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How does an air pressure regulator work?

by B.B. Pelletier

This question popped up earlier this week, so I thought I would address it today.

What IS a pressure regulator?
An air pressure regulator is a mechanical device that controls the air pressure and volume available to the firing valve of a precharged airgun. Because the pressure is always the same, a gun with a regulator shoots with very consistent velocity, plus it may get a few more shots on a fill. As long as there’s enough pressure in the reservoir, it operates as described. When the reservoir pressure drops below the regulated pressure, the regulator remains open all the time and the gun becomes unregulated. It continues to fire, although most shooters notice a change in the discharge sound when their gun is “off the reg.”


Without getting into design details, this is how an air regulator functions. As long as the air pressure in the reservoir is greater than the pressure setting for the reg, the reg closes after the regulated pressure has passed into the firing chamber. Once the reservoir pressure drops below the reg pressure setting, the reg never closes and the gun operates as an unregulated gun.

Okay, let’s examine this closer. The reg allows high-pressure air to flow into a small chamber called the firing chamber. When the pressure in the firing chamber reaches a certain level, the regulator closes the air flow. The firing valve of a regulated PCP opens to release the pressurized air from the firing chamber. This air is at optimum pressure for the way the firing valve has been tuned…the size of the air passageway through the valve, the strength of the valve return spring (which affects the speed at which the valve closes) and the volume of the firing chamber. The gun is perfectly tuned when the air from the firing chamber expends all of its energy (to the extent that is practical) just as the pellet reaches the end of the barrel.

The output of a regulated airgun is affected by both the pressure inside the firing chamber and the volume of the firing chamber. Change either one and you change the tune of the gun. Although the illustration shows the firing chamber to be relatively large, in fact, it is much smaller than shown. In the AirForce Micro-Meter valve, the entire firing chamber fits in a small compartment inside the valve body, and even then they had to take steps to reduce the chamber volume so the gun wouldn’t be too powerful. The Micro-Meter valve and tank are not regulated, but they operate by a similar design that severely restricts airflow to the firing chamber.

How does an air pressure regulator actually work?
The pressure regulator contains a powerful spring that acts on a valve. However, this spring is not powerful enough to keep the check valve closed against the high pressure of the air reservoir. Air forces its way through the check valve and into the firing chamber. When the pressure builds inside the firing chamber, it pushes on the check valve, helping the spring close the valve against the air reservoir. To control how much pressure is in the firing chamber, the spring is adjusted until the desired pressure closes the check valve.


The inside of a regulator, simplified. When the air pressure inside the firing chamber grows high enough to assist the spring to close the regulator check valve, air stops flowing from the reservoir.

Regulators take up space!
Air volume is lost to make room for the regulator. The tradeoff for that lost space is more shots, because the reg lets the firing valve operate on a lower air pressure. Sometimes, it’s an even trade and no additional shots are gained. Other times, the regulated gun delivers a few additional shots. However, the firing valve must be tuned to work well at the reg output pressure. It’s never a given that the combination of the reg setup and the firing valve tune work well.

What prevents shooters from filling their guns to an even higher pressure to get more shots? Nothing, except the regulator itself. The spring has to be small to fit inside the reg, yet it also has to be powerful. Most regs use a special type of spring called a Belleville washer, or more correctly, a Belleville spring washer. These are cone-shaped washers stacked in different ways to achieve desired spring rates through a range of values. Once set, the spring operates within a narrow band. Belleville washer springs are strong, relative to their diameter, which makes them perfect for the inside of a regulator. However, they do have limits. They’ll do their job within the limits of their design, but they won’t hold back pressure that’s much higher than they were designed for. If you overfill the reservoir, the firing chamber will be filled with higher-pressure air and there goes the sensitive balance of the gun’s tune.

Regulators fail
It isn’t a question of “if” a regulator will fail, it’s a question of “when.” All regs fail, and when they do they have to be serviced. I have owned regulated airguns that worked fine for about five years, but then the O-rings went bad and the regs had to be rebuilt. Leaking seals are a real problem with a reg, as are failed Belleville washers, though in my experience they’re not as much a problem as seals. The point is that all guns with regulators eventually require maintenance, though they may give many good years of service.

Because reglators are complex and less reliable, the USFT rifle doesn’t have one. Instead, it operates on lower-pressure air for which a firing valve can be tuned to give an incredible number of uniform shots. That’s an interesting direction that no other airgun manufacturer has yet taken. Walther, on the other hand, has gone the opposite route of greater dependence on regulators to moderate their 300-bar (4,350 psi) operating pressure level. Both approaches work and both have good reasons for their use. It isn’t a question of whether it is better to have a regulated gun or not; it’s really up to the shooter to understand the technology he’s shooting, so he can get the maximum benefit from it.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

34 thoughts on “How does an air pressure regulator work?”

  1. Sumo,

    The Umarex website makes no mention of a Lothar Walther barrel, and they would brag if it had one, so I will say no, it doesn’t.

    The looks come from the CO2 850 AirMagnum that they have sold under the RWS and Hammerli names. Great little gun, but quite a stretch to bump it up to over $800, I think.

    Plus that, the 300-bar fill will be the kiss of death for American sales.


  2. BB,

    Thanks for Explanation Of regulated Valves. I understand it completely now. BB why will the 300 bar fill be the kiss of death?

    BB, Have you no mercy? I think that half the people who read this blog are on suicide watch waiting for these next two “surprises”, I know I am.(smile)

    Sumo, when you say the Walther looks terrible for the money, do you mean that it’s ugly?

  3. B.B.

    This is intense. There must be something to pre-charged airgunning to make you guys put up with all this. I’ll ask something more basic. I seem to recall reading somewhere that pre-charged guns were best for long-distance shooting, and I would like to hear more. Given that a powerful springer like the BAM B30, reported at 1175fps, has equivalent velocity/muzzle energy to many PCPs, why would an equivalent PCP be better for longer ranges? I know the PCP is easier to shoot without recoil, so if that’s the answer I understand. And I’m also assuming there is no difference in twist rate or bullet. Do PCPs have more consistent velocity? Is there something else?


  4. BobC,

    300 bar is the kiss of death because Americans are not set up for it. We will be in another five-ten years, but we’re not even a nation that embraces PCPs, so don’t ask us to like something that is three times as difficult to get filled.

    Yes, if you have already found the 300-bar solution this doesn’t apply to you, but many Americans are not located where there is 300-bar air.


  5. Matt,

    PCPs are SO MUCH EASIER to shoot accurately that there is no contest! It isn’t that they are more accurate.

    And if a person practices a lot they can become deadly with a springer. But the average shooter coming over from firearms will find a PCP about 3-4 times more accurate at ranges beyond 40 yards.


  6. B.B.

    Thanks, this is interesting. How do PCPs/pneumatics compare to CO2 guns which also have little or no recoil? That was the case with my Crosman 1077 before the disaster.

    Also, I’ve read, from Robert Beeman among others, that airgun shooting can improve firearms marksmanship, but it seems that both spring guns and pneumatics diverge from firearms in significant ways. Springers require a soft hold and pneumatics have no recoil. Do both improve firearms marksmanship, or one more than the other?


  7. Matt,

    PCPs and CO2 guns compare very nicely. PCPs are about 25 to 50 percent more powerful (and some are many times more powerful) and they are not temperature-dependent.

    CO2 guns get many more shots per fill, because the CO2 is in liquid form, while the air is a gas, only.

    Both springers and PCPs improve marksmanship. but the springers do more than the PCPs. Because a spring gun starts moving while the pellet is still inside the barrel a neutral hold and follow-through are very important to accuracy.


  8. Bobc,

    I can get 300 bar air no prob. I cant see myself picking that over other guns in the same price range like an air arms.

    The gun is the same as the Walther 850 but with air operation.

    With that said. Its a $200 gun with a $600 air tank (yes i know the inner parts like the valve are more complicated).

    The 850 is an decent gun but thats for its class. The 1250 is a $200 in a $800 class.

    …….and a guns only as good as its barrel.

    remember what i say is just another opinion.

    Does that answer your question?


  9. B.B.

    This may jangle some nerves but I merely wish to know. Apart from its looks, does a wood stock have any practical advantage over a synthetic stock? When I read about accurizing rifles, one of the first things they talk about is getting a synthetic stock which does not deform in response to the weather. Sounds like a good idea. So, why have a wood stock at all?


  10. Sorry to get off topic, B.B.
    here in Pennsylvania, it is illegal to hunt with airguns. Something I’m not so sure about is springers. one of The PA Game Commissions classifcations of ‘firearms’ is “An instrument that propels an object by force of a mechanical device under tension.”
    Could a spring piston airgun be classified as this?

  11. PA gunner,

    I’m not a judge but that description sounds like a spring to me.

    However, the Penn. legislators may have made a mistake here, because they are not supposed to declare an airgun to be a firearm, which sounds like what they have done. To do that violates federal law. They don’t seem to be using the BATF&E description of a firearm, which contains words about chemical combustion etc. as a propulsive force, unless that is another of their definitions.

    Still, you have to abide by the law, which in this case seems to be trying to exclude airguns. Yes, a PCP would get around this part of the law, but I haven’t read the rest of it.


  12. i just wanted to let you know about something i tryed, i have a condor and noticed on lot power it was very inconsistant, so i had the co2 adaptor, so i got a 3000 psi regulated paintball tank, out pressure is 800psi. it shoot cp’s at 720 in .22 cal with 15 fps spread. i love it i get a ton of shoots and can run my scuba tank almost empty. and i still have the original tank for high power hunting. plus the tank was 85 dollars compared to 200 for the micro meter tank. jus thought i would let people know about this alternative.


  13. Here in Canada you need a permit for anything above 500 fps.
    So a lot of airguns are advertise at 495 fps.
    But I see LOTS of guns that are also sold in the US but are advertise at higher speeds.
    Does anybody can help me with this?
    Are they the same gun but tested with a heavier pellet or is some kind of regulator used etc.


  14. Sumo,

    I think I gotcha Sumo. Thanks for your response to that question and last weeks PCP question.

    You seem to be one of the PCP gurus on this blog. And like the professor said to Klatu in “The Day The Earth Stood Still”, I have several thousand questions to ask you. What was your first PCP and what is your fav PCP?

    BB, Thanks for your explanation also.


  15. Bobc,


    If you look at the comments from last week you will see that the career 707 was my first airgun.

    i cant say i have a favorite but i must say Theoben has served me well. The Daystate Airwolf is at least as good as it if not better but it shouldn’t have come with the problems that it did (the pellets let the door (shroud end cap) hit them on the way out). The Theoben was less expensive too. Money is not an issue when buying guns though. LOL with the Theobens i can put a scope on them sight them in and have them shooting perfectly in under a half hour. BB can do that with any gun in less time. Nobody could with the pellets hitting the shrouds end cap.

    If i were to recommend 1 pcp to anyone it would be a Theoben rapid mk2. I would recommend the airwolf strongly too but not as a first pcp. That wouldn’t do anyone any good. It discouraged me.

    lets see:
    Theoben took under 30 minutes to get going.
    Daystate took 3 months.

    I am proud of myself for not giving up on it (airwolf). With the custom shroud on it and the big scope it looks soooo cool! I wouldn’t feel complete without both of them. LOL

    I think they have the same barrels. Anchuts or luther Walther. As the bluing is identical.

    These two guns are expensive but they are my favorite. Thats the question you asked. You may fly privately and eat more caviar than goldfish but very few are willing to spend that money on a “bb gun”. Its silly for me to have done so, again, money aside. Its justified by the fact that its one of the things i enjoy.

    Never too old to play with bb guns.


  16. J-F

    The airguns that go to Canada are power-restricted guns. They may not generate velocity greater than 500 f.p.s. with any pellet, so the manufacturer has to test them with every potentially fast pellet. Every time a company like Gamo comes out with a fast pellet like the Raptor, they force the airgun companies to further restrict the power potential of their guns going to Canada.

    How they do it depends on the powerplant. Spring guns are de-stroked, which means the piston stroke is reduced. CO2 and pneumatic guns get smaller gas passages in their valves. Pneumatics can also get things like reduced firing chambers, shorter barrels and so on.


  17. Are the QB 57 side springers a thing of the past? All of a sudden, they seem to be out of stock, another model name (66 or 67), with synthetic stock, but very similar rifle, being available.

  18. BB, thanks for the “three in one oil remedy” for my daisy 120. power has definately improved. any recommendations for future maintanance/ improvements? keep up the good work, yamadogg.

  19. B.B.

    Nice explanation on the regulator. I had been googling to find how a PCP works and landed, well, where else…..

    Surprisingly have not yet come across a detailed explanation on how PCP’s work.

    So how about a detailed writeup on how PCP’s work…diagrams and all…



  20. Springers are effective enough and generally more economical than precharged, but their big disadvantage is that there is absolutely no possibility of maintaining a consistent posture between successive shots. The expenditure of effort and the large range of motion required to recock any design of spring piston gun mean you have to release your grip (invariably with your stock hand, not your trigger hand) and move practically your whole body, so you have to get back into a good firing posture from scratch every single time. Not to mention, trying to recock a springer when prone (my favourite position, unfortunately) is simply farcical. Oh, and unless it’s got a magazine of some kind, you could never hope to recock a springer fast enough for snapshooting.

    If you’re hunting, for example, and only likely to get one shot anyway, springers are fine. At the other extreme, if you’re trying to get a get a good grouping of five shots or so from prone on a range, trying to use a springer is pure masochism. Of course, if a springer’s all you can afford, it’s still better than nothing.

  21. Thanks for the straight forward explanation of regulators!

    What I fail to understand from the diagram is how the gun goes “off the reg”. Once the pressure in the main reservoir is less than the spring setting, how does it fill the firing chamber at all?

    More importantly, I seem to see two approaches to regulator design: one that requires a small hole drilled into the reservoir tube next to the body of the regulator, between O rings that isolate the hole from the air reservoir and from the firing chamber, and another approach where the vent appears to be via the screw threads around the firing valve.

    – What is the purpose of this vent in the operation of the regulator?
    – Is there a benefit of one design over the other (aside from the reluctance to drill a permanent hole in your air tube)?
    – How does the second design (without the drilled hole) work without spilling all the pressure from your firing chamber?

    Thanks again,

    • Ronbow,

      Welcome to the blog.

      The diagram above is not exact. It just coveys the idea of a reg, not how one is actually built. You are correct that the design above wouldn’t open at all after the pressure dropped too low.

      Please join us on the current page if you want to continue this discussion.



      • Hey, I’m working on a project and I think a regulator out of an airsoft or other air gun that will work with a standard 12g CO2 cartridge would be perfect for it. The problem I’m having is that I can’t find a source to buy just a regulator, replacement part places don’t seem to have them and neither does any where else I’m looking. Do you have any idea where I could found what I’m looking for? Thanks

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