Safety apparatus for oxygen system

June 4, 1963

W. B. CASSIDY

3,092,104

SAFETY APPARATUS FOR OXYGEN SYSTEM

Filed April 21, 1958

Sheets-Sheet 1

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AGENT

June 4, 1963

3,092,104

W. B. CASSIDY

SAFETY APPARATUS FOR OXYGEN SYSTEM

Filed April 21, 1958

Sheets-Sheet 2

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WILLIAM B. CASSIDY INVENTOR.

^by

AGENT

3,092,104

Patented June 4, 1963

United States Patent Office

092 104

SAFETY APPARATUS FOR OXYGEN SYSTEM William B. Cassidy, Arlington,. Tex., assignor, by mesne assignments, to Ling-Temco-Vought, Inc., Dallas, Tex., a corporation of Delaware

Filed Apr. 21, 1958, Ser. No. 729,829

Claims. (Cl. 128—142)

This invention relates to oxygen systems, and more particularly to a safety apparatus for a closed oxygen _:system. . . . , ,.

In a “closed” oxygen system (i.e., a system in which tne user wears a mask, helmet or the like connected to a source of compressed oxygen and into which, by virtue ot the construction of the system, no air may be drawn by the inhalation of the user), the pilot or other user of the system is entirely dependent for breath on the oxygen supplied to him by the system. In these systems the oxygen is released on demand into the mask or helmet through and by action of a demand-type regulator and often at a small but positive pressure which is greatly reduced from the pressure at which the oxygen is supplied, to the regulator through its inlet line. As long as the inlet pressure is normal, i.e., above a critical value, the user will upon inhalation receive enough oxygen to sustain consciousness. At a subnormal (less than critical) inlet pressure, he will not receive enough oxygen, and because of the mask or helmet will not be able to breathe ambient air, by which term is meant not necessarily air outside or at pressures equal to those outside a cockpit or other enclosure, but rather air in directly ambient relation to the regulator and the mask or helmet of the user, whether or not he be enclosed in a cockpit, etc. The user, hence, is entirely dependent on an adequate inlet pressure at the regulator. If this pressure fails, and if he cannot take any measure successful in restoring an adequate inlet pressure, he may remove his mask, if he is wearing one and capable of doing so, and breathe ambient air. This he cannot do if he is unconscious; and even if he is conscious, the timely removal of the mask or particularly a helmet, if ' such be worn, is frequently not possible.

A condition of less than critical pressure at the regulator inlet can be caused by one or more of a number of factors including, for example, a rupture, clogging, crack break, or malfunction in the oxygen system upstream of the regulator. The supplementary source of oxygen which the user ordinarily takes with him if, in an emergency, he must leave the aircraft during flight is ordinarily small and may soon be depleted, thus adding or constituting another cause of low inlet pressure. In the case of a break (for example, if the supply line to the regulator becomes disconnected), no oxygen at all is supplied, and the amount of air which can be inspired through the regulator and/or supply line is likely to be too small to be of significant benefit to the user.

To save the user from smothering, masks, helmets, and conduits have been provided with check valves and other arrangements which allow the breathing of ambient air when the supply becomes disconnected or if for any other reason the oxygen supplied to the user becomes insufficient These arrangements have all had a serious failing in that the user has no way of knowing if he is breathing air or oxygen. Thus, when above critical altitude (by which is meant: when at an ambient air pressure too low to supply sufficient oxygen for avoiding anoxia), the user can be stricken by anoxia without ever haying known that the oxygen flow to him has been discontinued.^ To pro vide warning of loss of oxygen, visual and auditory indicators have been supplied to signal the impending or actual oxygen loss, but these have sometimes been disregarded or unnoticed and of course are of no avail when the user has in some way been rendered unconscious.

It is, accordingly, a major object of this invention to provide a safety apparatus for automatically supplying a user of an oxygen system with oxygen from a supplementary source upon failure of the system to deliver adequate oxygen from a normal or primary source.

Another object is to provide a safety apparatus which, if the normal oxygen supply fails while the air ambient to the user of the oxygen system is at or above a critical pressure altitude, connects the user with a supplementary oxygen supply by initiating an ejection sequence and, where desired in such an apparatus, to provide means for warning the oxygen user that the ejection is imminent and means allowing him to stop the ejection sequence if he so desires. .

Yet another object is to provide a device which, upon failure of the oxygen system to furnish adequate oxygen to the user, supplies him with a warning which, if he is conscious, cannot be ignored, and thereafter allows him to breathe ambient air if he has not taken action effective । in restoring the oxygen system to normal working order.

Further objects and advantages will be apparent from the specification and claims and from the accompanying drawing which illustrates an embodiment of the invention.

In the drawing:

&gt; FIGURE 1 is a schematic representation of an oxygen system to which an illustrative embodiment of the safety apparatus has been applied, the oxygen regulator being shown in central, vertical cross-section;

FIGURE 2 is a fragmentary sectional view of an oxygen regulator similar to that represented in FIGURE 1 and showing a modification in which the bellows chamber is omitted from the apparatus;

FIGURE 3 is a fragmentary, sectional view of an oxygen regulator similar to that in FIGURE 1 and showing a modification of the device wherein the bellows is housed in the demand chamber of the regulator; and

FIGURE 4 is a view similar to FIGURE 3 and showing a different placement of the bellows.

With reference now to FIGURE 1, the breathing oxygen system comprises a normal source of oxygen such as a container (not shown) storing liquid or gaseous oxygen. Compressed oxygen is delivered through a line 10, disconnect 11, check valve 12, and line 13 from the container to a demand-type oxygen regulator 14. One-half of the disconnect 11 may be mounted on, for example, a pilot’s ejection seat 17, and the other half attached, as at 15, by a lanyard 16 or equivalent, to a fixed item of an aircraft in which the seat is mounted.

The demand-type regulator 14 may be of any type having an inlet passage 18 connected to the oxygen supply line 13, a vessel 19 having a wall enclosing a volume identified ^as a demand chamber 20 with a port 21 which will be understood to open directly or through a suitable conduit into the user’s mask or helmet, and a demand valve 22 which governs the flow of oxygen from the inlet passage 18 into the demand chamber 20 in accordance with movements of a spring-loaded diaphragm 23 interposed between the demand chamber 20 and a lower chamber 24 housing an aneroid or closed bellows 25. Although use¹ ful with any regulator such as described above and not limited in its usefulness to application to any particular regulator, the invention is shown in the drawing, in order to provide one specific example, in association with a miniature oxygen breathing regulator 14 of the 100% demand type with automatic safety pressure and pressure breathing such as shown and fully described in the U.S. Department of the Navy publication AER-AE-512/217, dated September 25, 1957, to which publication reference is made for all details not herein provided concerning the construction and operation of the regulator.

A supplementary supply of oxygen is stored, for example in a bottle 26 mounted in a convenient location

3,082,104 3 such as on the person of the user or on the seat 17. The flow control means comprises a valve 27, which where required should be of the pressure-reducing variety and which is mounted on and which communicates with the interior of the supplementary bottle 26. The valve 27 contains a mechanism, such being well known in the art, which is connected to and positionable by a lanyard or equivalent 28 attached to an airframe fixed item as at 29. When the lanyard is pulled manually by the user, automatically by ejection of the seat 17 from the aircraft, or in any other manner, the flow-control means valve 27 is positioned for connecting the supplementary source 26 through a line 30 into the line 13 between the regulator 14 and check valve 12. The electrically actuatable motor means may be any means connected to the lanyard 28 or valve 27, actuatable by an electrical signal, and energized electrically, by an explosive force, or in any desired way whereby it is effective in displacing the lanyard 28 or valve 27 relative to each other and causing the valve 27 to connect the supplementary bottle 26 to the regulator 14. Such motor means is readily provided by the seat catapult 32 firmly attached to the seat 17 as by fittings 31 and operative, in response to an electrical signal delivered thereto through a lead 33, for ejecting the seat 17 from the aircraft, thereby pulling the valve 27 away from the lanyard 28 and connecting the sup- ^!plementary bottle 26 to the regulator 14. Since ejection seats, their mountings, the catapults for their ejection, etc have been well described in readily available publications they will not be further touched upon herein except as may be necessary in the complete disclosure of the present invention.

The wall of the vessel 19 enclosing the demand chamber 20 lies between the latter and ambient air (air surrounding the vessel 19). The safety device comprises a portion 34 of the wall of the vessel 19, which portion 34 has an orifice 36 leading from the ambient air into the demand chamber 20. The wall portion 34 cooperates with an adjoining wall portion 42 of the chamber 19 to define a recess closed off from the remainder of the demand chamber 20 by a wall or partition located within the demand chamber 20 and identified as having an opening 38 providing communication between the remainder of the chamber 20 and the chamber portion 37 divided off therefrom by the partition.

Otherwise stated, and from another point of view, the ⁴³above construction may be described as one in which the partition with the opening 38 is a part of the wall of the vessel 19 cooperating to enclose, rather than to subdivide, the demand. chamber 20. Where this point of view is adopted, as it has been for the remainder of the descrip- ⁵⁰tion of FIGURE 1, the wall portion 34 is regarded as additional to the wall of the vessel 19 and the volume 37 which it cooperates in enclosing is then a bellows chamber separate and distinct from the demand chamber 20. In both modes of viewing and describing the construction, ³³the demand chamber port 21 leading to the user’s mask or helmet has communication through the partition opening 38 and wall orifice 36 with the ambient air.

The closure means 41 is any body suitably proportioned and mounted for movement between a first position 39A 60 wherein it obstructs and preferably entirely closes the wall orifice 36 and a second position in register, for example, with 39B in which it is well spaced from and permits ambient airflow through the orifice 36. The closure means might be, for example, a hinged flap or 65 other movable element, and conveniently may be a surface of a part borne by or integral with the pressure-sensitive motor means 40 for positioning the closure means, which means will now be described.

The pressure-sensitive means for moving the closure 70 means 41 may be any device linked to the latter and sensitive and responsive to pressures in the inlet passage 18 for moving the closure means 41 to its first position 39A when pressures in the inlet passage 18 equal or exceed the predetermined, critical inlet pressure at which the 75 user is unable to obtain adequate oxygen through the regulator 14 and for moving the closure means 41 toward its second position 39B when inlet pressures fall below the critical pressure (i.e., to subnormal values). The energy utilized by the pressure-sensitive means in moving the closure means may be pneumatic, electrical, springstored, etc. In the specific example shown in FIGURE 1, the pressure-sensitive means is a fluid motor such as a bellows 40 housed in the chamber 37. The bellows 40 has a free end which faces the orifice 36, and the outer surface of its free end may form the closure means 41. Alternatively, as shown in the drawing, the closure means 41 may be a plate or similar body shaped for good closing of the orifice 36 and linked to the bellows 40 by rigidly mounting it on the free end of the latter. The opposite end of the bellows is mounted in fixed relation to the wall portion 34 and orifice 36, as for example, on the wall 42 separating the bellows chamber 37 from the inlet passage 18.

The means providing restricted communication between the interior of the bellows 40 and the normal oxygen source 10 may be a small, calibrated metering opening 43 made through the fixed end of the bellows 40 and wall ^{tbe in}'^et P^assa8^e I*· This opening 43, whose size will be discussed below, allows gaseous flow to pass between the interior of the bellows 40 and the inlet passage 1». Pressures admitted into the bellows 40 from the inlet passage 18 tend to expand the bellows and hence to force the closure means 41 toward the orifice 36 The bellows 40 of the example is biased by its own construction i.e., by its resiliently expandable wall, and may additionally or alternatively be biased by springs, etc., toward the second position 39B of the closure means 41. This bias must be weak enough to allow the bellows 40 to expand sufficiently to hold the closure means 41 in its first position 39A when pressures in the inlet passage 18 are normal or above and strong enough to move the closure means 41 away from the orifice 36 toward its second posi^passage Pressures are less than norma (below the previously defined, predetermined critical value). The resiliently expansible wall of the bellows 0 of the example thus is a resilient means biasing the closure means 41 to its second (open) position. The size nLn °u^Pe?^{lng 43 if of} importance since upon it depends whether or not one of the more important objectives of the invention, yielding one of its most X wkh Xn τ '^{S attained&gt; l e}· Providing the oxygen user With a positive warning, which he cannot ignore, that e will soon be supplied by operation of the invention Should ^atiler,^{tflan ox}^^en· The size of the opening 43 betwelJto t^aS ‘° ^Provide restricted communication between the inlet passage 18 and the interior of the belted “restrict'd ^P’^aCe· ⁱⁿ.^{which Jt is used} herein, the η X ^{d communic}ation” (as applied to the relationship between the bellows 40 and inlet passage 18) refers to a communication which is restricted to a degree that upon a sudden and extensive drop in pressure in the caSed^Pbv^a^r¹⁸t ^(SUu^h ?^S-^a^abrUpt Pressure change and n J th^{C aC}m?^{r break in} °^ne °^{f tbe oxygen} lines 10 and 13 or their fittings, etc.), a few seconds will elapse between the time of the pressure drop in the inlet pasthroug^the^{6 tlme}-°^f 41 ^{bIeeding of the} bellows pressure through the opening 43 to a value at which the bias of the bellows 40 can effect movement of the closure means 41 to its second position 39B. The calibrated opening to nrnv^SJ^{S a}.^meu^r‘^{ng opening and must} be small enough o provide the above-specified degree of restriction. The above-mentioned term “restricted communication” is ,-/^^yS?^rther herein to a communication whererestriction Is less than that at which the Xie ^t™^ebetwee” ‘he pressure drop in the inlet passage 18 and the opening of the wall orifice 36 would be so great as to force unconscious or excessive discomfort on the oxygen user Hence, when it is stated herein that the calibrated orifice 43 “restricts flow,” it is meant that it

3,092,104 .

is of such size as to provide the restricted communication between the bellows 40 and inlet passage 18 which has been precisely defined above. The bias of the bellows 40 and the size of the opening 43 must be carefully balanced against each other to provide the desired time interval between the loss of inlet pressure and the opening of the wall aperture 36, and it is recommended, to provide a general example, that this interval be no shorter than 5 nor longer than 30 to 40 seconds, although of course a longer period would not often seriously affect the oxygen ] user.

Where desired, and for reasons which will become apparent, a check valve comprising a plate or other suitable element 44 is mounted where it will, when closed, cut off any gaseous flow into or out of the demand chamber 20 through the wall orifice 36. A convenient location for the check valve 44 is adjacent the opening 38 between the bellows and demand chambers 37, 20.. The check valve 44 should be lightly biased as by a spring 45 to a position in which it closes the opening 38, and it should be located on the side of the opening 3« facing the demand chamber 20 so that positive pressures in the latter will augment the bias exerted by the spring 45 and so that any negative pressures occasioned by inhalations of the oxygen user will tend to open the check valve 44. From the above, it will be understood that the check valve 44 is movably interposed between the interior of the demand chamber 20 and ambient air adjoining the outer side 35 of the wall portion 34 provided with the orifice 36.

The first electrical switch 46 is linked with the pressuresensitive means 40 by any suitable mechanical linkage such as symbolized in the drawing by 47. The linkage 47 may be, for example, a pin, set of levers, etc. mechanically connecting the movable contact of the switch 46 with the closure means 41. Operated by motion of the pressure-sensitive means 40, the switch 46 is held open whenever the closure means 41 is in its first position 39A and is closed when the closure means is moved to or toward its second position 39B.

The second and third switches 48, 49 are connected in series with each other and with the first switch 46 and are connectable through the latter to an electrical power source (not shown) by an electrical lead 50.

The pressure-sensitive means for operating the second switch 48 may be a closed bellows or aneroid 51 which holds the switch 48 open when ambient air pressure exceeds a predetermined, critical value (a pressure below which the oxygen concentration in the ambient air is not sufficient to sustain efficient conscious action on the part of the oxygen user), and which expands and thereby closes the switch 48 when the air pressure is below this predetermined value. Linkage of the second pressure-sensitive means 51 with the second switch 48 may be effected, for example, by a pin 52 mounted on a movable end of the bellows 51 and bearing against the member carrying the movable contact of the second switch 48.

The means for closing the third switch 49 at a time following, by a predetermined interval, concurrent closure of the first and second switches 46, 48 is linked to the third switch by any chosen and appropriate mechanical linkage 53. As used herein, “concurrent closure” refers not to a simultaneous closing, but rather to a simultaneous state of being closed. The means for closing the third switch is responsive to a signal received from the electrical power source 50 when the first and second switches 46, 48 experience concurrent closure, and upon reception of such a signal begins a time-measuring operation at the end of which it moves the third switch 49 to its closed position. This device may be chosen from any of a number of devices which will provide the above-described operation, and may comprise, for example, an electrically triggered clockwork mechanism, an electrical timer with means for moving the switch 49, etc. In the drawing, 54 represents an electrical motor connected to the second switch 48 and linked with the third switch through a gear ⁶ train or other timing mechanism and a mechanical linkage

53.

The means for electrical connection of the third switch 49 with the electrically actuatable motor means comprises the electrical lead 33 extending between the seat catapult 32 and the third switch. Where, as ordinarily will be the case, the aircraft is provided with other manually and/or automatically controlled ejection provisions governing the delivery of an electrical signal to the seat catapult 32 for actuation of the latter, they may readily be connected to or into the lead 33, and their components (governed by the electrical signal from the third switch 49 for sending a signal to the catapult 32 or through which the signal from the third switch passes on its way to the catapult) are comprised by the means for electrical connection of the third switch 49 with the electrically actuatable motor means 32 and are symbolized in the drawing the item 56. Since manually or automatically controlled provisions are well known in ejection systems and vary from aircraft to aircraft they accordingly will not be further described herein.

The warning device, where provided, should preferably be electrically actuatable and connected to the second switch 48 in parallel with the third switch 49. The warning device may comprise, for example, a light 57 and/or a horn 58 which are energized by the electrical power source through the first and second switches 46, 48 upon their concurrent closure.

An override switch 59 may be provided in series with and between the second switch 48 and electrical power source 50; or, if desired, it of course may be provided in any other location in the circuit in which it will, when opened by the user of the oxygen system, prevent delivery of an electrical signal from the electrical power source 50 to the electrically actuatable motor means 32 for positioning the flow control means valve 27 if this is desired following concurrent closure of the first and second switches.

It will be evident that the above-described items constitute a safety apparatus utilized in combination with an ¹ oxygen system including a regulator, normal and supplementary sources of oxygen, flow control means positionable for connecting the supplementary source to the regulator, and electrically actuatable means for positioning the flow control means. Upon omission of the electrical ; components of the apparatus, the remaining features of the invention provide a safety construction in the oxygen regulator, or a safety device combined with the oxygen regulator, whose operation, together with that of the entire safety apparatus, is described in later paragraphs.

FIGURE 2 shows a modification of the safety apparatus in which the wall 34 (FIGURE 1) with the orifice 36 and check valve 44 are omitted. The connection of the bellows 40 to the inlet passage 18 through the calibrated opening 43 and the linkage 47 connecting the bellows’ free end to the first switch 46 remain the same as shown in FIGURE 1. It will be understood that the electrical power source remains connected to the first switch through the lead 50 and that the remaining electrical items described in connection with FIGURE 1 are interconnected as before with the first switch 46 through the lead 60. In this modification, no openings leading from ambient air into the demand chamber 20 are provided. The free end of the bellows 40 is movable between extended and retracted positions 39A, 39B for opening and closing the switch 46.

FIGURE 3 shows a modification of the safety construction or device wherein the portion of the demand chamber 20 adjacent the wall portion 34A provided with the orifice 36A associated with the closure means 41A is not partitioned from the remainder of the demand chamber 20. The bellows 40A of FIGURE 3 is rigidly mounted at one of its ends in the demand chamber 20 by, for example, a bracket 61, and its free end bears the closure means 41A, which faces the wall orifice 36A and is movable by the bellows 40 between a first position 62A wherein it

3,092,104 closes and a second position (for example, a position in register with the point 62B) in which it is spaced from the orifice 36A. A passageway 63 containing a calibrated opening 43A connects the fixed end of the bellows 40A with the interior of the oxygen inlet passage 18. It will be noted that, whereas in FIGURE 1 the wall portion 34 is validly describable as a part or portion of the wall of the vessel 19 enclosing the demand chamber 20 but from another point of view was with equal validity describable as additional to the wall of the vessel 19, in the case of FIGURE 3 (also, FIGURE 4) the description must be from the point of view regarding the wall portion 34A as a portion of the wall of the vessel 19, for no partition separates the chamber portion immediately adjacent the wall portion 34A from the remainder of the demand chamber 20 as would be required to support a concept of a separate bellows chamber apart from the demand chamber 20.

FIGURE 4 shows a form of the safety device which in all important respects is the same as that shown in FIGURE 3 except that a different placement of the motor means is employed, this means (in the specific example) again being in form of the bellows 40A. The wall portion 34A of the vessel 19 retains the orifice 36A opening therethrough into the demand chamber 20, and the bellows 40A is rigidly mounted, at one of its ends, outside the demand chamber 20 by means of, for example, a fixed bracket 66. The surface 41A of the free end of the bellows remains the closure means and is located in register with the orifice 36A in order that, when the free end of the bellows is forced into its position 65A in which it lies against the wall portion 34A having the orifice 36A, the orifice 36A is thereby closed. The interior of the bellows 40A is connected as before to the oxygen inlet passage 18 through the calibrated opening 43A and a passageway 63A. The surface 41A of the free end of the bellows 40A is movable by action of the bellows to a position, in register with the point 6SB, to which the bellows 40A is baised and in which the orifice 36B is unobstructed by the bellows.

With reference again to FIGURE 1, any of the factors previously mentioned, for example, a break in the lines 10 or 13 between the normal oxygen source and the regulator 14, may occasion a relatively fast drop in oxygen pressure at the inlet passage 18 to a value below that previously defined as normal. If and when this occurs, oxygen in the bellows 40 immediately begins bleeding into the inlet passage 18 through the restricted opening 43, and in a few seconds the oxygen pressure in the bellows falls to a value at which the bellows bias is able to move the closure member 41 away from its first position 39A and toward its second position 39B. During the interval following the pressure drop in the inlet passage 18 and ending with the opening of the orifice 36 by the closure member 41, the user of the oxygen system is unable to draw an adequate flow of oxygen or air through the regulator’s demand valve, and since it is obstructed by the closure member 41, he can draw no breath through the orifice 36. Though he might conceivably disregard a light, an audible signal, etc. employed to warn him that the inlet pressure was subnormal and that he was being switched from oxygen to ambient air, the deprivation of breath which the oxygen user experiences during this interval occasions him some real discomfort of so fundamental a nature that, if conscious, he cannot disregard it. As previously explained, the restricted opening 43 and the built-in bias of the bellows 40 are large enough to prevent this interval from being so long as to injure the user of the oxygen system or to render him unconscious, but is long enough to guarantee that there will occur an unmistakable

Tiindrance to breathing which cannot be disregarded. At the end of the above-described interval, the closure means '41 is moved by the bellows 40 toward its second position

39B, and the user of the oxygen system is easily able to draw air into the demand chamber 20 through the wall orifice 36 and the portion opening 38 past the lightly biased check valve 44. Previously informed of the workings of the apparatus, the oxygen user is fully aware of 5 the transition he has experienced from oxygen to ambient 'air.

While the closure means 41 is in its first position 39A, the first switch 46 is held open by its linkage 47 with the pressure-sensitive means 40. Upon movement of the 10 closure means 41 away from the orifice 36, however, the linkage 47 pulls the first switch 46 closed. Always kept, except as explained below, in its “normal” (closed) position, the override switch 59 connects the first switch 46 to the second switch 48. If the pressure of the ambient 15 air is at or above the predetermined safe value, i.e., if the critical altitude is not exceeded, the second pressure-sensitive means bellows 51 is contracted by the ambient air pressure sufficiently to allow the second switch 48 to remain open, and hence the balance of the circuit 2o beyond the second switch 48 is not energized. If the ambient air pressure is below the predetermined value, however, the bellows 51 expands and closes the second switch 48, thereby energizing the warning device light 57 and/or horn 58 and the motor 54 of the means for 25 closing the third switch 49. At the end of a measured, predetermined interval of time commencing with concurrent closure of the first and second switches 46, 48, the motor 54, through the linkage 53, effects closing of the third switch, thus connecting the electrical power source 30 50 to the electrically actuatable motor means 32. If the latter is, as is herein contemplated, an electrical motor which operates to move only the flow control means valve 27, it may, for example, pull the lanyard 28 and thus position the flow control means for connecting the 35 supplementary bottle 26 with the regulator 14. Where the electrically actuatable motor means is, as shown in FIGURE 1, the seat catapult 32, the latter fires and ejects the seat 17 from the aircraft, thus pulling the valve 27 away from the lanyard 28 and positioning the valve 27 40 for connecting the supplementary bottle 26 to the regulator 14 through the lines 30, 13. Reverse flow toward the disconnect 11, whose lower portion is retained in the aircraft by its lanyard 16, is prevented by the check valve 12 between the line 30 and the upper portion of the disconnect 11.

Upon admission of oxygen at or above normal pressures into the inlet passage 18, oxygen flows into the bellows 40 through the opening 43 and expands the bellows until the latter moves the closure means 41 into its first 50 position 39A wherein it obstructs the orifice 36, thus blocking the entry of ambient air into the demand chamber 20 through the orifice. Before this time, however, the oxygen user is enabled, by virtue of the normal pressure at the oxygen inlet 18, to receive adaquate oxygen 55 through the demand valve 22.

Where the check valve 44 is installed, and where the regulator 14 is a positive-pressure type (shown in the example), the communication of the demand chamber with ambient air through the orifice 36 and opening θθ 38 is terminated when (or because of the spring 45, shortly before) the oxygen pressure in the demand chamber 20 becomes positive relative to ambient air pressure. As a consequence, the oxygen drawn by the user through the demand valve 22 is not diluted with air, and wast55 age of oxygen through the orifice 36 is obviated.

If, during the sequence of events described above, the oxygen user has been notified by stoppage of breath (and, where they are installed, by the warning device light 57 and horn 58) that the supplementary supply 26 of oxy70 gen will shortly be connected to the regulator 14 following closure of the third switch 49, he may prevent closure of the third switch 49 by moving the override switch 59 to its “override” (open) position, thereby disconnecting the third switch from the electrical power source 50.

After opening the override switch 59, he may connect

3,092,104 the supplementary bottle 26 to the oxygen regulator 14 by manually pulling the lanyard 28, or if so preferred, he may descend to an altitude at which the oxygen concentration of the ambient air is adequate for his needs, during the descent breathing ambient air through the orifice 36 after the latter is opened by action of the bellows 40. Alternatively, he may remain at his original altitude and adjust the oxygen system, re-join any of its elements such as the disconnect 11 which are accessible to him and which have become disconnected, or take any other corrective action effective in restoring normal pressure of oxygen at the inlet passage 18. If the pilot should be unconscious when concurrent closure of the first and second switches 46, 48 occurs, he of course will not be able to accomplish any of these actions, and the safety apparatus automatically connects the regulator 14 with the supplementary bottle 26 as explained above; and if the electrically actuatable motor means chosen for use in the apparatus be the seat catapult 32 as shown in the drawing, he also is freed, by ejection, from the aircraft.

Where, as shown in FIGURE 2, the wall orifice 36 and opening 38 into the demand chamber 20 are omitted, the operation of the bellows 40, first switch 46, and the other electrical components is the same as described in connection with FIGURE 1. Though making no provisions for switching the oxygen user to ambient air after the above-recounted warning period typified by partial to complete stoppage of breath, the modification shown in FIGURE 2 operates to connect the regulator 14 with the supplementary bottle 26 as already made clear above. It will be apparent that the warning period may be shortened (or, if desired, eliminated) by choosing a calibrated opening 43 of such size that movements of the bellows 40 lag little if at all behind pressure changes in the inlet passage 18, and that such modification lies within the scope of the invention, as does a form of the apparatus in which one or all of the items identified as the override switch 59, warning device light 57 and horn 58, third switch 49, and the motor 54 and linkage 53 for closing the third switch 49 are omitted, thus eliminating their several functions from the operation of the apparatus.

Operation of the safety device or construction employing the orifice 36, closure means 41, and pressure-sensitive means 4ft such as shown in FIGURE 1 but omitting the electrical components is the same as already described in the case where operation of the electrical components is halted by moving the override switch 59 to its open position. A similar case is encountered where the electrical components are employed and ejection has occured. Upon depletion of the supplementary bottle 26, the oxygen user is switched (as described) to air. This is of particular importance in case the oxygen user is unconscious, injured, or for any reason unable to remove the mask or helmet, by which, if it were not for the invention, he would be choked to death. The operation of the safety device as shown in FIGURES 3 and 4 will be understood from the description of the elements and construction thereof and from the detailed description of the operation of the device as shown in FIGURE 1.

While only one embodiment of the invention together with several modifications thereof have been described herein and shown in the accompanying drawing, it will be evident that various further modifications are possible in the arrangement and construction of the components of the safety apparatus for an oxygen system without departing from the scope of the invention.