Respiratory device pressurization fail-safe

Abstract

Disclosed is a first stage pressure reducer for a breathing apparatus, comprising: a body comprising an inner cavity and an end cap for closing an opening of the inner cavity; and a piston slidably disposed within the inner cavity, the piston including a piston head, the piston head including a bore configured to receive a plunger, the plunger and the piston being slidably movable relative to each other, and the plunger having a seal configured to seal the plunger when the plunger is received a sufficient distance into the bore. An effective length of the plunger is greater than an effective length of the bore when the proximal end of the plunger contacts the end cap such that the sealing portion and the sealing seat are in sealing contact when the piston is maximally displaced toward the end cap. A self-contained breathing apparatus including the first stage pressure reducer is also disclosed.

Description

Technical Field

[0001] The present disclosure relates to a first stage pressure reducer and a self-contained breathing apparatus. Background Art

[0002] Self-contained breathing apparatus (SCBA) products are commonly used by firefighters to provide safe breathing gas in environments with contaminated air. Typical SCBA products have a high-pressure system that includes a breathing gas tank with a nominal pressure of about 300 bar. The high-pressure system is connected to the medium-pressure system via a first-stage pressure reducer (first-stage pressure reducer). This device outputs breathing gas from the high-pressure system to the medium-pressure system at a low pressure of about 7 bar. This medium-pressure breathing gas can then pass through a second-stage pressure reducer to further reduce the pressure to a level suitable for the user to breathe.

[0003] The first stage pressure reducer is designed to be "normally open", which means that breathing gas can flow freely through the system. This is beneficial because it ensures that any failure of a component inside such a pressure reducer causes the pressure reducer to fail "safely", thereby ensuring that breathing gas is always supplied to the user. However, this may also lead to an excessive flow of gas into the medium pressure system and, therefore, overpressurizing the medium pressure system.

[0004] Therefore, there is a need for a new first stage pressure reducer that minimizes the possibility of downstream overpressure while maintaining the "normally open" safety standard to protect users. Summary of the invention

[0005] In a first aspect, a first-stage pressure reducer for a respiratory device is disclosed, comprising: a main body, comprising an inner cavity and an end cap for closing an opening of the inner cavity; and a piston, slidably arranged in the inner cavity, the piston comprising a piston head, the piston head comprising a hole, the hole being configured to receive a plunger, the plunger and the piston being slidably movable relative to each other, and the plunger having a sealing portion, the sealing portion being configured to selectively seal a sealing seat in the hole of the piston head when the plunger is received in the hole a sufficient distance, wherein when the proximal end of the plunger contacts the end cap, the effective length of the plunger is greater than the effective length of the hole, so that when the piston is displaced toward the end cap to the maximum extent, the sealing portion and the sealing seat are in sealing contact.

[0006] The effective length of the plunger should be understood as the minimum first distance between the sealing portion of the plunger and the end cap. The effective length of the hole should be understood as the minimum second distance between the sealing seat and the end cap when the piston is maximally displaced toward the end cap.

[0007] The piston is slidably arranged in the inner cavity so that the piston head is opposite to the end cover, and the piston slides along an axis perpendicular to the end cover.

[0008] Displaced to the maximum extent towards the end cap should be understood as a position in which the piston is at a point in its travel closest to the end cap. In other words, the distance between the piston and the end cap is minimized. Such a position may correspond to the piston and the end cap being in contact.

[0009] The minimum first distance and the minimum second distance are measured as straight lines extending perpendicularly between parallel planes defined at the start and end points of each line. In the case where the start and / or end points are on faces, the planes are defined at the surfaces of these faces.

[0010] A sufficient distance should be understood as a distance sufficient for the sealing portion to seal against the sealing seat when the plunger is received in the bore.

[0011] The end cap may include a protruding seat extending from the end cap, and the proximal end of the plunger is configured to contact the protruding seat such that the protruding seat forms a portion of the effective length of the plunger.

[0012] The end cap may include an adjustment element configured to vary the effective length of the plunger.

[0013] The protruding seat can be a raised portion of the end cap extending from the end cap face. The end cap face can be a major face of the end cap, which is the major surface of the end cap in contact with the inner cavity of the body. The protruding seat can increase the distance between the end cap and the sealing portion of the plunger, thereby increasing the effective length of the plunger. In other words, the protruding seat can define the minimum distance between the end cap and the proximal end of the plunger, thereby defining the effective length of the plunger (because the length of the plunger is fixed).

[0014] The adjustment element may be manually actuated, or may be electrically driven or otherwise driven. The adjustment element may be accessible from outside the body, so that the adjustment element can be set from outside the body by, for example, a manufacturer or maintenance worker on a production line. The adjustment element may require the use of an additional tool, such as a hexagonal wrench, for adjustment.

[0015] The adjusting element may be a set screw disposed in the threaded through hole of the end cap, the distal end of the set screw may be configured to contact the proximal end of the plunger, and rotation of the set screw may change the effective length of the plunger.

[0016] The protruding seat may be a raised portion of the end cap extending from a surface of the end cap, and when the set screw is adjusted so that the distal end of the set screw extends beyond the protruding seat, the distal end may contact the proximal end of the plunger.

[0017] The set screw is adjustable between a first position corresponding to the distal end not extending beyond the protruding seat and a second position corresponding to the distal end extending beyond the protruding seat, and the set screw may be adjustable to any position between the first position and the second position.

[0018] The protruding seat can be an annular protrusion surrounding the through-hole of the set screw.

[0019] The annular protrusion can be provided at the edge of the through-hole to extend the length of the through-hole through the annular protrusion, or can have a diameter larger than that of the through-hole, thus deviating from the edge of the through-hole.

[0020] The length of the plunger between the sealing portion and the proximal end can be greater than the effective length of the hole.

[0021] In other words, when the sealing portion of the plunger seals against the sealing seat of the piston, the proximal end of the plunger can extend out of the hole.

[0022] The effective length of the plunger can be at least 0.1 mm greater than the effective length of the hole, and optionally at least 0.3 mm greater than the effective length of the hole. The effective length of the plunger can also be at least 0.5 mm greater than the effective length of the hole, and optionally can be at least 0.7 mm greater than the effective length of the hole.

[0023] The sealing portion of the plunger can be formed of a polymer, optionally nylon. The sealing portion of the plunger can be part of the distal sealing end of the plunger, which can be replaceable. The distal sealing end can have a shape complementary to the shape of the distal end of the plunger to allow the distal sealing end to be detachably attached to the distal end.

[0024] The sealing seat can be a convex portion, optionally an acutely convex point.

[0025] The end cap can be detachably installed in the opening of the main body. Optionally, the end cap can be held in the main body by a snap ring. The end cap can include a threaded portion, and the opening of the main body can include a corresponding threaded portion, allowing the end cap to be threadedly installed in the opening of the main body.

[0026] The inner cavity of the main body can have: a high-pressure region configured to receive high-pressure gas from a gas source; a low-pressure region configured to receive low-pressure gas from the high-pressure region; and a piston hole connecting the high-pressure region and the low-pressure region;

[0027] The piston can be configured to reciprocate between an open position and a closed position within the piston hole. The open position corresponds to a state allowing gas to flow from the high-pressure region to the low-pressure region via the inner hole of the piston, and the closed position corresponds to a state prohibiting gas from flowing from the high-pressure region to the low-pressure region via the inner hole; the piston can be configured to move from the open position to the closed position when the pressure difference between the high-pressure region and the low-pressure region drops below a lower threshold value; and the piston can be configured to move from the closed position to the open position when the pressure difference between the high-pressure region and the low-pressure region rises above an upper threshold value.

[0028] In another aspect, there is provided a self-contained breathing apparatus comprising a first stage pressure reducer as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Arrangements of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0030] Figure 1 A cross-sectional view showing a design of a first stage pressure reducer known in the art;

[0031] FIG. 2A to FIG. 2C Each shows Figure 1 An enlarged view of the first stage pressure reducer shown in;

[0032] Figure 3A A first stage pressure reducer according to the present invention is shown with the piston in an open position;

[0033] Figure 3B A first stage pressure reducer according to the present invention is shown with the piston in a closed position; and

[0034] Figure 4 Other embodiments of the first stage pressure reducer according to the present invention are shown with the piston in the closed position. DETAILED DESCRIPTION

[0035] refer to Figure 1 , an example of a known first stage pressure reducer 10 is shown. The first stage pressure reducer 10 includes a body 110 defining a chamber 111. The chamber 111 has a high pressure region 112, a low pressure region 114, and a piston hole 160. The high pressure region 112 and the low pressure region 114 are fluidly connected by the piston hole 160. The body 110 is connected to a pressurized breathing gas supply source (such as a pressurized breathing gas tank 12) via a connector (not shown), which enables the high pressure region 112 to receive high pressure breathing gas from the tank 12. The low pressure region 114 is configured to receive low pressure breathing gas from the high pressure region 112 via the piston hole 160. The low pressure breathing gas is generally lower in pressure than the high pressure breathing gas, but higher in pressure than the breathing gas that can be delivered to the user. The breathing gas may be referred to as medium pressure breathing gas or low pressure breathing gas.

[0036] Typically, the breathing gas within the tank 12, and therefore the high pressure region, is pressurized to between 10 MPa and 40 MPa, typically about 30 MPa. Before the low pressure region 114 receives the breathing gas, the pressure of the breathing gas must be reduced.

[0037] The piston 120 is disposed in the body 110 and includes a head portion 122 and a tail portion 124. The piston head 122 is mainly located in the low pressure region 114, while the piston tail portion 124 is mainly located in the high pressure region 112 and the piston hole 160.

[0038] The piston 120 is used to reduce the pressure of the high-pressure breathing gas when the breathing gas enters the low-pressure area 114, thereby providing low-pressure (medium-pressure) breathing gas to the low-pressure area 114. Starting from the "open" position of the piston 120, the high-pressure breathing gas flows from the high-pressure area 112 through the inner hole 126 of the piston tail 124 and flows into the piston head 122, where the gas enters the low-pressure area 114 via the outlet 121 in the piston head 122. The introduction of the high-pressure gas causes the pressure in the low-pressure area 114 to increase and begin to push the piston head 122, thereby causing the piston 120 to move in a manner that expands the volume of the low-pressure area 114. Figure 1 From the perspective of the piston 120, the piston 120 moves in a direction away from the high pressure area 112. As a result, the spring 123 is compressed until the seal 134 on the distal sealing end 132 of the plunger 130 seals against the corresponding seal seat 128 at the neck 127 of the inner bore 126, thereby blocking the neck 127 at the junction between the inner bore 126 and the head 122.

[0039] After the neck 127 is blocked, the high-pressure breathing gas in the high-pressure region 112 is blocked from flowing through the inner hole 126 into the low-pressure region 114. This state corresponds to the "closed" position of the piston 120. When the user consumes the breathing gas in the low-pressure region 114 (via the second-stage pressure reducer and / or the demand regulator, not shown), the pressure in the low-pressure region 114 decreases, thereby reducing the force acting on the piston head 122. Therefore, the spring 123 returns the piston 120 to the "open" position, thereby resetting the position of the piston 120.

[0040] With sufficient breathing gas in the tank 12, the movement of the piston between the open position and the closed position is repeated according to the user's breathing gas demand, causing the piston 120 to reciprocate through the piston hole 160. In particular, the tail 124 reciprocates through the piston hole 160, while the head 122 reciprocates within the low pressure region 114. The discrete transfer of high pressure gas from the high pressure region 112 to the low pressure region 114 is what causes the controlled decompression of the breathing gas, where the high pressure gas is able to expand (and thereby reduce pressure).

[0041] FIG. 2A to FIG. 2C An enlarged view of the piston head 122 and the plunger 130 is shown ( Figure 1 ). Go to Figure 2A, an end cap 140 is disposed in the body 110 opposite to the piston head 122 to close the opening of the body 110. A set screw 150 is disposed in a threaded through hole 142 in the end cap 140. The set screw 150 can be rotated to adjust the distance that the distal end 152 of the set screw 150 extends from the face 144 of the end cap 140. The distal end 152 contacts the plunger 130 at the proximal end 136. Therefore, the extension distance of the distal end 152 from the end cap face 144 determines the minimum distance between the proximal end 136 of the plunger 130 and the end cap face 44, which is the inward-facing face of the end cap. Therefore, the extension distance also determines the minimum distance between the sealing portion 134 of the distal sealing end 132 of the plunger 130 and the end cap face 144 (because the length of the plunger 130 is substantially constant).

[0042] In normal operation, changing the position of set screw 150 and thus the extension distance of distal end 152 causes the point at which piston 120 will move from the closed position to the open position (or vice versa) to change. In other words, changing the extension distance causes a change in the displacement of spring 123 required for sealing seat 128 to seal or unseal (as the case may be) from sealing portion 134. By changing this displacement, the pressure differential between high pressure area 112 and low pressure area 114 required to compress spring 123 will also change. Figure 2B The plunger 130 is shown in a closed position (normal operation) wherein the seal portion 134 seals against the seal seat 128, thereby preventing gas from flowing through the neck 127 into the low pressure region 114. The distal end 152 of the set screw 150 extends from the end cap face 144.

[0043] However, if Figure 2C As shown, with the set screw 150 fully retracted and thus no portion of the distal end 152 extending beyond the end cap face 144, the seal 134 can no longer seal against the seal seat 128, no matter how far the piston 120 moves toward the end cap 140. This position of the set screw 150 may be due to a component failure (e.g., a failure of the threads of the through hole 142), or user error in manually withdrawing the set screw 150 too far or not replacing it after maintenance. The set screw 150 may also loosen on its own due to vibration during use of the reducer 10.

[0044] In this state, the piston 120 moves from the open position toward the closed position (away from the high pressure region 112) and toward the end cap 140 as usual. However, due to the position of the set screw 150, the piston head 122 contacts the end cap face 144 (as shown) before the seal 134 and the seal seat 128 form a seal. The breathing gas is therefore free to flow uninhibited from the high pressure region 112, between the seal 134 and the seal seat 128, and into the low pressure region 114. In this fault state, the breathing gas stored in the tank 12 will be rapidly lost through the reducer 10, potentially causing damage to downstream components and / or injury to the user. Since the high pressure gas contacts downstream components that are not designed to operate at such pressures, downstream components may be damaged due to overpressure.

[0045] Figure 3A and Figure 3B An embodiment 20 of the present invention is shown. Similar features between designs known in the art and the embodiment 20 of the present invention are labeled with like reference numerals incremented by 100.

[0046] Figure 3A An embodiment according to the present invention is shown in which the piston 220 is in an open position. A set screw 250 is provided, which is shown to be located in a position where the distal end 252 does not extend any distance beyond the end cap face 244. However, as shown, the proximal end 236 of the plunger 230 does not abut the end cap face 244 as in the known reducer 10. Instead, the end cap 240 includes a protruding seat 246 extending from the end cap face 244, against which the proximal end 236 of the plunger 230 contacts. The end cap face 244 is the main surface of the end cap 240, which faces the inner cavity 211 of the body 210. The end cap face 244 is substantially planar, and the protruding seat 246 extends in a direction substantially perpendicular to the plane of the end cap face 244.

[0047] The protruding seat 246 forms a portion of the effective length of the plunger 230, which is defined as the minimum length between the sealing portion 234 and the end cap face 244. In other words, the protruding seat 246 sets a fixed minimum extension distance that separates the proximal end 236 from the end cap face 244.

[0048] As will be appreciated, if the set screw 250 is adjusted to extend from the end cap face 244 by an amount at least equal to the amount that the protruding seat 246 extends from the end cap face 244, the distal end 252 of the set screw 250 will contact the proximal end 236 of the plunger 230. Adjusting the set screw 250 so that the distal end 252 extends further than the protruding seat 246 will cause the effective length of the plunger 230 to increase. In other words, the set screw 250 can control the extension distance between the proximal end 236 and the end cap face 244 to be greater than the minimum distance set by the protruding seat 246. Likewise, the protruding seat 246 forms a portion of the effective length of the plunger 230 and therefore (at least in part) defines the minimum value of the effective length.

[0049] In this embodiment, the set screw 250 is generally rotatable so that the effective length greater than the minimum value set by the protruding seat 246 varies between about 0.73 mm and about 2.48 mm, with a nominal extension distance of about 1.60 mm. It should be understood that these measurements are provided as examples only, and many other minimum, maximum and nominal extension distances can and do apply to the present invention. These measurements represent a balance between the open / closed position threshold and the customization of the adjustment distance, while minimizing the space occupied by the plunger and piston. It is generally important that the first stage reducer is as compact as possible to improve the maneuverability of the user.

[0050] If the set screw 250 is adjusted so that the distal end 252 does not extend to the protruding seat 246 (or is in a fault condition having the same effect), then (eg Figure 3A ) proximal end 236 contacts the protruding seat 246. In other words, the proximal end 236 is prevented from being closer to the end cap surface 244 than the minimum value allowed by the protruding seat 246.

[0051] Figure 3B Shown with Figure 3A The same position of the set screw 250 and the known design Figure 2C However, unlike Figure 2C Different, in Figure 3B , the sealing portion 234 is shown as forming a seal against the sealing seat 228. This is because, although the distal end 252 is not in contact with the proximal end 236, the protruding seat 246 maintains the effective length of the plunger 230, which is greater than the effective length of the plunger bore 229 (the effective length of the plunger bore is defined as the minimum distance from the sealing seat 228 to the end cap face 244). As a result, the sealing portion 234 is farther from the end cap face 244 than the sealing seat 228, and therefore the sealing portion 234 and the sealing seat 228 can contact. In other words, compared to the case without the protruding seat 246, the plunger 230 is pushed further into the piston plunger bore 229, thereby allowing the sealing portion 234 to seal against the sealing seat 228.

[0052] As shown, the protruding seat 246 is annular and surrounds the threaded through hole 242 of the end cover 240. The outer diameter of the protruding seat 246 is smaller than the inner diameter of the plunger hole 229, so when the piston head 222 is in contact with (or closest to) the end cover surface 244, the protruding seat 246 is allowed to extend into the plunger hole 229.

[0053] It should be understood that the relationship between the effective length of the plunger 230 and the effective length of the plunger bore 229 (i.e., the difference between the two) determines the position to which the piston 220 must move to form a seal between the sealing seat 228 and the sealing portion 234. In turn, this position of the piston 220 determines the maximum pressure in the low pressure region before the gas in the low pressure region moves the piston 220 to the closed position.

[0054] In some embodiments, when the piston 220 is moved from the open position ( Figure 3A ) moves to the closed position ( Figure 3B ), the effective length of the plunger 230 corresponds to a maximum pressure of about 1.2 MPa in the low pressure region.

[0055] Typically, the equipment connected directly downstream of the first stage pressure reducer 20 may include a pressure relief valve (not shown) configured to operate at about 1.3 MPa. Thus, in these embodiments, the piston 220 can be moved to a closed position (thereby preventing any further increase in pressure in the low pressure region) before the pressure relief valve is activated. These embodiments reduce the possibility of loss of breathing gas to the surrounding environment while maintaining a safe breathing gas supply to the user.

[0056] As discussed above, the effective length of plunger 230 (by selecting the length of plunger 230 and the length of protruding seat 246 ) is configured to ensure that seal 234 is always able to contact and seal against seal seat 228 regardless of the position of set screw 250 .

[0057] Therefore, it should be understood that other embodiments according to the present invention may not include the protruding seat 246. Figure 4 As shown in , as an alternative, a suitable effective length of the plunger 330 can be formed by increasing the plunger length (between the sealing portion 334 and the proximal end 336 of the plunger 330) and / or reducing the effective length of the plunger bore 329. Figure 4 The plunger 330 is clearly shown extending from the plunger bore 329. This difference in length allows sealing at the seal 334 when the piston 320 is maximally displaced toward the end cap 340.

[0058] In further embodiments, one or two effective lengths (the plunger effective length and the plunger hole effective length) may be provided as described above, with a protruding seat provided on the end cap to further increase the effective length of the plunger (and reduce the effective length of the plunger hole relative to the plunger). Thus, it should be understood that the effective length of the plunger is formed in part by the protruding seat and in part by the length between the sealing portion and the proximal end.

[0059] It should be understood that the operation of the first-stage pressure reducer according to the present invention does not require a set screw. In such embodiments, the effective length of the plunger and piston is set to define a threshold for the piston to move from an open position to a closed position, and vice versa. In some embodiments where the operation of the first-stage pressure reducer does not require a set screw, a set screw may still be provided for use during normal operation. Then, during a failure mode of the first-stage pressure reducer (such as unintentional withdrawal or loss of the set screw), the ability of the first-stage pressure reducing valve to operate without the set screw can be utilized to allow the first-stage pressure reducing device to continue to operate without the set screw during the failure mode.

[0060] In all embodiments according to the present invention, the seal seat 228, 328 should be able to deform the seal portion 234, 334 of the distal seal end 232, 332 by at least 0.1 mm, and ideally by at least 0.3 mm. A deformation of at least 0.1 mm ensures that a tight seal is formed between the seal portion 234, 334 and the seal seat 228, 328. A deformation of at least 0.3 mm also ensures that a tight seal is formed, and further means that such deformation can tolerate a greater degree of mechanical wear on the seal portion 234, 334. Therefore, the distal seal end 232, 332 does not need to be replaced frequently and lasts longer.

[0061] This level of deformation is required to form a properly secure seal. To achieve this deformation, the distal sealing end 232, 332 is typically formed of a material such as nylon or other polymers. In some embodiments, the shape of the sealing seat 228, 328 is convex, which makes the force applied by the sealing seat 228 and 328 to the sealing portion 234 and 334 more localized (i.e., high pressure), thereby forming a stronger seal than when the sealing seat 228 or 328 has a higher contact area. The distal sealing end 232, 332 of the plunger 230, 330 can be user-removable and replaceable.

[0062] Based on the above minimum deformation distance, the minimum difference between the effective length of the plunger 230, 330 and the effective length of the plunger hole 229, 329 must be greater than 0.1 mm, and ideally greater than 0.3 mm. In some embodiments, the difference is greater than 0.5 mm, 0.7 mm, or 1 mm. The measurement of the effective length of the plunger 230, 330 from the sealing portion 234, 334 to the end cap surface 244, 344 is always considered to be based on the undeformed position of the sealing portion 234, 334.

[0063] In some embodiments, the end cap 240, 340 is removable from the body 210, 310, thereby allowing the user to install a different end cap 240, 340. In some embodiments, a replacement end cap 240 having a protruding seat 246 with a different extension distance can be installed, which will cause the effective length of the plunger 230 to be different. The end cap 240, 340 can be retained in the body 210, 310 by a retaining spring 213, 313.

[0064] The minimum distance referred to in this specification refers to the distance along a line drawn between two parallel planes, the line being perpendicular to those planes. For example, the effective length of the plunger (defined as the length between the seal 234 on the plunger 230 and the end cap face 244) is the length of a straight line extending perpendicularly from the plane defined at the seal 234 to the parallel plane defined at the end cap face 244.

[0065] It will be appreciated by those skilled in the art that although the present invention has been described by way of example with reference to one or more exemplary embodiments of a first stage pressure reducer, it is not limited to the disclosed examples and that alternative examples may be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. A first stage pressure reducer (20, 30) for a breathing apparatus, comprising: A main body (210, 310) comprising an inner cavity (211, 311) and an end cover (240, 340) for closing an opening of the inner cavity (211, 311); as well as A piston (220, 320) is slidably arranged in the inner cavity (211, 311), the piston (220, 330) includes a piston head (222, 322), the piston head (222, 322) includes a hole (229, 329), the hole (229, 329) is configured to receive a plunger (230, 330), the plunger (230, 330) and the piston (220, 320) are slidably movable relative to each other, and the plunger (230, 330) has a sealing portion (234, 334), the sealing portion is configured to selectively seal a sealing seat (228, 328) in the hole (229, 329) of the piston head (222, 322) when the plunger (230, 330) is received in the hole (229, 329) to a sufficient distance, When the proximal end (236, 336) of the plunger (230, 330) contacts the end cover (240, 340), the effective length of the plunger is greater than the effective length of the hole (229, 329), so that when the piston (220, 320) is displaced to the maximum extent toward the end cover (240, 340), the sealing portion (234, 334) and the sealing seat (228, 328) are in sealing contact.

2. The first stage pressure reducer (20) according to claim 1, wherein: The end cap (240) includes a protruding seat (246) extending from the end cap (240), and the proximal end (236) of the plunger (230) is configured to contact the protruding seat (246) so that a portion of the effective length of the plunger (230) is formed by the protruding seat (246).

3. The first stage pressure reducer (20) according to claim 2, wherein: The end cap (240) includes an adjustment element (250) configured to change the effective length of the plunger (230).

4. The first stage pressure reducer (20) according to claim 3, wherein: The adjusting element is a set screw (250) disposed in the threaded through hole (242) of the end cap (240), the distal end (252) of the set screw (250) being configured to contact the proximal end (236) of the plunger (230), and wherein rotation of the set screw (250) changes the effective length of the plunger (230).

5. The first stage pressure reducer (20) according to claim 4, wherein: The protruding seat (246) is a raised portion of the end cap (240) extending from the end cap face (244), and wherein, when the set screw (250) is adjusted so that the distal end (252) extends beyond the protruding seat (246), the distal end (252) of the set screw (250) contacts the proximal end (236) of the plunger (230).

6. The first stage pressure reducer (20) according to claim 2, wherein: The protruding seat (246) is a raised portion of the end cover (240) extending from the end cover surface (244).

7. The first stage pressure reducer (20, 30) according to claim 4 or 5, wherein: The protruding seat (246) is an annular protrusion surrounding the through hole of the set screw (250).

8. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The length of the plunger (230, 330) between the sealing portion (234, 334) and the proximal end (236, 336) is greater than the effective length of the hole (229, 329).

9. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The effective length of the plunger (230, 330) is at least 0.1 mm greater than the effective length of the aperture (229, 329), and optionally at least 0.3 mm greater than the effective length of the aperture (229, 329).

10. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The sealing portion (234, 334) of the plunger (230, 330) is formed from a polymer, which may optionally be nylon.

11. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The sealing portion (234, 334) of the plunger (230, 330) is a part of the distal sealing end (232, 332) of the plunger (230, 330), and the distal sealing end (232, 332) is replaceable.

12. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The sealing seat (228, 328) is a convex portion, optionally a sharp convex portion.

13. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The end cover (240, 340) can be detachably mounted in an opening of the main body (210, 310), and optionally, the end cover (240, 340) is retained in the main body (210, 310) by a retaining spring (213, 313).

14. A first stage pressure reducer (20, 30) according to any one of the preceding claims, wherein: The inner cavity (211, 311) of the body (210, 310) has: a high-pressure region configured to receive high-pressure gas from a gas source; a low pressure region configured to receive low pressure gas from the high pressure region; and a piston hole connecting the high pressure region and the low pressure region; The piston (220, 320) is configured to reciprocate between an open position and a closed position in the piston hole, the open position corresponding to a state in which gas is allowed to flow from the high-pressure area to the low-pressure area via the inner hole of the piston (220, 320), and the closed position corresponding to a state in which gas is prohibited from flowing from the high-pressure area to the low-pressure area via the inner hole; The piston (220, 320) is configured to move from the open position to the closed position when the pressure difference between the high pressure region and the low pressure region drops below a lower threshold; and The piston (220, 320) is configured to move from the closed position to the open position when the pressure difference between the high pressure area and the low pressure area rises above an upper threshold.

15. A self-contained breathing apparatus comprising a first stage pressure reducer (20, 30) according to any one of the preceding claims.

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