EP4656508A1

EP4656508A1 - Pressure reducing system for a breathing apparatus

Info

Publication number: EP4656508A1
Application number: EP25171463.0A
Authority: EP
Inventors: Gabriele Canella; Sergio Alfonso ANGELINI; Valerio Palmieri
Original assignee: Mares SpA
Current assignee: Head Watersports SpA
Priority date: 2024-05-30
Filing date: 2025-04-18
Publication date: 2025-12-03

Abstract

A pressure reducing system for a breathing apparatus, comprising:
i) a conduit (2) for supplying a breathable gas under pressure;
ii) a mouthpiece (3) for the intake of the breathable gas by a user;
iii) a valve (4) interposed between the supply conduit (2) and the intake mouthpiece (3);
said valve (4) comprising:
-a shutter (43) movable between an open position and a closed position in which it respectively allows or prevents the passage of the breathable gas from the conduit (2) to the mouthpiece (3);
-a pressure balancing chamber (44), said shutter (43) extending internally to the pressure balancing chamber (44);

iv) a first and a second fluid dynamic sealing means (61, 62) between the balancing chamber and said shutter (43);
v) a system (8) for adjusting the location of the balancing chamber (44) between at least a first predetermined location and a second predetermined location.

The pressure in the balancing chamber (44) exerting a smaller force on the shutter (43) in the first location than in the second location.

Description

The present invention relates to a pressure reducing system for a breathing apparatus. It is typically used for diving applications, preferably in the second pressure reduction stage; more in general it could be employed in applications in which breathing takes place with the aid of a pressurised tank for accumulating a breathable gas (for example for moving around in underground environments or at the disposal of rescue teams that could find themselves operating in emergency zones).
There are known breathing systems that comprise a cylinder of a pressurised breathable gas, downstream of which a first pressure reduction stage is provided; downstream of the first stage, at the regulator, the second pressure reduction stage is provided. The first reduction stage allows the breathable fluid to be brought from the pressure of 280-300 bar which is found in the cylinder to an intermediate pressure of about 10 bar. The second stage further reduces the pressure, bringing it to the ambient value (a function of depth) so that the gas can be breathed in by the user. A second stage is known, described for example in patent application US4002166 . In this case, a valve comprising a stem shutter is placed between the supply conduit of the pressurised breathable gas and the mouthpiece; a helical spring exerts an action directly on the stem of the shutter to press it against an inlet hole of the valve and prevent the passage of the breathable gas towards the mouthpiece. Negative pressure induced by the user's breathing brings about a deformation of a diaphragm which in turn induces the shifting of a lever and the distancing of the shutter from the inlet hole (overcoming the action of the elastic spring). In this manner, the breathable gas flows in a zone surrounding the shutter stem and reaches the mouthpiece.
A solution is also known in which the stem has an inner central conduit connecting two opposite ends thereof. One of these ends faces the inlet of the valve and prevents/permits the passage of gas to the mouthpiece. The other end leads into and slides inside a pressure balancing chamber that is in a fixed position. The conduit thus allows the pressure in the balancing chamber to be balanced with the pressure at the valve inlet. Due to the ratios between the surfaces, the force exerted by the pressure in the balancing chamber only partly compensates for the force induced by the pressure at the valve inlet. The pressure present in the balancing chamber nonetheless helps the opposing spring to maintain the shutter in a position in which it prevents the passage of the breathable gas towards the mouthpiece. The solutions described above are also known as "downstream valves". However, there is the drawback that the presence of the spring makes it necessary to calibrate and test the second stage. This has a negative impact on product costs, production speed and maintenance.
In addition, an increase in the intermediate pressure (that immediately upstream of the second stage) could cause an annoying vent.
A further solution of the type described in US7171980 is also known.
This solution lacks the helical spring, but the stem has a first and a second opposite end and a central conduit connecting them. The first end is intended to prevent the passage of gas towards the mouthpiece whereas the second end leads into and is sliding inside a pressure balancing chamber which is in a fixed position. The conduit thus allows the pressure in the balancing chamber to be balanced with the pressure at the valve inlet. Due to the surfaces involved, during use there is normally a force present that pushes the shutter against the valve inlet. In this manner the passage of the breathable gas towards the mouthpiece is prevented. Negative pressure induced by the user's breathing allows the movement of a diaphragm, which in turn activates a lever that moves the shutter away from the valve inlet, thus enabling the supply of the breathable gas to the mouthpiece.
This type of solution is known in the technical field as "upstream valve". Such a solution also does not lack drawbacks.
A first drawback is related to the fact that in the absence of intermediate pressure, there is no force acting on the shutter, whose position is therefore undefined when the system is depressurised. This implies two potential criticalities. The first criticality is related to the fact that there could be problems during the rinsing of the equipment after diving. In fact, in a configuration in which the second stage is depressurised and the valve is open, carrying out rinsing after diving would risk passing seawater through the valve of the second stage, causing it to reach the first stage. This situation should be avoided, given the corrosion problems associated with seawater.
A second criticality is linked to the fact that, if the valve is open, when the second stage is pressurised, there is a risk that the shutter will never be able to close the delivery. This is because the balancing chamber, in order to be able to exert its action, needs the gas to penetrate therein and pressurise it sufficiently. If the shutter were open, the gas delivered would continue to push the first end of the shutter, preventing it from moving near the closed position. Furthermore, a good part of the gas would flow outside the shutter towards the mouthpiece without being able to flow through the conduit inside the shutter in an amount capable of pressurising the balancing chamber sufficiently.
A solution of the type described in patent 102022000003899 is also known in which the balancing chamber, upon the occurrence of predetermined conditions, is pushed towards the shutter to occlude an inlet of the valve that places a supply conduit of the breathable fluid in fluid communication with the mouthpiece.
In this context, the technical task underlying the present invention is to propose a pressure reducing system for a breathing apparatus that allows maximum flexibility by allowing the user an optimal balance between the need to avoid unwanted self-delivery and breathing comfort.
The stated technical task and specified objects are substantially achieved by a pressure reducing system for a breathing apparatus comprising the technical features disclosed in one or more of the accompanying claims.
Additional features and advantages of the present invention will become more apparent from the approximate, and thus non-limiting, description of a preferred but not exclusive embodiment of a pressure reducing system for a breathing apparatus as illustrated in the accompanying drawings, in which:

figure 1 shows a breathing apparatus integrating a breathing system according to the present invention;
figures 2 and 3 show two positions of a component of the breathing system in a first configuration;
figures 4 and 5 show two positions of a component of the breathing system in a second configuration;
figures 2a, 3a, 4a, 5a show an enlarged detail of figures 2, 3, 4, 5, respectively.

In the accompanying figures, a pressure reducing system for a breathing apparatus is denoted by the reference number 1.
As mentioned previously, the system 1 is advantageously used for diving applications, but could also be employed in other applications. With reference to the schematic view in figure 1, the present description preferably makes reference to a breathing system 10 comprising:

a tank 9 of a breathable gas;
a first pressure reduction stage 91 located downstream of the tank 9;
a second pressure reduction stage 92 located downstream of the first stage 91;
a tube 93 (for example a sleeve or also a flexible hose) that connects the first stage 91 to the second stage 92 and inside which the gas moves. The pressure reducing system 1 to which the present description relates is advantageously applied to the second stage 92.

Appropriately, in the course of the present description, intermediate pressure is understood as the pressure between the first and second stages 91, 92 (and, therefore, in the preferred application, the pressure immediately upstream of the system 1). For example, the intermediate pressure can be equal to about 10 bar (though it may vary for example with depth).
The reducing system 1 comprises a supply conduit 2 for supplying a breathable gas under pressure. Such a supply conduit 2 typically originates from the tube 93 which in turn comes from the first stage connected to the tank 9 (the gas could also be in liquid form inside the tank 9). The breathable gas can be of various types: compressed air, Nitrox, mixtures of oxygen, nitrogen and helium, or still others.
The system 1 also comprises a mouthpiece 3 for the intake of the breathable gas by a user. This enables the user to keep the second stage firmly in their mouth and thus to breathe.
The system 1 comprises a valve 4 interposed between the supply conduit 2 and the intake mouthpiece 3.
The valve 4 allows or prevents the passage of the breathable gas from the supply conduit 2 to the intake mouthpiece 3.
The valve 4 comprises an inlet 41 of the breathable gas coming from the supply conduit 2. It is defined by the end portion of the conduit 2 that is abutted by the shutter 43 in the closed position. In the technical field, the inlet 41 is also referred to as the "seat" of the valve. Typically it is an integrated sharp profile intended to abut a "pad" of the shutter 43. The seat could be fixed or screwable (which allows to adjust the position as best as possible to facilitate the opening thereof). The valve 4 comprises an outlet 42 for the breathing gas directed to the intake mouthpiece 3. Suitably, the outlet 42 is defined by a by-pass conduit 420 not further described, being well known in the technical field.
The valve 4 also comprises a shutter 43 movable between an open position (see for example figures 3 or 5) and a closed position (see for example figures 2 or 4) in which it respectively allows or prevents the passage of the breathable gas from the conduit 2 to the mouthpiece 3 (or from the inlet 41 to the outlet 42 of the valve 4). In the closed position, the shutter 43 is near the inlet 41. In the open position, the shutter 43 is distanced from the inlet 41 (with reference to figures 3 and 5, this means that it is moved to the right relative to the depicted image). In the open position, the shutter 43 is therefore distanced from the inlet 41. In a zone intended to come into contact with the inlet 41, the shutter 43 comprises a sealing element 410. Such a sealing element 410 is called "pad" in technical jargon. The inlet 41 against which the pad is pressed can leave an imprint on the latter (called "marking" in technical jargon). In fact, the inlet 41 can typically have a thin profile to optimise the seal with the pad. As exemplified in the accompanying figures, the pressure reducing system 1 comprises a lever 45 for moving the shutter 43 between the open and closed positions. Conveniently, the reducing system 1 comprises a diaphragm 450 which is deformable by the user's breathing in. In fact, by breathing in, the user causes a negative pressure that deforms the deformable diaphragm 450, causing it in turn to shift the lever 45. This in turn induces a shifting of the shutter 43 from the closed position to the open position, thereby permitting the passage of the breathable gas. Once the effect of breathing in is over, the diaphragm "swells" again, the lever 45 goes back into the original position and thus also the shutter 43. Appropriately the valve 4 comprises a pressure balancing chamber 44. The expression "balancing chamber 44" is well known in the technical field, as during operation it enables at least a partial balancing of the force exerted by the pressure at the inlet 41. In the specific case, appropriately, an elastic spring is absent between the shutter 43 and the balancing chamber 44.
The shutter 43 extends (typically only partially) inside the balancing chamber 44.
The shutter 43 is (at least partially) interposed between the inlet 41 of the valve 4 and the balancing chamber 44. The shutter 43 defines a passage 430 which puts the conduit 2 (or the inlet 41 of the valve 4) and the pressure balancing chamber 44 in fluid communication (appropriately this also occurs in the closed position of the shutter 43). The passage 430 extends inside the shutter 43. Purely by way of non-limiting example, the passage 430 can have an outflow cross section of a size comprised between 1 mm² and 2 mm².
When the shutter 43 is in the closed position, during normal operation the balancing chamber 44 takes on the pressure value existing at the inlet 41 of the valve 4. This is thanks to the gas which flows from the inlet 41 to the chamber 44 by means of the passage 430. When the shutter 43 is in the open position, the gas also flows outside the shutter 43 (and reaches the mouthpiece 3 through the outlet 42). In this case the gas flows into a space interposed between the shutter 43 and a seat 7 laterally surrounding the shutter 43. The outlet 42 is advantageously obtained on a wall of the seat 7.
The pressure reducing system 1 comprises a first fluid dynamic sealing means 61 between the balancing chamber 44 and said shutter 43. Appropriately, the first sealing means 61 is of annular type. For example, it comprises/is an O-ring. In the preferred solution, the first fluid dynamic sealing means 61 wraps the shutter 43 and is located inside the balancing chamber 44. The balancing chamber 44 comprises a back wall 441 and a side wall 442. The balancing chamber 44 is shaped like a cup. Appropriately, the first fluid dynamic sealing means 61 applies a seal between a side wall of the shutter 43 and the side wall 442 of the balancing chamber 44 (in particular it applies a seal between an outer side surface of the shutter 43 and an inner side surface of the balancing chamber 44). Appropriately, the fluid dynamic seal is radial.
The pressure reducing system 1 also comprises a second fluid dynamic sealing means 62 between the balancing chamber 44 and said shutter 43. Appropriately, the fluid dynamic seal is radial.
Appropriately, the second sealing means 62 is of annular type. For example, it comprises/is an O-ring. In the preferred solution, the second fluid dynamic sealing means 62 wraps the shutter 43 and is located inside the balancing chamber 44. The balancing chamber 44 is shaped like a cup. Appropriately, the second fluid dynamic sealing means 62 applies a seal between a side wall of the shutter 43 and the side wall 442 of the balancing chamber 44 (in particular it applies a seal between an outer side surface of the shutter 43 and an inner side surface of the balancing chamber 44). The second fluid dynamic sealing means 62 is to the side of and spaced apart from the first fluid dynamic sealing means 61. In particular, the first and the second fluid dynamic sealing means act along two parallel planes. The distance between the valve inlet 41 and the second fluid dynamic sealing means 62 is less than the distance between the inlet 41 and the first fluid dynamic sealing means 61.
The pressure reducing system 1 comprises a system 8 for adjusting the location of the balancing chamber 44 between at least a first predetermined location (see figures 2 and 3) and a second predetermined location (see figures 4 and 5). Such an adjustment system 8 is typically a mechanical system. It is mechanically operated by hand. In a non-preferred alternative solution, it could be operated by electronic means.
In the second location of the balancing chamber 44, both in the open position (figures 5 and 5a) an in the closed position (figures 4 and 4a) of the shutter 43, the second fluid dynamic sealing means 62 applies a fluid dynamic seal between the balancing chamber 44 and the shutter 43 while the first fluid dynamic sealing means 61 allows a fluid communication between said passage 430 and a zone 435 interposed between the first and the second fluid dynamic sealing means 61, 62.
In the first location of the balancing chamber 44, both in the open position and in the closed position of the shutter 43, the first fluid dynamic sealing means 61 applies a fluid dynamic seal between the balancing chamber 44 and the shutter 43.
In the first location, the second fluid dynamic sealing means 62 does not apply a fluid dynamic seal between said shutter 43 and said side wall 442 of the balancing chamber 44 (see figures 2a and 3a).
The pressure in the balancing chamber 44 exerts a different (in the specific case lower) force on the shutter 43 in the first location than in the second location. In fact, the extension of the surfaces responsible for pushing the shutter 43 towards said inlet 41 changes between the first and the second location.
The pressure reducing chamber 44 defines a passage section with a variable area (such a passage section is evaluated orthogonally to the movement direction of the shutter); narrower in a first zone 414 in which the first fluid dynamic sealing means 61 exerts its action in the first location; wider in a second zone 424 in which the second fluid dynamic sealing means 62 exerts its action in the second location.
In fact, a passage section of the balancing chamber 44 at the first zone 414 has an inner diameter comprised between 5.5 and 5.7 mm. Instead a passage section of the balancing chamber 44 at the second zone 424 has an inner diameter comprised between 5.8 and 6.2 mm. Suitably, the passage section of the balancing chamber 44 at the second zone 424 has a diameter that is greater than the diameter of the first zone 414 by a value comprised between 8 and 12%.
In the first location the balancing chamber 44 is farther away from the inlet 41 of the valve 4 than in the second location.
As mentioned above, the shutter 43 is movable along a movement direction 439 to pass from the open to the closed position (of the valve 4). In particular, the shutter 43 is translatable along the direction 439. In the first location, the balancing chamber 44 is moved, with respect to the second location, along said movement direction 439 of said shutter 43. Appropriately, the balancing chamber 44 can also translate along the movement direction 439 to pass from the first to the second location and vice versa.
Advantageously, the system 8 for adjusting the position of the balancing chamber 44 comprises a pusher 80. Appropriately, the pusher 80 can be actuated by an operator. The pusher 80 is movable at least between a first and a second position. Appropriately, the pusher 80 can be locked in the first and in the second position. Appropriately, the pusher 80 can stably assume only a plurality of discrete positions. Alternatively, it could permanently assume a plurality of positions that follow each other continuously.
In the first position (see figures 2 and 3) the pusher 80 is farther away from the inlet 41 of the valve 4. In the first position, the pusher 80 is suitable for abutting the balancing chamber 44 in the first location.
In the second position (see figures 4 and 5) the pusher 80 is closer to the inlet 41 of the valve 4. In the second position, the pusher 80 is suitable for abutting the balancing chamber 44 in the second location.
Therefore, the pusher 80 defines the maximum distancing position of the balancing chamber 44 from said inlet of the valve 4.
During normal "full" operation of the system 1, the balancing chamber 44 is in a stable position (it remains stationary). This occurs due to the intermediate pressure acting on the back wall 441. The shutter 43 moves from the closed position to the open position as a consequence of the negative pressure determined by the user on the mouthpiece 3 that calls gas to inhale it (see the passage from figure 2 to figure 3). Once the negative pressure induced by the user's breathing ends, the shutter 43 returns from the open to the closed position due to the absence of negative pressure that leads the diaphragm to push on the lever 45 and the pressure exerted by the balancing chamber 44 (thus returning from the situation of figure 3 to that of figure 2 or from that of figure 5 to that of figure 4). In fact, in this step the pressure in the balancing chamber 44 is the same as the pressure at the inlet 41, but the force that causes the shutter 43 to close is greater than the one opposing it (as a consequence of the fact that the pushing surface that is usable in a closing direction of the shutter 43 is larger than the pushing surface that is usable in the opening direction; this is because inside the chamber 44 the shutter 43 has a pushing surface for closing that is larger than the surface of the shutter 43 which in the closed position faces the section for the passage of gas in the inlet 41).
The shutter 43 extends between a first and a second end 431, 432. The first end 431 is near the inlet 41 of the valve 4 relative to the second end 432.
The second end 432 comprises a groove 434 that intersects the passage 430. Appropriately, the passage 430 and the groove 434 extend along two mutually transverse or rather orthogonal directions. The groove 434 allows to facilitate the exit of gas from the passage 430 when the second end 432 abuts against the back wall 441 of the balancing chamber 44.
The system 1 further comprises a movement system 5 for moving the balancing chamber 44 towards the inlet 41 of the breathable gas to push the shutter 43 from the open position to the closed position, for example upon the occurrence of predetermined operating conditions (typically depressurisation after diving to be able to disassemble the system from the cylinder). As better explained below, the movement system 5 intervenes spontaneously if there depressurisation occurs immediately upstream of the inlet 41 (depressurisation of the second stage, typically occurs when the pressure immediately upstream of the inlet 41 is brought to "ambient pressure").
The balancing chamber 44 is therefore movable relative to the inlet 41 (although the movement in actual fact only occurs under certain conditions). The movement means 5 induces the movement of the shutter 43 from the open position to the closed position as a consequence of the push received from the balancing chamber 44 in its travel towards the inlet 41 (thus the movement system 5 pushes the balancing chamber 44, which in turn pushes the shutter 43). The balancing chamber 44 is conveniently shaped like a cup having an opening through which the shutter 43 is inserted.
During a travel of the balancing chamber 44 towards the inlet 41, a back wall 441 of the balancing chamber is intended to push the shutter 43 against the inlet 41. Therefore, the system 1 can take on a configuration in which the back wall 441 of the balancing chamber 44 abuts against and pushes the shutter 43 towards the closed position. The balancing chamber 44 slides along the seat 7 under the action of the movement system 5. In particular, the balancing chamber 44 slides along the seat 7 parallel to a preponderant extension direction of the shutter 43.
The movement system 5 for moving the balancing chamber 44 can be of varying type. The system 5 is located outside the balancing chamber 44. The balancing chamber 44 is interposed between the shutter 43 and the movement means 5. Typically, the movement system 5 comprises/coincides with thrust means of the balancing chamber 44.
As exemplarily illustrated in figures 2-5, the movement system 5 comprises/coincides with elastic means 50 exerting a force that pushes the balancing chamber 44 towards the inlet 41 of the valve 4. This force is embodied in an actual movement when the system is depressurised. For example, the elastic means 50 comprises a spring, typically a helical spring. There could possibly be a plurality of helical springs arranged in series (possibly with an interposing element therebetween). The elastic means 50 is outside the balancing chamber 44. The balancing chamber 44 is interposed between the elastic means 50 and the shutter 43. The elastic means 50 pushes on a rear wall (back wall 441) of the balancing chamber 44. The elastic means 50 is such as to offer a force lower than that exerted by the intermediate pressure on the back wall 441 of the balancing chamber 44; consequently it does not intervene in the operation of the system 1 if pressurised. However, when the line is purged (depressurised upstream of the valve 4) the elastic means 50 allows the shutter 43 to be repositioned (by dragging) in the closed position of the valve 4.
Furthermore, the elastic means 50 could be such that in the closed position of the valve 4 (i.e. when the elastic means 50 is in the minimum compression configuration) it exerts a minimum force (so as to minimise the marking of the pad, a drawback described above). This effect can be optimised since as the spring expands the force exerted by it decreases, whereby the spring can be designed so as to provide a sufficient force to start the movement of the balancing chamber 44 but such that after the excursion travel thereof (for example about 2 millimetres) the residual force is just sufficient to prevent the entry of water towards the first stage during rinsing.
In other solutions not illustrated, the movement system 5 of the balancing chamber 44 comprises an auxiliary chamber placed in fluid communication with said balancing chamber 44 (these are, for example, solutions already described in the Italian patent application 102022000003899 ).
A further object of the present invention is an operating method of the system 1 (having one or more of the characteristics described hereinabove). In particular, this method comprises the steps of:

adjusting the adjustment system 8 so as to allow the balancing chamber 44 to take on the first location described above; in particular, in the first location of the balancing chamber 44, both in the open position and in the closed position of the shutter 43, the first fluid dynamic sealing means 61 applies a fluid dynamic seal between the balancing chamber 44 and the shutter 43;
modifying the adjustment system 8 so as to allow the balancing chamber 44 to take on a second location in which both in the open position an in the closed position of the shutter 43, the second fluid dynamic sealing means 62 applies a fluid dynamic seal between the balancing chamber 44 and the shutter 43 while the first fluid dynamic sealing means 61 allows a fluid communication between said passage 430 and a zone 435 interposed between the first and the second fluid dynamic sealing means 61, 62.

The invention as it is conceived allows multiple advantages to be achieved.
Firstly, it allows to make the system very flexible. Thereby, it can be made adaptable to different user needs.
In particular, the operation with the balancing chamber 44 in the first location allows to make breathing more comfortable. In fact, the user must counteract a lower force that opposes the opening of the valve 4 to allow the delivery of the breathable fluid.
On the other hand, operation with the balancing chamber 44 in the second location allows to make uncontrolled self-delivery less likely. This is particularly useful if diving in very cold water or in the event of bumps or stresses.
Therefore, it allows the user to choose whether to privilege one or the other of these aspects.
Furthermore, the same equipment can be intended for a wider user pool thanks to this operational flexibility.
The invention thus conceived is susceptible of numerous modifications and variants, all falling within the scope of the inventive concept that characterises it. Moreover, all the details may be replaced by other technically equivalent elements. All the materials used, as well the dimensions, may in practice be any whatsoever according to needs.

Claims

A pressure reducing system for a breathing apparatus, comprising:
i) a conduit (2) for supplying a breathable gas under pressure;

ii) a mouthpiece (3) for the intake of the breathable gas by a user;

iii) a valve (4) interposed between the supply conduit (2) and the intake mouthpiece (3);
said valve (4) comprising:
- a shutter (43) movable between an open position and a closed position in which it respectively allows or prevents the passage of the breathable gas from the conduit (2) to the mouthpiece (3);

- a pressure balancing chamber (44), said shutter (43) extending internally to the pressure balancing chamber (44); the shutter (43) defining a passage (430) that places the conduit (2) and the pressure balancing chamber (44) in fluid communication both in the open position and in the closed position of the shutter (43); a mechanical spring being absent between the shutter (43) and the pressure balancing chamber (44);

iv) a first fluid dynamic sealing means (61) between the balancing chamber (44) and said shutter (43);

v) a second fluid dynamic sealing means (62) between the balancing chamber (44) and said shutter (43);
characterised in that it comprises a system (8) for adjusting the location of the balancing chamber (44) between at least a first predetermined location and a second predetermined location;

in the first location of the balancing chamber (44), both in the open position and in the closed position of the shutter (43), the first fluid dynamic sealing means (61) applying a fluid dynamic seal between the balancing chamber (44) and the shutter (43);

in the second location of the balancing chamber (44), both in the open position an in the closed position of the shutter (43), the second fluid dynamic sealing means (62) applying a fluid dynamic seal between the balancing chamber (44) and the shutter (43) while the first fluid dynamic sealing means (61) allows a fluid communication between said passage (430) and a zone (435) interposed between the first and the second fluid dynamic sealing means (61, 62);

the pressure in the balancing chamber (44) exerting a smaller force on the shutter (43) in the first location than in the second location.
The pressure reducing system according to claim 1, characterised in that said balancing chamber (44) comprises a back wall (441) and a side wall (442); in the first location, the second fluid dynamic sealing means (62) does not apply a fluid dynamic seal between said shutter (43) and said side wall (442) of the balancing chamber (44).
The pressure reducing system according to claim 1 or 2, characterised in that the balancing chamber (44) defines a passage section with a variable area; narrower in a first zone (414) in which the first fluid dynamic sealing means (61) exerts its action in the first location; wider in a second zone (424) in which the second fluid dynamic sealing means (62) exerts its action in the second location.
The pressure reducing system according to claim 3, characterised in that:
- a passage section of the balancing chamber (44) in the first zone (414) has an inner diameter comprised between 5.5 and 5.7 mm;

- a passage section of the balancing chamber (44) in the second zone (424) has an inner diameter comprised between 5.8 and 6.2 mm.
The pressure reducing system according to any one of the preceding claims, characterised in that said shutter (43) is movable along a movement direction (439); in the first location the balancing chamber (44) being shifted, relative to the second location, along said movement direction (439) of said shutter (43).
The pressure reducing system according to any one of the preceding claims, characterised in that said valve (4) comprises an inlet (41) defined by the end portion of the conduit (2) which is abutted by the shutter (43) in the closed position.
The pressure reducing system according to claim 6, characterised in that said system (8) for adjusting the position of the balancing chamber (44) comprises a pusher (80) actuatable by an operator and movable at least between:
- a first position in which it is farther away from the inlet (41) of the valve (4); in the first position said pusher (80) being suitable for abutting the balancing chamber (44) in the first location;

- a second position in which it is closer to the inlet (41) of the valve (4); in the second position said pusher (80) being suitable for abutting the balancing chamber (44) in the second location.
The pressure reducing system according to claim 7, characterised in that said pusher (80) defines the position of the balancing chamber (44) farthest away from said inlet of the valve (4).
The pressure reducing system according to any one of the preceding claims, characterised in that it comprises a movement system (5) for moving the pressure balancing chamber (44) towards the inlet (41) of the breathable gas in order to move the shutter (43) from the open position to the closed position upon the occurrence of at least one predetermined operating condition.
The pressure reducing system according to claim 9, characterised in that the movement system (5) comprises an elastic means (50) that pushes the pressure balancing chamber (44) towards the inlet (41) of the valve (4).
A breathing system comprising:
- a tank (9) of a breathable gas;

- a first pressure reduction stage (91) located downstream of the tank (9);

- a second pressure reduction stage (92) located downstream of the first stage (91) and comprising a pressure reducing system (1) according to any one of claims 1 to 10;

- a conduit (93) connecting the first stage (91) to the second stage (92) and inside which the gas moves.