Steve Debénath, 11 Impasse du Caladon, 06480 La Colle sur Loup, France Tél : (+33) 0620614920 eMail : steve.debenath@cegetel.net

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List of reference numerals

Further features and objectives, effects and advantages of the present invention will be apparent from the detailed description of exemplary embodiments thereof given below with reference to the accompanying drawings wherein

The breathing apparatus schematically represented in Figure 1 comprises a diving bottle 1 containing a pressurized breathing gas, the initial pressure being 200 bars, for example, and the breathing gas including an inert diluent gas (or a mixture of inert gases), such as nitrogen or helium, and a certain percentage of oxygen, e.g. 32% to 60%. The percentage of oxygen supplied to a diver's lungs determines the maximum diving depth because the partial pressure of the oxygen must not exceed 1.6 bars in order to avoid any toxical effect on the diver's central nervous system. If the percentage of oxygen in the breathing gas is 32%, for example, then the partial pressure of oxygen is 0.32 bar at sea level (i.e. on the water surface) and 1.6 bars at a depth of 40 metres. If the percentage of oxygen in the breathing gas is 21% (like in normal air), then the partial pressure of oxygen is 0.21 bar on the water surface and 1.6 bars at a depth of approximately 66 metres. In an open-circuit mode, when the diver inhales the breathing gas provided from a single supply bottle, the percentage of oxygen supplied from the bottle is constant and therefore limits the diving depth. (On the other hand, if the oxygen content in the bottle is chosen low, this will restrict the diving duration.) Conversely, in a closed-circuit mode, the oxygen content in the absorber circuit can be reduced to a desired level during diving because the diver uses up the oxygen in the absorber circuit and the oxygen content of the gas in the absorber circuit may be topped up only to the level suitable for descending further.

The inner volume of diving bottle 1 may be five litres or less, e.g. two litres, which may still allow extended diving periods owing to the possibility of a closed-circuit mode in which the oxygen supply can be used almost completely whereas in the open-circuit mode only part of the inhaled oxygen is absorbed by the diver's lungs while a major rest is discharged into the ambient water. The diving bottle 1 is provided with a standard bottle valve 3 for selectively shutting off or opening an outlet passage of the bottle. A standard first-stage pressure-regulating valve 4 is provided at the bottle outlet to reduce the pressure of the exiting bottle gas, which may be 200 bars, to an intermediate level, which may be 10 bars above ambient pressure. A flexible intermediate-level pressure pipe 6 connects the pressure-regulator 4 to a mouthpiece unit 8 where a second-stage regulation of the gas pressure takes place to reduce the intermediate pressure to a breathable level. The end of pipe 6 connected to the mouthpiece unit 8 may comprise a safe quick-connector plug 7 (self-locked, by the gas pressure, on a mating inlet pipe of the mouthpiece unit) or a cap nut to be screwed onto a threaded inlet pipe of mouthpiece unit 8. For safety reasons, another flexible intermediate-level pressure pipe 5 may by provided to connect the first-stage pressure-regulating valve 4 to another second-stage regulator 2 to be used in emergency situations, e.g. if mouthpiece unit 8 fails or when an accompanying diver needs to be supplied.

The mouthpiece unit 8 is further connected to an absorber circuit comprising an exhalation hose 9, a first breathing bag or counterlung 13, an absorbent container 10, a second breathing bag or counterlung 12, and an inhalation hose 11. As will be explained in greater detail below, each of the circuit hoses 9, 11 includes a checkvalve, or non-return valve, to ensure that the diver can exhale gas only into the exhalation hose 9 and inhale gas only from the inhalation hose 11, in other words the gas in the absorber circuit can circulate only in one direction (counterclockwise in Figure 1, as indicated by little arrows). During that circulation, CO₂ is removed from the exhalation gas by an absorbent, e.g. soda lime crystals, provided in container 10 so that the diver can re-inhale the purified gas from inhalation hose 11 to make maximum use of the oxygen left in the circulating gas. The small amount of oxygen mass resorbed by the diver's lungs is continuously or constantly replenished with oxygen from diving bottle 1 by a gas flow valve to be described below.

The breathing apparatus outlined in Figure 1 is designed to operate selectively in an open circuit mode or a semi-closed circuit mode. In the semi-closed circuit mode, the diver may get additional breathing gas from the diving bottle 1 by making use of a demand valve (described below) that typically forms part of an open circuit; therefore, the breathing apparatus of the present invention may be referred to as, and is an improvement on, a hybrid-circuit apparatus or hybrid breather.

The heart of the breathing apparatus is formed by mouthpiece unit 8 which will be explained in greater detail now referring to Figure 2A. The components of mouthpiece unit 8 are schematically depicted in an enlarged cross-sectional view of the mouthpiece housing, with identical reference numerals being used for components also illustrated in Figure 1. It should be noted that the mouthpiece unit 8 may be used on its own or may be incorporated in a diver's face mask.

By means of the (quick-)connector plug or cap nut 7, the flexible intermediate-pressure pipe 6 is connected to an inlet channel 20 of the mouthpiece housing. The central part of the mouthpiece housing defines a breathing chamber 21. A mouthpiece channel 22 opens from breathing chamber 21 to the outside of the mouthpiece housing and carries a mouthbit for a diver's mouth, an exemplary mouthbit 8a being indicated in Figure 4A. The mouthbit 8a may form an integral part of the mouthpiece channel 22 or may be fitted (screwed or snapped, for example) on the end of mouthpiece channel 22 for separate replacement when the mouthbit 8a is worn out or when two different users of the mouthpiece unit 8 wish to change mouthbits for hygienic reasons.

To admit gas from the inlet channel 20 to the breathing chamber 21, the mouthpiece unit 8 comprises a demand valve formed by a poppet valve 23 arranged in the inlet channel 20, a trigger lever 24 arranged in the mouthpiece housing, and an elastic diaphragm 25 forming a wall portion of the mouthpiece housing. The poppet valve 23 provides a passage for gas from the inlet channel 20 to the breathing chamber 21, said passage being normally blocked by a closing member 23a that is (spring-)biased towards an opening of the poppet passage. One end of the trigger lever 24 is arranged close to the diaphragm 25. When the pressure inside the mouthpiece housing is lower than the outside pressure, due to a diver inhaling (demanding) gas through mouthpiece channel 22, the diaphragm 25 is warped inwards and acts on trigger lever 24 such as to release the closing member 23a from the passage of poppet valve 23 and admit gas into the breathing chamber 21. When the diver stops inhaling, pressure in the breathing chamber 21 builds up to return the diaphragm 25 to its initial state shown in Figure 2A, disengaging the trigger lever 24 so that the spring-loaded closing member 23a again blocks the passage of poppet valve 23 as soon as the internal pressure of the mouthpiece housing is no longer lower than the outside pressure.

An exhaust valve 28 is arranged in communication with the breathing chamber 21, said exhaust valve 28 including an exterior diaphragm 28a biased toward the breathing chamber 21 (i.e. in the direction of a short arrow depicted at the central axis of exhaust valve 28). When the diver exhales gas from his lungs, the pressure inside the breathing chamber 21 exceeds the outside pressure so that the exhaled gas lifts the diaphragm 28a and exits the breathing chamber 21. On the other hand, when the ambient water pressure exceeds the gas pressure in the breathing chamber 21, diaphragm 28a is pushed towards the body of exhaust valve 28 to obstruct the exhaust valve 28 so that no water can enter the breathing chamber 21.

The inlet channel 20, demand valve 23/24/25, breathing chamber 21, and exhaust valve 28 of the mouthpiece unit form an open circuit for scuba diving: The breathing gas is taken in from diving bottle 1 and ejected to the ambient water through exhaust valve 28.

A purge button 26 may be disposed externally of the diaphragm 25, a diaphragm cover 27 supporting the purge button 26 on the mouthpiece housing. When the purge button 26 is depressed by a diver, the diaphragm 25 is moved inwards to actuate trigger lever 24 which in turn will open the poppet valve 23 so that pressurized gas is injected into breathing chamber 21 to purge breathing chamber 21, i.e. to blow out any water that may have seeped into the mouthpiece unit. The water may be expelled through the mouthpiece channel 22 or/and through the exhaust valve 28.

Referring to Figures 2A and 2B, the mouthpiece unit may be converted to a closed-circuit mode in which the diver exhales gas (containing CO₂) into a first, or exhalation, rebreather channel 9a and inhales gas (containing substantially no CO₂) from a second, or inhalation, rebreather channel 11a, the first rebreather channel 9a being connectable to the exhalation hose 9 (Figure 1) and the second rebreather channel 11a being connectable to the inhalation hose 11 (Figure 1) so as to circulate gas from the diver's lungs through the absorbent container 10 and back to the breathing chamber 21. In order to impose one defined direction of circulation, two checkvalves are provided in the circuit; in the exemplary embodiment shown, these checkvalves are provided in the first and second rebreather channels 9a, 11a of the mouthpiece unit 8, in the form of an exhalation checkvalve 9b in the first rebreather channel 9a and in the form of an inhalation checkvalve 11b in the second rebreather channel 11a. The exhalation checkvalve 9b comprises a diaphragm biased toward the breathing chamber 21 (as indicated by an arrow in the central axis of exhalation checkvalve 9b) and does not allow any gas to return from the exhalation rebreather channel 9a into the breathing chamber 21. The inhalation checkvalve 11b comprises a diaphragm biased away from the breathing chamber 21 (as indicated by an arrow in the central axis of inhalation checkvalve 11b) and does not allow any gas to return from the breathing chamber 21 into the inhalation rebreather channel 11a.

To activate the semi-closed circuit mode of mouthpiece unit 8, the rebreather channels 9a, 11a  are made to communicate with the breathing chamber 21 by displacing, or switching, a slidable inner wall portion 32 to a position shown in Figure 2B (i.e. opening a rebreather passage 21h), and locking the wall portion 32 in that position. The displacing and locking functions may be achieved using a push button 30 that is caught and latched by a hook 31 when reaching the displaced position shown in Figure 2B. In addition, to ensure that all of the diver's exhalation gas enters the exhalation rebreather channel 9a in the semi-closed circuit mode, the exhaust valve 28 is prevented from exhausting the diver's exhalation gas. In the embodiment shown, this is achieved by displacing the exhaust valve 28 together with the wall portion 32 such that the diaphragm 28a of exhaust valve 28 is pressed against an abutment 29. The abutment 29 is preferably embodied by a resilient member, such as a spring (e.g. coil spring), so that the diaphragm 28a can still be released from the body of the exhaust valve 28 when the pressure inside the breathing chamber 21 becomes considerably higher than the pressure outside the mouthpiece housing. Under these circumstances, the exhaust valve 28 serves as a safety valve to protect the diver's lungs from excessive pressure in the breathing apparatus.

In the semi-closed circuit mode, carbon dioxide is removed from the exhaled gas so that the gas can be re-inhaled by the diver to make maximum use of its oxygen content. However, the mass of oxygen consumed by the diver's metabolism has to be replenished. This replenishment is best effected continuously or constantly in the circuit (rather than intermittently resorting to the demand valve) in order to provide a smooth and comfortable oxygen supply to the diver. To be able to provide a continuous or constant oxygen flow, the embodiment shown in Figures 2A and 2B comprises a flow valve 33 arranged in the mouthpiece unit 8. The flow valve 33 is interposed between the inlet channel 20 and the breathing chamber 21 and is designed to admit gas to the breathing chamber 21 from the inlet channel 20 at a substantially continuous, preferably constant, flow rate. The flow rate may be adjusted by rotating a knob 33a, for example, that projects from the mouthpiece housing. The knob 33a may also be used to shut the flow valve 33 completely when the mouthpiece unit 8 is to be employed in the open-circuit mode where the diver fully relies on the demand valve. In the closed-circuit mode, the diver may still receive fresh gas from the inlet channel 20 using the demand valve when he feels the need (due to a special physical effort, for example) but it is less strenuous for his organism to receive a continuous basic flow of fresh gas. Such a flow is advantageously provided by a flow valve arranged in the mouthpiece unit 8 (rather than in a backpack, for example) because this design allows a simple, reliable and versatile implementation of the hybrid breathing apparatus.

Instead of providing a dedicated flow valve 33, the demand valve already present in the mouthpiece unit 8 may be utilized and adapted to provide a continuous, preferably constant, gas flow from the inlet channel 20 to the breathing chamber 21. In another conceivable configuration, the flow valve 33 and the demand valve may cooperate to provide a continuous or even constant flow of fresh gas to the diver.

The demand valve may be made to provide an adjustable continuous or constant minimum flow in a number of ways. The trigger lever 24 may be biased to a slightly open state of the poppet valve 23 by pre-setting (e.g. screwing) the purge button 26 deeper into the diaphragm cover 27, as indicated by an arrow 26a in Figure 2A, so that the purge button 26 abuts on the diaphragm 25 even when not being pushed manually. Alternatively or in addition, the diaphragm cover 27 as a whole may be arranged to be displaced (e.g. screwed) toward the diaphragm 25, as indicated by an arrow 27a in Figure 2A, so that the purge button 26 again abuts on the diaphragm 25 even when not being pushed manually. Screwing operations are particularly preferred in doing so because they permit a delicate setting of the flow rate of poppet valve 23 and, thus, allow an economic gas consumption to be achieved.

Figures 3A, 3B, 4A and 4B relate to exemplary arrangements of absorbent containers reflecting the advantageous modular structure of the rebreather circuit. Figure 3A is a schematic cross-sectional view of a series assembly of two absorbent containers 10a, 10b and two counterlungs 13, 12 connected thereto. Each of the containers 10a, 10b may comprise a cylindrical housing for receiving an absorbent material therein. The absorbent material (not shown in the drawings) is preferably filled into the containers in granular form (e.g. in the form of soda lime crystals) to provide a maximum active surface for absorbing CO₂ from the gas circulating in the rebreather circuit. The container 10a comprises a pair of retainer screens 40a to retain the absorbent crystals in the container 10a (when the latter is opened) while allowing gas to flow across the crystals. When container 10a needs to be (re)filled with absorbent material, a lid 41a or 42a may be removed (e.g. unscrewed) from the cylindrical body of container 10a, the associated retainer screen 40a is taken out, absorbent material is filled into the inner space of the cylindrical body, the retainer screen 40a is placed back and held by the lid 41a or 42a that is secured (e.g. screwed) again onto the cylindrical body. Lid 41a preferably comprises a three-way pipe connector 43a for admitting gas to the inner space of container 10a and to a first breathing bag or counterlung 13. The pipe connector 43a may be arranged rotatable around its longitudinal axis. Preferably, the free ends of pipe connector 43a allow for quick connection and disconnection of an exhalation hose 9 and a counterlung hose 13a. Lid 42a comprises an output pipe connector 44a for discharging gas from the container 10a. The output pipe connector 44a may be arranged rotatable around its longitudinal axis. A short interconnecting pipe 45 connects the output pipe 44a of first container 10a to an input pipe connector 44b of second container 10b. With a view to universal usage, the output pipe connector 44a and input pipe connector 44b may be three-way connectors of the same type as the one used for input pipe connector 43a; in that case, a plug 46a may be inserted in the free end of output pipe connector 44a and a plug 46b may be inserted in the free end of input pipe connector 44b to ensure water tightness of the rebreather circuit. Preferably, the interconnecting pipe 45 can be connected to, and disconnected from, each pipe connector 44a, 44b in a simple and rapid manner so that the diver can assemble the containers 10a, 10b easily by himself. Gas flowing from the interconnecting pipe 45 to the input pipe connector 44b enters the second container 10b and passes through a first retainer screen 40b (having the same function as each retainer screen 40a in container 10a) to flow across absorbent material (not shown) present in container 10b to remove CO₂ from the circulating gas. The circulating gas then exits the second container 10b through a second retainer screen 40b and an output pipe connector 43b. The output pipe connector 43b is preferably another three-way connector of even type and may be rotatable around its longitudinal axis. One free end of output pipe connector 43b communicates with the inhalation hose 11, while the other free end of output pipe connector 43b communicates with the counterlung 12.

The counterlungs 13 and 12 serve to buffer breathing gas in the absorber circuit. Counterlung 13 allows the diver to exhale his lung volume of gas easily and completely toward the absorbent container 10a even though the flow resistance to gas across of the densely packed absorbent crystals may be high. Gas that cannot be blown through the container 10a is buffered in counterlung 13, and subsequently, when the diver has stopped exhaling, the ambient pressure acting on counterlung 13 will keep the gas flowing across the absorbent crystals from counterlung 13. A spacer 13b may be provided inside counterlung 13 to prevent the counterlung from collapsing entirely when no gas is left therein.

Counterlung 12 allows the diver to inhale gas easily from the absorber circuit even though the flow resistance to gas across the densely packed absorbent crystals may be high. Cleansed gas emanating substantially continuously from container 10b is buffered in counterlung 12 for easy intake during the subsequent inhalation cycle. A spacer 12b may be provided inside counterlung 12 to prevent the counterlung from collapsing entirely when no gas is left therein.

Where the breathing resistance of the absorber circuit is low enough for the diver, a single counterlung 13 or 12 may be used instead of two as this may be sufficient to buffer the breathing gas in the absorber circuit between subsequent exhalation and inhalation strokes of the diver.

The directions of flow of the circulating gas are indicated by little arrows in Figure 3A. Double-headed arrows in the counterlung hoses 13a, 12a indicate that gas is alternately buffered in and discharged from the counterlungs 13, 12. Mechanically speaking, the containers 10a and 10b shown in Figure 3A are arranged parallel to each other but functionally they form a series arrangement in that the circulating gas first flows through container 10a and then through container 10b.

While the modular containers 10a, 10b are shown in an upright position in Figure 3A, a diver may carry them in an upright, transverse or inclined orientation on his chest, belly or back, according to his personal preferences, technical requirements, and/or envisaged diving circumstances. To facilitate a transverse arrangement of the containers 10a, 10b, the exhalation hose 9 and inhalation hose 11 may be connected to the pipe connectors 43a and 43b perpendicularly to the longitudinal axes of the absorbent containers 10a and 10b, with the counterlungs 13, 12 being connected to the longitudinal ends of the pipe connectors 43a and 43b, respectively (similar to the use of pipe connector 43a shown in Figure 3B).

In an alternative embodiment not shown but apparent to those skilled in the art, the modular containers 10a and 10b may be arranged to operate in parallel, i.e. the circulating gas might enter both containers 10a, 10b in parallel, e.g. through pipe connectors 43a and 43b, and exit from both containers 10a, 10b in parallel, e.g. through pipe connectors 44a and 44b.

The pipe and hose connectors of the containers 10a, 10b are preferably made up of uniform quick connectors so that (i) the components of the absorber circuit can be transported individually, interchanged easily and assembled quickly for diving and (ii) the absorber circuit can be reconfigured and adapted to a diver's current needs. For example, as shown in the schematic cross-sectional view of Figure 3B, a single absorbent container 10a may be inserted in the absorber circuit if the diver is planning on a short diving period only. This configuration represents a basic modular form of the absorber circuit and is particularly compact. The counterlung 13 connected to the input pipe connector 43a of container 10a and the counterlung 12 connected to the output pipe connector 44a of container 10a in Figure 3B may work like in the preceding example according to Figure 3A. However, the flow resistance of a single absorbent container may be low enough for a single counterlung to be sufficient in the rebreather circuit. In that case, either counterlung 13 or counterlung 12 may be omitted, and the open end of input pipe connector 43a or output pipe connector 44a, respectively, may be closed by a plug similar to plug 46a or 46b depicted in Figure 3A.

On the other hand, the modular structure of the absorber components may be utilized to insert more than two absorbent containers 10a, 10b, 10c (not shown) etc in the absorber circuit if the diver desires to extend his absorber capacity and diving period.

Figure 4A is a schematic overview representation of a hybrid-circuit breathing apparatus illustrating three optional aspects of the breathing apparatus:

(i) a single counterlung may be used in the absorber circuit.

(ii) any counterlung may be provided with two ports, i.e. an input port and an output port; and

(iii) the absorbent material may be held in container modules connected to each other coaxially.

It is to be noted that the aforementioned three aspects can be used individually or in any combination with each other in the breathing apparatus.

The alternative design using a single counterlung in the absorber circuit if the gas flow resistance is low enough has been mentioned above in the context of Figure 3B. The exemplary absorber circuit depicted in Figure 4A comprises a single counterlung in the form of counterlung 12 arranged in the inhalation branch 11 of the circuit. While the counterlungs 13, 12 shown in Figures 3A and 3B each comprise a single counterlung hose 13a, 12a for receiving and discharging gas, the counterlung 12 illustrated in Figure 4A comprises an input port 12.1 for receiving and accumulating cleansed gas from absorbent container 10b through a first hose portion 11.1, and a separate output port 12.2 for discharging gas to the mouthpiece unit 8 through a second hose portion 11.2 and an inhalation checkvalve 11b. The first hose portion 11.1 may be shorter than in the illustrated version; in particular, the input port 12.1 of counterlung 12 may be connected directly to the output pipe connector of container 10b, like in Figure 3A or 3B. A spacer (not shown but similar to the spacers 13b, 12b represented in Figures 3A and 3B) may be provided inside counterlung 12 to prevent the counterlung from collapsing entirely when no gas is left therein.

Regarding the absorbent containers 10a, 10b provided in the rebreather circuit according to Figure 4A, these containers are arranged serially and coaxially to each other to form another modular configuration available to the diver when he has to decide on how to carry the absorber circuit on or around his body. In still another embodiment (not shown), the cylindrical containers 10a, 10b may have different diameters to be nested coaxially into one another.

Figure 4B illustrates alternative arrangements of absorbent containers 10a, 10b to be substituted for the absorbent containers 10a, 10b of Figure 4A. Instead of plugging an interconnecting pipe 45 (Figure 4A) between the absorbent containers 10a and 10b, a lid 42a may be screwed from container 10a and an adjacent lid 42b may be screwed from container 10b, and the open cylinders of the containers 10a, 10b may be joined to form a double container 100. By adding on further containers, triple or quadruple containers may be formed.

As shown in Figure 4B, two neighbouring containers 10a, 10b may be joined by screwing the open end of container 10a into or onto the open end of container 10b to form a double container 100. Alternatively, the open ends of the containers 10a and 10b may be screwed into or onto a sleeve ring 50 to form a double container 101. In each case, appropriate mating threads are provided on the outer or inner surfaces of the ends of the container cylinders and on the inner or outer surface of the sleeve ring 50, respectively.

In a preferred implementation of any container arrangement disclosed herein, at least part of the wall of at least one absorbent container is transparent so that colour changes of the absorbent (crystal) material as it becomes contaminated with carbon dioxide can be noted by the diver. In this way, as the diver will know when the absorbent material is going to be used up, he can enjoy a maximum diving period without having to waste absorbent capacity, or he can adapt the filter capacity (before diving) more precisely to a planned diving schedule to minimize the required filter capacity and bulk without jeopardizing safety.

Figures 5A to 5G schematically illustrate the sequence of operations occurring in the mouthpiece unit 8 according to Figure 2A when the mouthpiece unit is used in the open-circuit mode. The reference numerals in Figures 5A to 5G resume those used in Figure 2A.

Figure 5A shows the mouthpiece unit 8 in its initial static state ready for open-circuit operation. The push button 30 has not been pushed, i.e. the wall portion 32 obstructs both the exhalation rebreather channel 9a and the inhalation rebreather channel 11a so that these channels do not communicate with the breathing chamber 21. The breathing chamber 21 communicates with the demand valve formed by poppet valve 23, closing member 23a, trigger lever 24 and diaphragm 25. No gas is being blown into or extracted from the breathing chamber 21, i.e. the pressure inside the breathing chamber 21 substantially equals the pressure outside the breathing chamber 21 so that the diaphragm 25 is flat and does not act on the trigger lever 24. In other words, the closing member 23a is seated on the opening of the poppet valve 23 to prevent any flow of gas from the inlet channel 20 into the breathing chamber 21 through the poppet valve 23.

Figure 5B illustrates a subsequent situation where a diver using the mouthpiece unit 8 inhales gas through the mouthpiece channel 22, the diver's inhalation action being indicated by an arrow 22a. The diver's inhalation results in a low pressure situation in the breathing chamber 21, which causes the diaphragm 25 to buckle toward the trigger lever 24 and to tip the trigger lever 24 such that the closing member 23a is lifted from the opening of poppet valve 23. As a result, there is an inrush of gas from the inlet channel 20 to the breathing chamber 21 via poppet valve 23, as indicated by an arrow 21a in Figure 5C.

When the diver stops inhaling through mouthpiece channel 22, as indicated by a bar 22b in Figure 5D, pressurized gas from the inlet channel 20 keeps flowing into breathing chamber 21 through poppet valve 23, as indicated by arrow 21a. The pressure building up in breathing chamber 21 restores the flat state of diaphragm 25 so that the trigger lever 24 is released and the spring-loaded closing member 23a returns toward the poppet valve 23 to obstruct the opening thereof, see Figure 5E. In this situation, gas is no longer admitted to the breathing chamber 21 from inlet channel 20. The static state of Figure 5A has been reached again, with the pressure inside breathing chamber 21 equalling the pressure outside breathing chamber 21.

When the diver then starts exhaling into breathing chamber 21 through mouthpiece channel 22, as indicated by an arrow 22c in Figure 5F, there is a high pressure situation in the breathing chamber 21, i.e. the pressure inside breathing chamber 21 is higher than the pressure outside breathing chamber 21. The high pressure in breathing chamber 21 propagates toward the exhaust valve 28 in a direction indicated by an arrow 21b in Figures 5F and 5G.

As shown in Figure 5G, the exhalation gas flow 21b lifts the diaphragm 28a from exhaust valve 28 and passes through exhaust valve 28 (arrows 28b) and finally exits the mouthpiece housing (arrows 28c) toward the ambient environment (= water during diving) without returning to any other breathing cycle (= open-circuit mode).

Figures 6A to 6L schematically illustrate a sequence of operations occurring in the mouthpiece unit 8 according to Figure 2A when the mouthpiece unit is used in the semi-closed circuit mode. The reference numerals in Figures 6A to 6L resume those used in Figure 2A.

Figure 6A shows the mouthpiece unit 8 in its initial open-circuit state from which it is going to be switched to a semi-closed circuit mode. The push button 30 is going to be depressed into the mouthpiece housing, as indicated by an arrow 30a, in order to displace the wall portion 32 obstructing the exhalation rebreather channel 9a and inhalation rebreather channel 11a.

Figure 6B shows the situation in which the push button 30 has been pushed into the housing of mouthpiece unit 8 and latched by hook 31. The wall portion 32 has been shifted so as to no longer obstruct the exhalation rebreather channel 9a and inhalation rebreather channel 11a. In other words, these channels now communicate with the breathing chamber 21 through the rebreather passage 21h. At the same time, the exhaust valve 28 has been shifted (to the left in Figure 6B) so that the diaphragm 28a of exhaust valve 28 abuts on the resilient abutment (e.g. coil spring) 29 which renders the exhaust valve 28 insensitive to normal variations of breathing pressure in the breathing chamber 21.

The breathing chamber 21 also communicates with the demand valve formed by poppet valve 23, closing member 23a, trigger lever 24 and diaphragm 25. In the situation depicted in Figure 6B, no gas is being inhaled from or exhaled into the breathing chamber 21. The pressure inside the breathing chamber 21 substantially equals the pressure outside the breathing chamber 21 so that the diaphragm 25 is flat and does not act on the trigger lever 24. In other words, the closing member 23a is seated on the opening of the poppet valve 23 to prevent any flow of gas from the inlet channel 20 into the breathing chamber 21 through the poppet valve 23.

On the other hand, the knob 33a of flow valve 33 may be rotated, as indicated by an arrow 33b in Figures 6B and 6C, to open the flow valve 33 slightly so that a continuous flow of fresh gas is admitted to the breathing chamber 21 from the inlet channel 20, as indicated by an arrow 33c in Figure 6C, at a low rate adjustable by the knob 33a. When the diver starts inhaling through the mouthpiece channel 22, as indicated by an arrow 22d in Figure 6C, he will inhale both fresh gas from flow valve 33 (arrow 33c) and cleansed gas returning from the absorber circuit through checkvalve 11b of the inhalation rebreather channel 11a (arrow 21c). During this part of the breathing cycle, exhalation rebreather channel 9a is blocked by a diaphragm of its checkvalve 9b.

When the diver starts exhaling through the mouthpiece channel 22, as indicated by an arrow 22e in Figure 6D, he will blow the gas from his lungs (arrow 21d) and some fresh gas from flow valve 33 (arrow 33c) into the absorber circuit through checkvalve 9b of the exhalation rebreather channel 9a (arrow 9c). During this part of the breathing cycle, inhalation rebreather channel 11a is blocked by a diaphragm of its checkvalve 11b.

Figure 6E illustrates a situation similar to that illustrated in Figure 6C, with the diver inhaling from the mouthpiece channel 22, the difference being that the diver starts inhaling strongly, as indicated by dual arrows 22d, due to a sudden effort or other particular need for oxygen. The diver's deep inhalation may require more breathing gas to provided than is being available from the rebreather channel 11a (arrow 11c) and flow valve 33 (arrow 33c), and thus results in a low pressure situation in the breathing chamber 21. The low pressure situation in breathing chamber 21 in turn activates the demand valve, i.e. the diaphragm 25 is buckled toward the trigger lever 24 to make the latter lift the closing member 23a from the opening of poppet valve 23 so that additional fresh pressurized gas is admitted to the breathing chamber 21 from the inlet channel 20 through the poppet valve 23, as indicated by arrow 21a in Figure 6F. In other words, the diver's exceptional inhalation demand (dual arrows 22d) is satisfied by the rebreather channel 11a (arrows 11c and 21c), the flow valve 33 (arrow 33c) and the poppet valve 23 (arrow 21a).

Figure 6G illustrates a situation similar to that illustrated in Figure 6D, with the diver exhaling into the mouthpiece channel 22, except that the diver starts exhaling strongly, as indicated by dual arrows 22e, due to a sudden lung reflex, for example. The diver's deep exhalation may require more breathing gas to be discharged than can be diverted to the rebreather channel 9a (arrows 21d and 9c), and thus results in an abnormal high pressure situation in the breathing chamber 21. The excessive pressure in breathing chamber 21 activates the exhaust valve 28, i.e. the diaphragm 28a is lifted from exhaust valve 28 against the resilient force of abutment spring 29 to exhaust the excess gas (arrow 21e) from breathing chamber 21 toward the ambient environment (arrows 28d). In other words, the diver's exceptional exhalation demand (dual arrows 22e) is satisfied by the rebreather channel 9a (arrows 21d and 9c) and the exhaust valve 28 acting as a safety valve (arrows 21e and 28d). It is to be noted that the exhaust valve 28 acts as a safety valve against excessive pressure in the breathing chamber 21 irrespective of the origin of the excessive pressure (i.e. the diver's lungs or any part of the breathing apparatus).

The modified mouthpiece unit 8' according to Figure 6H illustrates how a continuous flow of fresh gas into the breathing chamber 21 can be assured (in the closed-circuit mode, for example) without having to provide a dedicated flow valve 33 in addition to the demand valve 23, 23a, 24, 25. If the demand valve itself is arranged to provide a continuous flow of fresh gas into the breathing chamber 21 from the inlet channel 20, a dedicated flow valve may be omitted from the mouthpiece unit 8' (Figure 6H) or may be provided in addition to the demand valve of the mouthpiece unit 8 (Figures 6J, 6K and 6L) to possibly provide two continuous flows of fresh gas in parallel, at least one of these flows being adjustable. While in Figures 6J, 6K and 6L a separate flow valve 33 (adjustable by a knob 33a) is shown, it may be omitted (like in Figure 6H) or inoperative.

To make the demand valve 23, 23a, 24, 25 work as a flow valve, the diaphragm cover 27 supporting the purge button 26 may be shifted (e.g. screwed) closer toward the diaphragm 25, as indicated by an arrow 27a in Figures 6H and 6J, so that the purge button 26 abuts on the diaphragm 25 which in turn tips the trigger lever 24 to lift the closing member 23a slightly from the opening of poppet valve 23 and to keep the closing member 23a in that position, as illustrated in Figure 6J. This ensures a continuous flow of pressurized fresh gas to the breathing chamber 21 from inlet channel 20, as indicated by an arrow 21f in Figure 6K. The arrow 21f is drawn in a dashed line to indicate a relatively low flow rate. The flow rate may be adjusted by screwing the diaphragm cover 27 closer to the diaphragm 25 (to increase the flow rate) or farther from the diaphragm 25 (to decrease the flow rate).

When the diver inhales strongly from the breathing chamber 21 through the mouthpiece channel 22, as indicated by dual arrows 22d in Figure 6L, the resulting low pressure situation in the breathing chamber 21 warps the diaphragm 25 further toward the trigger lever 24 to open the poppet valve 23 to a greater extent such that an intensive flow of gas exits into the breathing chamber 21 from the inlet channel 20, as indicated by a wide arrow 21g in Figure 6L. In other words, the demand valve may provide both the continuous basic level of fresh gas and any instantaneous or periodic peak supply.

Figure 7 is a sectional view of an alternative design of the mouthpiece unit according to the invention, and Figure 8 is a sectional view of the alternative mouthpiece unit 8" taken along line VIII-VIII in Figure 7, with like parts and parts of similar function being designated by the same reference numerals as those used in the preceding drawing figures.

Irrespective of the different (e.g. more compact) arrangement of the mouthpiece components and housing, as apparent from Figures 7 and 8 (which are more realistic than the diagrammatic explanatory representations in Figures 2A and 2B, for example), the following main parts will be immediately identified and recognised: (i) the flow valve 33 and its knob 33a; (ii) the demand valve comprising diaphragm 25, trigger lever 24, closing member 23a, poppet valve 23 and purge button 26; and (iii) the push button 30 for switching the mouthpiece unit 8" from its open-circuit mode to the closed-circuit mode. The state shown in Figure 8 is the (semi-)closed circuit mode of the mouthpiece unit 8" as the push button 30 has been actuated, i.e. pressed into the mouthpiece housing (even though the mode-switching action of the push button 30 may be reversed in an alternative implementation), so as to open a rebreather passage 21j which allows the rebreather channels 9a, 11a to communicate with the breathing chamber 21. This rebreather passage 21j extends substantially in the direction of displacement of the push button 30, in contrast to the embodiment described in relation to Figure 2B where the rebreather passage 21h extends substantially transversely to the direction of displacement of the push button 30. An axial shaft 30b of push button 30 may support a disc 30c which is selectively spaced from the rebreather passage 21j (when the push button 30 has been actuated to enable the closed-circuit mode) or obstructs the rebreather passage 21j (when the push button 30 has not been actuated).

When the push button 30 is depressed, an inner end of its axial shaft 30b or the disc 30c may act on a displaceable exhaust valve 28 to slide the exhaust valve 28 toward a resilient abutment 29 so as to convert the exhaust valve 28 into a safety valve that is insensitive to normal variations of the breathing pressure but will allow any excessive, hazardous pressure to escape from the breathing chamber 21 into the ambient environment, as described above in relation to mouthpiece unit 8. Alternatively, the exhaust valve 28 may be fixed to the inner end of the axial shaft 30b of the push button 30. These design alternatives - a sliding exhaust valve 28 shifted by the push button 30; a fixed exhaust valve 28 carried by the push button 30 - are likewise applicable to the embodiment shown in Figures 2A and 2B.

Figure 9 is a sectional view of another alternative design of the mouthpiece unit according to the invention, and Figure 10 is a sectional view of this alternative mouthpiece unit 8"' taken along line X-X in Figure 9, with like parts and parts of similar function being designated by the same reference numerals as those used in the preceding drawing figures.

Irrespective of the different (e.g. more compact) arrangement of the mouthpiece components and housing, as apparent from Figures 9 and 10 (which are more realistic than the diagrammatic explanatory representations in Figures 2A and 2B, for example), the following main parts will be immediately identified and recognised: (i) the flow valve 33 and its knob 33a; (ii) the demand valve comprising diaphragm 25, trigger lever 24, closing member 23a, poppet valve 23 and purge button 26; and (iii) the push button 30 for switching the mouthpiece unit 8"' from its open-circuit mode to the closed-circuit mode. The state shown in Figure 10 is the open-circuit mode of the mouthpiece unit 8"' as the push button 30 has not been actuated, i.e. has not been pressed into the mouthpiece housing (even though the mode-switching action of the push button 30 may be reversed in an alternative implementation), so that the rebreather passage 21j is being obstructed and does not allow the rebreather channels 9a, 11a to communicate with the breathing chamber 21. Like in Figure 8, the rebreather passage 21j extends substantially in the direction of displacement of the push button 30, in contrast to the embodiment described in relation to Figure 2B where the rebreather passage 21h extends substantially transversely to the direction of displacement of the push button 30. The axial shaft 30b of push button 30 may support a disc 30c which is selectively spaced from the rebreather passage 21j (when the push button 30 has been actuated to enable the closed-circuit mode) or obstructs the rebreather passage 21j (when the push button 30 has not been actuated, as shown in Figure 10).

An exhaust valve 28 is mounted in an exhaust passage 21k. In the open-circuit mode (as shown in Figure 10), breathing chamber 21 communicates with the exhaust passage 21k to allow the diver to exhale gas into the ambient environment via the exhaust valve 28. When the push button 30 is actuated (which means depressed in the embodiment shown) to switch the mouthpiece unit 8"' to its closed-circuit mode, the exhaust passage 21k is closed by a disc 30d mounted on an inner end of the axial shaft 30b of push button 30. As the exhaust passage 21k is obstructed by disc 30d while the rebreather passage 21j is unobstructed by disc 30c when push button 30 has been depressed, the gas exhaled from a diver's lungs is forced into the absorber circuit through exhalation rebreather channel 9a and cannot exit into the ambient water via exhaust valve 28.

In this embodiment, depressing the push button 30 does not automatically convert the exhaust valve 28 into a safety valve for diverting excessive pressure. Therefore, a dedicated safety valve 28e may be provided in communication with the rebreather channels 9a, 11a, as shown in Figure 9, or with the breathing chamber 21.