GB2135197A - Improvements in and relating to breathing apparatus - Google Patents

Abstract

A backpack for a closed-circuit breathing apparatus has a hollow baseplate 3 which is arranged to be strapped to the user's back and has parts 4 to 13 of the apparatus mounted on it. A breathing bag 20 is of flattish shape and is mounted within the hollow baseplate 3. <IMAGE>

Description

SPECIFICATION Improvements in and relating to breathing apparatus The invention relates to breathing apparatus, and especially to closed-circuit breathing apparatus having a back pack to be worn by the user that includes, together with other parts of the apparatus, a flexible breathing bag that in use expands and con-tacts to tend to maintain the total volume of gas in the breathing circuit constant as the volume in the user's lungs varies as the user breathes.

Such closed-circuit breathing apparatus is well known, but in existing designs the breathing bag is situated either on the outside of the apparatus to the rear of the other parts of the apparatus or in a space between other (commonly awkwardly shaped) parts of the apparatus. Locating the breathing bag on the outside of the apparatus makes it especially difficult to protect the breathing bag against damage except by enclosing the entire backpack in a solid casing, which is unnecessarily heavy and may in fact be undesirable, especially as closed-circuit breathing apparatus usually includes a purifier that removes carbon dioxide from the breathing gas by exothermic chemical reactions and such a casing makes it more difficult to dissipate the heat generated.Furthermore, the casing does not protect the breathing bag against damage from other parts of the apparatus, and that is quite a serious problem, especially when the breathing bag is located within the apparatus and adjacent to awkwardly shaped parts. In order to reduce the vulnerability of the bag, and to fit it among the other parts of the apparatus, it is usually made in generally cubical shape, with the further disadvantage that such a shape gives a very poor ratio of swept volume to volume when full.

The invention provides a backpack for a breathing apparatus, which comprises a baseplate arranged in use to rest with one face against the back of a user and to have parts of the apparatus mounted on the other face, wherein the baseplate is hollow and has disposed within it a receptacle of variable volume to accommodate changes in the volume of gas in the lungs of the user as the user breathes.

The receptacle advantageously comprises a flexible bag that is arranged never to be completely full or empty in normal use and that preferably tends when full to conform to the shape of the baseplate and tends when empty to be flat, giving a very favourable ratio of swept volume to volume when full, the ratio being nearly 1 in the most favourable case.

For most purposes the exterior of the bag is preferably arranged to be exposed to ambient pressure, for example, by allowing the interior of the baseplate to communicate with the exterior, and the volume of the bag varies over at least a major portion of its normal range over a narrow range of internal pressures near to ambient pressure.To comply with the relevant British Standard a swept volume of 5 litres between 1 mmHg below and 1 mmHg above ambient pressure is usually required, but because the backpack according to the present invention can have a flattish breathing bag entirely closed within a rigid structure it is possible to provide a degree of additional bias to the bag, for example, by a plate spring-loaded to compress the bag against one wall of the baseplate, giving the possibility of a positive-pressure breathing apparatus, which is virtually impossible with conventional closed-circuit systems.

Two forms of backpack for closed-circuit breathing apparatus constructed in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a rear elevation view of the first form of backpack; Figure 2 is a side elevation view of the backpack shown in Figure 1; Figure 3 is a rear elevation view of a rear panel of a baseplate of the backpack shown in Figure 1; Figure 4 is a section on the line A-A of Figure 3; Figure 5 is a section on the line B-B of Figure 3; Figure 6 is a front elevation view of a front panel of the baseplate of the backpack shown in Figure 1; Figure 7 is a section on the line A-A of Figure 6; Figure 8 is a section on the line B-B of Figure 6; Figure 9 is a bottom elevation view of the front panel shown in Figure 6; Figure 10 is a perspective view of a breathing bag for the first form of backpack;; Figure 11 is a rear elevation view of the breathing bag shown in Figure 10; Figure 12 is a section through a connectorforthe breathing bag shown in Figure 10; Figure 13 is a schematic rear elevation view of the second form of backpack; Figure 14 is a side elevation view of the backpack shown in Figure 13; Figure 15 is a rear elevation view of a rear panel of a baseplate of the backpack shown in Figure 13; Figure 16 is a section on the line A-A of Figure 15; Figure 17is a section on the line B-B of Figure 15; Figure 18 is a bottom plan view of the rear panel shown in Figure 15; Figure 19 is a front elevation view of a front panel of the baseplate of the backpack shown in Figure 13; Figure 20 is a section on the line A-A of Figure 19; Figure21 is a section on the line B-B of Figure 19;; Figure 22 is a bottom plan view of the front panel shown in Figure 19; Figure 23 is a perspective view of a breathing bag for the second form of backpack; and Figure 24 is a rear elevation view of the breathing bag shown in Figure 23.

Referring to the accompanying drawings, and initially to Figures 1 and 2, the first form of backpack is arranged to be secured to the back of a user by straps attached to anchorages 1 and 2 on a baseplate indicated generally by the reference numeral 3. On the baseplate are mounted an gas purifier 4, to extract carbon dioxide from the gas exhaled by the user, an oxygen cylinder 5, to replenish the oxygen supply in the gas, and a cooler 6 to cool the gas, which tends to be heated undesirably by chemical reactions taking place in the purifier. The backpack is connected by flexible pipes (not shown) to a facemask or mouthpiece (not shown) to transfer gas exhaled by the user through a connector 10 to the purifier 4, and purified gas from the cooler 6 through a second connector 11 to be inhaled by the user.

Oxygen from the cylinder 5 flows through a system of valves 12, which may be conventional and may include a demand valve arranged to supply extra oxygen if the pressure in the apparatus falls more than 1 mmHg below ambient pressure, and a tube 13 to the second connector 11. The oxygen is then either mixed with the purified gas or led along a flexible tube within the inspired gas pipe to the face mask. A relief valve arranged to vent gas from the apparatus if the pressure there rises more than 1 mmHg above ambient pressure may also be provided.The cooler 6 is advantageously a convection cooler similar to those decribed in our co-pending British Patent Application No.82 10277 with a pluraiity of cooling tubes extending in parallel from an external plenum chamber of the purifier 4 to a manifold (not shown) on the opposite side of the backpack, but any suitable cooler of appropriate size and cooling power could be used instead.

Aflexible breathing bag is provided opening into the breathing gas circuit of the apparatus to compensate for the changes in the volume of gas in the user's lungs as the user breathes. In the present apparatus the breathing bag is a generally flattish bag 20 housed in the baseplate 3, which is hollow and made up of shaped rear and front panels 21 and 22, respectively, and connected into the breathing gas circuit of the apparatus by a connector 23 near the outlet from the cooler 6.

Referring now to Figures 3 to 5 of the drawings, the rear panel 21 of the baseplate is generally rectangular about 60 cm high by 40 cm wide, with sides 24 extending forwards about 25 mm (with respect to the user) around its entire circumference, and a cradle 25 for the oxygen bottle 5 formed in it near the bottom edge. An aperture 26 is provided for the connector 23 of the breathing bag 20, and any other mountingsforthe equipment of the backpack may be formed in or fixed on the rear panel 21 as required. The panel 21 is advantageously moulded in plastics material which may be reinforced, for example, with glass-fibre. In some uses, it is advantageous for the plastics material to be filled with carbon black or the like to make it electrically conducting, reducing the risk of a build-up of static electricity.As may be seen from Figures 3 and 5, a central portion 27 of the rear panel 21, which carries comparatively little load, is made of thinner material than the rest, stiffened by moulded ribs 27a.

Referring now to Figures 6 to 9 of the drawings, the front panel 22 of the baseplate 3 is also generally rectangular, with rearwardly extending sides 28 which, when the baseplate is assembled, seat inside the sides 24 of the rear panel 21, determining the spacing between the panels and providing a sufficiently close seal to protect the breathing bag 20 from environmental hazards. The front panel 22 is made of the same material as the rear panel 21. The two panels 21 and 22 may be held together by any suitable means, but are preferably readily separable for maintenance of the breathing bag 20. As may be seen from Figures 7 and 8, the front face of the front panel 22 is curved, both in plan and inside elevation, in such a way that all four corners project further forwards than the centre, in order that the backpack shall sit comfortably and securely on the back of the user.

Referring now to Figures 10 and 11,the breathing bag 20 is made from flexible material impervious to air, for example, from a laminated material of butyl rubber sandwiched between two layers of nylon cloth or of polyethylene terephthalate film between two layers of polyethylene. The bag 20 is constructed from elongate top and bottom panels 30, which are slightly shorter than the baseplate 3 is wide and are substantially narrower (about 25 mm wide) in the middle than they are (about 50 mm) near the ends, and a main piece 31 forming a tube with a single vertical seam. All of the seams are preferably backed by a reinforcing strip of bag material bonded to the material on both sides of the seam.Because of its flattish shape, the bag 20, if it is made of material of suitable stiffness, can sweep out a volume of 5 litres between the pressures of 1 mmHg above and below ambient pressure mentioned above, although, as will be appreciated from the dimensions given, its full volume is only 8 or 9 litres.

Referring now to Figure 12, the connector 23 consists of a tube 33 that at one end is externally screw-threaded to carry two clamping nuts 34 and 35, which clamp beween them a portion of the bag 20 that has a reinforcing washer 36 of bag material bonded to it surrounding an aperture for the tube 33, and a lock nut 37. The clamping nut 35 has an annular bead that mates with an annular groove in the clamping nut 34 through the reinforced portion of the bag 20 to give a tighter seal. At the other end the tube 33 has a conventional air-tight connection, here using a captive nut 38 and an O-ring 39, to the breathing gas circuit of the breathing apparatus.

Referring now to Figures 13 and 14, the second form of backpack is similar to the first except in that the oxygen bottle 5, instead of being strapped across the bottom of the baseplate 50 is mounted in a housing 40 on the right hand side. The housing 40 is double walled, with the space between the two walls preferably serving as the manifold on the right hand side of a cooler (not shown) similar to the convection cooler preferred for the first form of backpack. It will be appreciated that the cooler of the second form of backpack is smaller than that of the first form, and if the same performance is to be achieved will normally require some form of forced-draught cooling where the first form relied on naturai convection The baseplate 50 of the second form of backpack consists of a rear panel 51 and a front panel 52, and is generally rectangular, about 45 cm high and 35 cm wide. Referring to Figures 15 to 18, the back panel 51 has a pair of raised sides 53 on either side, the inner faces of which are curved to seat the cylindrical purifier 50 and oxygen cylinder housing 40, and has a ledge 54 across the bottom on which shoulders of the purifier 4 and the housing 40 rest. As with the first form of backpack, any anchorages and attachments required for the equipment of the backpack may be provided on the rear plate 51 is a thinner area 27 stiffened by ribs 27a.

Referring now to Figures 19 to 22, the front plate 52 is curved in both plan and elevation similarly to the front plate 22 of the first form, and has a side wall 58 which, like the side wall 28 of the first form, seats within the rear plate 51 to determine the thickness of the baseplate 50.

Referring now to Figures 23 and 24, the breathing bag 59 of the second form of backpack is generally similar to the bag 20 of the first form, except that it is smaller from top to bottom and from side to side, and may be deeper from front to back to give the same volume as the first form. The bag 59 is constructed similarly to the bag 20, with waisted top and bottom panels 60 and a single body panel 61, with the same reinforced seams and from the same materials. The bag 59 is provided with a connector 23 to connect it to the breathing gas circuit of the apparatus through a hole (not shown) in the back panel 51.

Instead of the tailored breathing bag 20 or 59 described above, there may be used in either form of backpack a breathing bag (not shown) formed from two flat sheets of laminated plastics material welded together near the edges with a moulded plastics connector 23 set into one sheet near a corner. The sheets of material may be simply rectangular, or they may be rectangular with the corners cut off. It will be appreciated that the latter arrangement is better functionally, but the former is cheaper to manufacture, and it may be possible to produce such bags so cheaply that they can be discarded and replaced fairly frequently, eliminating the maintenance necessary to keep a permanent breathing bag airtight. In this case, the material of the bag may be polyester vacuum-metallised wih aluminium on both sides, with a further layer of polyester adhesive-bonded to the inside and a layer of polyethylene with 8% of ethylvinyl acetate adhesive-bonded to the outside.

Claims (16)

1. A backpack for a breathing apparatus, which comprises a baseplate arranged in use to rest with one face against the back of a user and to have parts of the apparatus mounted on the other face, wherein the baseplate is hollow and has disposed within it a receptacle of variable volume to accommodate changes in the volume of gas in the lungs of the user as the user breathes.

2. A backpack as claimed in claim 1, wherein the receptacle comprises a flexible bag that is arranged never to be completely full or empty in normal use.

3. A backpack as claimed in claim 2, wherein the arrangement is such that the bag tends when full to conform generally to the shape of the baseplate and tends when empty to be flat.

4. A backpack as claimed in any one of claims 1 to 3, wherein the exterior of the receptacle is exposed to ambient pressure and the receptacle is arranged to vary in volume through a major portion of its normal range over a narrow range of pressure near to ambient pressure.

5. A backpack as claimed in claim 4, wherein the receptacle is yieldably biased in a sense to reduce its volume and the said narrow range of pressure is entirely above ambient pressure.

6. A backpack as claimed in claim 5 when dependent upon claim 3, wherein the bag is yieldably biased by a spring-loaded plate pressing it flat against the interior of one of the two said faces of the baseplate.

7. A backpack as claimed in any one of claims 4 to 6, wherein the said narrow range of pressure is not more than 2 mmHg and the said major portion of the normal range of volume of the receptacle is at least 5 litres.

8. A backpack as claimed in any one of claims 1 to 7, wherein the baseplate comprises a front panel defining the said one face and a rear panel defining the said other face releasably secured together with the receptacle between them.

9. A backpack as claimed in claim 8, wherein the front panel is a moulded shell with the said one face concave to the exterior and arranged to seat securely on the back of the user.

10. A backpack as claimed in claim 9, wherein the rear panel is a moulded shell and the said other face is formed with a seating for at least one said part of the apparatus.

11. A backpack as claimed in any one of claims 1 to 10, wherein the baseplate is made of plastics material with an electrically conductive filler.

12. A backpack for a breathing apparatus, substantially as hereinbefore decribed with reference to, and as shown in Figures 1 to 12, or Figures 12 to 24, of the accompanying drawings.

13. A breathing apparatus including a backpack as claimed in any one of claims 1 to 12.

14. A baseplate suitable for use as the said baseplate of a backpack as claimed in any one of claims 1 to 12.

15. A bag suitable for use as the said bag of a backpack as claimed in claim 2, or in any of claims 3 to 11 when dependent upon claim 2, or in claim 12.

16. Any new or novel feature herein disclosed.