CO2 cannisters... why not compressed air?

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CO2 cannisters... why not compressed air?

Postby chriscole » Wed Mar 20, 2013 11:49 am

Hi folks,

Being a habitual frame pump devotee (not _too_ habitual... I don't pop tyres toooo often), I have just bought my first CO2 cannisters and valve attachment bits, as my particular frame pump tends to get a bit unmanageable once I've got the patched or replaced tube up to about 60-80 PSI (road bike).

What I'm curious about is why the gas cannisters marketed for this purpose are filled with (mostly?) carbon dioxide? I'm guessing it's purely economics, since unless I'm missing something (and I suspect I very well might be), re-inflating your tube with air is a better option than CO2 (i.e. you wouldn't have to re-inflate the tube with air again later if the cannister had air in it to start with).

I find it difficult to believe that it costs more to compress ambient air into a cannister than it does to compress CO2.

Is the cycling industry just decades ahead of the curve on carbon dioxide sequestration initiatives, or is there some other mystical reason at play here? :-)

Chris
Last edited by chriscole on Wed Mar 20, 2013 2:34 pm, edited 1 time in total.
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by BNA » Wed Mar 20, 2013 12:01 pm

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Re: CO2 cannisters... why not compressed air?

Postby MattyK » Wed Mar 20, 2013 12:01 pm

Probably because cheap CO2 cannisters existed before CO2 refillers for bikes existed, and they're just leveraging an existing (read: cheap) supply chain.
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Re: CO2 cannisters... why not compressed air?

Postby il padrone » Wed Mar 20, 2013 12:05 pm

Yep. Readily available CO2 canisters..... used for soda bottles in bars and pubs, amongst other things. You don't get carbonated water with pressurised air :wink:
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Re: CO2 cannisters... why not compressed air?

Postby TDC » Wed Mar 20, 2013 12:30 pm

and because of safety...you saw what happened to Jaws, didn't you?
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Re: CO2 cannisters... why not compressed air?

Postby rebilda » Wed Mar 20, 2013 12:33 pm

Isnt the CO2 cannister filled with liquid CO2? (ultimate compression) CO2 is also an inert gas, meaning that it doesnt really react with anything adversly, or ignite with a spark or flame.
Nitrogen could also be an alternative, but you might not like the price. Oxygen has a tendency to intensify flames or even explode under the right conditions, so that isnt a great idea either.

"Air" is a cocktail of loads of different gasses, so compressing it to a size that fits into your pocket could be tricky. Normal compressed air, say from a home or even an industrial air compressor would require a very large canister to fill a bike tube.

Readlly available, pre-existing CO2 canisters, addapted to suit your bike, is an inexpensive and convenient solution.
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Re: CO2 cannisters... why not compressed air?

Postby petie » Wed Mar 20, 2013 12:40 pm

rebilda wrote:Isnt the CO2 cannister filled with liquid CO2? (ultimate compression) CO2 is also an inert gas, meaning that it doesnt really react with anything adversly, or ignite with a spark or flame.
Nitrogen could also be an alternative, but you might not like the price. Oxygen has a tendency to intensify flames or even explode under the right conditions, so that isnt a great idea either.

"Air" is a cocktail of loads of different gasses, so compressing it to a size that fits into your pocket could be tricky. Normal compressed air, say from a home or even an industrial air compressor would require a very large canister to fill a bike tube.

Readlly available, pre-existing CO2 canisters, addapted to suit your bike, is an inexpensive and convenient solution.

worth quoting
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Re: CO2 cannisters... why not compressed air?

Postby Magnum9 » Wed Mar 20, 2013 1:12 pm

Yes its liquid, which is why they get so cold when used, the liquid is boiling off as a gas generating massive volumes of gas. You would never get the volume and pressure required with plain air.
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Re: CO2 cannisters... why not compressed air?

Postby clackers » Wed Mar 20, 2013 2:01 pm

Obviously there are safety reasons, but if we concentrate just on the economics, a measure of how costly it is to compress a gas is its boiling point.

CO2 liquefies at -60 degrees at normal pressure.

The main component of air is nitrogen (-196 degrees) and the secondary component is oxygen (-180 degrees).
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Re: CO2 cannisters... why not compressed air?

Postby MattyK » Wed Mar 20, 2013 2:21 pm

Whipped cream bulbs would be more fun though...
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Re: CO2 cannisters... why not compressed air?

Postby a » Wed Mar 20, 2013 5:18 pm

Don't think cacking myself would get the tyre inflated.....
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Re: CO2 cannisters... why not compressed air?

Postby human909 » Wed Mar 20, 2013 9:41 pm

As others have said it is simply economics. CO2 is the cheapest safest, physically easiest gas to supply in a liquid form. The other two obvious ones of O2 and N2 have MUCH lower boiling points. Also it would be an interesting experiment to see how long your inner tubes would last in a high pressure pure oxygen environment!
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Re: CO2 cannisters... why not compressed air?

Postby ironhanglider » Thu Mar 21, 2013 4:41 pm

clackers wrote:Obviously there are safety reasons, but if we concentrate just on the economics, a measure of how costly it is to compress a gas is its boiling point.

CO2 liquefies at -60 degrees at normal pressure.

The main component of air is nitrogen (-196 degrees) and the secondary component is oxygen (-180 degrees).


Really? I thought CO2 went straight to a solid at normal pressure (and somewhat colder).

This discussion goes from the sublime to the ridiculous.

Cheers,

Cameron
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Re: CO2 cannisters... why not compressed air?

Postby human909 » Thu Mar 21, 2013 5:11 pm

ironhanglider wrote:Really? I thought CO2 went straight to a solid at normal pressure (and somewhat colder).

This discussion goes from the sublime to the ridiculous.


I see what you did there! :D You quite rightly point out that liquid CO2 cannot exist at atmospheric pressure.

However the overal point still stands that it is thermodynamically easier and cheaper to create and store liquid CO2 than N2 or O2. Getting into the exact reasons is definitely outside of the scope of discussion here. :wink:
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Re: CO2 cannisters... why not compressed air?

Postby clackers » Thu Mar 21, 2013 6:04 pm

ironhanglider wrote:
This discussion goes from the sublime to the ridiculous.


I'll pay that mark - good, clean grab out of the pack! :-D
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Re: CO2 cannisters... why not compressed air?

Postby jules21 » Sat Mar 23, 2013 2:28 pm

it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.
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Re: CO2 cannisters... why not compressed air?

Postby brit_in_oz » Sat Mar 23, 2013 6:19 pm

jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.


The cost of the gas is negligible compared to the cost of the cylinder its stored in. Its a moot point as to the cost of which gas as except for rare gases such as Argon, the gas is fraction of a cent to fill a 16g cylinder
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Re: CO2 cannisters... why not compressed air?

Postby Red Rider » Sun Mar 24, 2013 4:04 pm

jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.
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Re: CO2 cannisters... why not compressed air?

Postby warthog1 » Sun Mar 24, 2013 4:33 pm

Where's that whoosh parrot?
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Re: CO2 cannisters... why not compressed air?

Postby find_bruce » Sun Mar 24, 2013 5:05 pm

Red Rider wrote:
jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.

You won't get a more authoritative source than Jules21 from BNA
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Re: CO2 cannisters... why not compressed air?

Postby Red Rider » Sun Mar 24, 2013 5:13 pm

find_bruce wrote:
Red Rider wrote:
jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.

You won't get a more authoritative source than Jules21 from BNA

Apologies for questioning jules :oops:
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Re: CO2 cannisters... why not compressed air?

Postby greatapoc » Sun Mar 24, 2013 5:54 pm

It's simple physics. When CO2 is compressed to a certain pressure it condenses into a liquid (at room temperature, this is the important part). Air would still be a gas and you would fit barely any of it in the same canister as you would with CO2. When you put your cartridge on the inflator and release it into the tire, the pressure change turns it back into a gas and inflates your tyre.

Unrelated, here's how they're made:
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Re: CO2 cannisters... why not compressed air?

Postby jacks1071 » Sun Mar 24, 2013 6:04 pm

Whoever comes up with a cheap way to re-fill these locally could make a lot of money.
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Re: CO2 cannisters... why not compressed air?

Postby brit_in_oz » Sun Mar 24, 2013 6:42 pm

find_bruce wrote:
Red Rider wrote:
jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.

You won't get a more authoritative source than Jules21 from BNA


Perhaps Jules must be trying to wind everyone uo. As soon as you release CO2 it goes back into the atmosphere, so actually zero reduction except the amount in stored ctg :idea: :idea: :idea: . In fact it actually INCREASES the amount of CO2 emissions once you take into account the energy used to form an aluminium cyclinder, liquify the gas, transport the cyclinders etc.

On the other hand a good old hand pump has zero effect
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Re: CO2 cannisters... why not compressed air?

Postby scotto » Sun Mar 24, 2013 7:47 pm

Red Rider wrote:
jules21 wrote:it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.

The canisters from trek at rouse hill state on the label that they are produced from volcanic sources . I lol'ed when I read that .
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Re: CO2 cannisters... why not compressed air?

Postby scotto » Sun Mar 24, 2013 7:50 pm

brit_in_oz wrote:
find_bruce wrote:
Red Rider wrote:[quote="jules21"]it's mostly for environmental reasons. the CO2 is sourced from the atmosphere, so it's reducing global warming.

Really? Have you got a source for that? It'd be good if it is true.

You won't get a more authoritative source than Jules21 from BNA


Perhaps Jules must be trying to wind everyone uo. As soon as you release CO2 it goes back into the atmosphere, so actually zero reduction except the amount in stored ctg :idea: :idea: :idea: . In fact it actually INCREASES the amount of CO2 emissions once you take into account the energy used to form an aluminium cyclinder, liquify the gas, transport the cyclinders etc.

On the other hand a good old hand pump has zero effect

When will you greenies wake up. Global warming is inevitable , regardless of cause. As such, all the evil by products of western consumerism such as disposable nappies, plastic bags, and cyclists CO2 canisters , when turned into landfill will be a godsend.
As the seawater level rises, you'll wish we had more landfill, or to use its PC title, protective dyke.
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