US2750744A

US2750744A - Prefill valve with automatic decompression means

Info

Publication number: US2750744A
Application number: US318599A
Authority: US
Inventors: Robert K Sedgwick
Original assignee: American Steel Foundries
Current assignee: American Steel Foundries
Priority date: 1952-11-04
Filing date: 1952-11-04
Publication date: 1956-06-19
Anticipated expiration: 1973-06-19

Description

June 19, 1956 R. K. SEDGW ICK 2,750,744

FREFILL VALVE WITH AUTOMATIC DECQMPRESSION MEANS Filed Nov. 4, 1952 2 Sheets-Sheet 1 E 66 6g 72 g8 70 110 5O/E a? 'IIVVENTOR.

2 142 W 9a 564 W R; K. SEDGWI CK 2,750,744

PREFILL VALVE WITH AUTOMATIC DECOMPRESsI-ON MEANS June 19, 1956 2 Sheets-Sheet 2 Filed NOV. 4, 1952 PREFILL VALVE WITH AUTOMATIC DECOMPRESSION MEANS Application November 4, 1952, Serial No. 318,599

11 Claims. (Cl. 60-52) My invention relates to hydraulic presses and more particularly to a novel prefill valve for a type of hydraulic press known in the trade as the pipeless press.

My invention comprehends a novel prefill valve operable to supply low pressure fluid, such as oil, to the press cylinder as the ram moves toward the work to engage a carried platen therewith, said valve being operable to cut off the low pressure fluid supply to the press cylinder after the platen has engaged the work and during the full pressure phase of the cycle. A similar valve is described in my Patent 2,544,731, issued March 13, 1951,

rates Patent F in the name of Robert K. Sedgwick, and the present invention constitutes improvements in valves of said type.

A general object of my invention is to design a prefill valve, as above described, wherein the dynamic effects of the flow of oil past the principal valve openings provides forces aiding in the operation of the valve.

Another general object of my invention is to provide a prefill valve with automatic decompression control Whereby high pressure surges from the main cylinder to the supply tank are eliminated with the consequent elimination of noise and damage to the press.

A more specific object of my invention is to provide spring means to aid in the closing stroke of the valve.

Another specific object of the invention is to design a vertical embodiment of the valve suitable for use on smaller capacity hydraulic presses.

These and other objeects of the invention will become apparent in the course of the following description and from an examination of the concerned drawings, wherein:

Figure lis a fragmentary diagram of a hydraulic circuit utilizing my novel prefill valve;

Figure 2 is a vertical sectional view, taken through the prefill valve and illustrating its various parts in detail;

Figure 3 is a vertical sectional view of a modification of my invention;

Figure 4 is a top view of the embodiment of Figure 4, and 1 Figure 5 is a side elevational view of the embodiment of Figure 4 taken along line 5-5 of Figure 4.

Describing the invention in detail, the press may comprise a cylinder 2 and a ram 4 reciprocal therewithin, said ram carrying a platen 5 for engagement with the work. A tank or reservoir 6 is mounted above the cylinder 2, said tank constituting a fluid supply sourc for a hydraulic circuit hereinafter described.

It will be noted that the pressure of the fluid in the tank. 6 may be considered as the datum pressure relative to the entire circuit. This datum or tank pressure may be atmospheric or above or below atmospheric as.de sired; however, the terms pressure and vacuum as herein- 2,750,744 Patented June 19, 1956 after used, must be construed to mean pressures above and below, respectively, the datum pressure in the tank.

Within the reservoir 6 my novel prefill valve, indicated generally at 8, is mounted in such a manner so as to communicate with the advance cylinder space or chamber 10 above ram 4 through the passage 12 on the top of the cylinder 2.

A pump 14 which may be of the conventional variable discharge, reversible delivery type, is mounted at some point on the press body and is connected to the advance line 16 on one side and to the pullback or return line 18 on its other side. As best seen in Figure 1, the advance line 16 communicates, through passage 20 in the cylinder head 2, with the advance cylinder chamber 10 above the ram 4. It will also be seen that the pullback or return line 18 communicates through

passages

22 and 24 in the cylinder head 2, with the pullback cylinder chamber 26 and with the prefill valve 8.

Referring now to Figure 2 wherein the prefill valve 8 is illustrated in detail, it will be seen that the valve comprises a body 36 having a cylindrical chamber 38 at one end thereof and another cylindrical chamber 40 at the opposite end thereof, both chambers communicating with the intervening outlet passage 42 which is connected to the beforementioned passage 12 in the top of the cylinder 2, the body 36 of the prefill valve being secured to the top of said cylinder by any suitable means such as stud and nut assemblies. At each side thereof the body 36 presents the cored inlet opening 44 establishing communication between the chamber 38 and the tank 6.

The valve stem 47 is provided at one end thereof with a relatively large diameter cylindrical portion or closing piston 49 which is atforded a sliding fluid tight fit within the chamber 40, the opposite end of the stem 47 being a piston-like membet 48 of reduced diameterextending into the cylinder 50 formed within the body 36. This opening piston 48 slidably reciprocates within the cylinder 50 and is in fluid tight engagement therewith.

The larger-diameter portion or closing piston 49 of the valve stem 47 is provided with'a seat 54 intermediate the ends of the stem for cooperation with a complementary seat portion of the body 36 formed at the inner extremity of the chamber 38, and the larger-diameter portion of the stem 47 is hollowed out as at 56 to form a cylindrical chamber communicating with the chamber 40.

Ports

60, 60 extend through the valve stem and communicate with the chamber 56 and provide an avenue of communication between the chambers 40 and 56 and the outlet passage 42.

The pullback or return line 18, as noted, communicates with

passages

22 and 24 and therethrough to the pullback chamber 26 and to the passage 62 of the prefill valve. As best seen in Figure 2, the passage 62 extends outwardly through the valve to the area of the forward edge of the opening piston 48 Whereat said passage 62 presents an annularly enlarged portion 66 which surrounds the opening piston and also communicates with an escape port 64 which in turn is open to the tank through the ports 44. It should be noted that the escape port 64 is machined to receive in fluid tight slidable engagement the opening piston 48 as will be hereinafter described.

Standard or conventional

pressure relief valves

63 and 65 may be mounted atop the prefill valve 8 communicating with the principal hydraulic passages through the holes 46 and 67, respectively.

A longitudinal hole 68 may be drilled in the opening piston 48 adjacent the lower end thereof and combines with a communicating cross drilled hole 70 to afford a passage extending from the surface of the piston 48 to the chamber 56. A one-way ball check valve 72 is provided in the piston 48 communicating with the hole 68 and therethrough with the chamber 50. The function of the valve 72 will be hereinafter more fully described.

It should be noted that in the closed or pressure position of the prefill valve as shown in Figure 2, the cross drilled hole 70 slightly overlaps the edge of the passage 62 as at 74.

The manner in which my novel prefill valve functions is best understood by a description of the press operation. Assuming, that it is desired to engage the platen 5 with the work, the pump directs pressure fluid into the line 16 and at the same time draws fluid from the pullback line 18, thus causing the ram to move downwardly engaging the platen 5 with the work. Under these conditions, the stem 47 of the prefill valve 24 is in its open position with the seat 54 disengaged from the complementary body seat and with the piston 48 disposed Within the port 64 in such a manner that the hole 70 is completed sealed. The manner in which the stem 47 is moved to its open position and held there is hereinafter more fully described in connection with the retraction stroke of the ram 4. Thus, with the prefill valve open, fluid is permitted to flow from the tank 6 through the

openings

44, 44 of the body into the chamber 38 thereof and downwardly through the

passages

42 and 12 into the cylinder space which becomes increasingly large as the ram 4 moves downwardly. As the downward movement of the ram occurs, fluid is forced by the weight of the ram from the pullback chamber 26 through the

lines

22 and 24 of the cylinder 2 and into the pullback line 18, and thence to the pump for delivery to the ram advance cylinder 10. The valve stem 47 is held in the open position during this action by static pressure exerted by oil which was trapped in chamber 50 during the previous cycle hereinafter described.

When the platen 5 engages the work, the resulting resistance to the downward movement of the ram 4 causes pressure to be built up in chamber 10 and also causes pressure of the fluid escaping from the pullback chamber 26 to diminish which enables the pump to pull a vacuum in the pullback line 18. In the valve open position, the oneway ball check valve 72 is disposed communicating with the line 62, through annular passage 66, and the vacuum of the pump causes a portion of the fluid in chamber 50 to escape through the one-way ball check valve 72 which in turn creates vacuum in chamber 50, thus initiating movement of the valve to the left or closed position as seen in Figure 2. As movement of the piston 48 registers the hole 70 with the line 62, more of the oil trapped in chamber 50 is drawn out by the pump through the

holes

68 and 70 thus moving the stem 47 further to the closed position. 7

Concurrently with the pressure drop in chamber 50 due to the platen contacting the work, a pressure is' directed'to the chamber 10, the passage 12, and the passage 42. The influx of high pressure fluid to the outlet passage 42, which is already prefilled, urges part of the fluid therewithin to flow to the tank 6 through the opening 44 and past the main closing piston 49 of the valve stem 47 thus temporarily reversing the prefllling action. At this instant the main stem 47 has been only partially moved to the closed position. As the stem 47 is urged to move to the closed position, the escape area between the large diameter piston 49 and the complementary seat 54 becomes progressively smaller, hence the velocity of the escaping fluid is increased causing a pressure drop at the leading edge of the closing piston 49. In addition a pressure head is built up in the chambers 56 and 40 by passage of the pressure fluid thereto through the ports 60. The pressure head in chambers 56 and 40 combines with the pressure dro at the leadin edge of the closing piston 4 49 and the vacuum in the chamber 50 to urge the valve stem 47 to move to the closed position. As soon as the leading edge of the piston 49 laps the edge of the body, the full power of the pump is available in chambers 40 and 56 to close completely the valve.

Upon closing of the prefill valve the full power of the pump is available to build high pressure in the ram advance chamber 10 to allow the ram to accomplish the work to be done by the press.

The pullback phase of the cycle is initiated by reversing the pump 14 directing pressure fluid into the line 18 and drawing fluid from the advance chamber and advance line 16.

With the prefill valve in closed position, the pump directed pressure fluid is allowed to escape to the tank through the line 62 and

ports

64 and 44. As the fluid enters port 64 and passage 66, its velocity is increased due to the decrease in area opening thereby causing a pressure drop at the leading edge of the piston 48. In addition some of the escaping fluid finds its way through the edge of the overlapping hole 70 into passage 68 to chamber 50 behind the opening piston whereat a small static head or pressure is built up. As the pump begins to pull a vacuum in the advance chamber 10 and consequently in chambers 56 and 40, that is, complete decompression has occurred behind the closing piston, the mentioned static head or presure behind the opening piston combines with the presure drop at the leading edge of the opening piston to urge the valve stem to move to the right toward the open position. As the leading edge of the opening piston laps the edge of port 64, the escape of the pullback pressure fluid is cut off and the full power of the pump is available to direct pressure through the holes 68 and 7t and into chamber 50, whereby the stem 47 is moved to the complete open position. With the prcfill valve open and the escape port 64 cut off, the full power of the pump is now directed into the pullback chamber 26 to return the ram 4.

Thus it is seen that my novel prefill valve and more particularly the method by which fluid flow is controlled therein, positively prevents the escape of high pressure fluid to the tank, and the consequent noise and damage, until complete decompression has occurred in the advance chamber.

It will be noted that there is shown in phantom lines in Figure 2 a compressed spring 84 disposed within the chambers 56 and 40 and abutting at opposite ends the stem 47 and the end cap of the body 36. The optional addition of the spring 84 constitutes a slight modification in the novel prefill valve described above. Inasmuch as the velocity of the fluid escaping from passage 42 by the port and piston 49 and into the tank is much lower than the like fluid movement at the opening piston end of the stem, the resulting dynamic effect or pressure drop is lessened and hence it may be desirable to aid the closing action of the valve stem by the addition of the spring.

Referring now to Figures 3 to 5 wherein is illustrated a different embodiment of the invention more adptable to hydraulic presses of smaller construction and capacity, the prefill valve is again disposed within the tank 6, positioned communicating with the passage 12, and may be bolted to the cylinder 2 as was done in the above described embodiment. The body 86 comprises a mounting plate 88 having a main substantially circular portion 90 with a partially rectangular portion 92 integraliy formed on the edge thereof. Centrally of the circular portion 90 and on the lower side of the plate 88 a boss 91 may be formed to register peripherally with the hole 12 of the cylinder 2. The boss and the plate 88 also define the machined cylindrical counterbored and chamfered hole 94 which receives the wings 102 of the valve stem indicated generally at 98. The conical portion 96 of the stern below the wings 102, in the closed position thereof, abuts the complementary formed valve seat thereby 5 sealing the passage 94 and preventing flow of fluid from the tank 6 to the passage 12. v

Above the hole 94 and substantially aligned therewith the body presents a housing 104. Said housing 104 may be supported in position by the vertical quadrantally spaced legs 106 integrally formed with the top of the plate 88 and the housing 104. The spaces 108 between the legs 106 accommodate free passage of the fluid in the tank 6 to the prefill valve.

A circular port 110 is formed in the bottom of the housing 104 communicating with the tank 2 and with a cylinder 112 formed within the housing 104. Both the port 110 and the cylinder 112 are machined to a close tolerance slidably fluid tight fit with the upper opening piston 114 formed on the related end of the valve stem 98.

An elbow 116 is integrally cast with the housing 104 and the plate 88. A passage 118 is defined within the elbow and communicates at one end with the line 24 which in turn communicates with the pullback line 18. At the other end, the passage 118 communicates with the cylinder 112 at the radially enlarged segment 120 of said cylinder 112. A groove 121 is formed on one side of the cylider 112 and offers an avenue of communication between the segment 120 and the chamber 123 behind the opening piston 114.

Counterbalancing means 122 are preferably added to counteract the weight of the stem 98 thus permitting the valve to act only in response to the fluid pressures hereinafter described. Said counterbalancing means may consist of an arm 124 pivoted intermediate its ends to the body 86 by means of horizontally spaced lugs 126 integrally formed with the adjacent spaced legs 106. The outboard end of the arm 124 may be connected to one end of a tension spring 128, which in turn is anchored to some relatively fixed object, such as the plate 88 by means of the hook 130. The inboard end of the arm 124 is bifurcated or forked to straddle the intermediate portion of the valve stem 98 and to engage the underside of a pin 132 which is horizontally press fitted within the intermediate portion of said stem and with opposite ends extending above the surface of said portion.

The operation of this embodiment is identical in principle with that of the previously described embodiment. It will be noted, however, that the groove 121 in the upper chamber 112 functionally replaces the

holes

68 and 70 and the check valve 72 of the previous embodiment. It will also be seen that the press body itself oifers the chamber wherein the closing piston 96 may reciprocate.

In the rapid advance phase of the cycle the valve is open and held open by static pressure by the fluid in chamber 123. Prefilling, of course, is occurring during the rapid advance from the tank 6 through the openings 108 between Wings 102 and hence to the passage 12 and chamber 10. In addition the pump is directing fluid directly to chamber while withdrawing fluid from the pullback or return chamber 26.

The full pressure phase of the cycle is initiated by the resistance of the ram striking the work whereby the pump pulls a vacuum in the return chamber drawing fluid from chamber 123 behind the opening piston through groove 121. The vacuum in chamber 123 combines with the pressure of the fluid below the cylindrical portion or piston 96 in the advance chamber and the pressure drop due to the velocity of the fluid escaping to the tank by the valve seat 100, to urge the stem 98 upwardly and into the closed position. With the stem in closed position escape of the pressure fluid at valve seat 100 is precluded and the pump is free to buid up full working pressure in the advance chamber 10.

The pullback phase of the cycle is initiated by pump reversal which draws fluid from the advance chamber and directs it to the pullback chamber. As noted above the fluid is allowed to escape through port 110 to the tank, a small portion of it, however, entering the chamber 123 through the groove 121. As before the flow of fluid through the escaping port causes a pressure drop at the leading edge of the piston 114. As the pump pulls a vacuum in the advance chamber 10, said vacuum combines with the static head in chamber 123 and the velocity pressure drop at the leading edge of the piston 114 to move the stem 98 to the open position. As the leading edge of the piston 114 laps the edge of the port 110 the full power of the pump is directed to chamber 123 through the groove 121, thereby urging the stem to the full open position. The pressure of the pump is then directed to completing the pullback stroke of the ram.

It will be understood to those familiar with the art that the

relief valves

63 and 65 shown and described in the previous embodiment may also be associated with the present embodiment by the simple expedient of connecting said valves at any convenient point to the related advance or pullback lines.

I claim:

1. An hydraulic press comprising advance and return chambers, ram means reciprocal therein, advance and pull back lines connected to the respective chambers, a reservoir of low pressure fluid, pump means for alternately delivering pressure fluid to one of said pressure chambers while withdrawing fluid from the other of said chambers through the respective lines, and a prefill valve offering separate avenues of communication between the reservoir and the respective chambers, said valve comprising a body having spaced substantially cylindrical valve chambers, one of which is of smaller diameter than the other, low pressure passage means through said body between said valve chambers and connected to said reservoir, high pressure passage means connected to said other valve chamber and advance chamber, a valve stem having a portion slidable in said other valve chamber, a seat on said portion engageable with the seat of said body to cut off communication between said passage means, said stem having a piston slidably fitted in said one valve chamber and said stem having a connecting segment interconnecting said piston and said portion, said segment being of smaller diameter than said piston, a substantially cylindrical port through said body between said valve chambers and communicating with said low pressure passage means, said port being substantially-coaxial with and of the same diameter as said one valve chamber, said port being open when the seats are engaged and being closed by said piston when the seats are separated, another high pressure passage means connected to said pull back line and extending between the port and said one valve chamber and communicating with said port when the seats are engaged, and passage means connecting said other high pressure passage means to said one valve chamber at the end thereof remote from said port.

2. In combination, a hydraulic motor comprising ,ram means with advance and return chambers associated therewith, a reversible hydraulic pump operatively connected to the advance and return chambers, respectively, a reservoir of hydraulic fluid at a datum pressure, a prefill valve, said valve comprising a body having a cylindrical chamber, passage means at opposite ends of the chamber communicating with the advance and return chambers, respectively, communicating means intermediate the ends of said cylindrical chamber connecting same to'the reservoir, and a valve stem reciprocal in said cylindrical'chamber operative to alternately open one of said passage means while closing the other exclusively in response to the alternate delivery by the pump of pressure fluid to the advance and return chambers, respectively, said valve stem being provided with fluid passageway means therein whereby pressure fluid is aflorded communication from a portion of the. cylindrical chamher on one side of the stem to a portion on the other side of the stem to facilitate reciprocation of the stem in said cylindrical chamber.

3. In combination, a hydraulic motor comprising a ram with advance and return Chambers associated therewith, a reservoir of hydraulic fluid, a reversible hydraulic pump operatively connected to each of said chambers, a prefill valve comprising a main chamber communicating with the reservoir, spaced ports in said main chamber communicating with the advance and return chambers, respectively, and piston means reciprocal within said main chamber operative to alternately and simultaneously close and open the spaced ports exclusively in response to the action of the reversible pump wherein said main chamber consists of a large diameter portion having the port communicating with the advance chamber and a smaller diameter portion having the port communicating with the return chamber, and said piston means consists of a valve stem having a large diameter piston formed on one end and a small diameter piston formed on the other end, said large piston being disposed in said large portion and said small piston being disposed 'i said small portion.

4. In combination, a hydraulic motor comprising a ram with advance and return chambers associated therewith, a reservoir of hydraulic fluid, a reversible hydraulic pump operatively connected to each of said chambers, a prefill valve comprising a main chamber communicating with the reservoir, spaced ports in said main chamber communicating with the advance and return chambers, respectively, and piston means reciprocal within said main chamber operative to alternately and simultaneously close and open the spaced ports exclusively in response to the action of the reversible pump, wherein said main chamber consists of a large diameter portion having a port communicating with the advance chamber and a smaller diameter portion having a port communicating with the return chamber, and said piston means consists of a valve stem having a large diameter piston formed on one end and a small diameter piston formed on the other end, said large piston being disposed in said large portion and said small piston being disposed in said small portion, wherein said pump alternately directs pressure fluid into the advance chamber while withdrawing the fluid from the return chamber and then directs pressure fluid into the return chamber while withdrawing it from the advance chamber, and said large piston is operative to close the related port in response to pump controlled fluid flow from the advance chamber through the related port and to the tank, and said small diameter piston is operative to close the related port in response to pump controlled fluid flow from the return chamber through the related port and to the tank.

5. In combination, a hydraulic motor comprising a ram with advance and return chambers associated therewith, a reservoir of hydraulic fluid at a datum pressure, a reversible pump connected to each of said chambers whereby pressure fluid may be alternately directed to one of said chambers while withdrawing fluid from the other of said chambers, and a prefill valve comprising a cylindrical chamber open to the reservoir and having at opposite ends thereof ports communicating with the ad- Vance and return chambers, respectively, a valve stem reciprocal within said cylindrical chamber and having pistons formed at opposite ends operative to close and open the related ports as the stem reciprocates with the cylindrical chamber, the reciprocation of said stem being exclusively responsive to the alternate direction by the pumping of pressure fluid to one of said chambers and through the related port and into the tank, and including passage means through each of said pistons, whereby pressure fluid in the related chamber may communicate with a segment of the cylindrical chamber behind the related piston and thereat exert pressure behind the related piston, thereby aiding the reciprocation of said stem.

6. In combination, a hydraulic motor comprising a cylinder having a ram reciprocal therein and defining therewith advance and return chambers, a reservoir of hydraulic fluid at a datum pressure, a reversible pump operative to alternately deliver pressure fluid to one of said chambers while withdrawing fluid from the other of said chambers, a prefill valve, comprising cylindrical pumping chambers of unequal bore and a valve stem with pistons of unequal diameter disposed for reciprocal movement within the respective pumping chambers, offering separate avenues of communication between the reservoir and said first mentioned chambers, respectively, said valve being operative to admit datum pressured fluid to the advance chamber through one of said avenues during rapid advance of said ram and to close said one avenue during the pressure advance of said ram exclusively in response to the flow of pump delivered pressure fluid from the advance chamber to the tank through said one avenue and to the pump created vacuum in the return chambet".

7. A prefill valve comprising a body member having spaced cylindrical chambers, one of which is of smallerdiameter than the other, a low pressure passage through said body member between said chambers, a high pressure passage connected to the other chamber, a valve stem having a portion slidably fitted in said other chamber, a seat on said portion engageable with a seat of said body member to cut oil? communication between said passages, said stern having a piston member slidably fitted in said one chamber, and said stem having a connecting segment interconnecting said piston memher and said portion, said segment being of smallerdiameter than said piston member, a cylindrical port through said body member between said chambers and communicating with said low pressure passage, said port being coaxial with and of the same diameter as said one chamber, said port being open when the seats are engaged and being closed by said piston member when the seats are separated, another high pressure passage extending between the port and said one chamber and communicating with said port when the seats are engaged, and passage means through one of said members connecting said other high pressure passage to said one chamber at the end thereof remote from said port.

8. A prefill valve according to claim 1 and including passage means in said piston whereby pressure fluid in the return chamber can communicate with a segment of said one chamber behind said piston and exert pressure behind said piston to aid reciprocation of said stem.

9. A prefill valve according to claim 1, wherein said valve stem portion is partially disposed within the advance chamber of said press.

10. An hydraulic press comprising advance and return chambers, ram means reciprocal therein, advance and pull back lines connected to the respective chambers, a reservoir of low pressure fluid, pump means for alter nately delivering pressure fluid to one of said pressure chambers while withdrawing fluid from the other of said chambers through the respective lines, and a prefill valve comprising a body having spaced substantially cylindrical valve chambers, one of which is of smaller diameter than the other, low pressure passage means through said body between said valve chambers and connected to said reservoir, high pressure passage means connected to said other valve chamber and advance chamber, a valve stem having a portion slidable in said other valve chamber, a seat on said portion engageable with the seat of said body to cut off communication between said passage means, said stern having a piston slidably fitted in said one valve chamber and said stem having a connecting segment interconnecting said piston and said portion, said segment being of smaller diameter than said piston, a substantially cylindrical port through said body between said valve chambers and communicating with said low pressure pas sage means, said port being substantially coaxial with and of the same diameter as said one valve chamber, said port being open when the seats are engaged and being closed by said piston when the seats are separated, another high pressure passage means connected to said pull back line and extending between the port and said one valve chamber and communicating with said port when the seats are engaged and passage means connecting said other high pressure passage means to said one valve chamber at the end thereof remote from said port.

11. A prefill valve according to claim 10, wherein said body comprises separate sections spaced from each other, each of said sections having one of said valve chambers therein.

References Cited in the file of this patent UNITED STATES PATENTS