US2871854A - Breathing apparatus - Google Patents

Description

` C. J. LAMBERTSEN Feb. 3, 1959 BREATHING APPARATUS 2 Sheets-Sheet 1 Filed Dec. 14, 1956 l v I N VEN TOR. ciamsfrlim J. LMBRRTS EN n l/l Illa 541114.

ATTQBNBYQ Feb. 3, 1959 c. J. LAMBERTsl-:N

Filed Dec. 14, 1956 INVENTOR CHRISTIAN J.

LAMBERTSEN mf 4MM W BY 'I f i7- ATTORNEW Patented Feb. 3, 1959 BREATHING APPARATUS Christian J. Lambertsen, Philadelphia, Pa. Application December 14, 1956, Serial No. 631,011

9 Claims. (Cl. 12S-142) This invention relates to breathing apparatus of the open-circuit or demand type, suitable for use under water, in rescue work, in aviation, and the like.

In an open-circuit or demand type of breathing apparatus, as heretofore used, air, oxygen or a predetermined mixture of oxygen and nitrogen is stored under high pressure (about 2000 p. s. i.) in cylinders. This high pressure gas is reduced to an intermediate pressure (about 20 to 100 p. s. i.) lby a one or t-wo stage reduction valve or regulator. This pressure supplies a demand valve from which the user obtains the gas he inspires. The demand valve is activated to deliver gas on inspiration -by the slighty negative pressure acting on a large diaphragm. The consequent movement of the diaphragm trips the stem of the valve holding back the gas supplied at low pressure to the demand valve, admitting gas for inspiration by the user. On exhalation the diaphragm is pushed away from the valve stern, allowing the delivery pressure to close the valve and stop the How of gas. yExhaled gas is discharged in its entirety into the surrounding medium, whether air or water. There is, therefore, no rebreathng of exhaled gas, as in a rebreathing type of apparatus.

Because exhaled gas isnot rebreathed no carbon dioxide absorption canister is required. This non-rebreathing feature makes the rate of gas utilization very high. It actually equals the entire volume of gas breathed out or in per minute by the user. For this reason a high pressure cylinder, weighing about 35 pounds and containing about 1500 liters of gas compressed to 2000 p. s. i. will last -a very short time. During moderate exercise such as underwater swimming the user breathes about 30 liters of gas per minute. The 1500 liters contained in the cylinder will therefore last only 50 minutes at one atmosphere. If the swimmer descends to 132 feet of sea water atmospheres) each liter of gas he inhales will actually contain 5 liters of gas removed from the cylinder. For this reason the available gas supply will last only one-fifth as long (l0 min.) at 132 feet as it does at sea level.

In spite of this very poor economy of gas utilization, the open-circuit or demand type of breathing apparatus is desirable for many purposes because of the ease with which it can lbe used.

The primary object of the present invention is to provide an open-circuit breathing apparatus which will retain the simplicity of operation of present open-circuit breathing apparatus, but which will substantially decrease the waste of gas which is characteristic of such type of breathing apparatus. p

The capacity of the air pasages connecting the lung alveoli with the air outside the body represents a dead space in the respiratory system, as far as respiratory exchange is concerned. This dead space varies only slightly with diiierentindividuals at rest and increases strikingly with increase in exertion due to increased depth of breathing. For example, anadult having a dead space 0f 160 cc. in his respiratory system when at rest, may

have his dead space increased to over 600 cc. merely by the exertion caused by walking at the rate of five miles per hour. See Journal of Physiology, vol. 45, pages 23S-238 (1912).

Since there is no, or practically no respiratory exchange of gas retained in the dead space of the respiratory system, it follows that the gas coming from the early phase of exhalation and which comes from this respiratory dead space ywill have a very low carbon dioxide content and would be suitable for rebreathing.

In accordance with the'present invention, I provide a portable, self-contained, open-circuit breathing apparatus designed for underwater use, rescue work, aviation, and the like, without use of air lines, in which the irst portion of the exhaled gases, which come from the physiological dead space, is trapped and rebreathed on the next inhalation. I thereby eliminate the waste gas which was retained in the respiratory dead space and subsequently exhaled without being used in the respiratory exchange. V

More speciiically, the breathing apparatus comprises essentially a breathing device such as a mouthpiece or face mask, breathing tubes connected thereto, and a demand-valve incorporating a small bellows or rebreathing bag, all of which may be mounted on the diver by an -appropriate harness.

The primary feature of the present breathing apparatus is the inclusion of a small rebreathiug bag or bellows as apart thereof and its association with the demand valve which supplies gas from the `cylinders on inspiration.

The rebreathing bag is connected by a valveless corrugated flexible tube to the mouthpiece and provides space for trapping for re-inhalation the first portion of each succeeding exhalation, which, being the early phase of exhalation. comes chiefly from the physiological dead space and contains a very low percentage of carbon dioxide. The remaining portion of each exhalation, coming from deep in the lungs and, therefore, containing the highest percentage of carbon dioxide, is exhaled through a separate flexible exhaling tube equipped with a oneway valve into the surrounding media. Thus, a considerable decrease in the requirement for new gas from the cylinders is effected without causing an important increase in the users actual ventilation, that is. the amount of new gas used plus the amount of gas rebreathed from the rebreathing bag or bellows.

The invention will be further described in connection y with the accompanying drawings which illustrate preferred forms of the improved breathing apparatus.

In the drawings:

Fig. 1 is an elevational view of one form of the breathing apparatus, Fig. 2 is a sectional view through the rebreathing bag and the exhaling valve of Fig. 1,

Fig. 3 is a sectional view through demand valve taken on line 3 3 of Fig. 2, showing the demand valve,

Fig. 4 is a detail View of the means for actuating the demand valve of Fig. 1,

Fig. 5 is a sectional view through the rebreathing bag of a second form of breathing apparatus, and

Fig. 6 is a sectional view on line 6-6 of Fig. 5.

Referring rst to the form of the invention lshown in Figs. l to 4, air, oxygen or a predetermined mixture of air and nitrogen is stored in tanks 1 and 1a under high pressure, for example, under 2000 p. s. i. These tanks are secured by a clamping member 2 to a plate 3 which may be secured in any manner to a suitable harness to be worn by the user.

Gas under high pressure is passed selectively from the tanks 1 or 1a through the cylinder valves 4 or 4av to a conventional reducing valve S, where the pressure is 1 reduced from that prevailing in the tanks' to a substantial? .0 1y lower pressure, say, to 20 to 100 p. s. i. From the reducing valve 5 the gas passes, at the reduced pressure through the conduit 6 to a demand valve 7, Fig. 3, and thence through a corrugated, flexible, inhalation tube 8 toa breathing mask 9 (or a mouthpiece). A corrugated, flexible, exhalation tube 10 passes from the breathing mask and conducts the gas to an exhalingy valve 11 through which it passes to the surrounding medium.

Both the inhalation tube 3 and the exhalation tube 1d are valveless, as is also the breathing mask 9. During respiration gasto be inhaled passes through the inhalation tube 8 to the breathing mask. The first portion of the exhaledgas passes back through the inhalation tube into the rebreathing bag, after which the last portion of exhaled gas passes through the exhalation tube 1% and out through the exhaling valve 11 to the surrounding medium.

Referring. to Fig. 3, it will be seen that the demand valve.7 to which gas is supplied bythe conduit 6, is secured to an upstanding flange 12Y of a base 13 for an elastic rebreathing bag 14. The rebreathing bag has its lower edge secured in gas-tight relationship with the upper edge of the flange 12.

The demand valve comprises a valve body 16 having a threaded stud 17 passing through the flange 12. T he valve body is rigidly held to the flange 12 by a nut 13. Suitable packing washers may be used to insure a gas-tight connection between the flange 12 and the valve body 16 and nut 1S. The gas supply pipe 6 may be secured in any manner to a reduced end' portion of the stud 17. The inner end portion of the valve body 16 has a shoulder 19 against which a valve seat 21 is held in airtight relationship by a nut 22. The valve body comprises the member 23 having a concave perimeter in which a rubber O-ring 24 -isseated The O-ring normally bears against the valve seat 21 to prevent the passage of gas into the rebreathing bag.

A valve actuating stem 26 extends from the member 23 and is actuated as hereinafter described. A spring 27 surrounds the stem 26 and is anchored at its ends to the valve seat 21 and the stern, respectively, thus always exerting a force tending to maintain the valve body in the relationship to the valve seat shown-in Fig. 3.

Where the breathing apparatus is used in air, as in aviation or rescue work, the design of the rebreathing bag is not important, since the external pressure exerted on it is substantially uniform throughout, and the bag will collapse more or less uniformly throughout on inhalation. However, in a water medium a simple breathing bag or cylindrical bellows will not permit' proper or complete filling and emptying of the reservoir unless the demand valve-bellows assembly is positioned such that the bag or bellows lls and empties along a vertical axis. When such a gas-saver assembly is positioned with the cylindrical bellows or bag acting along a horizontal axis, water pressure is not uniformfover the end of the bellows or bag. The higher pressure at the lowermost portion of the bellows or bag causes selective collapse of this lower portion, interfering with or preventing complete filling as well as distortion during emptying. The distortion during emptying prematurely causes activation of the demand valve trigger mechanism, Moreover, the water pressure on the lowermost portion of the bellows or bag, being several inches of water greater than that at the level of the exhaling valve, tends to cause the exhaling valve to open before the bellows or bag is distended.

The accordion-pleated rebreathing bag 14 is made in its expanded position, so that when it is in its expanded position it is unstressed and causes only slight resistance to inhalation. However, when the rebreathing bag is compressed to the desired volumeor has collapsed after an inhalation, it will exert an elastic force to selectively draw into itself the first portion of the gas exhaled. This elastic force tends to produce a decrease in pressure in the bag itself, in the inhalation and exhalation tubes 8 and 10, and in the lung air space. The reduced pressure in the rebreathing bag and in the inhalation tube 8 tends to cause the first portion of the exhaled gas to be forced back into the rebreathing bag. On the other hand, the decrease in pressure in the exhalation tube keeps the exhalation valve 11 closed and prevents exhalation therethrough until the rebreathing bag has lled. ln a sense, the self-restoring force of the collapsed elastic rebreathing bag functions the same as a spring load pressure for the exhaling valve, making the use of a spring loaded valve unnecessary.

A rigid plate 28 is positioned in the outermost corrugation of the rebreathing bag. The diameter of the plate 2i; is equal to the internal diameter of the outermost corrugation, so that it may be snapped into place and retained in the position shown without the use of cement or other fastening means. l

A U-shapedrodZ has the free end of its legs attached to the plate 28 and is sopositioned that when the rebreathing bag is depressed or collapsed, the base of the U-shaped rod will engage and depress the valvc stem 26. Thus, on inhalation, when the gas in the inhalation tube and in the rebreathing bag has been inspired, the bag will collapse, as shown in dotted lines in Fig. 3, and the U-shaped rod will engage and depress the valve stem 26, therebyk causing the valve body 24 and the Owing carried thereby to tilt and open the valve for the passage of gas from the conduit 6 into the rebreathing bag and inhalation tube 8. As soon as the rebreathing bag begins to expand, the plate 28 will move away from the stern 26 and the demand valve will close.

The decreasing diameter of the bellows reduces the influence of uneven water pressure, allowing essentially complete filling of the reservoir before thev pressure differential between top and' bottom of the bellows becomes significant. By this means an almost uniform function of the bellows in any normal swimming position is obtained.

A perforated casing 29 is secured to the outer edge of the flange 12 and extends over the rebreathing bag 14 to provide protection against activation or damage by external forces while allowing exit and entry of the surrounding medium to occupyv the volume of expansion and collapse of the rebreathing bag.

The exhalation valve 11 comprises a rubber or other flexible disc 31 having a central projection 32 which extends through an opening in the base 13 to which the exhfalation tube 10Y is connected. The inner end of the projection 32 is enlarged, so that when forced through the opening it will normally hold disc 31 against the outer face of the base 13. Exit openings 33 are formed in the base`13, withinitheperirneter of the disc 3l. The disc 31 is sufficiently flexible that, upon an increase of pressure to the desired amount in the exhalation tube, it Willyield and let the exhaled gases pass through the openings 33 to the surrounding medium.

A perforated cover 34 is secured to the base 13 and extends over the disc 31 to protect it against damage or opening by external forces.

In an air medium the location of the demand valve 7 with respect to the wearers body is not important. In a water medium, however, the gas pressure within the breathing tubes, rebreathing bag, lungs, etc., is determined by the location of the exhaling valve during exhalation and by the position of demand valve mechanism during inhalation. In each instance these breathing pressures should be equal to the mean water pressure on the chest wall. In the vertical position the mean water pressure on the divers chest is at a level approximately even with the nipples. The demand valve assembly may be mounted anteriorly or posteriorly at this level.

In an air medium the location of the exhaust valve with respect to the demand valve or users body is not important since air pressure is essentially uniform over the body surface and no difference in' pressure on the |11 3 (bfcmand) and cxpiratory (exhaust) valves Y irafaf 1555- ,Vater medium the external or water pressure tllggagainst the exhaust valve must be equal to or tightly greater than that acting against the demand valve Liiaphragm or bellows. If the reverse is true, the greater pressure on the demand valve will maintain it in a collapsed and activating position, causing gas to flow-con` tinuously, even during exhalation or breathholding, with gross waste ofthe compressed gas supply. Since a diver may assume almost any conceivable position under water it is necessary that the exhaust valve be mounted at a location with respect to the demand valve such that external pressure differences between these two components will be minimal regardless of the divers position under water. With the relationship of the inspiratory` and expiratory valves, as shown in the drawings, gas will ow on the demand of inspiration but will cease as exhalation causes the bellows to move away from the trigger mechanism.

In operation of the breathing apparatus of this invention, inhalation will cause a reduction of pressure in the inhalation tube 3 and the bag 14, resulting in a collapse of the bag and the triggering of the demand valve 7 by the rigid plate 28. This opens the demand valve and supplies all the gas necessary for inhalation. When inhalation ceases the demand valve closes and cuts oi the supply of gas to the collapsed bag 14, which remains collapsed until the beginning of exhalation. This co1- lapsed state of the elastic bag causes a reduced pressure in the bag and in the inhalation and exhalation tubes 8 and 10. When the wearer next exhales, the reduced pressure in the inhalation tube and the rebreathing bag will cause the rst portion of the exhaled gas, that is, that portion coming from mouth, trachea, and large bronchi, or, in other words, from the physiologically dead space of the respiratory system which contains little carbon dioxide, to be forced into them for rebreathing on the next inhalation. After they have been lled with the tirst phase of exhalation, the remaining exhaled gas, coming from deeper in the lungs and, therefore, containing most of the carbon dioxide, cannot enter the inhalation tube 8 and the rebreathing bag 14, and passesthrough the exhalation tube 10 to be discharged to the surrounding medium through the exhalation valve 11.

On the next inhalation the first gas to be inspired will be that trapped from the preceding exhalation, which will enter the deeper portion of the lungs and be lutilized in the respiratory exchange. This will be the last portion of the gas exhaled on the next exhalation and will be discharged into the surrounding medium as lexplained above. The additional volume required to complete the inhalation will be delivered from the demand valve as inspiration collapses the rebreathing bag against the demand valve level of the system. Thus, none of the gas is inhaled a third time, and on each exhalation, the portion of the exhaled gas which is trapped for rebreathing will be a portion of the additional volume required from the demand valve on the preceding inhalation.

The rebreathing bag of Figs. and 6 is connected through a valveless, corrugated, ilexible, inhalation tube 8' and a valveless, corrugated, exible, exhalation tube to a valveless breathing mask in the same manner as shown in Fig. l. It also is connected through conduit 6' to tanks in which oxygen or a mixture of oxygen and nitrogen is stored under high pressure, although in this instance it is not necessary that the rebreathing bag be connected to the source of gas under pressure through `a pressure reducing valve, like the valve 5 of Fig. l.

Oxygen or a mixture of oxygen and nitrogen is introduced into the rebreathing bag from a conduit 6', through a demand valve 7. Instead of being secured to an upstanding side ange of the base 13', as in Fig. l, the valve 7' is secured to the bottom plate of the base, and the valve operating stem 26 is short and is actuated, in

a manner to be described, by means of a bifurcated or forked lever 40 having outer ends 41 and 42, and pivoted at 43 to the top of the demand valve casing. Otherwise the structure and operation of the valve 7 is the same as valve '7 of Figs. l to 3, and like reference characters, primed, designate corresponding parts.

The elastic rebreathing `bag 14 is accordion pleated, like the bag 14 of Fig. 2, and has its inner edge secured in gas-tight relation to the upper edge of the side flange 12 of the base 13'. The rebreathing bag 14 is also made in its expanded position, so that when it is in its expanded position it is unstressed and causes only a slight resistance to inhalation, but when compressed will exert an elastic force to selectively draw into itself the first portion of the exhaled gases, as described in connection with the form of the invention previously described.

A rigid plate 44, preferably a metal disc, is positioned in one of the corrugations of the breathing bag adjacent the side flange 12'.v The plate 44 has perforations 45 to permit free flow of gas from one side of the plate to the other. The diameter of the plate is equal to the internal diameter of the corrugation of the breathing bag in which it is positioned, so that it may be snapped into place and retained in the position shown without the use of cement or other fastening means.

The rebreathing bag in this form of the invention is also of dome or bee-hive shape. It is provided with a centrally-positioned, integrally formed, bellowsed tube 46 which extends through a central opening 44' of the rigid plate 44. The edge of this tube is integrally connected to the outer portion of the rebreathing bag 14' and its inner end is secured about the edge of a cup-like member 47 secured to the bottom plate of the base 13'. This cup-like member is connected by a passageway 43 to the exhalation tube 10'. Thus, the passageway 4S and the bellowsed tube 46 form an extension of the exhalation tube lil', and the tube 46 will collapse and expand with the breathing bag 14'.

An exhalation valve 11' is positioned in the outer end of the bellowsed tube and comprises a rigid plate 49 secured in the outer corrugation of tube 46 and a rubber or other flexible disc 50 having a central projection 51 which extends through an opening in the plate 49. The inner end of the projection 51 is enlarged, so that when forced through the opening it will normally hold the disc 5t) against the outer face of plate 49. Exit openings 52 are formed in plate 49, within the perimeter of disc 50. The disc 50 is sutliciently lexible that upon an increase of pressure of a predetermined amount in the exhalation tube, it will yield and let the exhaled gases pass through the openings 52 to the surrounding medium.

A perforated casing 34' is secured to the outer edge of the flange 12' and extends over the rebreathing bag 14' to provide protection against activation or damage by external forces While allowing exit and entry of surrounding medium to occupy the volume of expansion and collapse of the rebreathing bag.

The operation of this embodiment of the invention is generally the same as the embodiment illustrated in Figs. l to 4, inclusive. Inhalation will cause a reduction of pressure in the inhalation tube S and the rebreathing bag 14', resulting in a collapse of the bag and the triggering of the demand valve 7 by the rigid plate 44 as it engages and depresses the outer ends 41 and 42 of the lever 40. The depression of the lever 40 opens the demand valve and supplies all the gas necessary for inhalation. When inhalation ceases, continued ilow of the gas will expand the rebreathing bag slightly until the rigid plate 44 is moved outwardly sufticiently to permit the demand valve to close. The demand valve will remain closed and the rebreathing bag will remain substantially collapsed until the beginning of exhalation. The collapsed state of the elastic bag causes a reduced pressure in the 'bag and in the inhalation and exhalation tubes S and 10. When the wearer next exhales, the reduced pressurein the inhalation tube and the rebreathing bag will cause the first portion of the exhaled gas, that is, the gas from the foresaid physiological dead space of the respiratory system which contains little carbon dioxide to be forced into them for rebreathing on the next exhalation. After they have been filled with the first phase of exhalation, the remaining exhaled gases, coming from deeper in the lungs, and therefore, containing most of the carbon dioxide, not being able to enter the inhalation tube 8 and the rebreathing bag i4', passes through the exhalation tube lil', passageway 48 and the centrally-positioned bellows tube 46 to be discharge to the surrounding medium through the exhalation valve 11.

Cn the next inhalation the lirst gas to be inspired will be that trapped from the preceding exhalation, all as described in connection with the first embodiment of the invention;

The form of the breathing apparatus just described functions properly regardless of its orientation in water.

The major problem encountered in use of air-saver breathing apparatus in water is that it functions perfectly only when the rebreathing bag is vertical, with its apex up. ln this position water pressure is less by several inches on the bellows than against the exhaust valve and complete filling of the bellows occurs before any gas escapes through the exhaust valve. Poorest function, and even failure of air-saving occurs when the diver, with the breathing apparatus strapped onto his back, lies on his back, causing the bellows to be inverted and the water pressure on the exhaust valve to be less than that on the bellows. ln this stiuation, exhaled air passes freely through the exhaust from the beginning of exhalation; the bellows remains compressed by the slight water pressure and noy air-saving occurs. in positions intermediate between the normal and inverted positions varying degrees of imperfect filling of the bellows occur.

To allow mounting of the demand valve such that it will lie close to the body of the user (in order to reduce inspiratory resistance) it is necessary to attach the valve assembly on the body side of the cylinder yoke. Such mounting, retaining direct connection to the gas supply, places the bello-ws in an inverted position in normal use where the breathing apparatus is strapped onto the back of the wearer, as is customary.

In the form of the invention shown in Figs. 5 and 6, the inner bellows serves as a compressible conduit extension of the exhalation tube i. This permits placement of the exhalation valve at the bellows apex, and exposes the exhalation Valve to the same pressure to which the apex of the bellows is exposed. This, together with the elasticity of the bellows, results in selective filling of the bellows with the first portion of each exhalation regardless of the orientation of the breathing apparatus.

The inclusion of the inner bellowsed tube 46 enables the exhalation valve to be mounted as a removable part of the breathing bag apex since it may be held in place in the outermost corrugation of the tube 46 merely by snapping it into place; it eliminates the necessity for using a pressure-reducing valve'in the gas-supply line to the rebreathing bag, such as the pressure-reducing valve of Fig. l; and it permits the demand valve 7 to be mounted eccentrically at any position about the base i3 and still be properly actuated by the triggering lever 4tlas the bag 14 collapses.

By trapping the first phase of each exhalation for rebreathing on the next inhalation, as contemplated herein, a saving of between and 40 percent of the gas `used may be obtained without appreciable respiratory stimulation.

This application is a continuation-in-part of my application Serial No. 456,990, tiled September 20, 1954.

Various changes may bemade'inthe details of construction of the breathing apparatus described herein without departing from the spirit of the invention or sacricing any of the advantages thereof.

I claim:

1. A breathing apparatus comprising a breathing device for supplying an oxygen containing gas to a wearer of the apparatus, an inhalation tube leading to the breathing device, an exhalation tube leading from the breathing device, a conduit for supplying an oxygen containing gas to the inhalation tube, a demand Valve controlling the passage of gas from said conduit to the inhalation tube, means for actuating said valve upon the reduction of pre"- sure in the inhalation tube to a predetermined extent, a collapsible rebreathing bag the interior of which cornmunicates with the inhalation tube, said breathing bag being dome-shaped and accordion pleated and so positioned that when the breathing apparatus is positioned on a person it lls and empties along a generally horizontal axis, said breathing bag, when in its expanded position, being unstressed so that it will offer only slight resistance to breathing, the parts being so constructed and arranged that during the first phase of exhalation a part of the exhaled gases will pass into the inhalation tube for rebreathing on the next inhalation and gas in the inhalation tube will iiow into said rebreathing bag, and an exhaling valve controlling the passage of gas from the exhalation tube to the surrounding medium, said exhaling valve being actuatable by an increase of pressure in the exhalation tube created by exhalation after the irst phase thereof.

2. A breathing apparatus as set forth in claim l in which the collapsible rebreathing bag is connected to a base member, the inhalation tube is in communication with the base member and extends therefrom, the conduit for supplying the oxygen-containing gas communi- Cates with the base member through the demand valve, and the exhaling Valve is outside of the base member and at a central position with respect thereto.

3. A breathing apparatus comprising a breathing device for supplying an oxygen-containing gas to a wearer of the apparatus, an inhalation tube leading from the breathing device, an exhalation tube leading to the breathing device, a conduit for supplying an oxygen-containing gas to the inhalation tube, a demand valve controlling the passage of gas from said conduit to the inhalation tube, means for actuating said valve upon the reduction of pressure in the inhalation tube to a predetermined amount, a collapsible rebreathing bag communicating with the inhalatio-n tube, said exhalation tube terminating adjacent the outermost portion of the collapsible bag in the direction of collapsing and expansion of said bag, the parts being so constructed and arranged that during the first phase of exhalation a part of the exhaled gases will pass into the inhalation tube for rebreathing on the next inhalation and gas in the inhalation tube will tlow into said rebreathing bag, an exhalation valve at the terminal end of the exhalation tube controlling the passage of gas from the exhalation tube to the surrounding medium, said exhalation valve `being actuatable by an increase of pressure in the exhalation tube created by exhalation after the first phase thereof.

4. A breathing apparatus as set forth in claim 3 in which the rebreathing bag is of dome shape and of bellows formation.

5. A breathing apparatus as set forth in claim 3 in which the exhalation tube extends through the collapsible rebreathing bag and is connected to the outer or smaller end thereof, and the portion of the exhalation tube which extends through the collapsible bag includes a collapsible section of bellows formation.

6. A breathing apparatus as set forth in claim 5 in which an actuating member for the demand valve is positioned within the collapsible bag and a rigid plate is secured within the corrugations of the collapsible bag to engage and actuate said actuating member when the collapsible bag collapses.

which the exhalatiorlv valve is removably secured in the 5 outermost corrugation of the bellows portion of the exhalation tube.

9. A breathing apparatus as set forth in claim 5 which includes a base member having a space for gas, the collapsible rebreathing bag is secured to one side of the 10 base member and s in communication with the space therein, and the demand valve is positioned within said base member and supplies gas to the space therein.

References Cited in the le of this patent UNITED STATES PATENTS 2,310,022 Neidbrink Feb. 2, 1943 2,385,786 Brubach Oct. 2, 1945 t 2,788,001

Brown Apr. 9, 1957

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