First-stage pressure reducer

Abstract

A first stage pressure reducer for a respiratory apparatus is disclosed, comprising: a body defining a cavity having: 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 bore connecting the high pressure region and the low pressure region; a piston configured to reciprocate through the piston bore and further configured to deliver gas from a high pressure region to a low pressure region; a bushing disposed coaxially with the piston bore and surrounding at least a portion of the piston, the bushing disposed to engage the piston and prevent contact between the piston and the piston bore; and a sealing element disposed between the high pressure region and the bushing, the sealing element configured to isolate the bushing from the high pressure region. A self-contained breathing apparatus including the first stage pressure reducer is also disclosed.

Description

Background Art

[0001] Self-contained breathing apparatus (SCBA) must be able to work reliably in a variety of environments, including both high and low temperatures. Therefore, each component of such an SCBA system must be able to operate at a variety of temperatures. An SCBA system typically includes a pressurized breathing gas tank, a first-stage pressure reducer, a second-stage pressure reducer, and a flow regulator. The breathing gas is stored in the tank at a high pressure, such as 30 MPa. The user cannot directly inhale this high-pressure gas, so a first-stage pressure reducer is used to reduce the pressure to a medium pressure of about 1 MPa. Then, the second-stage pressure reducer further reduces the medium pressure to a safe pressure for the user to inhale through a flow regulator.

[0002] In addition to the typically very cold ambient conditions experienced by SCBA systems, the expansion (i.e., decompression) of the breathing gases in the first stage pressure reducer also causes a significant degree of adiabatic cooling. These factors of adiabatic cooling and ambient cooling, whether occurring alone or together, can result in extreme cooling of components within the first stage pressure reducer. This extreme cooling of the pressure reducer components can lead to reliability issues, and thus safety issues.

[0003] A new pressure relief mechanism is needed that decouples the effects of adiabatic cooling from the performance of the pressure relief mechanism, thereby improving reliability and safety. Summary of the invention

[0004] In a first aspect, a first-stage pressure reducer for a breathing apparatus is provided, comprising: a body defining a cavity having: 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; a piston configured to reciprocate through the piston hole and further configured to transport gas from the high-pressure region to the low-pressure region; a sleeve arranged coaxially with the piston hole and surrounding at least a portion of the piston, the sleeve being configured to engage the piston and prevent contact between the piston and the piston hole; and a sealing element disposed between the high-pressure region and the sleeve, the sealing element being configured to isolate the sleeve from the high-pressure region.

[0005] The bushing may be arranged inside the piston bore, i.e., at the inner surface of the piston bore. The sealing element may be configured to prevent fluid from entering along the entry path from the high pressure area, thereby preventing the fluid from contacting the bushing. The entry path may be defined between the outer surface of the piston and the inner surface of the piston bore.

[0006] The bushing may be a single annular component or may comprise a plurality of separate components which cooperate to engage the piston inside the piston bore. The separate components may be evenly arranged around the piston bore.

[0007] The high pressure region is configured to contain gas at a higher pressure than in the low pressure region. The high pressure region may be a high pressure region containing gas at a pressure substantially the same as the pressure of the gas source. The low pressure region may be a medium pressure region containing gas at a lower medium pressure than the high pressure region but higher than the pressure of the gas delivered to the user. The gas source may be a pressurized breathing gas bottle or a pressurized breathing gas tank.

[0008] The sealing element can prevent the fluid in the high pressure area from exerting a longitudinal force on the bushing relative to the piston bore. Therefore, the combined longitudinal force acting on the bushing due to the hydrostatic pressure can be zero or close to zero.

[0009] The inner diameter of the bushing may be smaller than the smallest inner diameter of the piston bore, thereby creating a spacing between the outer surface of the piston and the inner surface of the piston bore.

[0010] The piston bore may include a first section near the high pressure region and may include a second section near the low pressure region, optionally, the second section has a diameter greater than the first section, and wherein a shoulder may be formed between the first section and the second section.

[0011] A bushing may be disposed in the second section, and a first end of the bushing may abut a shoulder of the piston bore, thereby preventing movement of the bushing in a first direction toward the high pressure region.

[0012] The first stage pressure reducer may also include a retaining element disposed at a second end of the bushing opposite to the first end, whereby the retaining element may prevent the bushing from moving in a second direction toward the low pressure region. The retaining element may include a washer, and optionally, the washer may be fixed to the body by a circlip. The retaining element may include a cutout or channel configured to allow fluid to pass through the retaining element. The bushing may be retained in the body by press fitting into the piston bore.

[0013] The bushing may include one or more longitudinal grooves extending in the longitudinal direction, optionally, the one or more longitudinal grooves are configured to allow fluid to pass through the bushing. In the event of a failure of the sealing element, the longitudinal grooves may allow fluid to flow from a high pressure area to a low pressure area. The failure of the sealing element may be a partial failure or a complete failure.

[0014] The bushing may be made of a polymer material or a metal material or a material containing a polymer and a metal. The bushing may be made of PTFE or metal-filled PTFE, and optionally, the bushing may be made of copper-filled PTFE. The bushing may be made of a material having a thermal expansion coefficient between 10x10 -6 K -1 With 100x10 -6 K -1 The thermal expansion coefficient is between 10x10-6 K -1 between 60 x 10 -6 K -1 and, or further optionally, between 20 x 10 -6 K -1 and 55 x 10 -6 K -1 The expansion of the gas in the pressure reducer can result in a large temperature range and, as a result, the coefficient of thermal expansion within the above range can provide good dimensional tolerances at different operating temperatures that the system may experience.

[0015] The distance between the inner surface of the bushing and the outer surface of the piston can be between 0.01 mm and 0.1 mm, optionally between 0.01 mm and 0.09 mm. The distance between the inner surface of the bushing and the outer surface of the piston can be determined at least in part by the outer diameter of the piston and the inner diameter of the bushing. These dimensions can provide a particularly good balance between the freedom of movement of the piston and the restriction of excessive lateral movement.

[0016] The piston can be configured to reciprocate between an open position and a closed position, the open position corresponding to a state that allows gas to flow from a high-pressure region to a low-pressure region via the inner bore of the piston, and the closed position corresponding to a state that blocks the flow of gas from the high-pressure region to the low-pressure region via the inner bore; 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; 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. In use, the user will periodically inhale. The inhaled gas is provided by the low-pressure region (optionally, via other "second-stage" pressure reducers). Each inhalation will deplete the gas (or a portion thereof) in the low-pressure region, thereby reducing the pressure in the low-pressure region. After the user takes one inhalation (or a sufficient number of inhalations), the pressure in the low-pressure region can drop low enough such that the pressure difference rises above the upper threshold, and then the piston can move to the open position to allow high-pressure gas to move from the high-pressure region to the low-pressure region to replenish the low-pressure region. After sufficient gas has been delivered to the low-pressure region, the pressure difference then drops below the lower threshold, and the piston moves to the closed position. Then the user inhales, repeating the cycle.

[0017] The speed at which the piston reciprocates between the open position and the closed position can vary according to the breathing needs of the user.

[0018] The piston can include a tail and a head connected to the tail, with the inner bore located in the tail. In the open position, high-pressure gas can flow through the inner bore into the head, where the high-pressure gas can leave via an outlet in the head and enter the low-pressure region.

[0019] When the piston moves to the closed position, the head of the piston can move to surround (inside the cavity of the head) a plunger that is in communication with the body. The plunger can include a distal sealing end that can seal against the neck of the inner bore in the closed position, thereby preventing high-pressure gas from being delivered from the inner bore to the head of the piston and delivered to the low-pressure area.

[0020] A biasing element (such as a spring) may be arranged between the piston head and the body, and the biasing element may be configured to push the piston from the closed position to the open position when the pressure difference rises above the upper threshold. When the pressure difference drops below the lower threshold, the spring may be pressed against the body by the force of the gas inside the low pressure area acting on the piston.

[0021] The bias of the biasing element (eg, the force applied by a spring) may be adjusted by changing the position of the plunger relative to the body. Adjustment of the plunger position (eg, the distance between the body and the plunger) may be achieved by rotating a grub screw (optionally a fixed grub screw).

[0022] Gradually and discretely introducing high-pressure breathing gas into the low-pressure region can cause the introduced high-pressure breathing gas to expand in the low-pressure region, thereby reducing the pressure to a pressure between the pressure of the high-pressure region and the pressure of the low-pressure region (before the high-pressure breathing gas is introduced). In this way, the pressure of the breathing gas flowing through the first-stage pressure reducer can be reduced.

[0023] 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

[0024] The device of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0025] Figure 1 A cross-sectional view of a previously known first stage pressure reducer is shown;

[0026] Figure 2A A cross-sectional view of a first-stage pressure reducer according to the present invention is shown;

[0027] Figure 2B Shows Figure 2A an enlarged view of a section of the view shown in ;

[0028] Figure 3A A perspective view showing a bushing according to the present invention; and

[0029] Figure 3B A cross-sectional view of a first-stage pressure reducer according to the present invention is shown. DETAILED DESCRIPTION

[0030] refer to Figure 1 , shows an example of a known first stage pressure reducer 10. The first stage pressure reducer 10 includes a body 110, which defines 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 pressure of the low pressure breathing gas is generally lower than the pressure of the high pressure breathing gas, but higher than the pressure of the breathing gas that can be delivered to the user. This breathing gas can be referred to as medium pressure breathing gas or low pressure breathing gas.

[0031] Typically, the breathing gas inside the tank 12 and therefore in 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.

[0032] A piston 120 is arranged inside the body 110 , and includes a head 122 and a tail 124 . The piston head 122 is mainly located inside the low pressure area 114 , while the piston tail 124 is mainly located inside the high pressure area 112 and the piston hole 160 .

[0033] The piston 120 is used to reduce the pressure of the high-pressure breathing gas when the breathing gas enters the low-pressure region 114, thereby providing low-pressure (medium-pressure) breathing gas to the low-pressure region 114. Starting from the "open" position of the piston 120, the high-pressure breathing gas flows from the high-pressure region 112 through the inner hole 126 of the piston tail 124 and into the piston head 122, in which the gas enters the low-pressure region 114 via an outlet (not shown) in the piston head 122. The introduction of this high-pressure gas causes the pressure in the low-pressure region 114 to increase and begins to push the piston head 122, causing the piston 120 to move in a manner that expands the volume of the low-pressure region 114. Figure 1 From the perspective of FIG. 1 , the piston 120 moves in a direction away from the high pressure region 112 . As a result, the spring 123 is compressed until the distal sealing end 127 of the plunger 125 blocks the neck 129 of the inner bore 126 at the interface between the inner bore 126 and the head 122 .

[0034] After the neck 129 is blocked, the high-pressure breathing gas in the high-pressure area 112 cannot flow into the low-pressure area 114 through the inner hole 126. This state corresponds to the "closed" position of the piston 120. When the user consumes the breathing gas in the low-pressure area 114 (via the second-stage pressure reducer and / or the flow regulator, not shown), the pressure inside the low-pressure area 114 decreases, so that the force acting on the piston head 122 decreases. Therefore, the spring 123 returns the piston 120 back to the "open" position, thereby resetting the position of the piston 120.

[0035] Sealing element 130 blocks breathing gas from flowing from high pressure region 112 to low pressure region 114 along entry path 163 defined between piston tail 124 and piston bore 160. Sealing element 130 also guides tail 124 by centering it inside piston bore 160.

[0036] The movement between the open position and the closed position is repeated based on the user's breathing gas demand, causing the piston 120 to reciprocate through the piston hole 160 as long as there is sufficient breathing gas in the tank 12. Specifically, while the tail portion 124 reciprocates through the piston hole 160, the head portion 122 also reciprocates inside the low pressure region 114. The discrete transfer of high pressure gas from the high pressure region 112 to the low pressure region 114 (where the high pressure gas can expand (thus reducing the pressure)) is what causes the controlled decompression of the breathing gas.

[0037] During this process, the expansion of the high pressure breathing gases results in significant adiabatic cooling. As a result, a number of components, including the body 110, cavity 111, piston 120, piston bore 160, and sealing element 130, become very cool. This cooling may be in addition to any ambient cooling effects resulting from the conditions of use of the device. As a result, some components experience a degree of thermal contraction, which may cause the tail 124 to be less effectively positioned centrally within the piston bore 160 by the sealing element 130. Due to variations in tolerances between components, this reduction in effectiveness may cause the piston 120 to become stuck within the piston bore 160.

[0038] As noted above, sealing element 130 is also responsible for retaining high pressure breathing gases in adjacent high pressure region 112. Any shrinkage of sealing element 130 due to low temperatures may impede the ability of sealing element 130 to perform both the functions of retaining high pressure gases and directing tail 124 simultaneously.

[0039] Figure 2A FIG. 2 shows a cross-sectional view of an embodiment of a first stage pressure reducer 20 according to the present invention. Figure 2A The segment view S marked on Figure 2B . The same components between the pressure reducer 10 and the pressure reducer 20 of the present invention are indicated by the same reference numerals plus 100. The first-stage pressure reducer 20 includes a body 210, which defines a chamber 211. The chamber 211 has a high-pressure area 212, a low-pressure area 214 and a piston hole 260. The first-stage pressure reducer 20 also includes a piston 220 having a head 222 and a tail 224, which reciprocates inside the body 210 in a manner similar to the piston 120 of the known first-stage pressure reducer 10. A sealing element 230 is also provided for maintaining high-pressure breathing gas in the high-pressure area 212. The first-stage pressure reducer 20 may also include a grub screw 215, which can be rotated to change the position of the plunger 225, thereby changing the pressure threshold that causes the plunger 220 to move from an open position to a closed position and from a closed position to an open position.

[0040] Figure 2A and Figure 2B The first stage pressure reducer 20 shown in the figure also includes a bushing 240. The bushing 240 is annular and is arranged coaxially with the piston hole 260 and surrounds at least a portion of the piston 220 (particularly the piston tail 224). The bushing 240 engages the piston 220 and is used to guide the piston tail 224 through the piston hole 260 during each reciprocating movement of the piston 220, while also ensuring that the spacing between the piston tail 224 and the piston hole 260 can be maintained. In the embodiment shown, the piston hole 260 includes a first narrow section 262 close to the high pressure area 212 and a second wide section 264 close to the low pressure area 214. A shoulder 266 is formed between these two sections 262, 264. In this embodiment, the bushing 240 is located in the wide section 264 and abuts the shoulder 266 on one side, thereby preventing any movement of the bushing 240 toward the high pressure area 212.

[0041] The outer diameter of the bushing 240 is substantially equal to the inner diameter of the wide section 264, thereby making the bushing 240 fit tightly inside the wide section 264, thereby preventing the bushing 240 from moving laterally inside the piston bore 260. The inner diameter of the bushing is smaller than the smallest inner diameter of the piston bore 260 (i.e., smaller than the diameter of the narrow section 262), and therefore, the inner surface of the bushing 240 is radially closer to the central axis of the piston bore 260 than the surface of the narrow section 262. That is, the thickness of the bushing 240 (the difference between the outer diameter and the inner diameter of the bushing 240) is greater than the height of the shoulder 266. Thus, the tail 224 is kept centrally positioned in the piston bore 260 and separated from the surface of the narrow section 262. This prevents the tail 224 from contacting any portion of the piston bore 260 (particularly the surface of the narrow section 262) and thus reduces the possibility of the piston 220 being stuck.

[0042] In some embodiments, the piston bore comprises only one section of constant diameter. In these cases, the bushing is arranged at the inner surface of the piston bore, and the inner diameter of the bushing is smaller than the inner diameter of the piston bore. In some embodiments, the piston bore comprises a tapered shape with the narrow end of the tapered shape facing the high pressure area. In these embodiments, a frustoconical bushing may be arranged inside the tapered piston bore.

[0043] In some embodiments, the bushing includes one or more discrete bushing segments rather than a single continuous annular portion. In these embodiments, the bushing segments can be evenly arranged around the inner diameter of the piston bore.

[0044] In some embodiments, the body 210 and the piston 220 are made of metal (same type or different types), and in particular, one or both of the body and the piston can be made of copper. In some embodiments, each of the body 210 and the piston 220 is also coated with a different metal (optionally nickel) by electrolytic deposition or any other appropriate method. The bushing 240 can be made of metal (particularly copper), or it can be made of a polymer. In the case where the bushing 240 is made of a polymer, polytetrafluoroethylene (PTFE) can be used. In some embodiments, metal-filled PTFE, such as copper-filled PTFE, is used. In these embodiments, the ratio of PTFE to copper can be 60:40. The ratio can be a weight ratio. However, in other embodiments, different ratios can be used. The material (or material mixture) selected for forming the bushing 240 is at least partially determined by one or more materials used to form the body 210 and the piston 220, and vice versa. The coefficient of thermal expansion of bushing 240 must match the coefficients of thermal expansion of body 210 and piston 220 to ensure that bushing 240 always maintains the spacing between piston bore 260 and tail 224 of piston 220 throughout the operating temperature range of reducer 20 (typically between -110°C and +100°C).

[0045] During normal operation, the clearance between the tail 224 and the piston bore 260 is between 0.01 mm and 0.09 mm (assuming a nominal average diameter of 6 mm between the tail 224 and the piston bore 260, and depending on whether a free running fit or a close running fit is selected). In alternative embodiments where the nominal average diameter is larger or smaller, the required clearance is correspondingly larger or smaller. Such clearance values ​​generally follow the ASME B4.2-1978 standard for "free running" or "close running" applications. In some embodiments, the bushing is made of a thermal expansion coefficient between 10x10 -6 K -1 With 100x10 -6 K -1 Made of materials in between.

[0046] In an embodiment according to the present invention, the sleeve 240 is arranged behind the sealing element 230 (relative to the high pressure area 212). Therefore, the sealing element isolates the high pressure breathing gas in the high pressure area 212 from the sleeve 240. Therefore, the sealing element 230 prevents the high pressure breathing gas from applying a longitudinal force to the sleeve 240 relative to the piston hole 260. Therefore, the combined longitudinal force acting on the sleeve 240 due to the hydrostatic pressure can be zero or close to zero. Therefore, the possibility of displacement of the sleeve 240 is reduced. When the user consumes the breathing gas, the pressure inside the high pressure area 212 will change over time. Since the sealing element 230 prevents the high pressure breathing gas from applying a force to the sleeve 240, this pressure change will not affect the operation of the sleeve 240. Thereby, the possibility of the piston 260 getting stuck due to low temperature shrinkage is reduced.

[0047] In this embodiment, the bushing 240 is press-fit into the piston bore 260, however in other embodiments, the bushing 240 may be screwed or adhered in place. As shown, in some embodiments, a retaining element 250 is used to prevent the bushing 240 from moving away from the shoulder 266 and out of the piston bore 260. Where the bushing 240 is press-fit or otherwise secured in place, the retaining element 250 generally acts as a failsafe to prevent the bushing 240 from moving if it becomes loose.

[0048] The retaining element 250 generally includes a washer 252 and a circlip 254. The washer 252 is arranged at the end of the bushing 240 opposite to the end that contacts the shoulder 266. Therefore, the bushing 240 is prevented from moving in both axial directions. The tail 224 of the piston 220 can move through the washer 252 and the circlip 254 without hindrance. In the embodiment shown, the circlip 254 is an internal circlip 254 that fits into the groove 213 in the body 210. The washer 252 is located between the bushing 240 and the circlip 254, thereby preventing the washer 252 from falling off.

[0049] In some cases, such as exceeding safe operating temperatures or after a long period of no maintenance, sealing element 230 may begin to fail. If such a failure occurs, high pressure breathing gas may begin to flow from high pressure region 212 into low pressure region 214 via inlet path 263. In order to safely allow for this failure mode and prevent the high pressure breathing gas from potentially causing further damage, liner 240 includes a groove 242 extending longitudinally (e.g., Figure 3A ). These longitudinal grooves 242 allow any high pressure breathing gas that passes through the sealing element 230 to also safely pass through the bushing 240 without causing the bushing 240 to be pushed out of position, thereby causing more damage. In normal operation, the longitudinal grooves are not used. The bushing 240 may also include chamfers 244 to help install the bushing 240 into the piston bore 260.

[0050] Figure 3B Shown along the Figure 2B In this embodiment, the gasket 252 includes a cutout 256 that allows both easy removal of the retaining ring 254 and allows any high pressure breathing gas that passes through the sealing element 230 and through the longitudinal groove 242 of the bushing 240 to escape into the low pressure region 214.

[0051] Those skilled in the art will appreciate that although the invention has been described by way of example and with reference to one or more exemplary embodiments, the invention is not limited to the disclosed examples and that alternative examples may be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

1. A first stage pressure reducer (20) for a breathing apparatus, comprising: A body (210), the body defining a cavity (211), the cavity (211) having: a high-pressure region (212) configured to receive high-pressure gas from a gas source (22); a low-pressure region (214) configured to receive low-pressure gas from the high-pressure region (212); and a piston hole (260), the piston hole (260) connecting the high-pressure region (212) and the low-pressure region (214); a piston (220) configured to reciprocate through the piston hole (260) and further configured to transport gas from the high pressure region (212) to the low pressure region (214); a bushing (240) arranged coaxially with the piston bore (260) and surrounding at least a portion of the piston (220), the bushing (240) being configured to engage the piston (220) and prevent contact between the piston (220) and the piston bore (260); and A sealing element (230) is disposed between the high-pressure region (212) and the bushing (240), and the sealing element (230) is configured to isolate the bushing (240) from the high-pressure region (212).

2. The first stage pressure reducer (20) according to claim 1, wherein: The inner diameter of the bushing (240) is smaller than the minimum inner diameter of the piston hole (260), thereby generating a gap between the outer surface of the piston (220) and the inner surface of the piston hole (260).

3. A first stage pressure reducer (20) according to any one of the preceding claims, wherein: The piston hole (260) includes a first section (262) close to the high-pressure area (212) and a second section (264) close to the low-pressure area (214), wherein the diameter of the second section (264) is larger than the diameter of the first section (262), and wherein a shoulder (266) is formed between the first section (262) and the second section (264).

4. The first stage pressure reducer (20) according to claim 3, wherein: The bushing (240) is disposed in the second section (264), and a first end of the bushing (240) abuts the shoulder (266) of the piston bore (260), thereby preventing the bushing (240) from moving in a first direction toward the high pressure region (212).

5. The first-stage pressure reducer (20) according to claim 4, further comprising a retaining element (250), wherein the retaining element is disposed at a second end of the bushing (240) opposite to the first end, wherein the retaining element (250) prevents the bushing (240) from moving in a second direction toward the low-pressure area (214).

6. The first stage pressure reducer (20) according to claim 5, wherein: The retaining element (250) comprises a washer (252), and wherein, optionally, the washer (252) is fixed to the body (210) by a snap spring (254).

7. The first stage pressure reducer (20) according to claim 5 or 6, wherein: The retaining element (250) includes a cutout or channel (256) configured to allow fluid to be transferred through the retaining element (250).

8. A first stage pressure reducer (20) according to any one of the preceding claims, wherein: The bushing (240) includes one or more longitudinal grooves (242) extending in a longitudinal direction, the one or more longitudinal grooves (242) being configured to allow fluid to be transmitted through the bushing (240).

9. The first stage pressure reducer (20) according to any one of the preceding claims, wherein: The bushing (240) is made of a polymer material or a metal material.

10. The first stage pressure reducer (20) according to any one of claims 1 to 8, wherein: The bushing is made of polytetrafluoroethylene or metal-filled polytetrafluoroethylene, and optionally, the bushing is made of copper-filled polytetrafluoroethylene.

11. The first stage pressure reducer (20) according to any one of claims 1 to 8, wherein: The bushing (240) has a thermal expansion coefficient between 10x10 -6 K -1 With 100x10 -6 K -1 Made of materials in between.

12. The first stage pressure reducer (20) according to any one of the preceding claims, wherein: The bushing (240) is retained in the body (210) by being press-fit into the piston bore (260).

13. A first stage pressure reducer (20) according to any one of the preceding claims, wherein: The distance between the inner surface of the bushing (240) and the outer surface of the piston (220) is between 0.01 mm and 0.1 mm.

14. A first stage pressure reducer (20) according to any one of the preceding claims, wherein: The piston (220) is configured to reciprocate between an open position and a closed position, the open position corresponding to a state in which gas is allowed to flow from the high-pressure region (212) to the low-pressure region (214) via an inner hole of the piston (220), and the closed position corresponding to a state in which gas is prevented from flowing from the high-pressure region (212) to the low-pressure region (214) via the inner hole; The piston (220) is configured to move from the open position to the closed position when the pressure difference between the high pressure region (212) and the low pressure region (214) drops below a lower threshold; and The piston (220) is configured to move from the closed position to the open position when the pressure difference between the high pressure region (212) and the low pressure region (214) rises above an upper threshold.

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

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