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Why aren't they filled with ambient air using air compressors? Isn't compressing ambient air cheaper than generating CO2? If it is, then those cartridges would have two benefits:

  • Cheaper to manufacture
  • CO2 filled tires deflate on their own far quicker than ambient air, so using air will mean, once you inflate your tire with a cartridge, you will not have to inflate it again when you are back home.
Argenti Apparatus
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Tooniis
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    Getting the water out of normal air is a bitch and needs lots of of equipment. Check any dive shop. – Aganju Sep 15 '17 at 01:09
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    It is technically impractical (if not impossible) to compress a sufficient amount of regular air into a cartridge the size/weight of the CO2 cartridge. CO2 is much more compressible than regular air. – Daniel R Hicks Sep 16 '17 at 02:16
  • @Aganju - Getting water out of air is not really that big of a deal. The problem with water is that if the folks doing the tank filling don't take proper care they can fill a tank with water rather than air. – Daniel R Hicks Sep 16 '17 at 21:12
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    @DanielRHicks "CO2 is much more compressable than regular air" that explains it all. Your comment should have been an answer. – Tooniis Sep 17 '17 at 12:56
  • Pressurized air will leak. Co2 turns into a liquid in these canisters so it will not leak. – SurpriseDog Sep 10 '19 at 16:18

3 Answers3

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CO2 charger cartridges are used for bike tire inflation because they are a common, inexpensive product that has been around since the 1950s. Their other uses include powering air guns and inflating life vests.

They were originally developed by the Crosman Corporation and marketed under the name "Powerlet".

Powerlet cartridges are filled with CO2 presumably because it's the most suitable gas. Reasons I can think of are:

  • CO2 turns into a liquid at relatively low pressure compare to other gases - liquids are much denser than gasses so a useful amount of CO2 can fit in a small container.
  • Containers are easy and cheap to make to withstand the required pressure
  • CO2 is cheap and easy to make (although probably not very environmentally friendly).
  • CO2 is inert, will not react with the container material. It isn't flammable but heating a cartridge probably isn't a good idea.

Updates to my answer seeing as it popped back up on the main page for some reason.

CO2 cartridges are not filled with compressed CO2, they are filled with liquid CO2. That has to be done to get enough of the stuff in the cartridge to be useful. The cartridge is not completely filled however, and the gas pressure in the space is essentially constant (the vapor pressure) as long as there is some liquid CO2 remaining.

You can't put liquid air in a cartridge because it's comprised of nitrogen, oxygen, water vapor and CO2, all of which have different boiling points. In fact, C02 turns to a solid before nitrogen turns to a liquid.

Argenti Apparatus
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    1,2 and 4 are good reasons, but is making CO2 cheaper than powering air compressors to compress air into the cartridges? – Tooniis Sep 14 '17 at 12:13
  • As the current state of climate engineering indicates, not easy to extract from the atmosphere at scale. (That would make it one of the mythical "negative emission technologies", which don't exist but which still form the basis of many climate modelling scenarios on which the Paris Agreement is based.) – compton Sep 14 '17 at 12:28
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    Obviously using atmospheric air is unsuitable, as we don't see any 'canned' pressurized air products (think cans of compressed gas for removing dust from keyboards, which are actually filled with refrigerant) perhaps you should ask this question in the Physics Stack Exchange site. – Argenti Apparatus Sep 14 '17 at 12:42
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    But my guesses are that much higher pressures have to be reached to get oxygen or nitrogen to liquify, and water vapor has to be removed – Argenti Apparatus Sep 14 '17 at 12:46
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    There is also the issue of the water vapor in compressed air freezing when the container is depressurized. – mikes Sep 14 '17 at 13:04
  • @Tooniis The cartridge handles about 5 atmosphere. That is not enough air to inflate a tire. – paparazzo Sep 14 '17 at 14:16
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    Similar CO2 cartridges have a long history for carbonating drinks as well, for which other gases don't work (soda syphon cartridges) – Chris H Sep 14 '17 at 14:58
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    FWIW this says In almost all cases, carbon dioxide which is captured and purified for commercial applications would be vented to the atmosphere at the production point if it was not recovered for transport and beneficial use at other locations. (Regarding point #3 parenthetical.) – Mr.Wizard Sep 14 '17 at 16:06
  • @Paparazzi The gas pressure in CO2 cartridges is about 60 atmospheres, depending on temperature. – Kevin Krumwiede Sep 14 '17 at 20:51
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    CO2 turning into a liquid at a relatively low pressure gives it a sort of self-regulating effect. The pressure of the gas on top of the liquid remains steady until the liquid is gone. This doesn't directly explain why they're used for tires, but it explains why they're used in airguns, which is what made them cheap and plentiful for other uses. – Kevin Krumwiede Sep 14 '17 at 20:55
  • @KevinKrumwiede Not buying – paparazzo Sep 14 '17 at 22:23
  • @Paparazzi "As long as a CO2 cylinder is at a reasonable, constant temperature, as gas is (slowly) used out of the cylinder liquid CO2 'boils' off as gaseous CO2, at the vapor pressure of CO2 at that temperature. This is about 860 psi at normal room temperature, or about 72 degrees Fahrenheit. This process of evaporation continues until all the liquid CO2 is gone." Link Many other sources give similar figures. – Kevin Krumwiede Sep 14 '17 at 22:28
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    @KevinKrumwiede And we use CO2 for these purposes instead of nitrogen because the 800-900 psi room temperature vapor pressure of CO2 is extremely manageable while the 60,000-70,000 psi vapor pressure of LN2 very definitely is not. – Perkins Sep 14 '17 at 23:38
  • @Paparazzi Well, I don't know what to tell you. I challenge you to find a single source that backs up your claim. I think you're confusing CO2's vapor pressure at its triple point (-56.6C) with its vapor pressure at room temperature. – Kevin Krumwiede Sep 15 '17 at 23:04
  • "CO2 is inert and therefore safe in a fire" Sure, CO2 isn't flammable... but exposing any pressurized container to fire is usually considered a bad idea. – NPSF3000 Sep 16 '17 at 02:45
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    @NPSF3000 - true, I made an edit. – Argenti Apparatus Sep 16 '17 at 13:33
  • CO2 is not inert. If one should have fancy-dancy magnesium rims there is a non-trivial chance that one could have a near explosion in some sort of accident or collision that ruptured the wheel and threw sparks. – Daniel R Hicks Sep 17 '17 at 01:01
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I believe you will find these articles informative:

At room temperature (below the 31°C/87.8°F critical temperature) a CO2 bottle is to a practical extent self-regulating. This is not possible with simple compressed air. You would need a larger, stronger, heavier "high pressure air" bottle with a regulator (and its associated cost and complexity) to serve the same function.

This makes CO2 far more suited to a bicycle repair kit due to:

  • small size
  • low weight
  • low cost
  • reliability (simplicity)

This video of supercritical carbon dioxide provides an interesting window (both literal and figurative) into the phase behavior described in the articles above:

Mr.Wizard
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  • Does this mean that CO2 cartridges don't work properly above 31°C? That's not a very high temperature. – David Richerby Sep 14 '17 at 14:51
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    @David It means that the pressure starts increasing substantially around that point. For tire inflation this shouldn't be a problem assuming the inflator itself is well designed, however there is a limit to the ambient temperature to which a cartridge may be safely exposed, which I believe is given as 120°F (quoted in the second article). It also shows a photo of a burst cartridge with the caption "Powerlet ruptured by exposure to 180° F temperature in manufacturer’s test" so I presume there is a healthy safety margin included in that 120°F specification. – Mr.Wizard Sep 14 '17 at 15:01
  • @David Practically speaking cold temperatures are likely more of a problem as the cartridge will be very slow when cold. A simple solution would be to keep one next to your body. – Mr.Wizard Sep 14 '17 at 15:04
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    Yeah, practically speaking, I'm gonna be more badly damaged by exposure to temperatures in excess 120°F than the cartridge is. :-D – David Richerby Sep 14 '17 at 15:06
  • Don't leave one on your dashboard in Phoenix in July however. :^) @David – Mr.Wizard Sep 14 '17 at 15:07
  • @DavidRicherby I'd much prefer 120F than to be around one of those cylinders exploding. While I've never been in 120F I've been close to it multiple times (just this year we tied our record high at 117F)--hot but not harmful so long as you have enough water. – Loren Pechtel Sep 16 '17 at 19:39
  • Cartridge exploding on video, see Going Full Gas here. I'm doubtful that the temp was over 120F, looks like an English school playing field, though it could have been baking in the sun during the swim (strapped to the frame). @David remember to put them inside a bag or box next time you're triathlonating ;) – Swifty Jul 11 '19 at 08:40
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    @Swifty Into Tri is a UK organization and on a cloudy day like that, the temperature isn't going to be above 25C/75F, and these events are usually in the morning when it's at least a few degrees cooler. Assuming the video is recent, the temperature hit 33C/91F a couple of weekends ago, but that was a sunny day, so not when the video was taken. The UK has never come close to 120F: the record is 101F (38C). Long story short, no idea why that cartridge went off but it wasn't heat. (Actually, the plume of vapour suggests that it leaked, rather than exploding.) – David Richerby Jul 11 '19 at 08:48
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This explains part of the reason in what may be too much detail:http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/deviation5.html If you're going to read any of it, read the material starting after the table listing "van der Waals Constants for the Various Gases". It calculates that compressing CO2 from 1 Liters to 0.2 Liters using the Ideal Gas Law (which will be nearly correct for air) "the pressure would have to be increased to 112 atm" but that for CO2 (at 0°C) "The van der Waals equation, however, predicts that the pressure will only have to increase to 52.6 atm". This is much less pressure for the same volume of gas (at normal atmospheric pressure). Think about the safety aspects: the container for this won't need to be nearly as strong (as expensive) as one for the same std. volume of air. Economically and safety wise, it's a no-brainer.

redrubberball
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