US2534966A - Pressure-responsive reversing valve for hydraulic motors - Google Patents

Description

Ema 19, 195(1 G. M. GEHGER ET AL 2,534,9fi6

PRESSURE-RESPONSIVE REVERSING VALVE FOR HYDRAULIC MOTORS Filed May 27, 1946 4 Sheets-Sheet 1 INVENTORS $505M? H. 95/659 HOWARD M. PURGELL ATTORNEY$ De W 195@ G. M. (BERGER ETAL PRESSURE-RESPONSIVE REVERSING VALVE FOR HYDRAULIC MOTORS 4 Sheets-Sheet 2 Filed May 27, L946 A TTOIWIE V3) GEORGE 41. 5mm EV HOWARD M. Pwmau Fii 2 Emu 319, 195@ G. M. GEHGER ETAL PRESSURE-RESPONSIVE REVERSING VALVE FOR HYDRAULIC MOTORS 4 Sheets-Sheet I5 Filed May 27, 1,946

" NEw E G. M. GEEGER ETAL PRESSURE-RESPONSIVE REVERSING VALVE FOR HYDRAULIC MOTORS 4 Sheets-Sheet 4 Filed May 27, 1946 WE WWNWW m; mswms 650/?65 M. GE/GER HOWARD M. PUWGELJL ATTORNEYS Patented Dec. 19, 1950 UNITED STATES PATENT OFFICE PRESSURE-RESPONSIVE REVERSING VALVE FOR HYDRAULIC MOTORS George M. Geiger and Howard M. Purcell, Mount Gilead, Ohio, assignors to H-P-M Development Corporation, Wilmington, Del., a corporation of Delaware Application May 2'7, 1946, Serial No. 672,603

12 Claims.

which is entirely shifted by hydraulic pressure from one position to another.

Still another object is to provide a valve which is operated by the ram which it controls in one direction of movement and employs pressure generated within the valve for its movement in the other direction.

' It is still another object to provide a control valve and in association therewith pilot valves which operate automatically to cause the said control valve to be shifted or to remain idle in response to predetermined movements of the press ram.

Still another object is to provide a fluid operated control valve which is shiftable selectively by a predetermined pressure or by a predetermined position of the control ram.

These and other objects and advantages become more apparent upon reference to the following specification taken together with the accompanying drawings, in which:

Figure 1 is a vertical section through a valve constructed according to this invention;

Figure 2 is a diagrammatic view of a press circuit employing the valve with this invention;

Figures 3, 4 and 5 are diagrammatic views of the valve in different stages of an operating cycle with the valve adjusted for automatic operation; and

Figure 6 is a view showing the valve adjusted for single cycle operation.

General arrangement According to this invention, there is provided a control valve which receives fluid from a fluid source and selectively directs the said fluid to one or the other of the ports of a motor such as a reciprocating press ram.

The movable member of the control valve is continuously urged into position to direct fluid to the retracting side of the control ram, and is moved into a neutral position to a predetermined retracting movement of the said ram, and is shifted into position to direct fluid to the advancing side of the ram by fluid pressure.

When the valve is in its centered position, there maybe a bypassing of fluid therethrough in in response which case the press ram remains at rest. An auxiliary valve is provided which is selectively adjustable to interrupt the aforementioned bypassed connection. When this is done, the pressure generated within the valve when it moves to neutral is suflicient to shift the valve into position to advance the ram.

Structural arrangement Referring to the drawings more in detail, it will be seen in Figure 1 that the valve of this invention comprises a body or casing portion Ill having a central bore I2 therethrough within which is reciprocable the valve member I4. The valve bore I2 has pressure fluid supplied thereto by a conduit I6 through a passage which opens into the valve bore substantially intermediate the ends thereof. Between the pressure opening in the bore I2 and the upperend thereof, there is an enlarged portion indicated by the numeral tween the pressure inlet and the lower end of the bore I2 and communicates with a conduit 24 leading to the retraction side of the press ram. The lower end of the bore I2 is closed as by a cap 26 which is apertured in any suitable manner to receive the actuating rod 28 of the valve member I4. The upper end of the bore I2 is similarly closed with a cap 30 which is bored to receive an exhaust conduit 32.

Returning to the valve member I4, this will be seen to comprise a plurality of spaced spool portions, the uppermost of which as at 34 and 36 are spaced so as at least to span the recess I8. Preferably, the spool portion 34 comprises the notches 38 by means of which communication is had between the recess I8 and the exhaust con-' duit 32 when the valve is in its neutral position;

Spaced from the spools 34 and 36 are another pair of spools 46 and 42 which have bevels as at 44 on their outer edges and which, when the valve member is centered, span the recess 22, thereby interrupting communication of the conduit 24 with either pressure or exhaust.

Spaced downwardly from the spool portion 42 is a fifth spool portion 46 which stops the valve in its uppermost position by abutting the cap 26 and, when the valve is in neutral, or in its upper position, fits closely within the bore I2. The valve member I4 between the spools 42 and 46 is cross-drilled as by the bores 48 and a central axial bore 50 in the valve member communicates the bores 48 with the upper end of the bore I2 3 and, hence, with the exhaust conduit 32. For a purpose which will become more apparent hereinafter, the bore I2 is provided with an undercut 52 adjacent the bottom end thereof which is greater in diameter than the spool portion 46 and also of somewhat greater axial length.

The valve body I also has therein a valve bore 54 which reciprocably receives a pilot or control valve member 56 that has an operating rod 58 extending through the cap 26 and terminating in a suitable actuating fitting 60.

The bore 54 is provided with an exhaust connection 62 at the upper end thereof by means of which leakage from around the valve member 56 is conducted to a reservoir.

At the level of the pressure conduit I6, there is a bore 64 which extends from the valve bore 54 toward the valve bore I2 and communicates with the latter through a restricted opening at 66. This bore provides a bypass channel for the pressure fluid when the valve member I4 is moved to neutral under certain conditions of operation as will become more apparent hereinafter.

Between the recess 22 and the recess 52 of the bore I2, there is a bore 68 connecting the valve bores I2 and 54.

Between the bores 64 and 68, there are a pair of passages or bores and I2 which communicate with the valve bore 54 and which are for a purpose to be explained hereinafter.

The valve member 56 is provided with a spool portion I4 at its upper end, spool portion I6 at its lower end, and an intermediate spool portion "I8. With the valve member 56 in its lowest position all of the aforementioned bores 64, I0 and I2 are interconnected. When the valve member is in position to eflect automatic operation of the main valve member I4, the bore 68 is closed off by the spool portion "I8. the valve member 56 is shifted into position for single cycle operation of the main valve member I4, the bores 68 and I2 are interconnected between the spool portions I6 and I8 while the bores 64 and I0 are interconnected between the spool portions I4 and I8.

The valve body or casing I0 also has therein a valve bore 80 within which is reciprocable a valve member 82 and a second member 84 which serves as a movable abutment for stopping valve member 82 in predetermined upper positions. The bore 80 comprises a recess 86 at its lower end which communicates with the recess 52 in the bore I2 by a passage 88 and is also connected with the valve bore 54 by the passage or bore I0.

A second recess 90 in the bore 88 is connected with the valve bore I2 by a passage 92 at the same level as the bore 68. Between the recesses 86 and 90 the valve member 82 engages a seat 04 so that communication between the said recesses is interrupted with the said valve member in its lower position.

The valve member 82 has an undercut 96 therein which is connected with the bore 80 above the said valve member by the cross drills 08 and axial passage I 00 in the said valve member. The bore 80 above the said valve member is closed by the member 84 which is shouldered and has the portion I02 reciprocable in the bore 88 and the portion I04 which is reciprocable in the enlarged portion I06 of the bore 80. The enlarged portion I06 of the bore 80 is connected with the valve bore 54 by the bore 72 in the valve casing. The space within the portion I06 beneath the portion I04 of the member 84 is connected with the upper 4 end of the valve bore 54 by a bore or passage I08 in the valve body. This passage is for the purpose of maintaining exhaust pressure beneath the portion I04 to permit its free reciprocation in the valve body.

At the level of the recess 96 in the valve member 82, there is a restricted bore I I0 which communicates the bore 80 with the pressure chamber of the bore I2. The bore I I0 also communicates the bore 80 with the inlet of a relief valve II2 which is connected by a passage I I4 to discharge into the recess 22 of the valve bore I2.

The relief valve I I2 may comprise any suitable type of pressure responsive mechanism and includes a spring I I6 adjustable by the hand wheel and stem arrangement at I it.

For a purpose which will become more apparent in setting forth the operation of this device, the bore IIO opens into the bore I2 at a level which is completely closed by the spool portion 40 when the valve member I4 is in its uppermost position. The bore I I0 opens into the bore 80 at a level such that the recess 96 remains in communication therewith when the valve member 82 is stopped in its upper position by the member 84 when the latter is in its lowermost position. When the valve member 82 is stopped in its upper position with the member 84 also in its upper position, the recess 96 is moved out of communication with. the bore H0 and the valve member 82 seals off the end of the said bore to prevent fluid flow therethrough.

The valve member I4 is continuously urged downwardly to its Figure 1 position by a spring I26 that bears between the cap 26 and a collar I22 fixed to the actuating rod I24 that is threaded into the end of the rod 28 of the valve member I4.

The valve body is preferably provided with mounting flanges I26 that are apertured at I28 to receive screws so that the valve may be mounted on the side of a press cylinder or in any other suitable manner.

In Figure 2, the valve is shown diagrammatically as it would appear in connection with a hydraulic press ram. In Figure 2, the press consists of a cylinder I30 in which there is reciprocable a double acting ram I32 to which is attached a platen I 34. The advancing side of the ram I32 is connected by the conduit 20 with the valve while the retracting side of the said ram is connected with the valve by the conduit 24. The platen I34 has an arm thereon that terminates in a collar I36 which is slidable over the rod I24 and which is adapted for abutting the collar I38 connected with the said rod.

The valve receives pressure fiuid from a fluid source such as a pump at I40 which is connected with the valve by the conduit I6 and which draws fiuid from a reservoir I42 as by a suction conduit I44.

In the circuit shown in Figure 2, there is provided an auxiliary means for reversing the press ram I32 in response to a predetermined position contained by the platen I34. For accomplishing this, the recess 86 of the valve bore 80 is connected by a conduit I46 with the inlet of a normally closed two-way valve I48 which has an exhaust connection I50. The valve member I52 of the valve I48 is normally urged into position to interrupt communication between the conduits I46 and I by a spring I54. The valve member includes an extension that carries a roller I56 which lies in the path of a cam I58 adjustably carried on the platen I34. In response to a predetermined advancing movement of the platen I34, the cam I58 engages the roller I56 and shifts the valve member. I52 into position to connect the conduits I46 and I50 thereby to exhaust the recess 86 of the bore 80 and the recess 52 of the bore I2. As will become more apparent hereinafter, this is effective to permit the spring I20 to shift the valve member I4 into position to bring about the retracting movement of the ram I32.

Operation In order better to understand the operation of the valve of this invention, reference may be had to the diagrammatic views 3, 4 and 5 in connection with Figures 1 and 2.

In Figure 2, the press ram is shown in its retracted postion with the valve member of the control valve shifted to its natural position by the collars I35 and I38. In Figure 2, the auxiliary or pilot valve member 56 is in its lowermost position and is providing a bypass channel for the fluid delivered by the source MD. This channel is through the conduit I5 to the bore I2, through the bores 66 and E i to the bore 54, and through the bore 68 to the valve bore I2 at the level of the cross drills 48. From this point the fluid passes throughthe axial bore 59 in the valve member I4 and then through the conduit 32 back to the reservoir I42.

In order to place the press on full automatic cycling, the pilot valve 56 is shifted upwardly into the intermediate position shown in Figure 3. This interrupts the aforementioned bypass channel by interrupting the communication between the bores 64 and 68 by the valve piston I8. With the bypass channel interrupted, fluid pressure builds I up within the bore I2 at the level of the conduit IS, in the bores 66 and 6 5, in the bore 54 between the valve spools Ill and I8 and also in the bore 11!. The bore ID is in communication with the recess 52 and the aforementioned rise in fluid pressure is thus effective to urge the valve member I4 upwardly against the thrust of the spring I20. It will be noted that at this time the valve member 82 is in its lowermost position thereby interrupting communication between the recesses 86 and 90. The valve member 52 is in this position because the fluid pressure from the valve bore I2 which passes through the conduit I I also passes through the cross drills 93 and bore It!!! in the valve member 82 and stands on the upper end thereof.

In Figure 3, the main valve member Hi, the pilot valve member 55, the auxiliary valve member 82 and the movable abutment 8A are all shown in the position they occupy when the press ram is advancing downwardly. At this time, the conduits I6 and 28 are interconnected to supply fluid to the advancing side of the press ram while the conduits 24 and 32 are interconnected to provide an exhaust passage for the retracting side of the said ram.

After the ram has advanced a predetermined amount and engaged the work, pressure builds up between the advancing side of the ram and the fluid source I so and is conducted by the bores 66, 64, 54, Ill, recess 52, and bore 88 to the recess 86 where it acts to urge the valve member 82 upwardly.

When the upward thrust on the valve member 82 reaches a predetermined amount, the relier valve I I2 opens to connect the recess 98 with the conduit I I 4 which, at this time is connected to exhaust. When the relief valve opens, the valve m m m es. u ward y. ndthe fluid t ere:

over is exhaustedto the conduit Il4-by way of theboreslflll,98andll0. 1

The pressure which is built up betweenthe ram and the fluid source also extends through thebore I2 and acts in the recess N15 to move the movable abutment member downwardly into the position shown in Figures 3 and 4. Thus, when the auxiliary valve member 32 moves from its Figure 3 to its Figure 4 position it abuts and is halted by the abutment member 84.

With the valve member 82 in its Figure 4 position, the recess 52 is connected with exhaust by way of the bore 88, the recess 85, the passage through the seat 94, the recess 9B, the bore 92, cross drills E8, the axial bore 59, and the conduit 32. This permits the spring I25 to shift the valve member I4 into its lowermost position in order to connect the conduit IS with the conduit 24 to supply fluid to the retracting side of the ram I32, and also to connect the conduit 29 with the exhaust conduit 32. The valve is shown in this position in Figure 5. During the retracting movement of the press ram the pressure established between the retracting means thereof and the source I il acts through the bore Hi; to return the valve member 82 to its lowermost posi tion thereby to reset the mechanism for a new cycle. Then, when the valve member :4 is again moved into its Figure 2 position by the interaction by the collars I35 and 138, fluid pressure is supplied to the recess 52 and again shifts the valve member I4 into position to institute an ad vancing stroke of the press ram.

It will be apparent, that the reversal of the press ram could be accomplished in accordance with the position of the press ram by means of the valve I %8 which is operable to exhaust the recess 52. The shifting upwardly of the valve member I 4 cannot take place until it has first been shifted to close 011 the recess 52 by the spool portion 45. While there is a continuous loss of fluid from the pressure level of the valve bore I2 through the bores 66, 64, 5 and i0 during the retracting movement of the press ram, this is not of serious consequence because at least the bore 65 is restricted and the press ram is operating under a low pressure. It will be understood that Figure 2 is diagrammatic and that the conduits It, 26, 24 and 32 are shown of a relatively small diameter, they are, in fact, considerably larger than the bore 56 so that a substantial amount of restriction to fluid flow is had by the said bore and circulation through the aforementioned conduits and the other bores within the valve is relatively free.

For single cycle operation of the press, the valve member 55 is moved to its Figure 6 position. In this position, the valve spool '58 interrupts communication between the bores 5 and I2 and connects the bore I2 instead with the bore 68 which is continuously at exhaust pressure. With the pilot valve member 55 in this position the movable abutment ti permits the valve member 82 to move upwardly until it closes ofi the bore IIIl. Then, when the valve member It is shifted to neutral and fluid pressure builds up in the conduit I5 due to the restriction in the bore 66, the valve member 82 cannot shifted downwardly to close off the exhaust passage for the recess 52. This permits the pump fluid to bypass continuously and prevents sufficient pressure being built up to shift the valve member I4 pwar r. i i

In order to cause the press to cycle, it is necessary to move the valve member 56 downwardly, at least to its Figure 3 position whereupon fluid pressure is conducted to the upper side of the member 84 suiflcient to urge the said member downwardly and to move therethrough the valve member 82 to uncover the end of the bore H0. As soon as the bore H is uncovered, the valve member 82 continues downwardly to its Figure 2 position and closes off the exhaust passage from the recess 52. Thereafter, the valve member I4 is shifted as explained in connection with Figures 2 and 3 to bring about an advancing movement of the press ram. In order to prevent the press ram from reversing automatically at the end of its retraction stroke, the pilot valve member 56 is returned to its uppermost position before the end of the advancing stroke of the said ram. Then, when the ram is fully retracted, it will halt and remain idle until the pilot valve member 56 is again shifted.

It will be apparent that this invention provides a valve mechanism for controlling the reciprocation of a press ram and which may be shifted in response to a predetermined pressure acting on the said ram, or in response to a predetermined position of the press ram. Furthermore, the valve is selectively adjustable for automatic cycling of the press or for single cycling thereof. The valve is entirely contained within a single valve body which includes a plurality of valve members interconnected by bores and passages within the said valve body.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it i desired to comprehend such modiflcations within this invention as may fall within the scope of the appended claims.

We claim:

1. In a valve; a valve casing having a bore intersected by a plurality of ports; a valve men ber movable in said bore for controlling said ports; yielding means continuously urging said valve member in one direction and fluid operable means to move said valve member in the other direction; means to supply actuating fluid to said fluid operable means; second valve means con nected between said fluid operable means and exhaust and having a member therein movable to connect or disconnect said fluid operable means with exhaust; and a third valve means respons've to fluid pressures at said fluid operable means for controlling the movement of said second valve means.

2. In a valve; a casing having inlet, outlet, and service ports; a valve member movable to control said ports; yielding means continuously urging said valve member in one direction and fluid operable means to urge said valve member in the opposite direction; a bypass channel between said inlet port and said outlet port; means movable in said bypass channel to open or close the same; means connecting said fluid operable means with the inlet end of said bypass channel to direct fluid to said fluid operable means when said bypass is closed; and means responsive to a predetermined fluid pressure acting on said fluid operable means for exhausting the latter.

3. In a valve; a casing having inlet, outlet, and service ports; a valve member movable to control said ports; yielding means continuously urging said valve member in one direction and fluid operable means to urge said valve member in the opposite direction; a bypass channel between said inlet port and said outlet port; means movable in said bypass channel to open or close the same; mean connecting said fluid operable means with the inlet end of said bypass channel to direct fluid to said fluid operable means when said bypass is closed; an exhaust passage for said fluid operable means; a member movable to interrupt the said exhaust passage; and means of moving said last-named member into and out of its passage interrupting position.

4. In a valve; a casing having inlet, outlet, and service ports; a valve member movable to control said ports; yielding means continuously urging said valve member in one direction and fluid operable means to urge said valve member in the opposite direction; a bypass channel between said inlet port and said outlet port; means of selectively interrupting said bypass; means connecting said fluid operable means with the inlet end of said bypass channel to direct fluid to said fluid operable means when said bypass is interrupted; an exhaust passage for said fluid operable means; a member movable to interrupt the said exhaust passage; an operating chamber to receive fluid to hold said member in its passage interrupting position; and means to exhaust said chamber to permit said member to establish said passage and to exhaust said fluid operable means.

5. In a valve; a valve casing having a valve bore therethrough which is intersected by inlet, outlet, and service ports; a valve member reciprocable in said bore for controlling said ports; means continuously urging said valve member toward one end position and fluid operable means to urge said valve toward its other end position; a bypass between said inlet and said outlet ports; means to interrupt said bypass; channel means connecting the inlet port end of said bypass with said fluid operable means to direct actuating fluid thereto when said bypass is in- 'terrupted; an exhaust passage for said fluid operable means; a member movable to interrupt said exhaust passage; an operating chamber adapted for receiving fluid to urge said member into, and to retain said member in its passage interrupting position; and relief valve controlled means to exhaust said chamber to permit said member to move into position to exhaust said fluid operable means.

6. In a valve; a valve casing having a valve bore therethrough which is intersected by inlet, outlet, and service ports; a valve member reciprocable in said bore for controlling said ports; means continuously urging said valve member toward one end position and fluid operable means to urge said valve toward its other end position; a bypass between said inlet and said outlet ports; means to interrupt said bypass; channel means connecting the inlet port end of said bypass with said fluid operable means to direct actuating fluid thereto when said bypass is interrupted; an exhaust passage for said fluid operable means; a member movable to interrupt said exhaust passage; an operating chamber adapted for receiving fluid to urge said member into, and to retain said member in its passage interrupting position; and means to supply fluid to said chamber for returning said membe to its passage interrupting position comprising a channel which is interrupted when said valve member is moved by said fluid operable means.

channel means connecting the inlet port end of said bypass with said fluid operable means to direct actuating fluid thereto when said bypass is interrupted; an exhaust passage for said fluid operable means; a member movable to interrupt said exhaust passage; an operating chamber adapted for receiving fluid to urge said member into, and to retain said member in it passage interrupting position; and means to supply fluid to said chamber for returning said member to its passage interrupting position comprising a channel extending from said chamber to the inlet of said valve and adapted for being interrupted when said valve member is moved by said fluid operable means.

8. In a valve; a casing having a valve bore; a pressure port, an exhaust port, and service ports intersecting said bore; a valve member reciprocable in said bore for controlling said ports; means normally retaining said valve member in one end position; fluid operable means for urging said valve member into its other end position; a bypass in said casing between said pressure and exhaust ports and including a restriction; means of interrupting said bypass between said restriction and said exhaust port; a channel connecting said fluid operable means with said bypass between said restriction and said interruption; an exhaust channel for said fluid operable means; a member movable to interrupt said exhaust channel; fluid operable means to urge said member into its channel interrupting position; conduit means normally connecting said last mentioned fluid operable means with the inlet of said restriction, said conduit means being adapted for interruption by said valve member when the latter is moved into said other end position; and a relief valve connected to exhaust said last mentioned fluid operable means in response to a predetermined pressure therein.

9. In a valve having pressure, exhaust and service ports controlled by a valve member movable into a first end position by yielding means and into a second end position by fluid operable means; a restricted passageway connecting said fluid operable means with said pressure port; a first exhaust passage for said fluid operable means established by the movement of said valve member into said first end position; a second ex-- haust passage for said fluid operable means established in response to a predetermined pressure acting thereon; means of moving said valve member away from said first end position and for interrupting said second exhaust passage thereby to move said valve member into said second end position; and means selectively operable, after the establishment of said second exhaust passage by a predetermined pressure rise in said fluid operable means, to permit or prevent interruption of said second exhaust passage to provide for single and automatic cycling of said valve member.

10. In combination with a fluid motor having first and second ports; a fluid source, a valve movable into a first position to connect said l0 source with said first port and into a second position to connect said source to said second port; yielding means to move said valve into said first end position; fluid operable means to move said valve into said second end position, and motor controlled means to move said valve into an intermediate position; means to supply actuating fluid to said fluid operable means to move said valve from its intermediate to its second end position; motor controlled means to exhaust said fluid operable means to permit the movement of said valve into its first end position; and means selectively operable to permit or prevent the resupply of fluid to said fluid operable means when said valve is returned to its intermediate position by said motor.

11. In a fluid operable circuit; a reciprocable ram having advancing and retracting means; a fluid source; a valve member movable into a first end position to connect said source with said retracting means, into a second end position to connect said source with said advancing means, and into an intermediate position to disconnect said source from both of said means; yielding means to move said valve into its first end position, fluid operable means to move said valve into its second end position, and means actuated by said ram at the end of its retracting stroke to move said valve into its intermediate position; means to supply fluid to said fluid operable means from said source when said valve member is in its intermediate position; means responsive to a predetermined pressure acting on said advancing means for exhausting said fluid operable means thereby to move said valve member into its first end position to direct fluid to said retracting means; and means selectively operable for permitting or preventing the re-supply of actuating fluid to said fluid operable means at the end of the retracting stroke of said ram to provide for single or automatic cycling of the said ram.

12. In a reversing valve for hydraulic motors; a valve casing formed with a main valve chamber intersected at different levels by a pressure inlet, an exhaust outlet and first and second service ports; a main valve member movable in the main chamber of said casing to control the flow of fluid between the pressure inlet, exhaust outlet and service ports of said casing, said valve member being formed at one end with a pressure-responsive face for moving said valve member in one direction with said chamber; yieldable means connected with said valve member for moving the same in the opposite direction; channel means in said casing connecting the pressure-responsive face of said valve member with the pressure inlet of said casing; a second channel means in said casing connected between the pressure-responsive face of said valve member and exhaust; a second valve member movable in said casing to open or close said second channel means, said second valve member being formed at one end with a pressure-responsive area in communication with said second channel means and at its opposite end with an opposed pressure-responsive area in communication with a substantially closed pressure chamber formed in said casing; and a pressure relief valve connected to exhaust fluid from the substantially closed pressure chamber of said casing in response to a predetermined high pressure within said second channel means to permit said second valve member to move in a direction to open said second channel means and connect the pressure- 11 responsive face of said main valve member with Number exhaust. 1,956,758 GEORGE M. GEIGER. 2,208,421 HOWARD M. PURCELL. 2,314,082 5 2,324,697 REFERENCES CITED 2,363,111 The following references are of record in the 2,367,241 file of this patent: 2,404,796 2,411,716 UNITED STATES PATENTS m Number Name Date 900,275 Fulton t, 190 Number 1,931,452 Wheeler Oct. 17, 1933 373,732

Name Date Ernst May 1, 1934 Hanna July 16, 1940 Field Mar. 16, 1943 Harrington July 20, 1943 Bennett Nov. 21, 1944 Stacy Jan. 16, 1945 Grant July 30, 1946 Ernst Nov. 26, 1946 FOREIGN PATENTS Country Date Great Britain June 2, 1932

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