Lung demand regulator fail-safe

Abstract

There is disclosed a demand regulator for a breathing apparatus comprising: a bypass mechanism configured to trigger a continuous flow of breathing gas into an internal cavity of the demand regulator when a pressure in the internal cavity is below a first threshold. Also disclosed is a breathing apparatus comprising a demand regulator.

Description

[0001] This disclosure relates to lung demand regulators for breathing apparatus and, more specifically to lung demand regulators including fail-safe mechanisms for protecting users.Background

[0002] Breathing apparatus commonly comprises a second-stage regulator, which is also known as a 'lung demand regulator' or 'demand regulator'. The demand regulator is configured to deliver breathing gas to the user via a mask at a suitable pressure for breathing. A demand regulator generally comprises a demand valve which supplies breathing gas to a user via a face mask in response to a user inhaling. Proper functioning of the demand valve is crucial to keep the user out of danger. However, given the extreme conditions in which breathing apparatus are used, it is occasionally possible for a demand valve of a demand regulator to fail. A demand valve can fail in a way that leads to increased danger for a user. For example, a demand valve can fail by partially or entirely ceasing to provide adequate breathing gas to the user.

[0003] It will be appreciated that advances in demand regulators which mitigate these issues would be desirable.Summary

[0004] Aspects of the present invention will now briefly be described.

[0005] In a first aspect there is provided a bypass mechanism for a demand regulator for a breathing apparatus. The bypass mechanism may comprise a sensing element configured to sense when a pressure in an internal cavity of the demand regulator falls below a threshold. In response, the bypass mechanism may trigger a continuous flow of breathing gas into the internal cavity.

[0006] In a second aspect there is provided a demand regulator for a breathing apparatus comprising: a bypass mechanism configured to trigger a continuous flow of breathing gas into an internal cavity of the demand regulator when a pressure in the internal cavity is below a first threshold.

[0007] The bypass mechanism may be configured to trigger the continuous flow of breathing gas into the internal cavity of the demand regulator once and / or after the pressure in the internal cavity is below a first threshold.

[0008] The demand regulator may further comprise a demand valve configured to permit a flow of breathing gas into the internal cavity when a pressure in the internal cavity falls below a second threshold. The second threshold may be greater than the first threshold.

[0009] It will be appreciated that the first and second thresholds are first and second threshold pressures, respectively. A pressure below the first threshold in the internal cavity may result in the bypass mechanism triggering a continuous flow of breathing gas into the internal cavity. A pressure below the second threshold in the internal cavity may cause flexing of a diaphragm in the internal cavity to cause movement of a demand valve.

[0010] The term "bypass mechanism" may be understood to mean a mechanism that avoids or circumvents a main mechanism. In this case, it will be understood that the bypass mechanism circumvents the demand valve such that breathing gas can be supplied to the internal cavity by the bypass mechanism if the demand valve begins to operate incorrectly. For example, in a situation where the demand valve is non-functional or functioning sub-optimally, the bypass valve circumvents demand valve, thus providing breathing gas to the internal cavity irrespective of the operation of the demand valve.

[0011] The bypass mechanism may not be capable of de-activation (i.e. being moved from a triggered position back to an untriggered position) in use by the end user. Therefore, once the bypass mechanism is triggered during use, it will remain triggered until it is reset during maintenance or repair after an emergency incident in which it is used. The bypass mechanism may be incapable of being reset once it is triggered without disassembly of the demand regulator.

[0012] It will be understood that the bypass mechanism triggers the continuous flow of breathing gas (i.e., a bypass flow) in response to the demand valve function incorrectly. The incorrect functioning of the demand valve may manifest as (and thus be detected by the bypass mechanism as) the internal cavity pressure being below a first threshold.

[0013] The demand regulator may further comprise a diaphragm coupled to the demand valve. The diaphragm may have a first side exposed to the pressure in the internal cavity and a second side exposed to an ambient pressure. When the pressure in the internal cavity falls below the second threshold the diaphragm may flex to cause the demand valve to open.

[0014] In this context, the term "coupled" may include a direct abutment of two components and / or a mechanical (or other) linkage arranged therebetween.

[0015] The demand regulator may further comprise a bypass channel configured to fluidically connect a breathing gas supply of the demand regulator and the internal cavity. The continuous flow of breathing gas may be triggered by the bypass mechanism to flow through the bypass channel.

[0016] It will be understood that the bypass channel may be separate to a main channel of the demand regulator. The main channel may supply breathing gas to and / or from the demand valve and on to the internal cavity. The bypass channel may be separated from the main channel such that even if the main channel blocked (whether partially or entirely), the bypass channel can continue to provide breathing gas to the internal cavity.

[0017] The bypass mechanism may comprise a plunger having an untriggered position configured to prevent the continuous flow of breathing gas when the pressure in the internal cavity exceeds the first threshold. The plunger may also have a triggered position configured to permit the continuous flow of breathing gas when the pressure in the internal cavity is less than the first threshold.

[0018] In this context, exceeding the first threshold may include meeting and / or exceeding the first threshold.

[0019] In the untriggered position, the bypass channel may be entirely blocked. In the triggered position, the bypass channel may be at least partially unblocked. A total cross-sectional area of the at least partially unblocked bypass channel may be at least 0.5 mm 2< and may be in the range of 0.5 mm 2< to 0.8 mm 2< . The total cross-sectional area may be at least 0.54 mm 2< . The total cross-sectional area may be up to 0.77 mm 2< . The total cross-sectional area may be in the range of 0.54 mm 2< to 0.77 mm 2< .

[0020] The bypass mechanism may further comprise a pressure responsive element having a first surface exposed to the pressure in the internal cavity and a second surface exposed to the ambient pressure. The pressure responsive element may be configured to move in response to the pressure in the internal cavity being lower than the first threshold.

[0021] The pressure responsive element may be coupled to the plunger such that movement of the pressure responsive element in response to the pressure in the internal cavity being lower than the first threshold causes the plunger to move from the untriggered position to the triggered position.

[0022] The pressure responsive element may comprise a piston having a head with a first surface exposed to the pressure of the internal cavity and a second surface exposed to the ambient pressure. The piston may be configured to move in a first direction in response to the pressure in the internal cavity being lower than the first threshold. Movement of the piston in the first direction may cause the plunger to move from the untriggered position to the triggered position.

[0023] The piston may be prevented from moving in a second direction opposite to the first direction once the plunger has moved from the untriggered position to the triggered position.

[0024] The piston may be prevented from moving in the second direction by a locking mechanism. The locking mechanism may comprise a ratcheting-style mechanism which allows the piston to move relative to the plunger in the first direction, but which prevents return travel of the piston relative to the plunger in the second direction. Specifically, the locking mechanism may comprise a shoulder of the piston which is permitted to travel past a distal portion of the plunger in the first direction, but which abuts the distal portion of the plunger when the piston attempts to move in the second direction, thus preventing movement of the piston in the second direction.

[0025] The pressure responsive element may comprise a sensing diaphragm having a first side exposed to the pressure of the internal cavity and a second side exposed to the ambient pressure. The sensing diaphragm may be configured to flex thereby causing the plunger to move from the untriggered position to the triggered position in response to the pressure in the internal cavity being lower than the first threshold.

[0026] The bypass mechanism may comprise: a burst disk disposed in line with the bypass channel and configured to prevent the continuous flow of breathing gas through the bypass channel. The bypass mechanism may comprise a piercing mechanism configured to pierce the burst disk in response to the pressure in the internal cavity being lower than the first threshold, wherein the piercing of the burst disk permits the continuous flow of breathing gas through the bypass channel.

[0027] The piercing mechanism may comprise a shuttle and a release element. The release element may be configured to prevent movement of the shuttle when the pressure in the internal cavity exceeds the first threshold and permit movement of the shuttle when the pressure in the internal cavity is less than the first threshold. The shuttle may be biased to pierce the burst disk when the shuttle is released by the release element.

[0028] The bypass mechanism may be configured to irreversibly trigger the continuous flow of breathing gas into the internal cavity when the pressure in the internal cavity is below the first threshold.

[0029] Irreversible in this context should be understood to mean irreversible during use by a user of the demand regulator. In other words, the term irreversible should be understood to mean irreversible by a user while the demand regulator is actively being used in responding to an emergency incident. The term irreversible in this context may not preclude a user (e.g., a technician) from 'reversing', 'replacing', or 'resetting' the bypass mechanism outside of an emergency incident such that it is no longer in a triggered state. Reversing the activation of the bypass mechanism may require at least some disassembly of the demand regulator.

[0030] The bypass mechanism may be a modular and / or replaceable component of the demand regulator.

[0031] The first threshold may correspond to a pressure greater than the ambient pressure.

[0032] The second threshold may correspond to a pressure greater than the ambient pressure.

[0033] It will be understood that where both the first and second thresholds correspond to pressures above the ambient pressure, the demand regulator may prevent a pressure in the internal cavity from being less than the ambient pressure.

[0034] The continuous flow of breathing gas triggered by the bypass mechanism may have a flow rate of at least 20 I / m. The flow rate may be at least 30 I / m, or at least 35 l / m, or at least 40 l / m. The flow rate may be in the range of 30 l / m to 40 l / m.

[0035] The first threshold may correspond to a pressure of at least 50 mbar less than the ambient pressure. The first threshold may correspond to a pressure of at least 100 mbar less than the ambient pressure. It will therefore be appreciated that the first threshold may correspond to a negative gauge pressure.

[0036] According to a further aspect, there is provided a breathing apparatus comprising a demand regulator.Brief Description of the Drawings

[0037] Arrangements of the invention will now be described, by way of example, and with reference to the accompanying drawings, in which: Figure 1 shows a schematic view of a breathing apparatus according to an example arrangement comprising a breathing mask and demand regulator; Figure 2 shows a schematic view of a face mask connected to a demand regulator according to the present invention; Figures 3A and 3B show cross-sectional views of a demand regulator according to an embodiment of the present invention; Figures 4A and 4B show cross-sectional views of a demand regulator according to another embodiment of the present invention; Figures 5A and 6B show cross-sectional views of a demand regulator according to another embodiment of the present invention; and Figures 6A-6D show cross-sectional views of a demand regulator according to a further embodiment of the present invention. Detailed Description of the Drawings

[0038] With reference to Figure 1, an example breathing apparatus 10 is shown. The breathing apparatus 10 is a self-contained breathing apparatus (SCBA) and comprises a support frame or backplate 12, straps 14 for securing the SCBA to a user, a breathing gas cylinder 16, a face mask 18, a lung demand regulator 100 connectable to the face mask 18, and a pneumatics system 20 for delivering breathing gas from the cylinder 16 via a hose or flexible conduit 22 to the lung demand regulator 100, to thereby deliver breathing gas to the user wearing the face mask 18 on demand.

[0039] The breathing apparatus 10 may further comprise other components or systems which are not shown, including but not limited to an electrical system, a monitoring system, and / or a communications system. The lung demand regulator 100 may be referred to as the demand regulator 100 or the regulator 100 throughout.

[0040] In this illustrated arrangement, the breathing apparatus 10 is a self-contained breathing apparatus (SCBA), but it should be understood that the lung demand regulator 100 may also have applications in other types of breathing apparatus, such as self-contained underwater breathing apparatus (SCUBA) and emergency escape breathing apparatus.

[0041] Turning to Figure 2, a schematic view of a face mask 18 attached to the regulator 100 is shown. A hose 22 of the pneumatics system 20 is connected to the regulator 100 to provide breathing gas from the cylinder 16 to the regulator 100. The pneumatics system 20 may comprise a first-stage pressure reducer (not shown) which reduces the pressure of the breathing gas from the cylinder 16 which may be stored at several hundred bar (e.g., 400 bar), to an intermediate pressure (e.g., 7 bar) for provision to the regulator 100 via the hose 22. The intermediate pressure may be too high for the breathing gas to be provided directly to the user to breathe. The regulator 100 or the pneumatics system 20 furthers comprise a second-stage pressure reducer (shown in Figures 3A and 3B as the demand valve 110) which further reduces the pressure of the breathing gas to a suitable pressure for delivery to the user to breathe. In other arrangements, more than two or fewer than two pressure reducers may be provided. In some arrangements, the regulator 100 is connected to a pressurised breathing gas circuit such as a ring main for workers to use (e.g., in a factory).

[0042] Figure 3A and Figure 3B show a regulator 100 according to an embodiment of the present invention. The views in these figures are cross-sectional views taken from the plane A-A shown in Figure 2. The regulator 100 includes a body 102 which defines an internal cavity 104. When the regulator 100 is connected to a face mask 18, the internal cavity is in fluid communication with the face mask and thus the user's lungs.

[0043] As shown, the regulator 100 includes a demand valve 110. The role of the demand valve 110 is to provide breathing gas received from the hose 22 into the internal cavity 104 for the user to breathe during an incident having unbreathable or dangerous ambient atmosphere. The demand valve 110 provides breathing gas intermittently from the hose 22 into the internal cavity 104 in response to the user inhaling. The demand valve 110 may deliver breathing gas to the internal cavity via a main channel (not shown).

[0044] Disposed in the body 102 is a diaphragm (not shown) with one side exposed to the pressure in the internal cavity 104 and the other side exposed to the ambient pressure. Inhalation by the user causes a decrease in the pressure in the internal cavity 104 relative to the ambient pressure, which causes the diaphragm to flex inwards into the internal cavity 104. The movement of the diaphragm is transferred to the demand valve 110 via one or more levers (not shown), which in turn causes the demand valve 110 to open, supplying breathing gas into the internal cavity 104. The supply of breathing gas into the internal cavity 104 causes the pressure in the internal cavity 104 to increase, which moves the diaphragm in the opposite direction - in turn closing the demand valve 110.

[0045] While demand valves are generally extremely robust and reliable, it is essential that a regulator can function even if its demand valve fails in some way. This type of system may be referred to as a 'fail-safe' system and is important for ensuring a user of the regulator is supplied with adequate breathing gas even when the demand valve 110 fails.

[0046] Therefore, embodiments of the present invention serve to provide bypass mechanisms capable of bypassing (i.e., circumventing) the demand valve (and the main channel) and supplying breathing gas to the user via an alternate route (a bypass channel) when the demand valve fails. Failure of the demand valve may be complete (e.g., no flow is provided by the demand valve) or partial (e.g., inadequate flow is provided by the demand valve). In either case, the bypass mechanism may circumvent the demand valve to provide adequate breathing gas to the user. There are various ways in which a bypass mechanism can be implemented while providing this functionality. Various embodiments are described below with reference to Figures 3A to 6D. It should be understood that the embodiments described are non-exhaustive and other embodiments are feasible within the principles of the invention.

[0047] Returning to Figure 3A, an embodiment of a bypass mechanism 120 is shown. The bypass mechanism 120 in this case includes two main components. Firstly, the bypass mechanism 120 includes a plunger 121. The plunger 121 is disposed in a bypass channel 106, formed in the body 102 of the regulator 100, which provides a fluid connection between the pneumatics system 20 and the internal cavity 104. In an untriggered state of the bypass mechanism 120, a sealing portion 122 of the plunger 121 seals against a narrowed portion 107 of the bypass channel 106, thus preventing any breathing gas from flowing through the bypass channel 106.

[0048] The bypass mechanism 120 also includes a pressure sensitive element, which in this embodiment is a piston 124. The piston 124 is disposed within a bore 108 of the body 102. The piston 124 includes a piston head 125 which is exposed to the ambient pressure on one side (via an opening 109 in the body 102). The other side of the piston head 125 is exposed to the pressure in the internal cavity 104. The piston 124 also includes a distal portion with a widened end 126. In an untriggered state of the bypass mechanism 120, the plunger 121 abuts the widened end 126, preventing the plunger from moving out of the bypass channel 106 and maintaining a seal between the narrowed portion 107 of the bypass channel 106 and the sealing portion 122 of the plunger 121.

[0049] If the demand valve 110 experiences a failure and inadequate breathing gas is supplied to the internal cavity 104, the inhalation by the user will cause a significant drop in the pressure in the internal cavity 104. If the pressure in the internal cavity 104 drops below a threshold pressure (referred to as the first threshold), the differences in pressures acting on the piston head 125 will cause the piston 124 to move inwards. The first threshold is generally a pressure relative to ambient pressure. For example, the first threshold may be 100 mbar lower than ambient pressure. Therefore, when the pressure in the internal cavity 104 falls at least 100 mbar below ambient pressure, the bypass mechanism 120 will trigger the continuous flow of breathing gas.

[0050] The second threshold will be understood to mean a pressure in the internal cavity 104 that causes the diaphragm to move and open the demand valve 110. The second threshold generally corresponds to a higher pressure than the first threshold, such that the bypass mechanism 120 does not trigger the continuous flow of breathing gas during normal operation of the demand valve 110.

[0051] In some embodiments, the second threshold will a pressure above ambient pressure and the first threshold will be a pressure below ambient pressure. In these embodiments, the bypass mechanism will not trigger a continuous flow of breathing gas unless the pressure in the internal cavity drops below the ambient pressure to the first threshold.

[0052] In some embodiments, both the first and second threshold will be a pressure above ambient pressure, with the second threshold being higher than the first. In these embodiments, as the first threshold is above ambient pressure, a lockout safety mechanism must be used to disarm the bypass mechanism and prevent it from triggering when the regulator is not in use. Otherwise, the pressure in the internal cavity when the regulator is not in use (which would be at ambient pressure) would cause the bypass mechanism to trigger. The lockout safety mechanism may take many different forms. For example, the mechanism may include a linkage that couples the arming of the bypass mechanism to the position of the diaphragm such that the bypass mechanism only becomes armed once the user takes their first breath through the regulator. Other lockout safety mechanism such as electronic mechanisms are also envisioned.

[0053] Figure 3B shows the bypass mechanism 120 after the piston 124 has been moved inwards by the pressure difference. As the piston 124 moves inwards, the plunger 121 is no longer supported by the widened end 126 of the piston 124 and thus falls (and / or is pushed by the pressure of the breathing gas supply) partially out of the bypass channel 106. As a result, the sealing portion 122 of the plunger 121 no longer seals against the narrowed portion 107 of the bypass channel 106 and breathing gas is permitted to flow through the bypass channel 106.

[0054] Notably, the narrowed portion 107 of the bypass channel 106 is sized to limit the flow rate of breathing gas therethrough. For example, in a case where the breathing gas delivered by the pneumatics system 20 is around 7 bar, the narrowed portion 107 of the bypass channel 106 may have a cross-sectional area of 0.54 mm 2< . By sizing the narrowed portion 107 in this way, the flow rate through the bypass channel 106 can be maintained at an approximately continuous rate of around 35 l / m - enough to sustain a user until they are able to evacuate to a safe area and doff their face mask 18. Although a typical user may only consume 10 l / m of air during normal use of the breathing apparatus, the increased flow rate is necessary as the bypass channel 106 provides a continuous flow of breathing gas, rather than only supplying breathing gas in response to the user inhaling. The continuous flow of breathing gas naturally leads to some unused breathing gas being lost, but this is necessary to ensure enough breathing gas is supplied when the user does inhale. As a result, the remaining breathing gas stored in the cylinder 16 may not last as long as it normally would.

[0055] If the regulator 100 malfunctions as described, the user will notice as they may be unable to inhale normally. When the user inhales without the correct functioning of the demand valve 110, the inhaled gas will not be replaced, and so the pressure in the internal cavity 104 will fall below the first threshold during inhalation. This in turn will activate the bypass mechanism 120. Once the bypass mechanism 120 triggers the continuous flow of breathing gas, the user of the regulator 100 will immediately be aware due to the increased pressure they will be able to feel on their face via the face mask 18. On noticing that the bypass mechanism 120 has triggered the continuous flow of breathing gas, the user will understand to urgently evacuate from their current location to a safe place. Owing to the constant flow of breathing gas via the bypass mechanism, the breathing gas supply (i.e., in the SCBA cylinder) will be depleted more rapidly than during normal use.

[0056] The discontinuous difference in thickness from the main body of the piston 124 to the widened end 126, prevents the piston 124 from returning to its untriggered position once triggered, even if the pressure in the internal cavity 104 climbs back above the first threshold. Specifically, the side of the widened end 126 abuts the plunger 121, preventing the piston 124 from returning to its untriggered position. This also prevents the plunger 121 from being pushed back into the bypass channel 106. Indeed, the plunger 121 is kept out of the bypass channel 106 once the bypass mechanism has been triggered by a combination of gravity and pressure from the breathing gas supply acting on the plunger 121. In some embodiments, the plunger 121 may also be kept out of the bypass channel 106 once the bypass mechanism 120 has been triggered by a biasing element which urges the plunger 121 out of the bypass channel 106.

[0057] In some embodiments, the piston 124 may be biased (e.g., by a spring) to move outwards. In such embodiments, the decrease in pressure in the internal cavity 104 relative to the ambient pressure must be greater (e.g., at least 120 mbar) to overcome the biasing and thus move the piston 124. By selecting the biasing of the piston 124, the first threshold pressure can be accurately controlled.

[0058] Turning to Figure 4A, another embodiment of a regulator 200 according to the present invention is shown. In this embodiment, the bypass mechanism 220 includes a single component which combines the functionality of the plunger 121 and the piston 124 of the previous embodiment. The plunger 221 includes a piston head 225 which is exposed to the ambient pressure on a first side (via an opening 209 in the body 202) and exposed to the pressure in the internal cavity 204 on a second side. In this case, the piston head 225 acts as the pressure sensitive element. Once the pressure in the internal cavity 204 falls below the first threshold, the ambient pressure pushes on the piston head 225, causing the plunger 221 to move downwards. The downward movement of the plunger 221 breaks the seal between the sealing portion 222 of the plunger 221 and the narrowed portion 207 of the bypass channel 206, allowing breathing gas to flow therethrough and into the internal cavity 204. In the embodiment shown, the plunger 221 has one or more features on its external surface which function as detents 223. Once the plunger 221 has moved from the untriggered position to the triggered position, the detents 223 prevent the plunger 221 to moving back to the untriggered position.

[0059] Figure 4B shows the bypass mechanism 220 in the triggered position. The detents 223 hold the plunger 221 in its triggered position so that the bypass channel 206 remains open. The force required to overcome the holding force of the detents 223 is greater that the corresponding pressure a user can exert by breathing, so the plunger 221 cannot accidently be moved back into the bypass channel 206.

[0060] In some embodiments, a biasing element (e.g., a spring) may be disposed in the bore 208 beneath the piston head 225 to bias the plunger 221 away from the triggered position. The strength of the biasing element can be selected to vary the first threshold, at which the bypass mechanism 220 triggers.

[0061] More generally, embodiments according to the present invention may include detents or other mechanisms which may collectively be referred to as locking mechanisms. Such locking mechanisms may prevent the biasing mechanism from being reset (e.g., preventing the plunger from returning to its untriggered position). The locking mechanisms may be resettable by a technician while the regulator is not actively being used to prevent a user from accidentally resetting the bypass mechanism. Other types of mechanism locking mechanisms may include friction-type or ratcheting-type mechanisms which physically hold one or more of components of the bypass mechanism in their respective triggered positions once the bypass mechanism has triggered the continuous flow of breathing gas. Electronic-type mechanisms which detect the state of the bypass mechanism and lock it in place are also envisioned.

[0062] Figure 5A and Figure 5B show another embodiment of a regulator 300 according to the present invention with a different bypass mechanism 320. In this embodiment, the bypass mechanism 320 includes a plunger 321 and a pressure sensing element in the form of a sensing diaphragm 327. The sensing diaphragm 327 has a first side which is exposed to the ambient pressure (via an opening 309 in the body 302) and a second side which is exposed to the pressure in the internal cavity 304. In the untriggered state, the plunger 321 rests on the sensing diaphragm 327. The sensing diaphragm 327 holds the plunger 321 in the bypass channel 306, maintaining a seal between the narrowed portion 307 of the bypass channel 306 and the sealing portion 322 of the plunger 321. Once the pressure in the internal cavity 304 falls below the first threshold, the ambient pressure pushes on the sensing diaphragm 327, causing it to deform (Figure 5B). The deformation of the sensing diaphragm 327 permits the plunger 321 to move down out of the bypass channel 306, breaking the seal between the narrowed portion 307 of the bypass channel 306 and the sealing portion 322 of the plunger 321.

[0063] As with the previous embodiment, the plunger 321 may include one or more detent features 323 which engage the bypass channel 306 once the plunger 321 is in its triggered position, preventing the plunger 321 from returning to the untriggered position.

[0064] Turning to Figures 6A-6D a further embodiment of a demand regulator 400 according to the present invention is shown. In this embodiment, the pressure sensitive element is a pressure pin 430. The pressure pin 430 is retained in a pin tube 403 of the body 402 by a flanged portion 432 of the pressure pin 430 and a compression spring 434. A distal end 436 of the pressure pin 430 extends up the pin tube 403 and at least partially blocks an opening to a cross tube 405.

[0065] Within the cross tube 405 is a release element 440. The release element 440 is prevented from moving by the distal end 436 of the pressure pin 430. In this position, the release element 440 holds a piercing shuttle 450 within a shuttle tube 452, against the biasing of a further compression spring 454. At an opposite end of the shuttle tube 452 to the piercing shuttle 450 is a burst disk or membrane 456.

[0066] In the untriggered state ( Figure 6A), the membrane 456 is intact and prevents breathing gas from flowing through the bypass channel 406 from the breathing gas source to the internal cavity 404 (via the shuttle tube 452 and pin tube 403).

[0067] Turning to Figure 6B, once the pressure in the internal cavity 404 falls below the first threshold, the pressure pin 430 is pulled down by the pressure differential, against the biasing of the compression spring 434. Once the pressure pin 430 has moved downwards by a sufficient distance, its distal end 436 no longer blocks the opening to the cross tube 405. As a result, the release element 440 is pulled (by the pressure differential) at least partially into the pin tube 403, meaning movement of the piercing shuttle 450 is no longer restricted. The spring 454 (now unrestricted) is allowed to expand and in doing so accelerates the piercing shuttle 450 along the shuttle tube 452, towards the membrane 456.

[0068] Figure 6C shows the bypass mechanism 420 in a triggered state, where the piercing shuttle 450 has pierced through the membrane 456, rupturing it. Once ruptured, breathing gas is permitted to flow from the breathing gas source, through the membrane 456 and into the internal cavity (via the shuttle tube 452 and the pin tube 403). It will be appreciated that the piercing shuttle 450 may comprise a sharpened tip to aid in piercing through the membrane 456.

[0069] Figure 6D shows the bypass mechanism 420 in the triggered state and the piercing shuttle 450 at rest. It will be appreciated that once the release element 440 has translated across over the distal end 436 of the pressure pin 430, the pressure pin 430 can no longer return to its untriggered position as it is blocked from moving by the release element 440. The continuous flow of breathing gas through the bypass channel 406 ensures that the release element 440 does not return to its original position.

[0070] As described above, the burst disk may be a membrane 456. The membrane 456 may be formed of, for example, a polymer material. Other forms of burst disk such as those made from metal or paper-based materials are also applicable to the present invention. The burst disk (e.g., membrane 456) may take the form of a flexible or rigid sheet. To secure the burst disk (e.g., membrane 456) within the body 402, the burst disk may be sandwiched between two sections of the body 402 (or the body 402 and a connector of the hose 22) which are then tightened down.

[0071] All of the embodiments of the present invention provide improvements to the reliability and safety of lung demand regulators. These improvements in reliability and safety result in users being better protected from danger, even in situations where their lung demand regulator experiences a failure.

[0072] It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more exemplary examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

1. A demand regulator for a breathing apparatus comprising: a bypass mechanism configured to trigger a continuous flow of breathing gas into an internal cavity of the demand regulator when a pressure in the internal cavity is below a first threshold.

2. The demand regulator of claim 1, further comprising a demand valve configured to permit a flow of breathing gas into the internal cavity when a pressure in the internal cavity falls below a second threshold, the second threshold being greater than the first threshold.

3. The demand regulator of claim 2, further comprising a diaphragm coupled to the demand valve, the diaphragm having a first side exposed to the pressure in the internal cavity and a second side exposed to an ambient pressure, wherein when the pressure in the internal cavity falls below the second threshold the diaphragm flexes to cause the demand valve to open.

4. The demand regulator of any of the preceding claims, further comprising a bypass channel configured to fluidically connect a breathing gas supply of the demand regulator and the internal cavity, wherein the continuous flow of breathing gas is triggered by the bypass mechanism to flow through the bypass channel.

5. The demand regulator of any of the preceding claims, wherein the bypass mechanism comprises a plunger having: an untriggered position configured to prevent the continuous flow of breathing gas when the pressure in the internal cavity exceeds the first threshold; and a triggered position configured to permit the continuous flow of breathing gas when the pressure in the internal cavity is less than the first threshold.

6. The demand regulator of claim 5, wherein: the bypass mechanism further comprises a pressure responsive element having a first surface exposed to the pressure in the internal cavity and a second surface exposed to the ambient pressure, the pressure responsive element being configured to move in response to the pressure in the internal cavity being lower than the first threshold, and wherein the pressure responsive element is coupled to the plunger such that movement of the pressure responsive element in response to the pressure in the internal cavity being lower than the first threshold causes the plunger to move from the untriggered position to the triggered position.

7. The demand regulator of claim 6, wherein the pressure responsive element comprises a piston having a head with a first surface exposed to the pressure of the internal cavity and a second surface exposed to the ambient pressure, the piston being configured to move in a first direction in response to the pressure in the internal cavity being lower than the first threshold, wherein movement of the piston in the first direction causes the plunger to move from the untriggered position to the triggered position.

8. The demand regulator of claim 7, wherein the piston is prevented from moving in a second direction opposite to the first direction once the plunger has moved from the untriggered position to the triggered position.

9. The demand regulator of claim 6, wherein the pressure responsive element comprises a sensing diaphragm having a first side exposed to the pressure of the internal cavity and a second side exposed to the ambient pressure, the sensing diaphragm being configured to flex thereby causing the plunger to move from the untriggered position to the triggered position in response to the pressure in the internal cavity being lower than the first threshold.

10. The demand regulator of claim 4, wherein the bypass mechanism comprises: a burst disk disposed in line with the bypass channel and configured to prevent the continuous flow of breathing gas through the bypass channel; and a piercing mechanism configured to pierce the burst disk in response to the pressure in the internal cavity being lower than the first threshold, wherein the piercing of the burst disk permits the continuous flow of breathing gas through the bypass channel.

11. The demand regulator of claim 10, wherein the piercing mechanism comprises a shuttle and a release element, the release element being configured to prevent movement of the shuttle when the pressure in the internal cavity exceeds the first threshold and permit movement of the shuttle when the pressure in the internal cavity is less than the first threshold, and wherein the shuttle is biased to pierce the burst disk when the shuttle is released by the release element.

12. The demand regulator of any of the preceding claims, wherein the bypass mechanism is configured to irreversibly trigger the continuous flow of breathing gas into the internal cavity when the pressure in the internal cavity is below the first threshold.

13. The demand regulator of any of the preceding claims, wherein the first threshold corresponds to a pressure greater than the ambient pressure.

14. The demand regulator of any of the preceding claims, wherein the continuous flow of breathing gas triggered by the bypass mechanism has a flow rate of at least 20 l / m, and optionally wherein the first threshold corresponds to a pressure of at least 50 mbar less than the ambient pressure.

15. A breathing apparatus comprising a demand regulator according to any of the preceding claims.

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