CO2 Systems for tire inflation

On Sat, 16 Oct 2004 09:05:39 +0100, Zog The Undeniable
wrote:

Werehatrack wrote:


For certain values of the word "well", yes. Be aware that air is a
better inflation gas; CO2 will escape through the pores of the tire
faster than air.

Does it? CO2 molecules (about 20g/litre at 10 bar) are heavier and
larger than O2 (14g/litre) and N2 (12.5g/litre) molecules. Were you
thinking of helium, which is very difficult to keep in any container?

Incidentally, a racing tyre isn't far off 1 litre in air volume.

Oops, you're right, CO2 is a larger molecule. If that was the only
criterion tha counted, then Xenon would be a better choice still, with
a molecular diameter that's significantly larger than any of those
mentioned.

Hmmm. I've seen it stated in numerous places that real-world
experience was that CO2 inflation was subject to high permeability
losses. I wonder if the problem might actually be that CO2 is
slightly soluble in the tire compound matrix instead? Certain
refrigerants have this problem with a number of common hose and o-ring
compounds, with the result that materials choice can be critical in
that area. Use the wrong compound in the o-rings of an R134 system,
for instance, and the o-rings will absorb the 134 on the system side,
and then try to expand out of the atmosphere side...as foam.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Sat, 16 Oct 2004 17:12:51 GMT, Werehatrack
wrote:

On Sat, 16 Oct 2004 09:05:39 +0100, Zog The Undeniable
wrote:

Werehatrack wrote:


For certain values of the word "well", yes. Be aware that air is a
better inflation gas; CO2 will escape through the pores of the tire
faster than air.

Does it? CO2 molecules (about 20g/litre at 10 bar) are heavier and
larger than O2 (14g/litre) and N2 (12.5g/litre) molecules. Were you
thinking of helium, which is very difficult to keep in any container?

Incidentally, a racing tyre isn't far off 1 litre in air volume.

Oops, you're right, CO2 is a larger molecule. If that was the only
criterion tha counted, then Xenon would be a better choice still, with
a molecular diameter that's significantly larger than any of those
mentioned.

Hmmm. I've seen it stated in numerous places that real-world
experience was that CO2 inflation was subject to high permeability
losses. I wonder if the problem might actually be that CO2 is
slightly soluble in the tire compound matrix instead? Certain
refrigerants have this problem with a number of common hose and o-ring
compounds, with the result that materials choice can be critical in
that area. Use the wrong compound in the o-rings of an R134 system,
for instance, and the o-rings will absorb the 134 on the system side,
and then try to expand out of the atmosphere side...as foam.

Dear Zog and Werehatrack,

Honest, Peter cited a link a few months ago that explains
this. Here's the relevant section:

In the "Polymer Handbook" (Ed. Brandrup & Immergut, 2nd Ed.
1975. Wiley), page III-230, it says:

'The permeation of small molecules through flawless polymer
films occurs by the consecutive steps of solution of
permeant in the polymer and diffusion of the dissolved
permeant.'

In the table for Natural rubber which follows (page
III-233), the following permeabilities are given: oxygen
23.3, argon 22.8, nitrogen 9.43, carbon dioxide 153.
Permeability is governed by solubility and diffusion. There
is little difference in the respective diffusion
coefficients: 1.73, 1.36, 1.17, and 1.25 for the four gases
(note that diffusion coefficients through the polymer do not
reflect either molecular size or molar mass directly).
The striking difference in the permeability figure for
carbon dioxide is associated with solubility in the rubber:
heat of solution figures are -4.2 kJ/mol for oxygen, -0.1
for argon, +2.1 for nitrogen, but -12.5 for carbon dioxide.

http://www.madsci.org/posts/archives...2329.Ch.r.html

Carl Fogel

On Sat, 16 Oct 2004 17:12:51 GMT, Werehatrack
wrote:

On Sat, 16 Oct 2004 09:05:39 +0100, Zog The Undeniable
wrote:

Werehatrack wrote:


For certain values of the word "well", yes. Be aware that air is a
better inflation gas; CO2 will escape through the pores of the tire
faster than air.

Does it? CO2 molecules (about 20g/litre at 10 bar) are heavier and
larger than O2 (14g/litre) and N2 (12.5g/litre) molecules. Were you
thinking of helium, which is very difficult to keep in any container?

Incidentally, a racing tyre isn't far off 1 litre in air volume.

Oops, you're right, CO2 is a larger molecule. If that was the only
criterion tha counted, then Xenon would be a better choice still, with
a molecular diameter that's significantly larger than any of those
mentioned.

Hmmm. I've seen it stated in numerous places that real-world
experience was that CO2 inflation was subject to high permeability
losses. I wonder if the problem might actually be that CO2 is
slightly soluble in the tire compound matrix instead? Certain
refrigerants have this problem with a number of common hose and o-ring
compounds, with the result that materials choice can be critical in
that area. Use the wrong compound in the o-rings of an R134 system,
for instance, and the o-rings will absorb the 134 on the system side,
and then try to expand out of the atmosphere side...as foam.

Dear Zog and Werehatrack,

Honest, Peter cited a link a few months ago that explains
this. Here's the relevant section:

In the "Polymer Handbook" (Ed. Brandrup & Immergut, 2nd Ed.
1975. Wiley), page III-230, it says:

'The permeation of small molecules through flawless polymer
films occurs by the consecutive steps of solution of
permeant in the polymer and diffusion of the dissolved
permeant.'

In the table for Natural rubber which follows (page
III-233), the following permeabilities are given: oxygen
23.3, argon 22.8, nitrogen 9.43, carbon dioxide 153.
Permeability is governed by solubility and diffusion. There
is little difference in the respective diffusion
coefficients: 1.73, 1.36, 1.17, and 1.25 for the four gases
(note that diffusion coefficients through the polymer do not
reflect either molecular size or molar mass directly).
The striking difference in the permeability figure for
carbon dioxide is associated with solubility in the rubber:
heat of solution figures are -4.2 kJ/mol for oxygen, -0.1
for argon, +2.1 for nitrogen, but -12.5 for carbon dioxide.

http://www.madsci.org/posts/archives...2329.Ch.r.html

Carl Fogel

On Sat, 16 Oct 2004 12:13:35 -0600, wrote:

On Sat, 16 Oct 2004 17:12:51 GMT, Werehatrack
wrote:

Hmmm. I've seen it stated in numerous places that real-world
experience was that CO2 inflation was subject to high permeability
losses. I wonder if the problem might actually be that CO2 is
slightly soluble in the tire compound matrix instead? [snip]

Dear Zog and Werehatrack,

Honest, Peter cited a link a few months ago that explains
this. Here's the relevant section:

In the "Polymer Handbook" (Ed. Brandrup & Immergut, 2nd Ed.
1975. Wiley), page III-230, it says:
[snip]

In the table for Natural rubber which follows (page
III-233), the following permeabilities are given: oxygen
23.3, argon 22.8, nitrogen 9.43, carbon dioxide 153.

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given that
data, I'd have to consider CO2 inflators to be merely a convenience,
not a valid substitute for a pump. On a tour, this could be an
important thing to take into consideration.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Sat, 16 Oct 2004 12:13:35 -0600, wrote:

On Sat, 16 Oct 2004 17:12:51 GMT, Werehatrack
wrote:

Hmmm. I've seen it stated in numerous places that real-world
experience was that CO2 inflation was subject to high permeability
losses. I wonder if the problem might actually be that CO2 is
slightly soluble in the tire compound matrix instead? [snip]

Dear Zog and Werehatrack,

Honest, Peter cited a link a few months ago that explains
this. Here's the relevant section:

In the "Polymer Handbook" (Ed. Brandrup & Immergut, 2nd Ed.
1975. Wiley), page III-230, it says:
[snip]

In the table for Natural rubber which follows (page
III-233), the following permeabilities are given: oxygen
23.3, argon 22.8, nitrogen 9.43, carbon dioxide 153.

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given that
data, I'd have to consider CO2 inflators to be merely a convenience,
not a valid substitute for a pump. On a tour, this could be an
important thing to take into consideration.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack wrote in
:

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given that
data, I'd have to consider CO2 inflators to be merely a convenience,
not a valid substitute for a pump. On a tour, this could be an
important thing to take into consideration.

Interesting, I didn't know this. But what's the practical result? I can't
tell from those numbers. How much pressure would you lose if you flatted
and re-filled with CO2 in the middle of a 7 day tour, for example? Would it
be enough to matter?

Someone with a couple of extra wheels sitting around should try filling one
with air, and the other with CO2 to the same pressure. Then let 'em sit for
a week or two, and compare the pressure loss.

BTW, I recently bought one of those systems (I forget the brand name) that
uses the same inflator head for both a CO2 cartridge and a mini-pump. So
(in theory) you're covered both ways... the CO2 for convenience, and the
pump if you need to top off, or if you get multiple flats and run out of
CO2. I haven't flatted since buying it, so I don't know how well it works
yet.

--
Mike Barrs

Werehatrack wrote in
:

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given that
data, I'd have to consider CO2 inflators to be merely a convenience,
not a valid substitute for a pump. On a tour, this could be an
important thing to take into consideration.

Interesting, I didn't know this. But what's the practical result? I can't
tell from those numbers. How much pressure would you lose if you flatted
and re-filled with CO2 in the middle of a 7 day tour, for example? Would it
be enough to matter?

Someone with a couple of extra wheels sitting around should try filling one
with air, and the other with CO2 to the same pressure. Then let 'em sit for
a week or two, and compare the pressure loss.

BTW, I recently bought one of those systems (I forget the brand name) that
uses the same inflator head for both a CO2 cartridge and a mini-pump. So
(in theory) you're covered both ways... the CO2 for convenience, and the
pump if you need to top off, or if you get multiple flats and run out of
CO2. I haven't flatted since buying it, so I don't know how well it works
yet.

--
Mike Barrs

Mike Harris writes:

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given
that data, I'd have to consider CO2 inflators to be merely a
convenience, not a valid substitute for a pump. On a tour, this
could be an important thing to take into consideration.

Interesting, I didn't know this. But what's the practical result? I
can't tell from those numbers. How much pressure would you lose if
you flatted and re-filled with CO2 in the middle of a 7 day tour,
for example? Would it be enough to matter?

Someone with a couple of extra wheels sitting around should try
filling one with air, and the other with CO2 to the same
pressure. Then let 'em sit for a week or two, and compare the
pressure loss.

If it is anything like latex tubes of tubulars, you need to pump
daily. I can recall that only in cold weather I could skip pumping on
some mornings. I don't care to even pump once a week, considering
that an air inflated tire, in the absence of a puncture, requires no
pumping in a month.

Jobst Brandt

Mike Harris writes:

Sonofagun, then, I had it right about CO2 being soluble in rubber
compounds. Well, that explains it adequately enough. So, given
that data, I'd have to consider CO2 inflators to be merely a
convenience, not a valid substitute for a pump. On a tour, this
could be an important thing to take into consideration.

Interesting, I didn't know this. But what's the practical result? I
can't tell from those numbers. How much pressure would you lose if
you flatted and re-filled with CO2 in the middle of a 7 day tour,
for example? Would it be enough to matter?

Someone with a couple of extra wheels sitting around should try
filling one with air, and the other with CO2 to the same
pressure. Then let 'em sit for a week or two, and compare the
pressure loss.

If it is anything like latex tubes of tubulars, you need to pump
daily. I can recall that only in cold weather I could skip pumping on
some mornings. I don't care to even pump once a week, considering
that an air inflated tire, in the absence of a puncture, requires no
pumping in a month.

Jobst Brandt

Werehatrack wrote:
Oops, you're right, CO2 is a larger molecule. If that was the only
criterion tha counted, then Xenon would be a better choice still, with
a molecular diameter that's significantly larger than any of those
mentioned.

I say we fill our tires with cholesterol.

--Blair
"Keep a supply with me at all times anyway."