder 5, the latter arresting movement of the ram andcausing a building up of pressure in the ram-returning chamber 9 and consequently in the pipe I3, the branch pipe 60, and the pressure chamber 6I, whereby the piston 53 will be moved toward the right so that the stem 54 will engage the stem 42 of the pilot valve and move the latter to the right to its Figure 1 position. Pressure fluid from the pipe II will then be delivered through the branch pipe 31, the pilot valve chamber I8, and the duct 36 to the pressure cylinder 32 so as to act upon the piston 33 and move the latter to the left to its Figure l position, whereupon another pressing stroke will automatically begin.'

If it is desired that the press operate under semi-automatic control, the collar 14 is moved to its full line position as shown in Figure 1 and there secured 1n fixed position to the stem 69. It will be assumed that a pressing stroke has been begun. The latter part of the pressing stroke, the reversal of the end thereof, and the first part of a return stroke will be performed in the same manner as when the press is arranged for fully automatic operation. When the ram approaches the end of a return stroke, the lug 10 on the platen will engage the collar 14 and move the stem 69 and by-pas valve 65 upwardly to the position shown in Figure 1. With the valve in this position, fluid will be by-passed from the pipe I3 by means of the pipe 60, the branch pipe 62, the by-pass valve, and the branch pipe 63, the fluid thus by-passed being returned to the tank C by means of the exhaust pipe I4, so that the upward movement of the ram will be arrested.

In actual operation, the ram will move upwardly until the head 66 has uncovered the pipe 63 to an extent to provide an opening of such size as to produce a suiiiciently throttled ow for maintaining enough back pressure to hold the ram and platen at rest in their upper positions.

When it is desired to start another Working stroke, the treadle 15 will be depressed, thereby raising the stem 69 and the valve 65 still further until the head 61 cuts oi ow through the branch pipe 62. Fluid then will flow to the ram-returning chamber 9 again, causing the ram to move upwardly until the platen 4 engages the lower end of the cylinder, thus causing a building up of pressure in the ram-returning chamber and in the pressure chamber 6I, whereupon the pilot valve will be shifted to its Figure l position in the same manner as when the press is operated under fully automatic control as described above.

Under some conditions it is desirable that, when the press is operating under fully automatic control, the reversals at the end of return strokes be effected when the ram reaches a predetermined position and without any building up. of pressure in the ram-returning chamber. In the modified embodiment of the invention illustrated in Figure 2, control mecha- Anism for effecting such a position-controlled reversal is provided. In this form of the invention the pressure-responsive device or piston 53 described in connection with Figure l, the associated spring 51, and branch pipe 68 are omitted, and ram-operated means are employed in place of the piston device 53 for shifting the pilot valve to the right at the end of a return stroke for automatically effecting the start of a return stroke. 'The means illustrated for accomplishing this purpose includes a stem 18 extending through the closure 56 at the left of the pilot valve chamber and in alignment with but normally spaced from the stem 42 of the pilot valve. A link 19 is connected between the outer end of the stem 18 and onearm 88 of` a pivoted bell crank lever 8|, the other arm 82 of which has pin-and-slot connection as at 83 with a vertically disposed valve operating rod 84. This rod extends through .a lug 85 carried by the press platen and a lug 86 on the base I of the press. A spring 81 is interposed between the lug 86 and a collar 88 adjacent the lower end of the rod 84 for urging the latter downwardly, and a collar 89 secured to the rod above the lug 86 limits the downward movement of the rod. A collar 90 secured to the rod 84 in adjusted position is adapted to be engaged by the lug 85 on the platen when the ram approaches the end of a return stroke, and to be lifted thereby so as to raise the rod 84 and to rock the bell crank lever 8I in a clockwise direction, thereby moving the stem 18 toward the right into engagement with the stem 42 of the pilot valve and moving the latter to its right hand or Figure 1 position.

With the exception of the substitution of the ram-actuated

means

84, 8I, 18, etc. for the pressure-responsive means 53, 54, etc. of the form shown in Figure i, the omission of the branch pipe 60, and the connecting of the branch pipe 62 directly to the pipe I3, the modification illustrated in Figure 2 is the same as that shown in Figure 1, so that a description of the other parts of the press-operating circuit and associated mechanism is not considered necessary. The same reference numerals have been applied in each figure to indicate corresponding parts.

The arrangement shown in Figure 2 may also be adapted for either fully automatic or semiautomatic control.

If it is desired that the press operate under fully automatic control, the collar 14 on the bypass valve stem 69 is raised to the dotted line position so as not to be engaged by the lug 18 on the platen. Assuming that the platen and ram are performing a return stroke, the lug 85 on the platen will eventually engage the collar 90 on the rod 84 so as to lift the latter and thereby to move the stem 18 inwardly into contact with the stem 42 of the pilot valve so as to move the 'latter toward the right to the Figure l position, which, as previously described, will cause the control valve 24 to be shifted tothe left to start automatically another pressing stroke.

If it is desired that the press shown in Figure 2 operate under semi-automatic control, the collar 14 is moved to its full line position on the by-pass valve stem 69. Assuming that' the ram and platen are moving upwardly on a return stroke, the by-pass valve will eventually be moved to the position shown in the drawings so as to effect a by-passing of fluid from the platen-returning chamber to the exhaust pipe I4 in the manner described with reference to the arrangement shown in Figure 1. This will cause the ram to be brought to rest. When it is desired to start another pressing stroke, the treadle 15 is operated to raise the by-pass valve 65 so as to cut off flow of fluid through the pipe 62. Fluid then will be delivered again to theram-returning chamber so as to move the ram upwardly until the lug 85 engages the collar 90 so as to raise the rod 84 and shift the pilot valve in the manner already described.

Although for the purposes of illustration the invention has been disclosed'as being embodied in connection with a press provided with a platen especially adapted for the performance of pressing operations, it is to be understood that the invention may also be embodied in connection with hydraulic motors the rams of which are provided with shears, punches, dies, or similar tools, and that various other modifications may be made in the arrangements disclosed without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. The combination with a hydraulic press including double-acting ram means; of a pump; means forming a hydraulic press-operating circuit With said press and pump; a pressure responsive reversing valve in said circuit; a pressure responsive flow-controlling pilot valve having its valve chamber connected to said pressoperating circuit for controlling operation of said reversing valve; and a ram operated by-pass valve connected to said press-operating circuit -for controlling communication between said press operating circuit on one side of said ram means and the intake side of said pump.

2. .The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-.returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said press-operating circuit; a pilot valve interposed in said connections; means for operating said pilot valve including pressure responsive means for operating the pilot valve in at least one direction; a hydraulic connection between said last named pressure responsive means and said press-operating circuit; a normally closed by-pass valve interposed between said ram-returning chamber and the intake side of said pump; and ram-operated means connected to said by-pass valve for operating the latter when said ram means approaches the end of a return stroke.

3. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating cir- -cuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said press-operating circuit; a ,pilot valve interposed in said connections; means associated with said pilot valve and being responsive to building up of pressure in said press-operating circuit at the ends of both advancing and return strokes of said ram means and irrespective of the length of the advance stroke thereof for operating the latter in vboth directions; hydraulic connections between said last named pressure responsive means and said pressoperating circuit; a normally closed by-pass valve interposed between said ram-returning chamber and an exhaust; ram operated means connected to said by-pass valve for opening the latter when said ram means approaches the end of a return stroke; and manually operable means connected to said by-pass valve for closing the latter when said ram means is at rest at the end of a return stroke.

4. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said press-operating circuit; a pilot valve interposed in said connections; means associated with said pilot valve and being responsive to building up or' pressure in said press-operating circuit at the ends of both advancing and return'strokes of said ram means and irrespective of the length of the advance stroke thereof for operating the latter in both directions; hydraulic connections between said last named pressure responsive means and said press-operating circuit; a normally closed bypass valve interposed between said ram-returning chamber and an exhaust; ram operated means connected to said by-pass valve for moving the latter in one direction to open said valve when said ram means approaches the end of a return stroke; and manually operable means connected to said by-pass valve for moving the latter in the same direction to close said valve while said ram means is at rest.

5. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said press-operating circuit; a pilot valve interposed in said connections; means associated with said pilot valve and being responsive to building up of pressure in said press-operating circuit at the ends of both advancing and return strokes of said ram means and irrespective of the length of the advance stroke thereof for operating the latter in both directions; hydraulic connections between said last named pressure responsive means and said press-operating circuit; anormally closed bypass valve interposed between said ram-returning chamber and an exhaust; ram operated means connected to said by-pass valve for opening the latter when said ram means approaches the end of a return stroke; disconnectable means adapted to be interposed between said ram and said ram operated means; and manually operable means connected to said by-pass valve for closing the latter when said ram means is at rest at the end of a return stroke.

6. The combination with a hydraulic press including reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; valve mechanism associated with said circuit including a main control valve in said circuit, a pressure cylinder, a double-acting hydraulic piston in said cylinder and being connected to said control valve, ducts adapted to aiford communication between both ends of said cylinder and said press-operating circuit; a pilot valve for controlling such communication, and means responsive to building up of pressure in said press-operating circuit and separate from but engageable with the pilot valve for operating the latter; and hydraulic connections between said pressure responsive means and said press-operating circuit.

7. The combination with a hydraulic press including reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; and valve mechanism associated with said press-operating circuit, including a. main control valve in said pressoperating circuit, a pressure cylinder, a doubleacting hydraulic piston in said cylinder and being connected to said control valve, ducts adapted to. afford communication between both ends of said cylinder and said press-operating circuit; a pilot valve for controlling such communication, a pressure chamber, a hydraulic piston therein, said piston being separate from but engageable with said pilot valve for operating the latter, means for urging said piston away from said pilot valve, and means for supplying pressure fluid from said press-operating circuit to said pressure chamber to move said-piston into engagement with said pilot valve.

8. The combination with a hydraulic press including reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; and valve mechanism associated with said circuit including a main control valve in said circuit, a'pressure cylinder, a double-acting hydraulic piston in said cylinder and being connected to said control valve,` ducts adapted to afford communication between both ends of said cylinder and said press-operating circuit; a pressure balanced pilot valve for controlling such communication, pressure chambers located respectively at opposite ends of said pilot valve, hydraulic pistons in said chambers and being separate from but independently engageable with said Valve for operating the latter in opposite directions respectively, means for urging said pistons away from said pilot valve, and means for supplying pressure iiuid from said press-operating circuit to said chambers.

9. The combination with a hydraulic press including reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit With said press and pump; and valve mechanism associated with said press-operating circuit including a pressure responsive control valve in said press-operating circuit, a pilot valve connected in said press-operating circuit for controlling operation of said control valve, and means responsive to building up of pressure in said press-operating circuit and separate from but engageable with the pilot valve for operating the latter.

10. The combination with a hydraulic press including reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; and valve mechanism associated with said press-operating circuit including a pressure responsive control valve in said circuit, a pilot valve connected in said press operating circuit for controlling operation of said control valve, a pressure chamber, a hydraulic piston therein, said piston being separate from but engageable with said pilot valve for operating the latter, means for urging said `piston away from said pilot valve, and means for supplying pressure fluid from said press-operating circuit to said pressure chamber to move said piston into engagement with said pilot valve.

11. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a freely shiftable reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said press-operating circuit; a pilot valve interposed in said connections; spring loaded means associated with said pilot valve and being responsive to building up of pressure in said press-operating circuit at the ends of both advancing and return strokes of said ram means and irrespective of the length of the advance stroke thereof for operating the latter in both directions; and hydraulic connections between said last named pressure responsive means and said press-operating circuit.

12. The combination with a hydraulic press including double-acting ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; a reversing Valve in said circuit; pressureresponsive means associated with said reversing valve for operating the latter; hydraulic connections between said pressure responsive means and said press-operating circuit; a pilot valve interposed in said connections; pressure responsive means associated with said pilot valve for operating, the latter when said ram means approaches one end of its travel; a hydraulic connection between said last named pressure responsive means and said pressoperating circuit; and ram operated means for operating said pilot valve when said ram means approaches the opposite end of its travel.

13. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said circuit; a pilot valve interposed in said connections; pressure responsive means associated with said pilot valve for operating the latter in one direction when said ram means approaches one end of its travel; a hydraulic connection between said last named pressure responsivemeans and said circuit; ram operated means for operating said pilot Valve in the other direction when said ram means approaches the opposite end of its travel; a normally closed by-pass valve interposed between said ram-returning chamber and an exhaust; ram operated means connected to said by-pass valve for opening the latter when said ram means approaches the end of a return stroke; and manually operable means connected to said by-pass valve for closing the latter when said ram means is at rest at the end of a return stroke.

14. The combination with a hydraulic press including cylinder means having a ram-advancing and a ram-returning chamber and cooperating double-acting ram means therein; of a pump; means forming a hydraulic press-operating circuit with said pump and said chambers; a reversing valve in said circuit; pressure responsive means associated with said valve for operating the latter; connections between said pressure responsive means and said circuit; a pilot valve interposed in said connections; pressure responsive means associated with said pilot valve for operating the latter in one direction when said ram means approaches one end of its travel; a hydraulic connection between said last named pressure responsive means and said circuit; ram operated means for operating said pilot valve in the other direction when said ram means approaches the opposite end of its travel; a normally closed by-pass valve interposed between said ram-returning chamber and an exhaust; ram operated means connected to said by-pass valve for moving the latter in one direction to open said valve when said ram means approaches the end of a return stroke; and manually operable means connected to said by-pass valve for moving the latter in the same direction to close said valve while said ram means is at rest.

15. The combination with a hydraulic press lncluding reciprocable ram means; of a pump; means forming a hydraulic press-operating circuit with said press and pump; and valve mechanism associated with said circuit including a main control valve in said circuit, a pressure cylinder, a double-acting hydraulic piston in said cylinder and being connected to said control valve, ducts adapted to afford communication between both ends of said cylinder and said circuit; a. pressure balanced pilot valve for controlling such communication, a pressure chamber, a hydraulic piston therein, said piston being separate from but engageable with said pilot valve for operating the latter in one direction, means for urging said piston away from said pilot valve, means for supplying pressure fluid from said circuit to said pressure chamber to move said piston into engagement with said pilot valve for operating the latter in one direction, and ram operated means also separate from said pilot valve but being engageable therewith for operating it in the opposite direction.

WALTER ERNST.