GB2118047A - Improvements in and relating to breathing apparatus - Google Patents

Abstract

Portable closed-circuit breathing apparatus comprises a facemask 1, a purifier 6 for removing carbon dioxide chemically from exhaled gas, a heat exchanger 9 for cooling the purified gas, a breathing bag 12 and a source of oxygen 14. The heat exchanger 9 may comprise a plurality of tubes through which the gas in the circuit flows in parallel, provided inside and out with looped-wire fins to improve heat transfer from the circuit gas to the atmosphere. <IMAGE>

Description

SPECIFICATION Improvements in and relating to breathing apparatus The invention relates to breathing apparatus of the closed-circuit or regenerative type, in which gas exhaled by a user is retained within the apparatus, carbon dioxide is removed, oxygen is added, and the gas is then returned to the user for inhalation.

The gas in such apparatus tends in operation to become hot, mainly because the normal method of removing the carbon dioxide is by an exothermic chemical reaction, but also from physiological effects and in some conditions from environmental heating. Various methods of cooling have been proposed in the past, including the evaporation of water, the evaporation of carbon dioxide, the melting of ice and the melting of certain salts, but none of these has proved entirely satisfactory in practice.

The present invention provides breathing apparatus comprising a container for gas, means for conveying gas exhaled by a user to the container and for conveying gas from the container to be inhaled by the user, purifying means for reducing the proportion of carbon dioxide in the gas, oxygenating means for increasing the proportion of oxygen in the gas, and cooling means comprising a heat exchanger arranged in operation to transfer heat from the gas in the apparatus to the external atmosphere.

Preferably the arrangement is such that in operation the exhaled gas passes through the purifying means, the heat exchanger, and the container, in that order before being inhaled by the user again. Advantageously, the gas is caused to flow round a circuit within the apparatus in one direction only by the use of non-return valves, which are advantageously provided in both limbs of the circuit between the container and the position of the user.

The heat exchanger preferably comprises a plurality of elongate heat exchanger tubes connected by a manifold at each end and so arranged that in use the gas flows along the tubes in parallel from one manifold to the other. Where an adjacent part of the apparatus comprises a plenum chamber for gas, for example, where gas passing through the purifier is collected by an external plenum chamber, the heat exchanger tubes preferably all open directly into that plenum chamber. That eliminates the need to provide a separate manifold and the conventional single outlet from the plenum chamber.The purifying means may be generally cylindrical (not necessarily right circular cylindrical) and have a central duct for gas to be purified and an outer plenum chamber for purified gas into which the heat exchanger tubes open and which is separated from the central duct by an annular purifying section, the arrangement being such that gas diffuses from the central duct through the purifying section to the plenum chamber and then flows directly into the heat exchanger tubes. The heat exchanger advantageously comprises one or more metal tubes provided with fin means both inside and out, one fin means of each tube being in contact with the external atmosphere and the other with the gas in the circuit. The fin means are advantageously helical and permeable to gas, and each fin means then preferably comprises a row of loops of wire.The fin means inside the tubes may be mounted on central elongate formers.

The gas in the apparatus may be inside the tubes, and the outsides of the tubes open to the atmosphere. Instead, each tube may be enclosed within a sleeve defining an annular duct between the tube and the sleeve, the fin means outside the tube substantially spanning the distance between the tube and the sleeve. The requirement of good heat transfer sets a limit on the depth of the fins, and hence on the radial width of the tube and duct; the result is that the annular duct can have a lower resistance to the flow of gas than can be achieved for the central tube. It is therefore advantageous that the gas in the apparatus, which is usually caused to circulate only by the lungpower of the user, be in the annular duct, and that the central tube be open to the atmosphere.

Especially in this case, means for supplying a forced draught of atmospheric gas to the heat exchanger is preferably provided. Such means may be powered by a turbine driven by the flow of oxygen into the breathing apparatus from an oxygen cylinder.

Instead of finned tubes, other forms of heat exchanger construction may be used where appropriate. For example, flat radiator panels may be used where the lower heat transfer is acceptable and the greater robustness is desirable.

Instead of the heat in the gas in the system being transferred directly to the atmosphere by the heat exchanger, a heat pump or the like may be provided to transfer the heat energy to the atmosphere through a heat exchanger at a higher temperature. With such an arrangement the bulk of the heat exchanger may be greatly reduced, especially in the case of apparatus designed for use in warm environments.

The purifying means may comprise a substance that removes carbon dioxide from the gas by reacting chemically with it. The oxygenating means may comprise a pressure-reducing valve arranged to permit oxygen from an oxygen cylinder to enter the gas within the apparatus. The container for the gas between breaths may comprise a flexible bag subject to ambient pressure on its external surface and arranged not to be completely filled at any time in normal operation.

Apparatus according to the invention is especially suitable for use in the case of portable breathing apparatus arranged to be carried by the user, who then breathes through, for example a facemask or mouthpiece connected to the rest of the apparatus by one or more flexible hoses.

Various forms of portable breathing apparatus constructed in accordance with the invention, and two forms of heat-exchanger tube suitable for use in it, will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of a first form of apparatus; Fig. 2 is a perspective view of the apparatus shown in Fig. 1, partly cut-away:: Fig. 3 is a fragmentary perspective view of a first form of a heat-exchanger tube; Fig. 4 is a schematic longitudinal section through a second form of heat exchanger tube; Fig. 5 is a schematic rear elevation view of a backpack forming part of the second form of apparatus; Fig. 6 is a side elevation view of the backpack as shown in Fig. 5; Fig. 7 is a top plan view of a backpack as shown in Fig. 5; Fig. 8 is a schematic rear elevation view of a backpack forming part of a third form of apparatus: and Fig. 9 is a top plan view of the backpack as shown in Fig. 8; Fig. 10 is a rear elevation view of a backpack forming part of a fourth form of apparatus; Fig. 11 is a side elevation view of the backpack shown in Fig. 10; Fig. 12 is a rear elevation view, partly in section, of a backpack forming part of a fifth form of apparatus; Fig. 13 is a side elevation view of the backpack shown in Fig. 12; Fig. 14 is a somewhat schematic exploded perspective view of the backpack shown in Fig. 12: Fig. 15 is a graph showing the performance of one sample of the fifth form of apparatus under British standard test conditions; and Fig. 1 6 is a similar graph for United States standard test conditions.

Referring to the accompanying drawings, and initially to Figs. 1 and 2, the first form of apparatus comprises a facemask or mouthpiece 1 arranged in use to be secured over the face of a person (not shown) using the apparatus. The facemask or mouthpiece 1 comprises an inhalation valve 2, which is a non-return valve permitting gas to flow only into the facemask from an inspired gas pipe 4. and an exhalation valve 3, which is a non-return valve permitting gas to flow only out of the facemask or mouthpiece into an expired gas pipe 5. The facemask or mouthpiece 1 may be of any conventional type suitable for use with separate inspired and expired gas pipes.

The expired gas pipe 5, which is made flexible in order to accommodate movement of the user's head, leads to the inlet of a purifier 6, which may be of any conventional type, in which carbon dioxide is removed chemically from the exhaled gas. As shown in the drawings, both in Fig. 1 and in the subsequent examples, the purifier comprises a hollow right-circular cylindrical unit containing a mixture of calcium oxide and sodium hydroxide, as sold, for example, under the tradename "Protosorb". The expired gas pipe 5 leads into the central cavity of the unit, from which the gas passes radially outwards through the sodalime to an annular outer plenum chamber, with which the outlet communicates. From the outlet of the purifier a pipe 7 leads to the centre of an inverted U-shaped manifold 8 on one side of the apparatus.From each arm of the U a plurality of heat-exchanger tubes 9 lead across to a second manifold 10, in the form of an erect U, on the other side of the apparatus. From the centre of the second manifold 10 a pipe 11 leads to the inlet of a breathing bag 12, which may be of any conventional type, and is provided with a relief valve 1 3. An oxygen cylinder 14 is connected, through its cylinder valve 1 5, a pressure reducing valve 1 6, and a pipe 1 7 to the inlet to the breathing bag 12.The reducing valve 1 6 both here and in the subsequent examples, may comprise a pressure reducing valve to reduce the cylinder pressure of up to 20 MN/m2 to about 700 kN/m2 with a manual bypass to give extra oxygen at the user's control, followed by a constant flow orifice to supply about 2 litres/min to the breathing circuit with a demand-valve bypass actuated by the pressure in the breathing circuit. A pressure gauge 1 8 is connected to the housing of the pressure reducing valve 1 6 to show the oxygen pressure in the cylinder 14. A drain tap (not shown) may be provided for removing condensed water that accumulates in the lower parts of the apparatus. The outlet of the breathing bag 12 is connected to the inspired gas pipe 4, which, like the expired gas pipe 5, is flexible.

Referring now to Fig. 3, the first form of heat exchanger tube 9 comprises a right circular cylindrical metal tube 21 connected to the manifolds 8 and 10. A helical fin 22, comprising loops of wire bonded to the tube 21, covers the exterior of the tube to provide good thermal contact between the external atmosphere and the tube, and an insert comprising a rod-like central former 24 bearing a similar looped-wire fin 23 in contact with the internal surface of the tube 21 provides good thermal contact between the gas in the breathing apparatus and the tube 21, and hence the external atmosphere. The loops of each fin 22 or 23 may be formed by constructing the whole fin from a helical coil of wire. The wire may be either tinned copper or aluminium, as may the tube 21. The loops of the inner fin 23 may be bonded to the tube 21, for example, by soldering.

Such heat exchanger tubing is available commercially. The heat exchanger tubes 9 may be cooled by natural convection of the external atmosphere or some form of blower unit (not shown) may be used to provide forced-draught cooling.

Referring to Fig. 4, the second form of heat exchanger tube 9 is similar to the first form, but an external sleeve 25 is provided around the outer fin 22, providing a sealed-off flow path outside the tube 21. The inlet 26 and outlet 27 of the outer sleeve 25 are connected to the manifolds 8 and 10, and the ends of the tube 21 are open to the atmosphere, as shown in Fig. 4. A blower, which comprises a fan 28 driven by a motor 29, is provided to produce a forced draught of atmospheric gas through the heat exchanger tube 9, in counter-current to the flow of gas in the breathing circuit. The motor 29 is an electric motor driven by a battery pack 30, but it could instead be a turbine driven by the flow of gas from the oxygen cylinder 14.

The blower could instead be arranged to produce the forced draught in co-current to the flow of gas in the breathing circuit, or in some cases could be omitted entirely. Where a plurality of tubes 9 are mounted in an apparatus, they may be provided with separate blowers.

The number and length of the heat exchanger tubes 9 are selected in accordance with the sort of tube being used and the degree of cooling required. It may be possible in some circumstances to dispense with the manifolds 8 and 10 and to use a single tube 9.

In operation, when the user exhales, warm CO2laden expired gas passes through the exhalation valve 3, along the expired gas pipe 5 to the purifier 6. The purifier 6 removes the carbon dioxide from the gas but, because the CO2 is removed by exothermic chemical reactions, the gas leaving the purifier is at an even higher temperature. The gas then passes through the heat exchanger tubes 9, where it is cooled to a suitable temperature. If the tubes 9 are provided with forced draught cooling, the blower or blowers may be so arranged that they can be regulated to suit the amount of cooling produced to the circumstances. The gas then flows into and inflates the breathing bag 12 and is mixed with oxygen from the cylinder 14 to produce gas that is fit to breathe in terms of both temperature and composition.

When the user inhales, the gas from the breathing bag 12 is drawn through the inspired gas pipe 4 and the inhalation valve 2 into the facemask and thence to the user's lungs. Air is prevented from flowing backwards through the circuit by the inhalation valve 2, the exhalation valve 3, and if necessary also by other non-return valves positioned at appropriate points along the circuit.

Referring now to Figs. 5 to 7 of the drawings, in the second form of apparatus the purifier 6 and the oxygen cylinder 14 are mounted on either side of a base plate 31 of a packplate to be worn by the user of the apparatus, with the breathing bag 12 mounted between them. The baseplate 31 is generally rectangular but with the section in front of the breathing bag 1 2 omitted to save weight.

Eight heat exchanger tubes 9 are arranged above the purifier 6 and oxygen cylinder 14 between the backplate 31 and a cage 32 of metal bars that protect the fins 22 of the heat exchanger tubes 9 against accidental damage. The connections between the various components of the backpack are the same as in the form of apparatus shown in Figs. 1 and 2; some of the pipes have been omitted from Fig. 5 in the interests of clarity.

Referring now to Figs. 8 and 9, the third form of apparatus is similar to the second form except in that the oxygen cylinder 14 is mounted across the bottom of the backpack with the purifier 6 and the heat exchanger side by side above it. As may be seen from Fig. 8, the purifier 6 comprises a hollow right circular cylindrical purifier cartridge, the central cavity 33 of which is connected to the exhaled gas pipe 5 while the outside is surrounded by a plenum chamber 34. Such cartridges are well known and are available commercially. The heat exchanger tubes 9 communicate directly with the plenum chamber 34 of the purifier 6, eliminating the first manifold 8 and thereby substantially reducing the resistance to gas flow in the system.

There are twelve heat exchanger tubes 9, in two columns of six, instead of the eight tubes of the second form of apparatus, to compensate for the fact that the tubes of the third form are shorter.

The breathing bag 12 is arranged between the front and back columns of tubes 9, and the expansion and contraction of the breathing bag automatically produces some draught over the tubes, enhancing the cooling of them. The breathing bag 12 may instead be mounted in front of the tubes 9, between the front column of tubes and the back of the user, in order to improve the exposure of the front tubes.

Referring now to Figs. 10 and 1 lithe fourth form of apparatus is generally similar to the third form, except as described below.

The heat exchanger tubes 9 are arranged in three columns of 4, 3, and 4 tubes, respectively, giving an array that is lower but deeper from front to back, and has a more compact shape as compared with the array in the third form of apparatus. The second manifold 10 is covered by a metal side-plate 35, and the back and top of the heat-exchanger are covered by metal mesh screens 36 to protect the fins 22 (not shown). The oxygen supply from the cylinder 14 passes through the usual valves 15 and 16 and along a pipe 17 to the top of the manifold 10. It then enters the inspired gas pipe 4 and passes along it in a separate flexible pipe 37 within the inspired gas pipe. This supply of clean, dry oxygen can be used for demisting the visor of a face-mask 1 before being mixed with the gas from the inspired gas pipe 4 for breathing.The breathing bag 12 is mounted within a flattish hollow plastics housing 38, one side of which is moulded to fit the back of the wearer and the other side of which is moulded to provide mountings for the other components of the apparatus.

Referring now to Figs. 12 to 14, the fifth form of apparatus has a gas purifier 6 similar to that of the third and fourth forms of apparatus, mounted verticaily on the left side (as seen in Fig. 2) of the backpack with the eight heat exchanger tubes 9 (not shown) communicating directly with the plenum chamber 34. On the right hand side is a double-walled vessel 39, which defines between the two walls a second plenum chamber 40 that replaces the second manifold 10. Although both walls of the vessel 39 are right-circular cylindrical, it will be seen that they are not coaxiai, the plenum chamber 40 being widest on the side towards the heat exchanger. The inner wall of the vessel 39 forms a housing for the oxygen cylinder 14, together with the valves 1 5 and 1 6. This has two main advantages.Firstly, because the oxygen cylinder 14 is in a housing, a cylinder made of aluminium can be used instead of a heavier steel cylinder even in environments such as mines where there is a high risk of fire or explosion and where exposed aluminium would create a danger of a thermite reaction. Secondly, because gases cool as they expand, the cylinder 14 and valves 1 5 and 1 6 tend to be slightly cooler than their surroundings, and because they are surrounded by the second plenum chamber 40 any cooling effect will provide extra cooling for the breathing gas flowing through the plenum chamber. An aperture is provided in the side of the vessel 39 for access to the valve controls.

A solid plate 45 spans the outer walls of the purifier 6 and the vessel 39 to the rear of the tubes 9, forming, together with the purifier, the vessel, and the backplate 38, a chimney around the heat exchanger. The top and bottom of the chimney are covered by perforated plates 46 and 47, respectively. An electrically driven fan 28 (not shown) having a power consumption of about 1 watt is mounted at the bottom of the chimney to blow gas up past the tubes 9. The electric motor 29 (not shown) and its power supply 30 (not shown) may be of known waterproof, sparkproof, type. It has been found possible to construct such a breathing apparatus, complying in all other respects with the relevant British Standard, that is over 2.5 kg lighter than a comparable conventional apparatus. If the motor 29 fails, then of course the eight short heat exchanger tubes 9 will not be able to provide such effective cooling, but under British Standard test conditions the user is supplied with gas that, while rather warm, is not so hot as to be harmful to the user. One example of what might happen is shown in Fig. 15, and a corresponding example under United States test conditions is shown in Fig. 16.

Rubber buffers 42 are fitted on the end-caps covering the bottoms of the purifier 6 and the vessel 39 so that the back-pack can be stood upright on a horizontal surface. The buffers 42 may be omitted if they are not required.

Claims (29)

1. Breathing apparatus comprising a container for gas, means for conveying gas exhaled by a user to the container and for conveying gas from the container to be inhaled by the user, purifying means for reducing the proportion of carbon dioxide in the gas, oxygenating means for increasing the proportion of oxygen in the gas, and cooling means comprising a heat exchanger arranged in operation to transfer heat from the gas in the apparatus to the external atmosphere.

2. Apparatus as claimed in claim 1, wherein the arrangement is such that in operation the exhaled gas passes through the purifying means, the heat exchanger, and the container, in that order, before being inhaled by the user again.

3. Apparatus as claimed in claim 1 or claim 2, wherein in operation the gas is caused to flow round a circuit within the apparatus in one direction only.

4. Apparatus as claimed in claim 3, which comprises non-return valves in both limbs of the circuit between the container and the position of the user arranged to prevent gas from flowing backwards round the circuit.

5. Apparatus as claimed in any one of claims 1 to 4, wherein the heat exchanger comprises a plurality of elongate heat exchanger tubes connected by a manifold at each end, and the gas is arranged to flow along the tubes in parallel from one manifold to the other.

6. Apparatus as claimed in claim 5, wherein a part of the apparatus adjacent to the heat exchanger comprises a plenum chamber into which the heat exchanger tubes open directly, and which also serves as the manifold for one end of the heat exchanger.

7. Apparatus as claimed in any one of claims 1 to 6, which comprises a housing for a container of compressed gas that in use forms part of the oxygenating means.

8. Apparatus as claimed in claim 7, wherein in operation the gas in the apparatus flows through a jacket round the said housing for a container of compressed gas.

9. Apparatus as claimed in claim 8 when dependent upon claim 6, wherein the said jacket is the said plenum chamber.

10. Apparatus as claimed in claim 6 or in any one of claims 7 to 9 when dependent upon claim 6, wherein another part of the apparatus comprises another plenum chamber into which the heat exchanger tubes open directly at their other ends and which serves as a manifold for the other end of the heat exchanger.

11. Apparatus as claimed in claim 6 or in any one of claims 7 to 10 when dependent upon claim 6, wherein the plenum chamber or the said other plenum chamber is a plenum chamber for purified gas in the purifying means from which the gas can pass to the heat exchanger tubes.

12. Apparatus as claimed in any one of claims 1 to 11, wherein the purifying means is generally cylindrical and has a central duct for gas to be purified and an outer annular plenum chamber for purified gas, separated by an annular purifying section through which gas diffuses from the central duct to the plenum chamber.

13. Apparatus as claimed in any one of claims 1 to 12, wherein the purifying means comprises a substance that removes carbon dioxide from the gas in the apparatus by reacting chemically with it.

14. Apparatus as claimed in any one of claims 1 to 13, wherein the heat exchanger comprises one or more metal tubes provided with fin means both inside and out, one fin means of each tube being in contact with the external atmosphere and the other with the gas in the circuit.

1 5. Apparatus as claimed in claim 14, wherein the fin means are helical and are permeable to gas.

16. Apparatus as claimed in claim 15, wherein each fin means comprises a row of loops of wire.

17. Apparatus as claimed in any one of claims 14 to 16, wherein the fin means inside the tubes are mounted on central elongate formers.

18. Apparatus as claimed in any one of claims 14 to 17, wherein each tube is enclosed within a sleeve defining an annular duct between the tube and the sleeve, the fin means outside the tube substantially spanning the distance between the tube and the sleeve.

19. Apparatus as claimed in claim 18, wherein the gas in the apparatus is in the annular duct, and the tubes are open to the atmosphere.

20. Apparatus as claimed in any one of claims 14 to 18, wherein the gas in the apparatus is inside the tubes and the outsides of the tubes are exposed to the atmosphere.

21. Apparatus as claimed in any one of claims 1 to 20, comprising means for supplying a forced draught of atmospheric gas to the heat exchanger.

22. Apparatus as claimed in claim 21 when dependent upon claim 20, wherein the tubes are enclosed within duct means open above and below the tubes, and a fan is provided to produce an upward current of atmospheric gas within the duct means.

23. Apparatus as claimed in any one of claims 1 to 22, wherein the container is a flexible bag subject to ambient pressure on its external surface and arranged not to be completely filled at any time in normal operation.

24. Apparatus as claimed in claim 23, wherein the flexible bag is so disposed adjacent to the heat exchanger that in operation the expansion and contraction of the bag causes currents of atmospheric gas past the heat exchanger.

25. Apparatus as claimed in any one of claims 1 to 24, wherein the oxygenating means comprises a pressure-reducing valve arranged to permit oxygen from an oxygen cylinder to enter the gas within the apparatus.

26. Apparatus as claimed in any one of claims 1 to 25, which is arranged in operation to be carried by the user.

27. Apparatus as claimed in claim 26, wherein the means for conveying gas comprises a mouthpiece or facemask arranged in use to be secured to the user's head.

28. Breathing apparatus substantially as hereinbefore described with reference to, and as shown in, Figs. 1 and 2, or Figs. 5 to 7, or Figs. 8 and9,orFigs. 10 and 11,orFigs. 12 and 14, of the accompanying drawings.

29. Apparatus as claimed in claim 29, modified substantially as hereinbefore described with reference to, and as shown in, Fig. 3 or Fig. 4 of the accompanying drawings.