US2072141A - Press system - Google Patents

Description

T. F. STACY March 2, 1937.

PRESS SYSTEM i'i-led May is, 1953 2 Sheets-Sheet 1 WQM March 2, 1937. T. F. STACY 2,072,141

PRESS SYSTEM Filed May 15, 1933 2 Sheets-Sheet 2 fi/ (7 a! if 55'- /fii 1% J Jif 61f" AZY'WJ.

?atented Mar. 2, 1937 UNITED STATES PRESS SYSTEM Thomas F. Stacy, Piqua, Ohio, assignor to The French Oil Mill Machinery (30., Piqua, Ohio Application May 15, 1933, Serial No. 671,197

27 Claims.

This invention relates to press systems and particularly to an improved manner of controlling the operations of a press. An object of the invention is to provide an improved system for hydraulic presses and the like, by which the operations of the press may be carried out more or less automatically, and which will be extremely simple, dependable, and inexpensive.

Another object of the invention is to provide an improved system for hydraulic presses and the like, in which changes in the operation of the press may be established quickly; with which the operation of the press will be rapid; with which there will be a maximum number of safeguards-against injury to the operators, and with which the power stroke of the press may be continued for any selected and predetermined interval of time after the platen passes a selected point in its travel and then automatically stopped.

Another object of the invention is to provide an improved controlling system for hydraulic presses and the like with which the operator must have both hands out of dangerous positions with respect to the press before the press can be started; with which the operation of the platen may be stopped and held in stopped position, or reversed quickly at any point in its forward or pressing movement, and with which the platen may be held in any position under a selected pressure.

Various other objects and advantages will be apparent from the following description of an embodiment of the invention, and the novel features will be particularly pointed-out hereinafter in connection with the appended claims.

In the accompanying drawings, Fig. 1 is an elevation, partly in section, of a hydraulic press constructed in accordance with this invention, and having associated therewith a controlling system which is illustrated diagrammatically;'

Fig. 2 is a sectional elevation, partially diagrammatic, of a simple form of a time limit relay;

Fig. 3 is an elevation of a portion of the press of Fig. l, and a diagram of the control apparatus which is associated therewith and illustrating another embodiment of the invention by which a full automatic operation of the press may be obtained with a time dwell at the open position; and

Fig. 4 is a view similar to Fig. 3 except that the control device does not start an opening movement of the platen until the pressure in the main ram has reached a predetermined pressure.

In the embodiment oi. the invention illustrated in Figs. 1 and 2, the press is hydraulic and includes a base i, and a platen 2 which is mounted for reciprocation ton upright posts 2, The platen 2 is moved downwardly toward the base I by ,a

main ram formed of a plunger or pistonl which reciprocates in a cylinder 5, the piston 4 being connected at its lower end to the platen 2. Rods 6 carried by the platen 2 extend upwardly therefrom and at their upper ends are connected by a yoke l which, in turn, is connected to a rod or piston 8 which reciprocates through one end of a cylinder 9. The piston 8 and cylinder 9, together, form a pull back ram which, operating through the yoke i and rods 6, serves to lift the platen 2 when fluid under pressure is admitted to the cylinder 9.

A reversible pump l0, which preferably .is of variable delivery, is connected at one side by a pipe II to the cylinder 5 of the main ram,

I and at its other side by a pipe 12 to the cylinder 9. The pipe i2 between the pump and the cylinder 9 includes a free check valve i3 which automatically opens to'permit flow of fluid from the pump through the pipe l2 to the cylinder 9 and automatically closes to prevent reverse flow. The pipe l2, between the pump i and the valve I3, is connected by a pipe it to another check valve i which, 'in turn, is connected by a pipe [6 to a source I! of a fluid under pressure. Since the fluids in such presses are usually liquid, the source of fluid may be a closed tank having an air chamber at the upper part thereof and otherwise filled with theoperating liquid.

A pipe l8 opens into the lower part of the tank I! and carries a valve l9 which, in the normal operation of the press, is always open,

but constitutes atankshut off valve which may be operated during repairs to the press. The pipe I 8, after passing the valve I9, opens into a differential check valve 20. This differential check valve 20 has a central or intermediate chamber 2| which opens into an'end chamber 22 through an apertured seat 23, and-also opens into an opposite end chamber 24 through an apertured seat 25. A valve stem 26 extends through both the end chambers and the central chamber, and within the end chamber 22 carries the valve element 21' which'moves within that end chamber into and out of closing or seating position on the seat 23 upon reciprocation of the stem 26.

A valve element 28 abuts, but is separate from, the lower end of the stem 26 and moves back and forth in the other end chamber 24 into and out of engagement with the seat 25 whereby communication between the central chamber 2| and the end chamber 24 is broken or established by the position 01 valve element 28. A spring 28a urges the valve element 28 into closed position on seat 25. Since the valve elements 21 and 28 are on opposite sides or the two valve seats 22 and 25, it follows thatwhen thevalve element 21 opens, the element 28 may or may not close,

and when valve element 28 closes, the element 21 must open.

It will thus be seen that the pipe l8 will conduct the operating liquid from the tank H to the central chamber 2| of the difierential check valve 28, and from the chamber 2| the liquid will pass into one end chamber or the other, depending upon the relative positions of the valveelements 21 and 28. The valve stem 26 extends upwardly through the end chamber 22 and into a piston chamber 29,- the passage from the end chamber 22 into the piston chamber 29 being provided with a suitable packing gland 38. The stem 26 at its end within the piston chamber 29 carries a piston or head 3| which reciprocates back and forth in the chamber 29 with the stem 26. i i

The piston 3| is forcibly reciprocated in the chamber 29 by an operating fluid, such as compressed air, the source of which is indicated by a compressed air tank 32." A pipe 33 connects the air tank 32 to the chamber of a valve box 34, and from this valve box pipes 35 and 36 lead to opposite ends of the chamber 29 and at opposite faces of the piston 3|. A reciprocating valve element is provided inthe box 34 to control the admission of fluid from the valve box alternately through the pipes 35 and 36 to opposite ends of the cylinder 29. For this purpose, the pipes 35 and 36 open into the chamber of the .valve box 34 through suitable ports arranged along the path of travel of a reciprocating valve element 31 and, in addition, an exhaust port 38 also opens into the valve box through a suitable port between the ports of the pipes 35 and 36.

When the valve element 31 is in the position valve shown by full lines in Fig. 1, the chamber 39 in the face thereof which moves across the ports of-the valve pipes will be in a position to establish communication between the exhaust pipe 38 and the pipe 36 which leads to the lower end of the chamber 29. At this time the port of the pipe 35 will be uncovered by the valve element 31 and, consequently, compressed air from the pipe 33 will pass through the valve box and pipe 35 into the upper end of the chamber 29 and force the piston 3| downwardly into the position shown in Fig. 1 and will hold it in that position.

If the valve element 31 is moved upwardly, it will uncover the port of the pipe 36 and will connect the port of the pipe 35 with the port of the exhaust pipe 38. This position is shown by dash lines in the drawings and when the valve is in this position, the upper end of the chamber 29 will be connected to atmosphere through the exhaust pipe 38 and the compressed air from the pipe 33 will pass through the pipe 36-to the lower end of the chamber 29 so asto force the piston 3| upwardly and thus move the valve element 21 away from its'seat, and concomitantly release the valve element 28 for possible movement into closed position on its seat. Thus, by operating the valve element 31 one may cause an operation of the differential check valve to establish communication between the tank l1 and the two rams alternately or concomitantly. The delivery oi the pump l8 may be reversed by reciprocation oi a control rod 48 which extends into the chamber of a cylinder 4| and, within the'cylinder 4|, carries a piston or head 42. Another valve 50:: 4-8,

similar to the box .34, is provided to controi the operation of the piston or head 42, and for this purpose pipes 44 and 45 extend from the opposite ends of the cylinder 4| to the valve box 43 and open into the chamber of the valve box through suitable ports, the same asin the box 34. This box also has anexhaust pipe 46, and a pipe 41' connects the pipe 33, leading from the compressed 7 air tank 32, to the chamber of the valve box 43.

pipe 46 alternately with the ports leading to the pipes 44 and 45. By shifting thevalve element 48 in the box 43, the compressed air may be admitted alternately to the opposite ends of the cylinder 4| which causes reciprocation of the piston or head 42 in alternate directions to reverse the delivery of the pump |8. By reversing the delivery of the pump, the operating fluid or liquid may be transferred alternately between said rams and, thereby, the platen 2 may be moved in either direction. z

' The check valve l5 also serves as a by-pass valve, and for this p p se its valve element 58 is mounted for free movement toward and from its seat 5|, so as to close automatically and pre vent flow of an operating fiuid from the pipe |4 into the pipe I6, yet open automatically and permit a reverse flow from the pipe Hi to the pipe I4. The valve element 58 abuts endwise against an operating stem 52 which depends through a.

packing gland 53 and terminates in a head 54. A

spring 55 acting between the head 54 and the packing gland 53 yieldingly urges the stem 52 away from valve element 58 to allow element 50 to engage its seat'5l.

An operating rod 56 is guidedin a'suitable bearing 51 on the basel and in a depending bracket 56A of the casing of the valve l5, so as to reciprocate endwise against the head 54. The rod' 56 is limited in its downward movement by v the engagement of a head on its upper end with the bracket 56A. The platen 2 is provided with an arm '58 which is adapted, as the platen 2 approaches its desired upward limited travel, to engage with a collar 59 adjustably carried by the rod 56. Thus, as the platen 2 approaches a selected point in its upward travel, it engages the collar 59 and through it' lifts the rod 56 and stem 52 and cams the valve element 58 into open position for a purpose which will appear as the description proceeds. When the platen 2 starts downwardly again, it will release the collar 59 and the spring 55 assisted by gravity will move the rod '56 and stem 52 downwardly and release the valve element 58 which is then free to move into closed position. Various means may be employed for operating the valve box elements 31 and 48 to control the operations of the press, but in the drawings I have illustrated an electrical system of control which I find to besatisfactory. With such a system the valve element 31 is operated by a stem 68 which extends. outwardly of the box and is operated by a suitable solenoid 6|. Similarly,

- a rod 62 is connected to the valve element 48 of 61 connects the power line Ll to one side of the solenoid. 63 which controls the reversal of the pump, and the other side of that solenoid is connected by a wire 68 to a contact 69. The contact 69 is connected by a switch bridge 18 to a contact II, which in turn is connected by a win '2 to the other power line L2. The switch bridge I8 is carried by and insulated from a stem 13 which is connected to the core 14 of a solenoid which functions as a main 'relay. One end or side of the relay or solenoid I5 is connected to the wire 61 and through it to the power line LI, and the otherside of the relay or solenoid I5 is connected by a wire 16 to the other power line L2. A pair of switches H are included in series with one another and with the wire I6, so that the circuit through the main relay I5 can only be closed by the closing of both switches H. type which are resiliently urged into open po sition, and together the two switches jointly control the main relay.

A holding or stick circuit for the main relay is provided for keeping the relay energized after the main relay circuit is closed, and for this purpose a bridge 78 is also carried by the stem I3 so as to bridge contacts I9 and 88. The contact 88 is connected by a wire 8I to one of the power wires, such as L2, and the other'contact I9 is connected by a wire 82 to one side of a switch 83 which is yieldingly urged into a closed position by a spring 84.

The other side of the switch 83 is connected by a wire 85 to one side of an emergency return switch 88 which is yieldingly urged into closed position by a spring 81. The-other side of the switch 86 is connected by a wire 88 to the wire l6 at a point between the switches TI and the relay 15. This stick circuit may, therefore, be traced as follows:From the power line LI, through wire 61, relay solenoid I5, wires '56 and 88, switch 86, wire 85, switch 83, wire 82, contact l9, bridge 58, contact 88 and wire 8I back to the other power line L2. It will thus be seen that this stick circuit is closed and opened by a bridge 18 which is operated by the relay when the relay is energized, and this circuit is also controlled by the normally closed switches 83 and 86.

One side of the solenoid winding 6| which controls the operation of the diflerentialvalve is connected by wire 89 to one of the power lines, such as LI, andv the other side of the winding is connected by wire 98 to a contact 9|. The contact 9| is connected at intervals by a bridge 92 to a contact 93 which, in turn, is connected by a wire 94 to the other power line L2. From this it will be observed that the solenoid winding 8| is connected to the power lines by the bridge 92 and this bridge forms part of an auxiliary relay 95. The winding of the relay 95 is connected at one side to the wire 89 which leads to the power line LI, and at its other side is connected by a wire 96 to a switch 91.

The other side of the switch 91 is connected by a wire 98 to a contact 99 which is connected at intervals by a bridge N8 to the contact III! that, in turn, is connected by a wire I82 to the other power line L2. Thus. when the main relay I5 is energized, the bridge I88, which is carried by the stem 13 of the relay I5, is shifted into bridging relation with the contacts 99 and I8I,- thereby closing the circuit through the switch 91 and the auxiliary relay 95, which closing of this circuit, in turn, through the operation of this relay 95, closes the circuit of the solenoid The switches are of any suitable GI which controlsthe operation of the differential check valve.

The switch 91 may be shifted into open position against a neutral post I83, and a spring I84 acting on the switch 9'! holds the switch in either open or closed positions yieldingly, owing to the fact that the spring I84 passes a dead center position while moving in eitherdirection between open and closed positions. The switch 91 may be designated as a maintaining contact switch, and its function will appear as the description proceeds.

A suitable timing device is associated with the switch 83 which controls the stick circuit of the main relay, and, is intended to open this stick circuit a predetermined and selected or adjustable interval of time after the platen has been started on the pressing stroke by the main ram. Such a timing device may be of any suitable type of which there are many on the market, including electric motors operating suitable cams through gear trains, such as are commonly employed in trafiic signals, for example, or suitable clock mechanisms or time limit relays may be employed. In this particular example, for simplicity, a time limit relay has been illustrated and is shown diagrammatically in Fig. 1 and des-" ignated by the reference character I85.

The winding of this relay I85 is connected across the lines 89 and 98 which lead to the solenoid BI which controls the operation of the diiferential check valve and, therefore, whenever the auxiliary relay 95 is closed through operation of the main relay I5, current will be supplied to the time limit relay at the same time that it is supplied to the solenoid'BI to effect a change in the position of the differential check valve. This time limit relay is arranged to engage and open the switch 83 automatically a, selected and adjustable, predetermined length of time after current is supplied to the relay, and upon the opening of the stick circuit, the main relay I5 is automatically deenergized. Since the time limit relay is energized only whilethe main relay 15 is energized, it follows that when the stick circuit is opened, the time limit relay also will be deenergized and will return to normal position.

Any suitable form of time limit relay may be employed but one is shown more or less diagrammatically on a larger scale in Fig. 2 and may include a winding I86, a magnetically attractable core I81 carrying a piston I88 which reciprocates in a cylinder I89 to form therewith a dash pot. When the winding I88 is energized, it lifts the core I81 with its piston I88 and the rate of this upward travel is controlled by the entrance of air through an adjustable valve II8 into the cylinder I89, inthe bottom thereof, that is, below the piston I88. When the piston I88, however, has nearly reached the position where it operates the switch 83, it uncovers a port III in the side of the cylinder I89, which relieves the partial vacuum created in the bottom part of the cylinder' I89 by the upward movement of the piston I88, and the core 181 may thenpass upwardly quickly and through a stem II2 thereof will engage and open the switch 83, thereby preventing arcing of the contacts of the switch.

' Following opening of the switch 83 of the stick circuit, the winding I88 will be deenergized, as explained herein above, and thereupon the core I81 with-v its piston I88 will descend through the action of gravity, or through the assistance of one or more springs H8, which act upon a cross arm I carried by the stem II2. A check valve H controls an air escape passage leading from the bottom part of the cylinder I09, so that the air displaced by the downward movement of the V piston I08 may freely escape, yet when the pis- 5 ton I08 moves upwardly, the ball valve H5 will automatically close and compel all the air to enter the cylinder I09 through the adjustable valve IIO. By adjusting the valve IIO, the rate of travel of. the piston I08 may be regulated, and thus. the time interval following energization of the main relay before the stick circuit is opened may be regulated. The upper end of the stem II2 may be guided by rods I I6 which have sliding engagement with the cross head H4. It frequently happens that full automatic operation of the-press is desired and, accordingly, I have provided means for reversing the press automatically when it reaches open position. In the illustrated example for accomplishing this result, and referring to Fig. 1 of the drawings, a normally open switch II 1 is provided on the frame or base 3 of the press in a position to be opened automatically by the platen when it reaches open position. Since the platen does not always occupy the same open position and since the open position is determined by the position of the collar 59 on the rod 56, I have provided another collar I I8 on the rod 55, the collar II8 being secured in the proper position on the rod 56 by aset screw or other suitable means. The collar his set to engage and close the switch III automatically when the rod 56 is elevated through engagement of the arm 58 of the platen 2 with the collar 58, because the open position of the platen is determined by the raising of the A wire H9 is connected to the wire I8, which Is connected to one side of the double starting I switch 11, and is also connected to one terminal or contact of the switch III. A wire I20 is connected to the other terminal or contact of the switch Ill and to a switch I2I which is yieldingly held in either of two positions, one of which is a closed position and the other of which is an open position. This switch isshown in closed position by full lines in Fig. 1 and in open position by dash lines in the same figure. The switch is similar to the switch 91, and the spring I22, which is connected thereto, in passing dead center or the pivot of the switch I2I, yieldingly urges the switch in either position. The switch I2I is infrequently operated and hence is preferably so located as to be less accessible than the dual con trol switches II. It also may be so disposed that this operator must remove his hands from the work in order to reach it. It also may be placed anywhere and locked in either position so that the control of the press operations is normally in the switches ll. A wire I23 connects the other 0 terminal of the switch I2I with the wire 8I which leads immediately to the power line L2 which is, in eifect, connecting the wire I23 to the other side of -the double switch II.

From this arrangement it will be observed that the switch I" is connected in parallel to the double switch I1, and that the closing of the switch I" will perform the same function as the double switch 71. Thus, as the platen 2 reaches its upper or open position, as determined by the adjustable collar 59, it lifts the rod 56 and closes the switch II! which closes a shunt circuitaround the double switch 11 and initiates a reversal of the travel of the platen. When the platen starts downwardly again, the rod 56 will 75 i' mediately be released and will descend. thus releasing the switch II! which automatically moves into open position, due to the resiliency of the contacts thereof.

If one desires to eliminate the automatic reversal of the platen when it reaches open or upper position, then one moves the switch I2I to the'open position shown by dash lines in Fig. 1 whereupon the shunt circuit around the double switch ll will be broken, and the closing of the switch I "by the platen will no longer cause a reversal of the direction of travel of the platen. It will be necessary then to close both switches TI in order to start a downward movement of the platen.

The operation .of the system which has been illustrated will now be described. With the parts in the position shown in Fig. 1, the press is idle with the platen 2 elevated. At this time the pump I0 is delivering operating liquid'through the pipe I2 to the pull back ram, but since the by-pass check valve, at this time, is in open position, the delivered liquid will pass through the pipes I4 and I6 back into the tank I1, and from the tank I! it will flow through the pipe I8 and the differential valve into the main ram cylinder 5 and thence through the pipe I I to the intake side of the pump. At this time, the check valve I3 is closed because the pressure in the pull back ram cylinder 9 will be greater than that delivered by the pump, and since the valve element 21 is in closed position, the pressure in the pull back cylinder 9 will hold the platen 2 in its upper position.

If now one desires to cause a descent of the platen 2,'such as in a pressing operation, the attendant or operator operates both ofthe start ing switches 11 simultaneously, because both of these switches must be closed at "the same time in order to establish a circuit through the main relay 15. By having two separate switches I1,

it will be necessary for the operator to use both,

hands to operate both switches at the same time before the press can be. started, and this is an important safety feature in that the operator must positively have both hands free of the press in order to start a downward or pressing move ment of the platen.

A momentary closing of the switches 71 is all that is required because immediately upon the closing of the circuit of the main relay IS, the upward movement of the stem 13 of that relay, which immediately follows,,causes a closing of three circuits through movement of the bridges 18, I0 and I00. The closing of'the bridge 18 immediately closes the stick circuit which thereupon holds the main relay l5 energized, regardless of the immediate opening of the switches I1, since the latter are immediately-returned to open position by their springs. At the same time that the relay I5 is energized, the bridge I0, which is operated, closes the circuit through the solenoid 63, and this solenoid, by attracting its core 65, shifts the valve element 48 of the valve box 43 time, the main relay I5, through the closingmovement of the bridge I00, closes the circuit through the auxiliary relay 95, and this relay 85 in turn operates the bridge 82 to close the circuit upwardly into the dotted line position shown in to the time limit relay and the solenoid 6!. The solenoid 6 I, when energized in this manner, shifts the valve element 31 into the dotted line position shown in the drawings and, in doing so, it con- 5 nects the compressed air from the tank 32 to the pipe 36 which conducts it to the underside of the piston 3| of the differential valve.

This compressed air acting on the under side of the piston 3| forces the differential valve stem 1 25 upwardly or outwardly and, in doing so, moves the valve element 21 away from its seat, at the same time releasing the valve element 28 which is elevated upwardly into closed position on its seat 25 by its spring 28a. Since the liquid in the 15 tank H is under pressure, because the liquid from the main cylinder has been displaced into the tank I! during the upward movement of the platen, and the air in the chamber in the top of the tank I i has been compressed, this liquid from the tank 11, which is under considerable pneumatic pressure, may now pass through the differential check valve into the pull back ram cylinder 9 and also is sufiicient to overcome the spring 28a and open the valve element 28 and flow into the main ram cylinder. The pressure in this cylinder 5 forces the platen 2 downwardly at a rapid rate,

and the liquid displaced by the pull back ram escapes through valve seat 23 into passage 25. f

2 At the same time, the pump i d is drawing liquid I5, and the pipes I l and I2, and delivers it through the pipe H to the main ram cylinder 5. A rapid movement of the platen 2 results because of the pressure created through the liquid delivered by both the pump and also the tank ll.

As soon as the platen 2 encounters resistance to such an extent that the pressure required to cause further movement of the platen approximately equals the pressure then existing in the tank ll,

40 the liquid will no longer flow from the tank ll directly into the main cylinder 5, because the pressure is approximately equal in both tank and ram cylinder, and thereupon the valve 28 will be closed by its spring 28a.

45 The operating liquid will then move from the tank ll through the pipe It, the valve 15, the pipes l4 and I2, through the pump, and thence through the pipe H to the main cylinder 5. When the platen 2 started downwardly, it re- 50 leased the collar 59, and the rod 56 then dropped, but the valve element 50 remained open owing to the suction through the pipes l2 and i 3 created by the pump, and the liquid passing through the pipe l6 holds the valve element 55 lifted. The

55 continued operation of the pump l0 will cause the gradual building up of pressure in the Ljlilldel 5 and an increasing pressure onthe platen 2.

The pump [0 is of a well known reversible and variable delivery type and automatically sets 60 itself to'neutral, or only sufficient delivery to offset leakage, when the pressure in the delivery side to the main ram reaches a selected, but adjustable, maximum pressure. This may be accomplished, for example, by connecting a branch pipe 65 a to the pipe H, and to a small cylinder b. A piston or ram 0 reciprocating in the cylinder b is connected to a pair of control levers d to operate them to neutral delivery position against the action of a spring 6 that reacts between an 70 adjustable abutment f upon the control rod 45 and a yoke g connecting the control levers d.

The rod fill passes freely through theyoke g and terminates in a head 40a so that the levers 01 may be positively moved to reverse the pump and cause an operation of the pull back ram and a from the tank l1, through the pipe Hi, the valve return of the platen. When the rod 40 is shifted to the left (Fig. 1) by operation of the piston 42, the spring e is compressed and forces the levers d yieldingly into positions in which the pump delivers to the main ram. By adjusting the abutment f to increase the pressure on the spring e, the greater will be the pressure required on the main ram, before the control levers d are shifted to approximately neutral delivery position.

At the same time that the downward moveinent of the platen 2 was initiated by the closing of the main relay [5, the time limit relay or other .timing device was rendered efiective and a predetermined and'adjustable length of time thereafter it opened the switch 83 of the stick circuit and caused a deenergization of the relay '15.

' Thereupon the bridges l8, l0 and I00 all moved into open position and broke the stick circuit at another point and opened the circuits controlling the solenoids 6! and 63. Thereupon the springs 56 and gravity operate the valve elements 31 and 48 of the valve boxes back to the full line positions and, in doing so, the compressed air is shut off from the pipes 36 and 45 and admitted to the pipes 35 and 45.

At the same time that the pipes 36 and 44 are connected to exhaust, so' that there will be no back pressure on the pistons 3i and 42. Compressed air is admitted to the pipes 35 and 45 and causes movement of the piston 42 to the right and reverses the delivery of pump l0. Thereupon the pump ill draws liquid from the main cylinder 5, through the pipe H, and delivers it through the pipe l2 and the valve iii to the pullback cylinder 9, through the valve cavity 22, the valvecavity 2i, and back into the tank H. In this manner the pressure in the press cylinder is dropped tozero. At the same time that compressed air is admitted to move the piston 52 it is admitted to operate piston 38 of the differential valve into the full line position shown in the drawings. As soon as the pump has dropped the pressure by pumping out of the main cylinder, the large valve 28 with the pressure removed from its face is free to open. The piston 3| then forces the valve element 21 into closed position and the stem 26 forces the valve element 28 into open position.

At this time the valve element 50 of the bypass valve !5 closes automatically so as to prevent flow from the pipe M into the pipe E6. The check valve l5 opens freely at this time and the liquid delivered to the pull back cylinder 9 will force the pull back piston or ram 8 upwardly and lift the platen 2 Since the liquid displaced by the .main ram or piston 5 is greater than that necessary to supply the pump for delivery to the pull back cylinder, the excess liquid in the main cylinder 5 will pass directly through the valve seat 25 and the differential valve chamber 2!, into the pipe i8, thence back into the tank ll, where the air in the tank I? is compressed and a new initial operating pressure built up.

The return movement of the platen 2 is, there fore, relatively rapid. When the platen approaches the desired upward limit of its travel, the arm 58 of the platen engages the collar 59 which has been adjusted into a selected position, and as the platen 2 moves further, the rod 56 is lifted and the stem 52 elevated to force the check valve element 50 of the by-pass valve i5 into open position. Thereupon, the delivery of the pump to the pipe l2, insteadof passing into the pull back ram, will take the path of least resistance through the pipe l4, valve I5, and pipe [6, to the tank l1, and since the check valve l3 will then ref to explain a mo'diflcationin/the details of the It will be noted that current is consumed for the electrical devices only when the platen is moving downwardly in a. pressing direction, and none will be used while the press is in idle position, as shown in thedrawings. If, for any reason, it is desired to stop the downward movement of the platen after a downward movement has been started and before. it has been completed, this may be done by manually opening the emergency return switch 86 whichbreaks the stick circuit and causes an immediate return movement of the platen, the same as would be caused by the opening of the switch 83. a

If one desires to stop the press at any point in the downward movement of the platen and hold the platen in that position, the switch 91 is moved into open position, shown by the dash lines in Fig. 1, at the desired point in the downward movement of-the platen 2. When this happens, the auxiliary relay 95 willbe deenergized, and this opens the circuits to the solenoid BI and the time limit relay or timing device I95. The current will continue indefinitely to the solenoid 63 because there is now nothing to break the stick'circuit until the manual switch 86 is opened, or the switch 9'I isreturned to closed position. When the auxiliary relay 95 opens the circuit controlled thereby, the valve element 31 in thevalve box will returnto the full line position in the drawmas and will reverse the diiferential valve. This causes a closing 01' the valve element 2.1 on its seat and a forced opening 01' the valve element 28. I

Since the delivery of the pump was not changed, it will continue to deliver the operating liquid to the main cylinder 5 but since the differential valve element 28 was opened, the operating liquid will travel through the cylinder 5 and back to the tank in an idle circuit, so, that no further downward movement of the platen will occur because oil in the pull back ram can not escape. No upward or-return movement can occur until the pump is reversed and, therefore, the platen 2 will remain in this position in which it is stopped until the switch 86 is opened or the switch 91 is closed. The switch 91 thus may properly be called a maintaining switch because, by opening it, the press is maintained or held in any position it may bein during. a pressing movement.

In the'foregoing statement of the operation, it has been assumed that the switch I2I ie in open position, and that there has been no automatic reversal of the press as the .platen reaches open position. If now one desires to have automatic operation of the press, the switch I2I is moved into closed position, shown by full lines in Fig. l,

and thereupon whenever the platen reaches open position, and which open position may varyas determined by the adjustment of the collar 59 on the rod 56, the closing of the switch I IIupon the elevation of rod 56 will automatically reverse the press and start a new downward movement in the same manner that the platen would be started downwardly by an operation of the double switch II. This automatic reversal at open position can be eliminatedat any time merelyby shifting switeh' I2I back into. open position, i:

Referring-next. to Fig. 3, the press is the same constructionas shown in Fig. 1, but-only ,a fragmentary portion of it is illustrated in order control thereof. In Fig. 3 parts'periorming the same functions as in Fig. 1 have been given the same reference characters, and will not be'further described in detail. The control system shown in this Fig. 3 is the same as in Fig. 1. except that a switch I24 is provided and is connected by wires I25 and I26 to opposite sides of the double switch 11. For example, wire I26 is connected to the wire 88 or the wire I6, and the wire I25 is connected to the power line L2 or to the wire which connects the power line L2 to one side of the double switch 11. The switch I24 is normally held in open position by a spring I2'I.

A time limit relay I28 is disposed in a position to close the switch I24 when the relay is energized, and the coil or solenoid I29 of this'time limit relay I 28 is connected at one side by wire.

I30 to the power line L2, and at the other side is connected to the wire I23 instead of having the wire I23 connected to the power line L2. In other words, this arrangement is exactlythe same as in Fig. 1 except that the switch I25 has-been added and the time limit relay I28 has been placed in series in the wire I23, so-thatwhen the reversing circuit, which isrendered operative by the platen as it reaches open position, is energized, it will energize the time limit relay I28 and after the lapse of a selected and adjustable period of time, the switch I24 will be closed automatically and a downward movement oi! the platen started a selected and predetermined interval or time after the platen has reached its open position. This provides for a brief period of rest for the platen-in its open position, and this period of time may be varied by adjusting the time limit relay to vary the period of time which will elapse after the relay is energized before the switch I24 is closed by it. This time limit relay' the voltage in that common circuit is divided between the windings of both relays I5 and I29,

its lifting power. ,Sinoe relay I5 must operate against-a fixed or definite load, it is so designed that when subjected to a current at such a reduced voltage it will not be operated, but when full voltage is applied, such as by closing switches 11, it will be operated. The relay I29 may, of course, be designed to operate at eitherthe reduced or full voltage. The operation or the control system shown in Fig. 3 is otherwise the same as describedfor Fig. .1.

In the embodiment of the invention shown in Fig.4, the arrangement of the control system is identical with that shown in Fig. 8, except that theswitch 83 of the stick circuit for the main relay I5, instead of being opened by the time limit relay I96, as in Figs. 1 and 3, a selected interval of time after the platen starts its downward or forward stroke, will be opened automatically after the pressure on the main ram 4 reaches a selected and adjustable, predetermined pressure. To accomplish this, the time limit relay I06 01 Fig. 3 is removed and in its place a pressure responsive mechanism is substituted. This *which means that relay I5 has only a portion of mechanism includes a hydraulic cylinder I3I in lswitch 83.

A pipe I33 connects the interior of the cylinder I3I to the interior of the cylinder 5, and theredirectly responsive to the pressure in the main cylinder 5. As the pressure in the cylinder I3! increases, it will force the plunger I32 upwardly or outwardly and cause it to open the stick circuit switch 83. The plunger I32 carries a yoke I34 and this yoke forms one end of a frame I35 which extends across the closed end of the cylinder and carries an adjustable abutment I36, between which and the end of the cylinder is disposed a compression spring I31. The upward movement of the plunger I32 is, therefore, resisted by the spring I31 and, hence, the plunger I32 will not move upwardly and open the stick circuit switch 83 until the pressure in the main cylinder has become great enough, when transmitted to the cylinder I3I, to overcome the resistance of the spring I31. This resistance, which must be overcome, may be varied by adjusting the adjustable abutment I36, which may include a screw threaded through the frame I35.

Thus, when the pressure in the main cylinder 5 of the press reaches a predetermined and selected pressure, the plunger I32 will open the stick circuit switch 83, thereby deenergizing the main relay I5 and initiating an upward or return movement of the platen. From this it will be seen that the termination of the downward movement of the platen will be automatically made after the pressure on the platen has reached a selected pressure, instead of a predetermined length of time after the downward movement of the platen began, as in the device shown in Figs. 1 and 3. Otherwise, the operation-is the same as in Figs. 1 and 3 and similar parts have corresponding characters.

In the system which has been hereinabove described, the timing relay or device I05, which automatically causes a reversal in the direction of travel of the platen and initiates an upward movement thereof, begins to operate at the beginning of the downward or pressing movement of the platen. The speed of closing of the press is not always constant, for example, varying with the temperature and consequent change in the viscosity of the oil and, therefore, it may at times be desirable to start the timing device in operation at approximately the end of the closing movement of the press and just before the real pressing operation begins.

To make this possible, I may provide on the platen 2 an arm or control finger I38, Fig. 1, which is mounted on the platen for limited vertical adjustment such as by'making it slidable upon the vertical guide rod I39 and securing it indifferent adjustable positions thereon by a set screw I40. The finger I38 thus moves with the platen 2 in both directions. In the path of travel of the finger I38, I mount a switch device I4I which is closed by the finger I38 at various selected points in the downward travel of the platen, the switch remaining closed during the remainder of the downward travel of the platen. This switch is included in series in the circuit of the time limit relay winding I00.

Any suitable switch for this purpose may be employed but, byway of example, I have shown a lever or member pivotally mounted at I42 upon a suitable part of the press frame. The switch member has two arms I43 and I44. A spring I45 is connected to the switch member and to the frame of the press in a manner to pass dead center or the pivot I42 of the switch when the switch member is oscillated. A stop pin I46 limits the clockwise movement of the switch member so as to place the arm I43 thereof in approximately a horizontal position in the path of travel of the finger I38. The spring I45 yieldingly holds the switch in this position.

When the finger I38 moves downwardly, it en gages the arm I43 and rocks the switch member until the spring I45 passes dead center, whereupon the' spring automatically snaps the switch further in the same direction until the arm I43 engagesa contact or switch terminal I41 suitably mounted onthe press frame. When the switch member is stopped in this position, the arm I 44 of the switch member is then above or behind and in the path of travel of, the finger I38 and the arm I43 is out of the path of travel of the finger I38. The spring I45 holds the switch member in this position. A wire I48 connects the wire 08 to the switch member MI and a wire I49 connects the contact or terminal I41 to one side of the time limit relay I06, the other side of the time limit relay I08 being connected to the wire 80.

With this arrangement, the winding I00 will not be energized when the solenoid winding BI is energized, but when the platen 2 reaches a selected intermediate position in its movement in a pressing direction, it will rock the switch member I4I into closed position and leave it in that position during the remainder of the downward or pressing movement of the platen. The time limit relay then functions and opens the stick circuit a predetermined time after the platen passes the selected intermediate position. When the stick circuit is opened in this manner, the mechanism sets the press controls to retract the platen 2 and, as the platen 2 travels upwardly, the finger I38 will engage the arm I44 of the switch member I49 and will rock it until the spring I45 again passes dead center position. whereupon the spring will snap the switch member into the position shown in Fig. 1 in which the arm I43 is in the path of travel of the finger I38 and the arm I44 is out of the path of travel of the finger I38. The circuit of relay I06 at the switch is operated to start the functioning of the time limit relay may be adjusted or varied. Similar means for accomplishing the delay in the starting of the timing device may also be applied to the construction shown in Fig. 3.

It will be obvious that various changes in the details, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention, as expressed in the appended claims.

I claim:

1. In a hydraulic press system, a main ram, a pull back ram, a. platen operated by said rams, a source of fluid, a reversible pump, connections between said rams, said source and said pump,

cause operation of said platen in either direction, and automatic means free of control by the pressure of fluid in either ram and rendered effective by the platen as the platen leaves a predetermined adjustable position during a pressing operation, for reversing said pump and causing operation of said rams a selected interval of time thereafter.

2. In a hydraulic press system, a main ram, a pull back ram, a platen operated by said rams ir alternate directions, a source of fluid, a reversible pump, connections between said rams, said source and said pumpand forming a hydraulic circuit by which fluid under pressure may be delivered under pressure in either direction between said rams selectively to cause opera tion of the platen in either direction, areservoir connected to said rams, a difierential valve having two check valve elements opening to pass fluid from 'said reservoir to each ram and automatically closing to prevent return flow, means i for operating said valve and reversing said pump to cause a reversal in the direction of travel of said platen, and means free of the pressure upon a said main ram and also free of the speed of the operationiof said main ram, for automatically operating said reversing means and causing a return operation of said platen a selected interval of time after said platen passes a selected and adjustable position in a pressing direction.

3. In a hydraulic press system, a main ram, a pull back rain, a platen operated by said rams in alternate directions, a source of operating fluid, pumping means, connections between said rams, said source and said means by which fluid may be delivered under pressure to said rams selectively, electrical means for controlling the delivery of operating fluid to one ram or the other and including a controlling circuit, and timing means exclusive of the hydraulic circuit but set in operation automatically when said electrical means is operated to initiate a pressing, movement of said platen, and operable to cause a return movement of said platen atpredetermined length of time after the pressing movement of said platen is initiated.

.4. In a hydraulic press system, a platen, hydraulic rams connected to said platen to operate it in both directions, means including a continuously operating pump connected to said rams for operating said platen in alternate directions depending upon which ram receives fluid from said pump, means for controlling the delivery of fluid to said rams selectively so as to control the direction of operation of said platen, and a timing device exclusive of the pump but set in operation automatically when said controlling means is operated to change the delivery of fluid from said pumpfrom one of said rams to the other and cause movement of the platen in a pressing direction, for causing a reversal of the platen a predetermined time after the desired movement of the platen in said pressing direction is ini-. tiated. v

" 5. In a-hydraulic press system, a platen, hydraulic rams connected to said platen to operate it in both directions, means including a continuously operating pump connectedto said rams for operating said platen in alternate directions depending upon which ram receives fluidirom said pump, means for controlling the delivery of fluid to said rams selectively so as to control the direction of operation of said platen, and a tim ing device connected to said controlling means while said platen is traveling in a pressing direction for changing the delivery of fluid by said pump from one ram to the other and causing a reversal of the direction of travel of the platen 'a predetermined interval of time thereafter, re-

gardless of the operating pressure upon, or rate of travel of, said platen.

6. In a hydraulic press system, a platen, means for operating said platen in alternate directions, means for controlling the direction of operation of said platen, a timing device exclusive of said operating means, set in operation automatically when said controlling means is operated to cause movement of the platen in one direction, for causing a reversal of the platen a predetermined time after the desired movement of the platen in said one direction is initiated, and means for interrupting theaction of said timing device and causing a return of said platen selectively at any time, whereby in an emergency the return of the platen may be accomplished before the expiration of said predetermined time.

7. In a hydraulic press system, a platen, hydraulic means for operating said platen in alternate directions, a pump, means connecting said pump and hydraulic means for causing operation of said platen in alternate directions, a control device for controlling the delivery of said pump to said hydraulic means for determining the direction of the operation of said platen, electrical means for controlling the activity of said control device, and means including said electrical means, a circuit and a relay for controlling the -activity of said electrical means so as to thereby control the operation of said platen, a stick circuit for saidrelay, a time limit relay-operable on said stick circuit to open it a predetermined length of time after the closing of the first relay, and a circuit for said time limit relay controlled by the first mentioned relay.

8. In a hydraulic press system; a platen, means,

relay, means including a timing device operable,

upon said stick circuit for opening it a predetermined interval of time after the energization of said relay and thereby causing a reversal in the direction of operation of said platen.v

9. In a hydraulic press system,-a platen, means for operating said platen in alternate directions, means including a relay and its circuit for controlling said operating means and having said circuit closed when operation of said platen in one direction is desired switch means for said relay circuit for closing it, a stick circuit for said relay, means including a timing device operable upon said stick circuit for opening it a predetermined interval of time after the energization of said relay thereby causing a reversal in the direction of operation of said platen, and means operable separately from said stick circuit forstopping travel of said platen in a pressing direction, at any point insaid travel and holding it at that point at any time for emergency purposes,

10. In a hydraulic press system, a platen, rams operating said platen \in opposite directions,

'means including continuously operating pumpning means connected to said rams fordelivering operating fluid to said'ramsalternately, and thus operating said platen in alternate directions, a

source of operating fluid, connections from said source to both rams, valve means in said connections, a relay and its circuit, means controlled by said relay for changing the delivery of said pumping means from one ram to the other, means also controlled by saidrelay for changing said valve means concurrently with the change in said pumping means, switch means for closing said relay circuit to initiate an operation of said platen in one direction, a stick circuit for said relay, and means including a timing device operable upon said stick circuit for opening it a predetermined interval of time after the energization of said relay and thereby causing a reversal in the direction of operation of said platen.

11. In a hydraulic press system, a platen, rams operating said platen in opposite directions, means includingcontinuou'sly operating pumping means connected to said rams for delivering operating fluid to said rams alternately, and thus operating said platen in alternate directions, a source of operating fluid, connections from said source to both rams, valve means in said connections, a relay and its circuit, means controlled by said relay for changing the delivery of said pumping means from one ram to the other, means also controlled by said relay for changing said valve means concurrently with the change in said pumping means, switch means for closing said relay circuit to initiate an operation of said platen in one direction, a stick circuit for said relay, means including a timing device operable upon saidstickcircuit for opening it a predetermined interval of time after the energization of said relay and thereby causing a reversal in the direction of operationof said platen, and means to operate said valve means while said relay remains unchanged and separately from said means for changing the direction of delivery of said pumping means.

12. In a hydraulic press system, a platen, means for operating said platen in alternate directions, means controlling the direction of operation of said platen andincluding a relay and its circuit, switch means for closing the circuit of said relay to initiate an operation of saidplaten, a stick circuit for said relay, and means including a timing device controlled by said relay and having a switch in series in said stick circuit which it opens for opening said stick circuit a predetermined length of time after said stick circuit is closed, whereby the relay will be deenergized and travel of the platen in one direction stopped.

13. In a hydraulic press system a platen, means for operating said platen in alternate directions,

means controlling the direction of operation of said platen and including a relay and its circuit, switch means for closing the circuit of said relay to initiate an operation of said platen, a stick circuit for said relay, a time limit relay operable to open said stick circuit a predetermined length of time after being set in operation, a circult for said time limit relay in turn controlled by the first relay, so that the time limit relay will be automatically set in operation upon the in either direction under pressure so as to cause operation of said platen in either direction; motor means for changing the delivery of said pump from one ram to the other, motor means for forcibly operating said valve from one position to another, means including a common control element for causing operation of both of said motor means at substantially, the same time, the control of both of said motor means causing the positioning of said valve to connect said source to said main ram when said pump is delivering fluid to said pull back ram, and means for additionally causing an operation of the second of said motor means during a pressing movement of said platen to position said valve to connect said source to said main ram while the first motor means is in a position to cause delivery of fluid by said pumping means to said main ram, whereby said platen may be held in any position.

15. In a hydraulic press system, a platen, hydraulic means for moving said platen in alternate directions to and from pressing position, means including a relay operable on said means for controlling the direction of travel of said platen, a regular circuit for said relay which when closed will energize said relay and initiate a forward movement of said platen, a stick circuit for holding said relay energized, means for' opening said stick circuit to terminate said forward movement of the platen and cause a reverse movement of the platen, and means including an electric circuit and a switch therein but operated by said platen during a return movement of said platen for closing said relay regular circuit and causing a reversal of travel of said platen and initiate another forward movement of the platen a predetermined and substantial length of time after operation of said switch by said platen.

16. In a hydraulic press system, a main ram, a pull back ram, a platen operated by said rams in alternate directions, a source of operating fluid, pumping means, connections between said rams, said source and said means by which fluid may be delivered under pressure to said rams selec tively, electrical means for controlling the delivery of operating fluid to one ram or the other and including a controlling circuit, timing means free of control by the pressure on said platen and set in operation automatically by said electrical means when said electrical means is operated to initiate a pressing movement of said platen, and

operable to cause a return movement of said platen a predetermined length of time after the pressing movement of said platen is initiated, and switch means for said circuit, operable by said platen at the end of its return movement for causing automatically a reversal of the platen and its start on a forward movement.

17. In a hydraulic press system, a platen, hydraulic means for operating said platen in alternate directions, means for controlling the direction of operation of said platen, and means exclusive of said hydraulic means and operable by said platen during a return movement for changing said controlling means to initiate a forward movement of said platenautomatically after the lapse of an appreciable length of time following completion of the return movement of said platen, said last named means including a control element adjustable into different selected positions along the path of travel of said platen.

18. In a hydraulic press system, a platen, hydraulio. means for operating said platen in alternate directions, means for controlling the di-- rection of operation of said platen selectively,

means operating said controlling means to reverse the direction of operation of said platen and I said platen, and a timing device, exclusive of said hydraulic means, set in operation by the platen at approximately the completion of a return movement for operating said controlling means to cause a forward movement thereof a predetermined and substantialinterval of time after said platen substantially completed its return movement.

19. In a hydraulic press system, a platen, hy-

draulic means including a continuously operating reversible pump, for operating said platen in alternate directions by hydraulic pressure from said pump, means for reversing said pump to control the direction of operation of said .platen selectively, and timing means set into operation automatically by said platen at an intermediate point in its movement in one direction for operating said controlling means to reverse the delivery of said pump and thereby the direction of operation of said platen, a predetermined interval of time thereafter. I

20.'In a hydraulic press system, a platen, a main ram and a pull back ram connected to said platen for operating it in alternate directions, a reversible, variable delivery pump, pipes connecting said pump to said rams for transferring fluid between the rams alternately upon reversal of the direction of delivery of the pump to control the direction of travel .of said platen, a pheck valve in the pipe connecting said pump to the pull back ram, opening to pass fluid from, the pump to that ram and closing automatically to prevent reverse flow, a source of fluid, pipes connecting said source to each of said rams and to-that side of the pump which is connected.

through said check valve to the pull back ram, and valves in the last mentioned pipes operable to prevent escape of fluid from the pull back ram and by-pass fluid delivered by the pump towards the main ram, back to said source and pump, for

stopping and holding said platen in any intermediate position during its pressing movement with the pump delivering at approximately the same rate and in the same direction.

21. In a hydraulic press system, a platen, rams connected to said platen for operating it in alternate directions, a continuously operating pump, connections from said pump to said rams, a source of fluid, a conduit from said source to each ram,-a differential valve having two valve elements connected in parallel in said conduits and effective when open to pass fluid from said source to said rams, fluid actuated means operating outside of said valve elements for forcibly operating said differential valve elements and for changing the delivery of fluid from said pump to one ram or the other depending upon which ram is to be operated, electrical means for controlling said fluid actuated means to cause forcible operation of said differential valve and to alter the direction of transfer of fluid from one ram to the other in a predetermined relation to one another that will cause operation of said platen in alternate directions, and means also controlling said fluid actuated means for effecting forcible operation of said differential valve out of said predetermined relation while continuing the delivery of fluid to one of said rams, whereby said platen may be selectively stopped and held in any intermediate position while travelling in one direction, and travel in the same direction resumed when desired.

22. In a hydraulic press system, a platen, a main ram connected to said platen for operating it in a pressing direction, a pull-back.ram for retracting the platen, a continuously operating pump connected to said rams for transferring fluid in either direction between them to determine the direction of operation of said platen, a reservoir, a differential .valve having two valve elements connected between said reservoir and said rams, a motor for forcibly operating said differential valve elements and connecting said reservoir alternately to said rams, means including another motor for changing the delivery of fluid from said pump from one ram to the other, means including an electrical circuit for operating said motors in a desired relation to one another and for causing travel of said platen in alternate directions, and means for additionally controlling the motor of the differential valve and operating said valve elements to close communication between said pull-back ram and reservoir and to open communication between said main ram and reservoir while said pump is delivering fluid to said main ram, whereby said platen may be stopped and held in any selected point in its travel in a pressing direction while said pump is delivering fluid to said main ram.

23. In a hydraulic press system, a platen, a main ram for operating said platen in a pressing direction, a pull-back ram for retracting said platen, a reversible delivery pump connected to said rams for transferring fluid between them in either direction, a check valve in the connection from said pump to the'pull-back ram for restrict! ing flow therethrough toward said pull-back ram, a reservoir, branch connections therefrom to said rams, a differential valve having two valve elements, one in each of said branch connections for connecting said reservoir alternately to said rams, a pipe connecting said reservoir to said pump at the side connected to said pull-back ram and between the pump and the check valve,

a free check valve in the pipe between said reservoir and pump and restricting flow therethrough to a direction toward said pump, means for reversing the pump to cause operation of said platen in alternate directions, and means for forcibly operating said differential valve elements to close communication betweensaid pull-back ram and reservoir while said pump continues to deliver fluid to said main ram whereby said platen may be stopped and held in any intermediate position in a pressing movement, and resumption of a pressing movement selectively obtained by a return of the differential valve elements to the positions in which the valve elements connect the reservoir to said pull-back .ram and close communication between said main ram and reservoir.

'24. In a hydraulic press system, a platen, a main ram for operating said platen in a pressing direction, a pull-back ram for retracting said platen, a reversible delivery pump connected to said rams for transferring fluid between them in either direction, a check valve in the connection from said pump to the pull-back ram for restricting flow therethrough toward said pull-back ram, a reservoir, branch connections therefrom to said rams, a differential valve having two valve eleand between the pump and the check valve, a free check valve in the pipe between said reservoir and pump and restricting flow therethrough to a direction toward said pump, means for reversing the pump to cause operation of said platen in alternate directions, means for forcibly operating said difierential valve elements to close communication between said pull-back ram and reservoir while said pump continues to deliver fluid to said main ram whereby said platen may be stopped and held in any intermediate position in a pressing movement, and resumption of a pressing movement selectively obtained by a return of the difierential valve elements to the positions in which the difierential valve connects the reservoir to said pull-back ram and closes communication between said main ram and reservoir, and means operated by said platen during a retraction movement for forcibly opening the free check valveand stopping the retraction of said platen while said pump is delivering said fluid toward said pull-back ram.

25. In a hydraulic press system. a platen, a main ram for operating said platen in a pressing direction, a pull-back ram for retracting said platen, a reversible delivery pump connected to said rams for transferring fluid between them in either direction, a check valve in the connection from said pump to the pull-back ram for restricting flow therethrough toward said pull-back ram, a reservoir, branch connections, therefrom to said rams, a differential valve having two valve elements, one in each of said branch connections, for connecting said reservoir alternately to said rams, a pipe connecting said reservoir to said pump at the side connected to said pull-back ram and between the pump and the check valve, a free check valve in the pipe between said reservoir and pump and restricting flow therethrough to a direction toward said pump, means for reversing the pump to cause operation of said platen in alternate directions, means for forcibly operating said diiierential valve elements to close communication between said pull-back ram and reservoir while said pump continues to deliver fluid to said main ram whereby said platen may be stopped and held in any intermediate position in a pressing movement, and resumption of a pressing movement selectively obtained by a return of the differential valve elements to the positions in which they connect the reservoir to said pull-back ram and close communication between said main ram and reservoir, means operated by said platen during a retraction movement for forcibly opening the free check valve and stopping the retraction of said platen while said pump is delivering said fluid toward said pullback ram, and electrical means for controlling the direction of delivery of said pump and of the forcible operation of said differential valve elements to control the direction of travel of said platen, said electrical means being operable by said platen during a retraction movement thereof for automatically reversing the delivery of said pump and forcibly operating said differential valve to automatically initiate a pressing operation of said platen after a desired return movement of the platen.

26. In a hydraulic press system, a platen, a main ram for operating said platen in aapressing direction, a pull-back ram for retracting saidv platen, a reversible delivery pump connected to 'said rams for transferring fluid between them in either direction, a check valve in the connection from said pump to the pull-back ram for restricting flow therethrough toward said pull-back ram, a reservoir, branch connections therefrom to said rams, a differential valve having two valve elements, one in each of said branch connections for connecting said reservoir alternately to said rams, a pipe connecting said reservoir to said pump at the side connected to said pull-back ram and between the pump and the check valve, a free check valve in the pipe between said reservoir and pump and restricting flow therethrough to a direction toward said pump, means for reversing the pump to cause operation of said platen in alternate directions, means for forcibly operating said differential valve elements to close communication between said pull-back ram and reservoir while said pump continues to deliver fluid to said main ram whereby said platen may be stopped and held in any intermediate position in a pressing movement; and resumption of a pressing movement selectively obtained by a return of the differential valve elements to the position in which they connect the reservoir to said pull-back ram and close communication between said main ram and reservoir, means operated by said platen during a retraction movement for forcibly opening the check valve in said pipe connecting said reservoir to said pump and stopping the retraction of 'said platen while said pump is delivering said fluid toward said pull-back ram, electrical means for controlling the direction of delivery of said pump and of the forcible operation of said differential valve elements to control the direction of travel of said platen, said electrical means being operable by said platen during a retraction movement thereof for automatically reversing the delivery of said pump andrections, means including a stick relay and its circuit for controlling said operating means and having a closed circuit condition for said relay when operation of said platen in one direction is desired, switch means connected in the circuit of said relay for energizing said relay to initiate a movement of the platen in one direction, a timing device for opening said stick circuit and causing a reversal of the direction of travel of said platen, means operated by said platen during its travel ina pressing direction for rendering said timing device active, whereby 'said stick circuit will be opened a predetermined interval of time after the timing device is rendered active, and means for incapacitating said platen operated device

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