US2988085A - Breathing apparatus - Google Patents

Description

June 13, 1961 L. JONES 2,988,085

BREATHING APPARATUS Filed June 17, 1957 2 Sheets-Sheet 1 INVENTOR LEON JONES BY M ATTORNEY June 13, 1961 L. JONES 2,988,085

BREATHING APPARATUS Filed June 17, 1957 2 Sheets-Sheet :2

22 I06 E I00 104 97 9O '4 2 98 I02 88 34 24 36 as 40 g A c w n4l H2 no 26 108 H2 '22 ns ns INVENTOR LEON JONES ATTORNEY United States Patent 2,988,085 BREATHING APPARATUS Leon Jones, Garden Grove, Calif., assignor to Robertshaw-Fulton Controls Company, Richmond, Va., a corporation of Delaware Filed June 17, 1957, Ser. No. 665,955 11 Claims. (Cl. 128- 142) This invention relates to breathing apparatus and more particularly to breathing apparatus for use in high altitude flight.

For high altitude flying where the atmospheric air is rarefied, it is desired to normally maintain a predetermined partial pressure of oxygen within the face mask or helmet to meet physiological requirements of the human body. It is, therefore, a principal object of this invention to incorporate in a breathing regulator a means which automatically varies the pressure within the mask or helmet with variations in altitude.

Another object of the invention is to subject the control diaphragm of a demand breathing regulator to the pressure of the oxygen source and to control the oxygen pressure on the control diaphragm in accordance with altitude.

Another object of the invention is produce an improved breathing regulator.

In the preferred embodiment of the invention, a demand regulator valve is connected between a suitable mask or helmet associated with the user of the apparatus and a source of oxygen under pressure. The regulator valve is operative to supply oxygen to the mask or helmet in response to inhalation by the user, and is provided with a means responsive to atmospheric pressure for maintaining a predetermined pressure of oxygen within the mask or helmet at low atmospheric pressure conditions such as when flying at high altitudes.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a breathing apparatus;

FIG. 2 is a plan view of a regulator valve embodying this invention;

FIG. 3 is a section taken along the line 1IIIH of FIG. 2;

FIG. 4 is a section taken along the line IV-IV of FIG. 2; and

FIG. 5 is a sectional view showing a modification of a portion of the structure illustrated in FIG. 3.

Referring more particularly to FIG. 1, the breathing apparatus includes a pressure reducing valve connected to a suitable source of oxygen under pressure (not shown) by aconduit 12. The reducingvalve 10 may be of any suitable form and serves to deliver oxygen at a workable pressure to abreathing regulator 14 by means of aconduit 16. Theregulator 14 is here shown as mounted on aface mask 18.

Referring more particularly to FIGS. 2, 3, and 4, theregulator valve 14 comprises a casing having a hollow tubular inlet fitting 22 extending upwardly from one side thereof. Thecasing 20 is also provided with an externally threadedlower portion 24, on which hollow tubular outlet fitting 26 is threaded. Theinlet fitting 22 is adapted for connection to the conduit 16 (FIG. 1), and theoutlet fitting 26 is adapted for connection to the mask orhelmet 18.

Theinlet fitting 22 has asuitable filter 28 mounted therein, and is connected by means of apassage 30 to avalve chamber 32 formed within thecasing 20. Thevalve chamber 32 communicates with the outlet fitting 26 by means of a plurality ofports 34 which communicate Patented June 13, 1961 with an opening 36 in the bottom wall of thecasing portion 24.

Anannular valve seat 38 is formed on thecasing 20 within thevalve chamber 32 for cooperation with a flexiblediaphragm valve member 40 for controlling fluid flow from theinlet passage 30 to theports 34. Thevalve member 40 is secured at its periphery to the wall of thecasing 20 by means of anannular retaining member 42.

Apassage 44 extends through thecasing 20 from theinlet passage 30 and opens into thevalve chamber 32 on the lower side of thediaphragm valve member 40 to subject the lower side of thediaphragm valve member 40 to the inlet fluid pressure. Thepassage 44 is provided with achamber 46 in which a fitting 48 having a metering orifice therein is positioned. With this arrangement, the upper side of thevalve member 40 is subjected to the inlet fluid pressure withinpassage 30, and the lower side of thevalve member 40 is subjected to the inlet fluid pressure by means ofpassage 44.

It will be apparent that the effective area of thevalve member 40 exposed to inlet pressure at the lower side thereof is greater than the exposed area of the upper side. This difference in area subjected to inlet fluid pressure accordingly establishes a pressure diiierential on thevalve member 40 which normally tends to hold the same in engagement with theseat 38.

Thevalve member 40 is moved out of engagement with theseat 38 to permit flow of fluid to theports 34 and outlet fitting 26 by venting the fluid pressure acting on the lower side thereof to reverse the pressure differential acting on thevalve member 40. To this end, apassage 50 formd in thecasing 20, extends from thevalve chamber 32 at the under side of thediaphragm valve member 40 and opens into achamber 52 formed in thecasing 20 which communicates with the interior of the mask orhelmet 18 by means of aport 54 opening into the outlet opening 36.

A flexiblediaphragm sensing element 56 is secured at its periphery to the upper end of thecasing 20 to enclose thechamber 52 and to define the upper wall thereof. The position of thediaphragm sensing element 56 is influenced by the fluid pressure within thechamber 52. Accordingly, since thechamber 52 is in communication with the mask orhelmet 18, a reduction in pressure will occur within thechamber 52 when the user of the apparatus inhales causing thediaphragm 56 to flex downward. This movement of thediaphragm 56 in response to inhalation by the user is used to control the venting of the fluid pressure acting on the under side of thevalve member 40 to thus control opening of thevalve member 40.

Ahollow fitting 58 has one end pressed within the end of thepassage 50 and the other end thereof projecting Within thechamber 52 to define a pilot valve seat. A pilot valve, indicated generally by thereference numeral 60, is cooperative with the end of thefitting 58 to control fluid flow from the valve chamber 3.2 through thepassage 50 to thechamber 52. Thepilot valve 60 comprises arigid lever arm 62 having one end engaging thediaphragm 56 and the other end thereof fixed to ablock 64 overlying thefitting 58. One end of astrip 66 of sealing material is secured to the underside of theblock 64 and the other end of thestrip 66 is clamped to an extending andmovable partition 68 of thecasing 20 by means of anut 70 tightened against thepartition 68 by ascrew 72 seated within thecasing 20. Aspring 74 has one end attached to theblock 64 and the other end thereof attached to thenut 70 for biasing theblock 64 downwardly and the end of thelever arm 62 into engagement with thediaphragm 56. During assembly, thescrew 72 is tightened to cause downward deflection of thepartition 68 until thestrip 66 engages the end of thefitting 58.

'with thepassage 44.

Thespring 74 normally biases theblock 64 and strip 66 into engagement with the end of the fitting 58. However, should thediaphragm 56 be flexed downwardly by reduction in pressure within thechamber 52 as a :result of inhalation, displacement of thelever arm 62 will'occur, and thespring 74 will yield adjacent to :thenut 70 againstits bias and move theblock 64 outofengagement with thefitting 58 to permit flow of fluid from thepassage 50. When the user exhales, the pressure in'chamber 52 will increase-to move the diaphragm '56 upwardly and close thepilot valve 60 tothus re-establish the pressure differential on the valve member 40ucausing the same to engage itsseat 38.

It has been found that chattering or vibration o-f the diaphragm valve member40 sometimes occurs due to the rapid pressure change inchamber 32 upon opening and closing of thepilot valve 60. To provide for a more gradual pressure build-up or relief on the underside'of thediaphragm valve member 40 during operation of thepilot valve 60, asurge chamber 76 having ametering orifice 77 is provided in thecasing 20 in communication It will be apparent that upon flow of fluid from thevalve chamber 32 as a result of opening of thepilot valve 60, the flow of fluid from thechamber 76 as determined by themetering orifice 77 will reduce the rate of pressure drop within thechamber 32. Likewise, the rate of pressure build-up within thechamber 32 will be decreased by pressure build-up in thechamber 76 when thepilot valve 60 is closed.

When the regulator thus far described is used'at high altitudes or under low atmospheric pressure-conditions, it is desired to establish a predetermined pressure within .the mask orhelmet 18 independently of-inhalation on the part of the user to provide pressure breathing. Accordingly, the regulator valve is provided with means for .maintaining a predetermined pressure Within'themask orhelmet 18 in accordance with the surrounding atmospheric pressure. To this end, a cup-shaped member 78 having an upper inwardly extendingflange 80 is-clamped to the upper end of thecasing 20 and to the periphery of thediaphragm 56 by means of acover 82 threaded on the upper end of thecasing 20 in engagement with a lower outwardly extending flange '81 of themember 78. Theflange 80 is provided with acentral bore 84 in which a cup-shaped valve member 86 is positioned. Thevalve member 86 is provided with an outwardly extendingflange 88 terminating in an annulardownwardlybent lip 90 above theflange 80.

The valve-member 86,member 78 anddiaphragm 56 define achamber 92 above thediaphragm 56 which communicates with theinlet passage 30 by means of apassage 94 formed in one side of themember 78. The passage thus establishes a fluid pressure withinchamber 92 which acts on the upper side of thediaphgarm 56 through a plurality ofports 95 in'the bottom wall of themember 78.

Thevalve member 86 is cooperative wtih the flange '80 to control the fluid pressure within thechamber 92. When thevalve member 86 is in the position shown in FIG. 3, thelip 90 is out of engagement with theflange 80 and fluid pressure is vented from thechamber 92 to the atmosphere through a plurality ofports 96 in thecover 82. However, if thevalve member 86 is moved toward thediaphragm 56, thelip 90 will be moved closer to theflange 80 to throttle the flow of fluid from thechamber 92 and increase the fluid pressure withinchamber 92.

A11expansible bellows member 97 is provided for actuating thevalve member 86 relative to theflange 80. Thebellows member 97 has one end sealed to the bottom wall of thevalve member 86 and the other end thereof sealed to a flange 98 of a cup-shaped member 100. The member 100 is provided with a central conical recess orindentation 102 which engages aflange 104 formed on one end of ascrew 106 threaded through'thecover 82 in axial alignment with thebellows member 97. Apr 107 is mounted in compression between thevalve member 86 and flange 98 within thebellows member 97 and serves to bias thebellows member 97 andvalve member 86 downward.

Thebellows member 97 is evacuated and will expand in response to .a decreaase in atmospheric pressure to actuate thevalve member 86 downward to move the lip toward theflange 80. Thus, thebellowsmember 97 will expand in response to an increase in altitude to move the "lip 90 toward engagement with theflange 80 to increase the fluid pressure withinchamber 92.

A relief valve, indicatedgenerally byreference numeral 108, is positioned adjacent the tubular outlet fitting .26 to vent fluid pressure from the interior of theoutlet :fitting 26 when the fluid pressure exceeds a predetermined value. To this end, a hollowtubular casing 110 is secured to the side of the tubular outlet fitting .26 and is provided with atplurality ofports 112 extending through the wall thereof. Avalve seating ring 113 is fixed within thetubular casing 110 and is adapted to be engaged by avalve member 114 which is slidably mounted on a guide stem 116 fixed to the end wall of thecasing 110. Aspring 118 encircles the stern and is mounted in com- .pression between the end Wall of thecasing 110 and the valve-member 114 for biasing thevalve member 114 into engagement with theseating ring 113.

Fluid is conducted from the hollow interior of the fitting 26 to the underside of thevalvemember 114 by means of a drilled passageway 120. The passage :120 also communicates with ahollow tube 122 which may be utilized to supply oxygen to a compensated exhaust valve :(not-shown) within themask 18.

It will be apparent that a pressure differential exists across thevalve member 114 when the same engages the seat therefor since one side of the valve member -1 14 is subjected tothe oxygenpressure within the outlet fitting 26 and'the other-side-thereof is subjected to atmospheric pressure. As long as the pressure diflerential force on thevalve member 114 is less than the bias of thespring 118, thevalve member 114 will engage the seat. If, however, due to an increase in the fluid pressure in the outlet fitting 26, the pressure differential force becomes greater than the biasing force ofthespring 118, thevalve member 114 will be moved out of engagement with the seat to vent the excessive fluid pressure in tube '122 to the atmosphere. This will allow the exhalation valve to relieve excess mask pressure.

In operation of the structure illustrated in FIGS. ,2, 3, and 4, when the apparatus is used at low altitudes or at relatively normal atmospheric conditions, the bellows member '97 will be in a contracted condition and the valve member86 will be in its uppermost position-wherein the lip!!!) is out of engagement with theflange 80.

In this'position of thevalve member 86, fluidpressure is vented from the chamber "92 to the atmosphere, and the lflnid pressure within chamber'92 will be minimum and approximately atmospheric.

When theuserof the apparatus inhales, a reduction in fluid pressure withinchamber 52 will occur and .thediaphragm 56 will be deflected downward .under'tthe influenceof thelfluid pressure withinchamber 92. Such movement of thediaphragm 56 will causeopening .of the pilot'valvet60 as previously described to effect opening of the 'valve member 40. When thevalve member 40 ,is thus opened, oxygen will be supplied to themask 18.

.Since thechamber 52 communicates with the interior of themask 18 by means of theport 54, exhalation on .thegpart of the user will increase the fluid pressure within thechamber 52 to return thediaphragm 56 toits original position to close thepilot valve 60 andvalve member 40.

If a decrease in atmospheric pressure should occur, such as during an increase in altitude, the bellows memberi97 will expand to move the valve member'86 downward. This movement ofvalve member 86 will accordingly position thelip 90 closer to theflange 80 to throttle the flow of fluid from thechamber 92 causing an increase in fluid pressure within thechamber 92.

The increased fluid pressure inchamber 92 will move thediaphragm 56 downward and open thepilot valve 60 to efiect opening of thevalve member 40 to cause oxygen flow to themask 18. However, since thechamber 52 is in communication with the mask, the supply of oxygen to the mask when the user is not inhaling will increase the pressure inchamber 52 causing a pressure force to be exerted on thediaphragm 56 in opposition to the fluid pressure acting on the upper side of thediaphragm 56. This build-up in pressure withinchamber 52 will continue until the pressure inchamber 52 equals the pressure inchamber 92 at which point thediaphragm 56 will have returned to its original position closing thepilot valve 60 andvalve member 40.

It will be apparent that in operation in the above manner, thediaphragm 56 serves as a pressure regulator to maintain a fluid pressure within themask 18 as determined by the position of thebellows member 97. Also, since inhalation on the part of the user is elfective to open thepilot valve 60 by establishing a pressure diflerential on thediaphragm 56, it will be apparent that the sensitivity of the device to inhalation is constant irrespective of the atmospheric pressure condition sensed by thebellows member 97. This is due to the fact that the fluid pressure inchambers 52, 92 is always substantially the same. Accordingly, when the user inhales, the same pressure difierence is established across thediaphragm 56 at high atmospheric pressure conditions as is established at low atmospheric pressure conditions. Thus, the device is operative to efiect pressure breathing at low atmospheric pressure conditions without effecting the sensitivity of the device to inhalation and exhalation on the part of the user.

If it is desired to calibrate the response of thebellows member 97 to a particular atmospheric pressure condition, thescrew 106 may be rotated to vary the axial position of thebellows member 97 andvalve member 86 relative to theflange 80. Such positioning of thebellows member 97 will accordingly vary the pressure condition at which thelip 90 engages theflange 80.

If due to any condition, the pressure within themask 18 becomes excessive, it will be apparent thatrelief valve 108 will open to vent the excessive fluid pressure intube 122 to the atmosphere and allow the exhalation valve (not shown) to vent excess mask pressure.

Referring now to FIG. 5, the tubular outlet fitting 26 is shownas provided with another embodiment of therelief valve 108. More particularly, the bellows-type expansible element 124 is mounted Within the fitting 26 and has oneend 126 clamped to the bottom wall of thecasing 20 by means of anannular clamp 128 which is engaged by a shoulder of the fitting 26. The other end 160 of theelement 124 is secured to aperipheral flange 132 of amovable spider 134 by means of alocking ring 136.

.Anannular valve member 138 is formed on the end of theelement 124 and is adapted to engage an annular shoulder 140 formed on the wall of the outlet fitting 26 to control communication between the interior of the fitting 26 and a plurality ofports 142 extending through the wall of the fitting 26.

Aspring 144 is mounted in tension between the center of thespider 134 and the center of a second spider 146 threaded within the end of the fitting 26. With this arrangement, thespring 144 serves to bias theelement 124 to cause expansion of the same and engagement of thevalve member 138 with the shoulder 140 to prevent communication between the interior of the fitting 26 and theports 142. If, however, the fluid pressure within the interior of the fitting 26 should exceed a predetermined value, theelement 124 will contract under the influence of the fluid pressure to move thevalve member 138 out 6 of engagement with the shoulder to vent the excessive fluid pressure to the atmosphere through theports 142.

It will be apparent that the pressure at which thevalve member 138 moves out of engagement with the shoulder 140 is readily adjusted by rotating the spider 146 to vary the axial position thereof and the tension of thespring 144.

While several embodiments of the invention have been herein shown and described, it will be apparent to those skilled in the art that many changes may be made in the construction and arrangement of parts without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In a regulator valve for controlling the flow of fluid from a source of fluid under pressure, the combination comprising a casing having an inlet passage and an outlet passage for fluid intersected by a valve seat, a diiferential pressure actuated valve member movable relative to said seat for controlling the flow through said passages, passageway means establishing communication between said inlet passage and each side of said valve member whereby each side of said valve member is subjected to inlet pressure, pilot valve means in said casing for controlling the operation of said valve member and including a pilot valve element movable from one position to another to relieve the pressure acting on one side of said valve member for causing actuation of said valve member relative to said seat, a flexible diaphragm sensitive to a pressure condition on one side thereof for actuating said element between said positions upon a change in said condition, means communicating with said inlet passage for subjecting the other side of said diaphragm to the fluid pressure in said inlet passage to actuate said element independently of a change in said pressure condition, and means carried by said casing and being operative in response to atmospheric pressure vari-- ations for varying the pressure acting on the other side of said diaphragm.

2. In a breathing apparatus for supplying fluid under pressure to a breathing mask or the like, the combination comprising a casing having an inlet passage and an outlet passage intersected by a valve seat, a differential pressure actuated valve member having oppositely disposed pressure responsive sides and being cooperable with said seat for controlling the flow of fluid through said passages, communicating means between each of said oppositely disposed sides and said inlet passage, said op positely disposed sides having diflerent effective areas whereby said valve member normally engages said valve seat, pilot valve means in said casing to control the operation of said valve member and including a pilot valve element movable from one position to another to relieve the pressure acting on one side of said valve member to cause movement of said valve member, a flexible diaphragm in said casing defining a chamber on each side thereof with said casing, one of said chambers communicating with said inlet passage and the other of said chambers communicating with the mask, said diaphragm being movable in response to a decrease in pressure in said other chamber caused by inhalation and movable in response to a change in fluid pressure in said one chamber, an operative connection between said diaphragm and said pilot valve element for actuating said pilot valve to open said differential pressure operated valve member upon movement of said diaphragm, means for venting fluid pressure from said one chamber to vary the pressure therein, and an expansible element operatively connected to said venting means for actuating the same to increase the pressure in said one chamber in response to a decrease in atmospheric pressure to eifect opening of said differential pressure actuated valve member to establish a predetermined pressure within the mask.

3. In a breathing apparatus as claimed inclaim 2 wherein said venting means comprises an annular membertclamping vsaid diaphragm to said housing having an annular flange on'the end thereof, and a cup-shapedvalve member having a flange overlying said flange .of .said annular member and cooperative therewith, said .expansible element engaging the bottom wall of said cupshaped member.

4. In a breathing apparatus as claimed inclaim 3 wherein said expansible element comprises an expansible bellows member.

5. In a breathing apparatus as claimed inclaim 4 wherein said bellows member has one end engaging said bottom wall and the other end thereof engaging an adjustable support fixed to said housing.

6. In a breathing apparatus for supplying fluid under pressure to a breathing mask or the like, the combination comprising a housing having an inlet passage and an outlet passage intersected by a valve 'seat, a diflerential pressure actuated valve member cooperable with said seat for controlling flow through said passages, said valve member having different pressure responsive areas, means establishing communication between said inlet passage and each of said areas whereby said valve member normally engages said valve seat, a flexible diaphragm in said housing defining a chamber on one side thereof in communication with said inlet passage and a chamber on the other side thereof in communication with one area of said valve member and the mask, said diaphragm being movable in response to a decrease in pressure in said other chamber caused by inhalation and movable in response to a change in fluid pressure in said one chamber, pilot valve means in said other chamber for controlling communication between said other chamber and said one area of said pressure actuated member including an actuating member engaging said diaphragm, said diaphragm being operative upon movement thereof to open said pilot valve means to vent fluid pressure from said one area of saidpressure actuated valve member to open said pressure actuated valve member to supply fluid to the mask, valve means for venting the fluid from said one chamber to the atmosphere to vary the fluid pressure in said one chamber, and means responsive to variations in atmospheric pressure for closing the last said valve means in response to a decrease in atmospheric pressure 'to cause opening of said pilot valve means for establishing 'a predetermined fluid pressure within the mask.

7. In a breathing apparatus as claimed .in claim 6 wherein means are provided for venting the fluid in said outlet passage to the atmosphere in response to a predetermined fluid pressurein said outlet passage.

.8. Ina relief valve, the combination comprising a casinghaving apassage therethrough for fluid, an expansible element positioned in said passage and having a central opening permitting flow through said passage, a valve'element formed on one end of said expansible element, "a vent passage in said casing, a shoulder on said casing adjacent said vent passageand positioned to be engagedby said valve element, and means for biasing said expansible element to cause said shoulder to be engaged bysaid valve element in opposition to the pressure force of 'the fluid within said passage.

9. In a relief valve, the combination comprising a casing having a passage therethrough for fluid, an expansible element positionedinsaid casing and having an opening for permitting fluid flow through said passage, venting means in said casing, an abutment member in said casing adjacent said venting means, a valve element formed on said expansible element and being movable into engagement with said abutment member to prevent fluid flow to said venting rneans,.rneans operatively connected to said 'ex-pansible element and having a predetermined biasing force urging said valve element into engagement with said abutment member in opposition to the pressure force of the fluid within said casing whereby the valve element will be moved out of engagement with said abutment member to permit fluid flow tosaid venting means when the .pressure force of the fluidexceedsrsaid predetermined biasing force, and means in ,said casing connected to said urging means and being operable .to adjust said predetermined biasing force.

10. In a breathing apparatus for supplying fluid .under pressure to a breathing mask or the like, the combination comprising a casing having an inlet passage and an outlet passage intersected by a valve seat, va differential pressure actuated valve member having oppositely disposed sides and cooperating with said seat for controlling the flow of fluid through said passages, means establis'hing communication between each of said sides and said inlet passage, one of said sides beingsubject to .a greater force than the other whereby said valve ,member normally engages said valve seat, pilot valve means in said casing to control the operation of said valve member and including a pilot valve element movable from one position to another to relieve the pressure acting on said one side of said valve member to cause movement of said valve member, a flexible diaphragm'in said casing and cooperating therewith to define a chamber, said chamber communicating with said inlet passage and said diaphragm being movable in response to a.change in fluid pressure in said chamber, means forming an operative connection between said diaphragm and said pilot valve element for actuating said pilot valve to open said differential pressure operated valve memberupon movement of said diaphragm, means for venting fluid pressure from said chamber to vary thepressure therein, and an expansible element operatively connected to said venting means for operating the same to increase'the pressure in said chamber in response to a decrease'in atmospheric pressure to eifect opening of said .difierential pressure actuated valve member to establish a predetermined pressure within the mask.

11. In a regulator valve, the combination comprising a casing having an inlet passage and an outlet passage intersected by a valve seat, a differential pressure .actuated valve member cooperable with said seat for controlling the flow of fluid through said passages, said valve member having oppositely disposed sides, means 'communicating with said inlet passage to subject each of said sides to inlet fluid pressure, one of said sides having a larger effective area than the other whereby said valve member normally engages said seat, pilot valve means in said casing to control the operation of said valve'member and including a pilot valve element movable fromone position to another to relieve the pressure acting on'said one side of said valve member to cause movement of said valve member, a flexible diaphragm in said casing and cooperating with said casing to define a chamber-oneach side of said diaphragm, one of the chambers communicating with said inlet passage and the other of the chambers communicating with said outlet passage, said diaphragm being movablein response to a change in pressurein the one chamber and being movable in response to a change in pressure in the other chamber, an operative connection between said diaphragm and said pilot valve elementfor actuating said pilot valve to open said differential pressure operated valve member upon movement of said diaphragm, means for venting fluid pressure from theone chamber to vary the pressure therein, and anexpansible element operable in response to variances of a predetermined condition and being operatively connected-toisaid venting means for controlling the operationofthe samezto effect opening and closing of said differential .pressureoperated valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,288 Fields et al. Aug. '33, 1954

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