GB2298141A - Counterlung breathing apparatus - Google Patents

Abstract

The apparatus, which forms life-support equipment for a diver, has a primary breathing system for normal use and an independently operable, secondary breathing system for emergency use, only one of the systems being usable at any one time. The primary system has at least one counterlung 23,(24) and so does the secondary system 32,(33), the primary and secondary system counterlungs being arranged so as to be able to occupy essentially the same space when respectively in use and inflated. Thus, the hydrodynamic stability of the combined systems is maintained resulting in a neutral effect on overall buoyancy whichever system is in use. The counterlungs may be positioned at the front and at chest level of the diver.

Description

Counterlung Breathing Apparatus 1 Field of the Invention and Background to the Invention The present invention relates to a counterlung breathing apparatus in the form of Life-Support Equipment (LSE) for a diver. The Life-Support Equipment has both a primary breathing system for normal use and an independently operable secondary life support breathing system for emergency use as an alternative to the primary system.

The primary system is preferably a closed circuit breathing apparatus and the secondary system is preferably a semi-closed circuit breathing apparatus. At any one time either the primary breathing system or alternatively the secondary breathing system is used by a diver for breathing. Breathig using both primary and secondary systems simultaneously is not possible and is prevented by use of suitable valve means.

One of the limiting factors to the duration of use of breathing apparatus underwater by a diver is the amount of breathing gas which is capable of being carried.

Potentially dive duration can be extended for a given amount of gas if the gas can be "recycled". It is important to ensure that recycled gas contains an appropriate physiologically acceptable oxygen partial pressure (to2) for breathing and that CO2 is removed by means of a CO2 scrubber and does not build up to a dangerously high partial pressure (pCO2).

The term "breathing circuit" as used herein generally should be understood to refer to an arrangement of hoses, valves, fixed or variable volume gas containers etc.

linked together so that a diver can inhale breathing gas from the breathing circuit and exhale gas into the breathing circuit. Clearly, the diver forms an essential element of the breathing circuit of a breathing apparatus when in use.

Known apparatus for recycling breathing gas is referred to in the art as "rebreather" apparatus. In a closed circuit rebreather essentially all of the gas in the breathing circuit is recycled. In a semi-closed circuit rebreather gas is recycled but is also topped up with additional gas with the result that excess gas supply occurs in the breathing circuit and some gas is expelled from the system. In a semi-closed rebreather topping up of gas and/or dumping of excess gas may be essentially continuous (e.g. by "bleeding" gas in or out of the system) or may be essentially periodic (e.g. by use of pressure sensitive valves and the like).

A diver in the water using an underwater breathing apparatus is subject to external ambient water pressure dependent on the water depth. Ten metres of seawater exerts a pressure of 1 bar. Doubling the ambient pressure halves the volume of any compressible gas filled space (and vice versa).

If a diver goes deeper or shallower in the water during a dive using underwater breathing apparatus the ambient pressure changes. It is important to regulate the breathing gas pressure in the breathing circuit (and hence in the diver's lungs) so that it is essentially in equilibrium with external ambient pressure. An imbalance equivalent to the pressure exerted by only a few centimetres of seawater can be sufficient to cause severe distress to the diver and adversely affect the ability to breathe.

It is known that in rebreathers at least one counterlung may be provided in the breathing circuit. A counterlung is a variable volume void space usually made of flexible gas impermeable material which can act as a reservoir for exhaled gas from the diver's lungs, and which can collapse to reduce its volume when the diver inhales gas, and which has its outer surface exposed to ambient external water pressure so that any gas within the counterlung at any one time is essentially in pressure equilibrium with ambient pressure. The inhalation and exhalation of the diver causes an essentially sinusoidal variation in lung volume with time and this change can be matched by a similar but inverse sinusoidal deflation and inflation of a counterlung.The net effect is flow of gas around the breathing circuit whilst the total volume of gas in the circuit remains essentially unchanged (subject to any topping up or venting necessitated by the divers depth change as mentioned above).

An advantage of using a counterlung in a rebreather is that if the overall net volume of the breathing circuit (including diver's lungs and counterlung) does not materially change over the breathing cycle, then the buoyancy of the breathing apparatus plus the diver in combination should not vary during the breathing cycle.

This is important because it is generally considered a desirable feature of underwater breathing apparatus that it should be possible to achieve a condition of neutral buoyancy and that this neutrality should not be upset by breathing.

Prior art counterlung rebreather apparatus is known having one or more counterlungs mounted at various positions relative to the diver's mouth and lungs - for example counterlungs may be mounted on each shoulder or a counterlung may be mounted in a back-pack or a counterlung may be mounted in a front pack over the diver's chest.

A diver in the water using an underwater breathing apparatus is at severe risk if the primary breathing system fails. This might be due to mechanical malfunction, lack of breathing gas, water flooding or, in the case of a rebreather, failure of the CO2 scrubber.

Immediate return to surface may not be possible or may not be advisable due to risk of Decompression Sickness.

Consequently it may be desirable to provide the diver with Life Support Equipment (LSE) having both a primary breathing system for normal use and an independent secondary breathing system for emergency use as an alternative to the primary system. Sometimes such a secondary system is referred to in the art as a "bail out". A specific example of a device entitled "Diver's Life Support System including a bail-out rebreather" is described in United Kingdom Patent Specification GB 2169209 (the content of which is incorporated herein in its entirety by reference). The characterising feature of that bail-out rebreather is that in the standby mode (i.e.

when not in use, when the diver is using the primary breathing system) it is maintained at a predetermined breathing gas pressure in excess of ambient external water pressure regardless of changes in the ambient pressure.

This has the advantage of keeping positive pressure in the rebreather which precludes leakage of water into the secondary breathing apparatus during standby mode.

Clearly there is no value to the diver in having a bailout system which he finds to be dysfunctional when needed in an emergency due to water leakage into the system.

The design of practical and effective LSE for divers is not a trivial or straightforward matter. Those skilled in the art will appreciate that a design which appears practicable on paper may not function acceptably when in the water in use by a diver. Simply proposing an assembly of hoses, valves, counterlungs etc. in a theoretically functional arrangement may not result in a workable product. Major factors which are difficult or impossible to reliably predict include: i) overall work of breathing when using the equipment in water: the diver is very sensitive to how hard he must breathe to operate a system and any breathing resistance is unwelcome; ii) comfort and ease of use: there is no virtue in having an arrangement which is so cumbersome or complex that a diver cannot use it effectively; iii) reliability of use: very complex and sophisticated systems may appear to be acceptable in controlled test conditions but are inherently problematic in actual application and under real diving conditions; (iv) sensitivity to divers depth and orientation: movements of the diver up or down in the water can cause material buoyancy changes and movements of the diver from one orientation to another (such as from prone to upright which changes the relative hydrodynamic position of equipment relative to the diver's mouth and lungs) can cause a major problem with the ease of breathing.

For these reasons the design of breathing apparatus still involves an empirIcal element and it is surprising that sometimes a minor modification can have a disproportionately beneficial effect on performances and acceptability of a complete LSE.

An existing counterlung breathing apparatus in use by the US Navy is known as the US Navy MK16, produced by Carlton Technology, Florida. This equipment has only a primary rebreather system. The primary system is a closed circuit rebreather. The primary equipment is carried by the diver and is principally arranged on a back-pack with shoulder harness. The primary breathing circuit includes a counterlung mounted in the middle of the diver's back between the shoulderblades. The primary scrubber is above the counterlung (i.e. further up the diver 5 back).

The USN MK16 counterlung is not of flexible bag type but rather comprises a chamber sealed by a large diaphragm of flexible material carrying a rigid plate which can move in and out (with respect to the diver's back) with the diver's breathing to cause variation in the volume of a chamber. Breathing hoses are connected to the chamber, which also contains a scrubber for CO2 removal. Oxygen content (to2) of the breathing gas in the chamber is monitored and, if required, topped up from an oxygen cylinder carried in the backpack.

Another counterlung breathing apparatus is the SIVA 55 made by Fullerton Sherwood Engineering Ltd. This uses a primary breathing apparatus mounted and carried in a backpack with primary counterlungs mounted at shoulder level at the diver's front. It is believed that an experimental version of this equipment may have also included a semi-closed circuit bail out secondary rebreather apparatus having a top up cylinder and counterlung; the bail out system including counterlung being slung beneath the front of the primary system harness and being carried at the front of the diver at about lower chest or waist level.

The present inventor has now found that LSE of known type can be surprisingly and significantly improved to provide counterlung breathing apparatus according to the invention, the improvement being characterised in that the primary system has at least one counterlung and the secondary system has at least one counterlung and the primary and secondary system counterlungs are arranged so as to be able to occupy respectively essentially the same space relative to the diver's mouth and lungs with the effect that the space occupied by a primary system counterlung when in use and inflated is essentially the same space as is occupied by a secondary system counterlung when in use and inflated.This has the advantage of maintaining the hydrodynamic stability of the combined systems and results in a neutral effect on the overall buoyancy irrespective of whether the primary system or alternatively the secondary system is in operation.

Furthermore, arranging for the secondary counterlung(s) to essentially replace the primary counterlung(s) both in function and in overall location in an emergency use of LSE allows for optimisation of positioning and hence dynamic performance of both primary and secondary counterlungs. With previous arrangements at least one counterlung would necessarily be in a compromise position relative to the diver's mouth and lungs with resultant detriment to performance.

Thus in the present invention it is possible to mount both primary and secondary counterlungs at the front of the diver over his lungs/chest area.

Those skilled in the art will appreciate that various possibilities could exist for means to result in the arrangement of counterlungs defined above and embodying the overall principle of the invention. The result to be achieved is to have both primary and secondary counterlungs mounted on the LSE in such manner that they are closely adjacent and to arrange that the primary counterlung can inflate and deflate in use during normal breathing whilst the secondary counterlung is restrained in a deflated not-in-use state; and to arrange that the primary counterlung is deflated whilst the secondary counterlung can inflate and deflate in use during emergency breathing.

It is yet a further advantage of the present invention that the secondary breathing apparatus may be maintained at a predetermined pressure in excess of ambient external water pressure when it is in the standby mode. Since the secondary counterlung is restrained in a deflated state when not in use the overpressure in the secondary apparatus does not cause inflation of the secondary counterlung until such time as the restraint is deliberately released in emergency on actuation of the secondary system. Thus, when not in use, the secondary counterlung has no significant adverse effect on overall buoyancy of the LSE.

Those skilled in the art will readily appreciate that the invention is applicable to breathing apparatus in general having at least one primary and at least one secondary counterlung. The invention will now be further described with reference to the example of a preferred embodiment known as "SDS 80" and the following description and drawings in which: : Figure 1 is a schematic representation showing important features of the LSE of the invention; Figure 2 is a schematic representation showing additional detail of features of the LSE of the invention; Figure 3 is a schematic front view of the LSE of the invention showing the exhale primary counterlung (inhale counterlung not shown) and showing the right side secondary counterlung in its stowed position (left side secondary counterlung not shown);; Figure 4 is a schematic cross section of the LSE of the invention from the left side showing the stowed secondary counterlung in its position over the in-use primary counterlung - it can clearly be seen that when the secondary counterlung is released from restraint and is in use in the secondary breathing circuit it will occupy essentially the same space relative to the diver's mouth and lungs as was previously occupied by the primary counterlung in use; and Figure 5 is a representation of how the complete LSE might look (partly cut away to show the stowed secondary counterlungs in protective pouches mounted on the bags within which are contained the primary counterlungs).

2 General Description 2.1 Introduction This Section gives a General Description of the SDS 80.

Reference is made by item number. A description of numbered items can be found in Table 1. A list of abbreviations can be found in Table 2. Table 3 shows a legend for some symbols used in the schematic figures.

2.2 General Description The SDS 80 is completely self contained comprising a closed circuit Primary LSE and fully redundant semi-closed circuit Secondary LSE.

The SDS 80 comprises a integrated Backpack, Dual Mode Mask and Buoyancy Compensator which include the following major sub systems: Backpack - Aluminium undertray with sheet metal cover - Primary CO2 scrubber - Diluent gas cylinder and controls - Oxygen cylinder and controls - Oxygen addition valve - Oxygen sensor housing - Electronics Module - Primary Battery - Buoyancy Compensator - Display Module Frontpack - Aluminium Breastplate - Secondary CO2 scrubber - Primary counterlungs - Secondary counterlungs - Secondary gas cylinder and controls - Gas injection and bypass blocks - Dual Mode Mask - Secondary system actuation controls The Primary LSE is fully automatic and will maintain the partial pressure of oxygen at a preset level of 1.5 bar (when deeper than 6 msw) regardless of depth or work rate.

This is achieved by three oxygen sensors [20] located in the Primary Scrubber Outlet Plenum [21] which detect the oxygen content of the gas returned to the diver and instruct an Oxygen Addition Valve [15] to admit sufficient oxygen to maintain the desired level. This real time system is very economic as it only injects the required amount of oxygen into the Scrubber Inlet Plenum to match that consumed by the diver; this is unlike semi-closed sets which have to admit a quantity of gas for an assumed work rate. Provided the diver does not ascend, no bubbles should normally be lost when the Primary LSE is used. A diluent supply is provided in order to add gas during descent.

The diluent can be either Air or 10/90 Heliox. Air could be used in a depth range from the surface to 54 msw and helium could be used from the surface to 80 msw.

The control system is of proven hardware electronics only.

An independent microprocessor audits the hardware functions and can provide warning to the diver if it disagrees with the hardware actions, but it cannot take control. The microprocessor also enables data storage, comprehensive graphic Display Module and future stretch potential including an integrated decompression algorithm.

Particular emphasis has been placed on achieving the optimum hydrostatic relationship between the diver's lungs and the SDS 80 counterlungs. This area is a major shortcoming of most existing closed circuit systems. The placement of the counterlungs and the design of the gas addition and relief valves is crucial in this regard. The diluent is automatically added by a Diluent Demand Valve [Attitude Sensitive] [16]. This valve maintains the collapse plane of the Primary Counterlung [23] [24] closer to the lung centroid plane. A manually controlled Diluent Bypass Valve (65) is also provided. This is located in a pendant housing with the Display Module (12). An adjustable Primary Counterlung Variable Exhaust Valve [22] also enables optimisation of the counterlung pressure by the diver.

The SDS 80 is provided with a Dual Mode Mask [31]. It incorporates a Mask Changeover Valve [29], Status LED [35], Secondary Exhaust Valve [36] and Mask Water Dump Valve [5B]. The mask retains the original oral nasal but is provided with a bite mouthpiece.

The Mask Changeover Valve [29] enables the diver to select either "Primary", "Secondary" or "SHUT" positions.

Tactile indication of the valve position is provided.

The Primary LSE is provided with a Status LED [35] in the diverts mask and Display Module [12]. These facilities monitor the performance of the primary system and provide the diver with information on the status cf the system.

The Status LED should be continuously GREEN when the primary system is switched on and all functions are normal. If an alarm condition is reached the LED blinks GREEN. The diver can view the LCD display on the Display Module and determine the source of the alarm and assess whether it is an abort situation or requires the use of the Secondary LSE. If an immediate abort condition occurs the LED blinks RED. The display provides the following information.

- Oxygen cylinder pressure - Diluent cylinder pressure - Current average oxygen partial pressure - Time of dive [from when pressure exceeded 3 msw for greater than 12 seconds] in elapsed minutes - Current depth/Maximum depth alternating - Status Message to advise the diver of any alarm conditions.

The display is provided with a back light operated by the diver and incorporates the on/off switch for the primary electronics.

The Primary LSE is provided with an XBS QC [4?] which enables the diver to optionally connect an external supply for the injection of oxygen make up gas. Routinely decompressions would be completed using the Primary LSE, thus benefiting from the constant oxygen partial pressure.

If the supply of oxygen is depleted then the diver can connect to the XBS during decompression in which case the Primary System operates in a semi-closed mode.

For Heliox dives we propose that the XBS comprises one cylinder (2320 litres) of 50% Heliox and one cylinder of pure oxygen. The 50% Heliox mix would be used for all stops until 9 msw when the diver would switch to pure oxygen.

For nitrox dives the mix would depend on the maximum planned decompression depth. The XBS is to be provided with a first stage reducer set to 18 bar.

The Secondary LSE is virtually independent from the Primary LSE and, therefore, provides a very high level of redundancy.

The Secondary LSE is all located in the Frontpack and is of semi-closed type. When not in use the secondary system is maintained at a positive pressure of 140 mbar relative to ambient from the Diluent Cylinder [1]. A Relief Valve [34] limits the maximum pressure to 170 mbar during ascent. The positive pressure is to ensure that there can be no water ingress whilst in primary mode.

To invoke the Secondary LSE, the diver must first pull a Rip Cord [48] which releases two Secondary Counterlungs [32] [33] from their stowed positions in protective pouches on the front of the Primary Counterlung Bag. This action also moves a shuttle valve in the Secondary Sonic Injection Block [40] to bring on the oxygen make up supply and isolate the positive pressure supply.

The second action is to push in the Mask Changeover Valve [29] on the front of the Dual Mode Mask [31]. Actioning the Changeover Valve simultaneously opens the secondary LSE and opens the Secondary Exhaust Valve [36]. The use of the Changeover Valve is reversible so that the diver may resume use of the Primary LSE.

The diver inflates the Secondary Counterlungs either from his own lungs or by opening the Secondary Injection Bypass Valve [42] manually to admit a charge of secondary gas.

Alternatively the overpressure in the secondary system may, at least partially, inflate the secondary counterlungs when they are released from their restrained condition. Generally it is preferred that the counterlungs are mounted external to other equipment so that they are exposed to the external water. However, an alternative is possible in which the frontpack is covered with a rigid protective carapace behind which is provided a void space of sufficient size to allow inflation of either primary counterlungs or secondary counterlungs, but not both sets together. This use of a carapace physically constrains the operation of the complete LSE to ensure that when in use the same space is used either for primary counterlung use or for secondary counterlung.A possible disadvantage of use of a carapace may be the added bulk and/or added rigidity of the apparatus which may be unduly restrictive to the diver's mobility under certain circumstances. An apparatus having the optional carapace [67] is illustrated in Figure 4 and shown in partial cutaway section in Figure 5.

The Secondary LSE provides differing durations of rebreathing capability depending on the gas used in the Secondary Cylinder. The duration is independent of depth and respiratory rate. The duration may for example be between 5 and 15 minutes.

The Secondary LSE is of all mechanical semi-closed design.

A single Secondary Breathing Hose [30] connects the bite tube to the radial Secondary Scrubber [37] located on the diver's chest. A contents gauge [49] is provided for the Secondary gas cylinder, retained in a pocket on the diver's right upper chest.

In the case of using air or the 25% Heliox mix, in the unlikely event that the diver must abort directly to the surface without stopping to connect to the XBS, then it would be necessary to enrich the oxygen make up gas when shallower than 6 msw, for high work rates. The Secondary Injection Bypass Valve [42] is used for the purpose.

A Secondary XBS QC [50] is provided on a whip stowed within the diver's right side Secondary Counterlung pouch.

This can be accessed by either the diver himself or an attendant diver after pulling the rip cord and removing the protective cap.

The XBS gas requirements are identical to those for the Primary LSE described above.

The Backpack incorporates a Buoyancy Compensator [53] giving 13.5kg of lift. This can be inflated by its own Fill Cylinder [56] or the Diluent Cylinder [1] using a valve on the Buoyancy Inflator [55]. Venting is achieved through the Buoyancy Mouth Inflator/Vent [55] on the diver's right side. The Fill Cylinder can either be a 0.35 lt cylinder for use to 54 msw or a 0.78 lt cylinder for use to 80 msw. Both cylinders would be charged to 250 bar with air. A Relief Valve [54] is on the diver's left side. Weight pockets are also provided to assist in trimming the diver with differing payloads. Two detachable weight pockets holding up to 5 kg each, are built into the BC.

The Backpack and Frontpack are normally connected together and donned/doffed as one unit. The harness system comprises a front and rear cummerbund with adjustable shoulder and leg straps. The SDS 80 is donned by lifting over the head tabard style with side closing.

3 Detailed Description 3.1 Introduction This section provides a more detailed description of important items of the SDS 80 to assist in understanding its function. Reference should particularly be made to schematic Figures 1, 2, 3 and 4.

3.2 Primary Counterlungs [23] [24] The Counterlungs are located in a protective bag on the diver's upper chest/shoulders. Separate inhale and exhale counterlungs are used to smooth the gas flow through the Scrubber Canister [19] and thereby improve scrubbing efficiency by reducing the peak velocities associated with sinusoidal breathing patterns. The counterlungs are siamesed to hold them in a close relationship.

The counterlungs are constructed from ultrasonically welded polyurethane impregnated nylon and are assembled around an internal plastic manifold which acts as a plenum for the hose connections. This design imposes significantly less work of breathing than conventional rubber counterlungs and occupies less space as it more readily collapses and can be intricately shaped. The counterlung protection bag is located on the shoulder straps of the harness. Each counterlung is fitted with an anti-collapse device to prevent squeeze.

The Inhale Counterlung (divers right side) incorporates a water dump non-return valve which opens automatically at a pressure of 33 mbar.

The Exhale Counterlung incorporates the Primary Counterlung Variable Exhaust Valve.

3.3 Primary Counterlung Variable Exhaust Valve [22] The Exhale Counterlung incorporates the Variable Exhaust Valve [22]. This is mounted on the diver's left upper chest and can be varied through a range of 8 to 70 mbar, through a rotary movement of 1800. This enables the diver to optimally set the exhaust relief pressure of the Primary LSE. This can be used to adjust for optimum hydrostatic characteristics by varying the degree of fill of the oversized counterlung. In the highest setting it enables the diver to achieve overpressure to dispel water from the Inhale Counterlung. It also assures the diver that no gas loss can occur without "feeling" considerable back pressure. This would be used at a constant depth when not wanting to create exhaust relief bubbles. Each counterlung can hold 3.25 litres when completely filled.

3.4(a) Breathing Hoses [25], [26], [27], [28], [30] All breathing hoses are unique mouldings manufactured in rubber. The design approximates to a smooth bore internally with a convoluted outer to give the desired flexibility, thermal insulation and low breathing resistance. Quick release hand connectors are located at each end for ease of removal.

3.4(b) Interconnecting Supply Hoses The Primary LSE includes a number of interconnecting hoses, namely: - Buoyancy Compensator Direct Feed Hose [52] - Primary Diluent Supply Hose [13] - (two) - Oxygen Supply Hose [14]- (two) - Diluent Bypass Supply Hose [61] - Diluent Bypass Hose [62] - Diluent Bypass/EBS Hose [65] All hoses are oxygen compatible, with all polymer construction and Kevlar reinforcing. Hose end fittings and permanently swaged and manufactured from beryllium copper with metal to metal sealing.

3.5 Mask Changeover Valve [29] The changeover valve has three positions, namely, "Primary", "Secondary" and "SHUT". In the SHUT position both primary and secondary breathing circuits are isolated so that the mask can be removed without concern for water entering either LSE. To shut the changeover valve the handwheel is rotated fully counter clockwise as viewed by the diver when the white indicator key is at 6 o'clock.

In this position the valve cannot be inadvertently knocked open and, therefore, should be left in this position at all times unless worn by the diver.

To open the Primary LSE the handwheel is simply rotated clockwise as viewed from the diver through 1800 until the white indicator is at 12 o'clock. To lock the changeover valve in this position the handwheel can be turned back through approximately 100 to 200. When at the 12 o'clock position the valve handwheel can be pushed in towards the diver. This isolates the Primary LSE and opens the Secondary LSE. It also sets the relief pressure of the Secondary Exhaust Valve [36] which is located in the handwheel.

3.6 Dual Mode Mask [31] The Dual Mode Mask is based on the Aga diver's mask and incorporates the Changeover Valve [29] and the Water Dump Valve [58].

The Aga nose clearing device, oral nasal and oral nasal retainer have been used, albeit the nose clearing device spring clip has been modified.

The standard Aga oral nasal mushroom valves are replaced.

An outward relief/water dump mushroom valve with a cracking pressure of 1 mbar is fitted to the divers left side.

An inward relief mushroom valve with a cracking pressure of 20 mbar is fitted to the divers right side.

The faceport has also been modified to accept the Status LED [35] which is held in a receptacle on the diver's right side.

3.7 Oxygen Addition Valve [15] This sealed unit is located between the Electronics Modules [10] and the Oxygen Cylinder [2] and is supplied from the Oxygen Regulator [6]. The outlet from the Oxygen Addition valve is connected to the Scrubber Inlet Plenum [17] The operational principle is based on that of piezoelectric crystal. The crystal deflects when a voltage is applied causing the valve to open. The primary electronics provides the required voltage to open the valve, admitting oxygen to the breathing loop at a rate of approximately 5 standard litres per minute (SLPM). The valve crystal is designed in such a way that it always remains in the closed position until primary electronic power (voltage) is applied.

3.8 Diluent Demand Valve [16] The Diluent Demand Valve has a weight biased diaphragm which makes the characteristics of the valve sensitive to the diver's attitude. It is located at the top of the backpack close to the diver's back. The demand valve responds to a negative pressure in the primary counterlungs relative to the position of the Diluent Demand Valve. The valve is also spring biased. The combined effects of the weight and spring is such that it approximates the position of the demand valve to that part of the counterlung which will remain inflated near the end of inhalation. When upright the weight has no affect, but the spring biases the valve by 10 mbar negative. When prone the weight and spring counteract each other as the collapse plane of the counterlung is close to the plane of the valve diaphragm.When on his back the weight and spring act together to bias the valve approximately 20 mbar positive. The mechanism is well protected within the floodable recess in the backpack. A purge hole is provided in the cap to allow finger access to depress the diaphragm.

A Diluent Bypass Valve is provided for manual control by the diver. It is integrated into the Display Module pendant assembly.

3.9 Scrubber Inlet Plenum [17] The Scrubber Inlet Plenum is a plastic moulding which interfaces between the Exhale Counterlung [23] and the Scrubber Canister [19]. The supply from the Oxygen Addition Valve and the XBS via the Primary XBS QC [47] passes into the Scrubber Inlet Plenum through an inlet venturi. An access plug in the top of the Plenum enables cleaning of the water trap.

3.10 Scrubber Canister [19] The Scrubber Canister is a GRP moulding, fitted with internal baffles and screens, thus creating internal inlet and discharge plenums. '0' ring sealed hand connectors attach the canister to the inlet and outlet plenums. The large '0' ring sealed recharging aperture cover ensures rapid filling. The cover is of quick release design. The scrubber holds 2.6 Kg of diving, grade soda lime. The scrubber canister has a recess to allow for the Diluent Demand Valve [16] and Battery [17].

3.11 Secondary Counterlungs [32] [33] The Secondary Counterlungs are constructed by the same method as the Primary Counterlungs, but each has a volume of 2.5 litres. They are installed onto the Secondary Scrubber Housing by swivelling '0' ring sealed elbows.

The Secondary Counterlungs are retained in light material pouches on the outside of the primary counterlung bag.

The secondary counterlung pouch assembly comprises a series of PTFE bobbins fitted alternatively to each side flap of the pouch. A nylon coated stainless wire Rip Cord [48] is threaded through the alternating bobbins to effectively lace up the pouch into a sausage shape. The upper end of the counterlung is held in ppsition by a plastic buckle. The pouches firmly constrain the Secondary Counterlungs from expanding when positively pressurised whilst not in use. After release, by pulling the Rip Cord handle, the counterlungs expand to release the positive pressure. As both sets of counterlungs can expand on ascent the diver can collapse the primary counterlungs to avoid excessive buoyancy.

3.12 Secondary Exhaust Valve [36] The valve is incorporated into the Mask Changeover Valve [29] handwheel. It has two settings. The higher setting of approximately 50 mbar is active when the Changeover Valve is in the "Primary" and "SHUT" positions.

This setting is achieved by a conical spring pressing on the Secondary Exhaust Valve mushroom.

When the Changeover Valve [29] is moved to the "Secondary" position, the conical spring is automatically moved away from the mushroom which is then only loaded by a lighter compression spring giving a setting of approximately 15 mbar.

3.13 Secondary Scrubber Housing [37] [34] The Secondary Scrubber Housing is a machined plastic housing which is fastened to the aluminium Breastplate of the Frontpack. It has a polycarbonate quick release lid, sealed by a piston '0' ring and holds a rechargeable canister which contains 0.7 kg of Diving Grade soda lime.

The scrubber is of radial pendulum flow design. This ensures a very efficient use of the material and is sized to have a life in excess of 30 min at a C02 production rate of 2 1/mien STPD.

The scrubber housing is connected to the Dual Mode Mask by a single hose through a swivelling banjo union fitted with '0' ring seals.

The Secondary Scrubber Housing has five side ports: two for counterlungs; one for the Secondary Relief Valve [34]; one for connection of the Secondary Sonic Injection Block [40] and one for the Secondary Injection Bypass Block [41] 3.14 Secondary Sonic Injection Block [40] The Secondary Sonic Injection Block is provided with a Heliox or nitrox/air gas mixture, as appropriate, at 250 bar. It can also be supplied from the XBS emergency connection point with gas at a pressure of 18 bar.

A first stage regulator provides an outlet pressure of 19 bar absolute. The discharge is protected by an interstage relief valve set to 22 bar. A spool valve actuated by the Rip Cord [48] serves to isolate the 1st stage regulator and allows a diluent supply to the regulator in the Secondary Injection Bypass Block [41] to flow directly into the Secondary Scrubber Housing [31] at a positive pressure of 140 mbar.

Upon actuation the spool valve isolates the positive pressure supply and allows gas to pass to the sonic jet.

The flow rate of gas into the Secondary Scrubber housing is determined solely by the size of the jet orifice and this can be predetermined depending on expected depth and required secondary duration.

3.15 Secondary Actuation System [48] The Secondary Actuation System comprises three PTFE coated stainless steel cords. The three cords attach to a single Rip Cord handle which is normally stowed on the divers left side on the front of the Breastplate. The Rip Cord is accessible by the diver's left and right hand. Two individual cords pass through the PTFE bobbins which close the Secondary Counterlungs pouches. One cord connects to the spool valve in the Secondary Sonic Injection Block.

Upon initially pulling the handle, the cords retaining the counterlung start to unlace the pouches, and the spool valve is moved to a position which isolates the positive pressure gas supply and opens the gas injection to the Secondary LSE. The design of the Rip Cord is such that it can be pulled completely free from the set to avoid snagging the diver.

After actuating the Rip Cord the second action is to open the changeover valve on the Dual Mode Mask.

TABLE 1

DESCRIPTION No.

1 DILUENT CYLINDER 1.1 LTR x 200 BAR 2 OXYGEN CYLINDER 1.1 LTR x 200 BAR 3 DILUENT CYLINDER SHUT-OFF VALVE 4 OXYGEN CYLINDER SHUT-OFF VALVE 5 DILUENT REGULATOR 6 OXYGEN REGULATOR 7 DILUENT PRESSURE TRANSDUCER 8 OXYGEN PRESSURE TRANSDUCER 9 DEPTH TRANSDUCER 10 ELECTRONICS MODULE 11 PRIMARY BATTERY 12 DISPLAY MODULE 13 DILUENT SUPPLY HOSE 14 OXYGEN SUPPLY HOSE 15 OXYGEN ADDITION PIEZO VALVE 16 DILUENT DEMAND VALVE (ATTITUDE SENSITIVE) 17 SCRUBBER INLET PLENUM 18 WATER TRAP 19 SCRUBBER CANISTER 20 OXYGEN SENSOR HOUSING 21 SCRUBBER OUTLET PLENUM 22 PRIMARY COUNTERLUNG VARIABLE EXHAUST VALVE 23 EXHALE COUNTERLUNG 24 INHALE COUNTERLUNG 25 EXHALE COUNTERLUNG TO SCRUBBER HOSE 26 INHALE COUNTERLUNG TO SCRUBBER HOSE 27 PRIMARY EXHALE HOSE 29 CHANGE-OVER VALVE

ITEM DESCRIPTION No 30 SECONDARY BREATHING HOSE 31 DUAL MODE MASK 32 SECONDARY COUNTERLUNG- RIGHT 33 SECONDARY COUNTERLUNG - LEFT 34 SECONDARY RELIEF VALVE 35 STATUS LED 36 SECONDARY EXHAUST VALVE 37 SECONDARY SCRUBBER HOUSING 38 SECONDARY GAS CYLINDER, 0.78 LTR x 250 BAR 39 SECONDARY GAS CYLINDER SHUT-OFF VALVE 40 SECONDARY SONIC INJECTION BLOCK 41 SECONDARY INJECTION BYPASS BLOCK 42 SECONDARY INJECTION BYPASS VALVE 43 SONIC JET 44 BYPASS JET 45 SECONDARY BYPASS HOSE 46 SECONDARY DILUENT CROSS-OVER HOSE 47 PRIMARY XBS O.C.

48 SECONDARY ACTUATION RIP-CORD 49 SECONDARY GAS CYLINDER CONTENTS GAUGE 50 SECONDARY XBS O.C.

51 SECONDARY DILUENT SUPPLY HOSE 52 BUOYANCY COMPENSATOR DIRECT FEED HOSE 53 BUOYANCY COMPENSATOR 54 BUOYANCY RELIEF VALVE 55 BUOYANCY MOUTH INFLATOR / VENT BUOYANCY FILL CYLINDER. 0.35 LTR x 250 BAR 56 OR 0.78 LTR x 250 BAR 57 BUOYANCY DRAIN PLUG 58 MASK WATER DUMP VALVE 59 PRIMARY EOC JET 60 INHALE COUNTERLUNG WATER DUMP VALVE

ITEM DESCRIPTION No 61 PRIMARY DILUENT BYPASS SUPPLY HOSE 62 DILUENT BYPASS HOSE 63 PRIMARY DILUENT SUPPLY TEE 64 DILUENT BYPASS/PRIMARY XBS TEE 65 OILUENT BYPASS VALVE 65 DILUENT BYPASS / PRIMARY X8S HOSE 67 Carapace TABLE 2 List of Abbreviations Item Abbreviation Buoyancy Compensator BC Cardinal Point Specification CPS Diluent Demand Valve DDV Dual Mode Mask External Breathing Supply XBS Electronic Unit EU Electronic Sub System ESS High Pressure (Above 25 Bar) HP Inside Diameter ID Liquid Crystal Display LCD Light Emitting Diode LED Low Pressure (Below 25 Dar) LP Life Support Equipment: LSE Monitor Microprocess Module 3M Oxygen O2 Outside Diameter OD Partial Pressure of Oxygen PO Pressure Relief Valve PRV Power Mangement Supply Unit PSMU Quick Connect QC Stealth Diving System SO SDSSD Tool and Test Kit TTK TABLE 3 LEGEND

7UM FILTER ABSOLUTE PRESSURE REGULATOR TRACKING PRESSURE REGULATOR TRACKING PRESSURE RELIEF HAND CONTROL SHUT OFF / CONTROL VALVE SELF SEALING QUICK CONNECT FLOW CONTROL ORIFICE PRESSURE INDICATOR HAND CONNECTOR MUSHROOM NON-RETURN VALVE ELECTRICAL/SIGNAL LINE

Claims (6)

1. Claims 1. Improved counterlung breathing apparatus in the form of Life-Support Equipment (LSE) for a diver, having both a primary breathing system for normal use and an independently operable secondary life support breathing system for emergency use as an alternative to the primary system, wherein at any one time either the primary breathing system or alternatively the secondary breathing system is used by a diver for breathing, and wherein breathing using both primary and secondary systems simultaneously is not possible; the improvement being characterised in that the primary system has at least one counterlung and the secondary system has at least one counterlung and the primary and secondary system counterlungs are arranged so as to be able to occupy respectively essentially the same space relative to the divers mouth and lungs with the effect that the space occupied by a primary system counterlung when in use and inflated is essentially the same space as is occupied by a secondary system counterlung when in use and inflated.
2. 2. Apparatus according to claim 1 wherein the primary system is preferably a closed circuit breathing apparatus and the secondary system is preferably a semi-closed circuit breathing apparatus.
3. 3. Apparatus according to claim 1 wherein the counterlungs are positioned and mounted on the LSE so as to be at the front and at the shoulder/chest level of a diver when the LSE is in use by the diver.
4. 4. Apparatus according to claim 1 having a pair each of both primary and secondary counter lungs mounted on the LSE in such manner that each primary counterlung is closely adjacent a secondary counterlung and arranged so that each primary counterlung can inflate and deflate in use during normal breathing whilst each secondary counterlung is restrained in a deflated not-in-use state; and arranged so that each primary counterlung is deflated whilst each secondary counterlung can inflate and deflate in use during emergency breathing.
5. 5. Apparatus according to claim 1 wherein the independent secondary breathing system for emergency use is a bail-out rebreather which in the standby mode (i.e.

   when not in use, when the diver is using the primary breathing system) it is maintained at a predetermined breathing gas pressure in excess of ambient external water pressure regardless of changes in the ambient pressure.
6. 6. Apparatus according to claim 1 including a primary counterlung located in a protective bag of flexible material, the bag being of sufficient size to allow inflation of the primary counterlung within it; secondary counterlung retained in a material pouch attached to the outside of the primary counterlung bag; and wherein the secondary counterlung pouch assembly comprises a series of bobbins fitted alternatively to each side flap of the pouch; and wherein a Rip Cord is threaded through the alternating bobbins to effectively lace up the pouch into a sausage shape to contain and restrain the secondary counterlung from expanding even when positively pressurised whilst not in use; and wherein after release, by pulling the Rip Cord to uniace the bobbins, the secondary counterlung is freed to expand to protrude out of the unlaced pouch whereupon it can inflate and deflate with the diver's breathing.