Innertube Porosity?

In article <[email hidden]>,

Steve Sr. said:

I was wondering if anyone has any information on the porosity of
various kinds / brands of innertubes. By porosity I mean the very slow
leakdown rate that occurs with sound tubes over days and weeks. You
know... The reason you are always topping up your tires to prevent
pinch flats.

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if
"brand" makes any difference as well.

Y'know, I've had tubes of the same brand with different seepage rates.
So IMO, the particular brand may not be a useful quantifier.
There may be a variation from batch to batch with tubes from
the same manufacturer (or factory.) There may even be a variation
within batches.

I believe getting an especially air-retaining or an especially
air-losing tube boils down to the luck of the draw.

In general, tubes made from natural latex are lighter than butyl
tubes, and are somewhat more porous[*]. Perhaps the weather
conditions at the rubber plantations might cause some variation
in the quality of batches of latex tubes? I dunno -- maybe how
closely latex or butyl tubes are stored to the ship's generators
(or other cargo whose out-gassings might react with "rubber"😉
en route from China might affect their quality too.

cheers,
Tom

[*] http://www.sheldonbrown.com/tires.html

--
-- Nothing is safe from me.
Above address is just a spam midden.
I'm really at: tkeats [curlicue] vcn [point] bc [point] ca

Steve Sr. said:

I was wondering if anyone has any information on the porosity of
various kinds / brands of inner tubes. By porosity I mean the very
slow leakdown rate that occurs with sound tubes over days and weeks.
You know... The reason you are always topping up your tires to
prevent pinch flats.

Quoted message said:

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if
"brand" makes any difference as well.

I doubt that anyone has numbers but you could buy one and see if you
can put up with its inflation demands. That is what counts isn't it?
I never liked daily pumping of tubulars with latex tube especially
because we did that with a Silca frame fit pump. It is one of the
things that inspired me to design a two stage pump.

Jobst Brandt

Dans le message de news:[email hidden],
[email hidden] <[email hidden]> a
réfléchi, et puis a déclaré :

Quoted message said:

Steve Sr. said:

I was wondering if anyone has any information on the porosity of
various kinds / brands of inner tubes. By porosity I mean the very
slow leakdown rate that occurs with sound tubes over days and weeks.
You know... The reason you are always topping up your tires to
prevent pinch flats.

Quoted message said:

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if
"brand" makes any difference as well.

I doubt that anyone has numbers but you could buy one and see if you
can put up with its inflation demands.

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

The results combined the attributes of leakage, weight, valve connection,
ease of installation, fragility, uniformity and price. For full results and
the charts, you may want to pick up a copy. This is addressed to a
world-wide English reading audience, although the narrative of the article
is only in French. The numbers, however, stick to the usual Arabic based
characters we all use. Sorry that the pricing is in euros.

--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

I notice the opposite effect, which I find curious. That is, a
completely deflated inner tube, with its valve (presta) tightly
closed, partially reinflates after several days if it is not tightly
compressed. That is, when I attempt to roll it back up I have to
again loosen the valve to let out some air. What causes this? Is it
leakage at the valve? This occurs on more than one brand of butyl
inner tube.

Joe

Steve Sr. said:

I was wondering if anyone has any information on the porosity of various
kinds / brands of innertubes. By porosity I mean the very slow leakdown
rate that occurs with sound tubes over days and weeks. You know... The
reason you are always topping up your tires to prevent pinch flats.

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if "brand"
makes any difference as well.

There's certainly a difference, but I've never noted exactly how much. Of
course latex tubes need to be pumped every day. Lightweight butyl tubes
maybe every 3-4 days, and regular tubes once a week or less.
Besides the difference between lightweight and regular tubes, there are
differences between brands. Some are thicker than others.

When I buy tubes, I worry more about valves, and how easily the tube can
be patched. These days I buy only Michelin tubes, because the valves
never leak, the pump seals well, and there's minimal
flashing/seams to interfere with patching. Either the regular
"Airstop" or lightweight models are fine.

Matt O.

Joe Riel said:

I notice the opposite effect, which I find curious. That is, a
completely deflated inner tube, with its valve (presta) tightly
closed, partially reinflates after several days if it is not tightly
compressed. That is, when I attempt to roll it back up I have to
again loosen the valve to let out some air. What causes this? Is it
leakage at the valve? This occurs on more than one brand of butyl
inner tube.

Joe

Tubes lose air because they are under high pressure relative to the
atmosphere, which causes diffusion from the tube back to its
surroundings. If you push out all of the tube and seal it, now the
atmosphere is at a higher pressure than the tube. So it would make
sense that air would diffuse back into the tube, right?

--
Paul M. Hobson
Georgia Institute of Technology
..:change the f to ph to reply:.

"Paul Hobson" wrote: (clip) So it would make sense that air would diffuse
back into the tube, right?
^^^^^^^^^^^^^^^^
Doubtful. It would be virtually impossible to squeeze a tube enough to
force ALL the air out. Since the walls are flexible, the pressure in the
tube will be equal to the atmospheric pressure outside it. Possibly the
tube is put away cold, and then warms up afterward, causing the air inside
to expand. Could it be that the rubber "outgasses," releasing a little air
after the tube is deflated?

Steve Sr. said:

I was wondering if anyone has any information on the porosity of
various kinds / brands of innertubes. By porosity I mean the very slow
leakdown rate that occurs with sound tubes over days and weeks. You
know... The reason you are always topping up your tires to prevent
pinch flats.

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if
"brand" makes any difference as well.

Thanks,

Steve

there's two factors: one is actual porosity, the other is diffusion.
rubbers are subject to both, with the former being a factor of quality,
the latter is natural and can't be stopped. [condom production is a
fine example of porosity control.] for quality, stick to name brands
and look for country of manufacture.

for air, butyl rubber offers the best air diffusion/mechanical
properties ratio, hence it's common use.

Leo Lichtman said:

"Paul Hobson" wrote: (clip) So it would make sense that air would diffuse
back into the tube, right?
^^^^^^^^^^^^^^^^
Doubtful. It would be virtually impossible to squeeze a tube enough to
force ALL the air out. Since the walls are flexible, the pressure in the
tube will be equal to the atmospheric pressure outside it. Possibly the
tube is put away cold, and then warms up afterward, causing the air inside
to expand. Could it be that the rubber "outgasses," releasing a little air
after the tube is deflated?

well yeah. I didn't mean that one would create a vacuum. But if you
fold a tube, push it flat, then seal the valve, it'll be under a
negative gage pressure. That's all I was trying to say. The
temperature-driven scenario is definitely plausible - especially if you
have to change a tube on the road this time of year. No clue on the
outgassing though.

\\paul
--
Paul M. Hobson
Georgia Institute of Technology
..:change the f to ph to reply:.

Joe Riel said:

I notice the opposite effect, which I find curious. That is, a
completely deflated inner tube, with its valve (presta) tightly
closed, partially reinflates after several days if it is not tightly
compressed. That is, when I attempt to roll it back up I have to
again loosen the valve to let out some air. What causes this? Is it
leakage at the valve? This occurs on more than one brand of butyl
inner tube.

Joe

diffusion/porosity works both ways. elasticity of the tube will create
a [minimally] lower pressure inside an evacuated tube, so there's no
reason air won't migrate to reestablish equilibrium.

Paul Hobson said:

Leo Lichtman said:

"Paul Hobson" wrote: (clip) So it would make sense that air would
diffuse back into the tube, right?
^^^^^^^^^^^^^^^^
Doubtful. It would be virtually impossible to squeeze a tube enough
to force ALL the air out. Since the walls are flexible, the pressure
in the tube will be equal to the atmospheric pressure outside it.
Possibly the tube is put away cold, and then warms up afterward,
causing the air inside to expand. Could it be that the rubber
"outgasses," releasing a little air after the tube is deflated?

[snip[

Quoted message said:

The
temperature-driven scenario is definitely plausible - especially if you
have to change a tube on the road this time of year. No clue on the
outgassing though.

If you change a tube, it probable has a hole in it. Sorry (I'm still on
vacation)

\\paul

Sandy said:

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

INDEFINITE PRONOUN ALERT!

What is "its"?

--
Tom Sherman - Fox River Valley

On 30 Dec 2005 18:15:22 -0800, "Someone" <[email hidden]>

Quoted message said:

Sandy said:

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

INDEFINITE PRONOUN ALERT!

What is "its"?

A possessive pronoun with no direct one-to-one corresponding
equivalent in French.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoted message said:

Joe Riel said:

I notice the opposite effect, which I find curious. That is, a
completely deflated inner tube, with its valve (presta) tightly
closed, partially reinflates after several days if it is not tightly
compressed. That is, when I attempt to roll it back up I have to
again loosen the valve to let out some air. What causes this? Is it
leakage at the valve? This occurs on more than one brand of butyl
inner tube.

Paul Hobson said:

Tubes lose air because they are under high pressure relative to the
atmosphere, which causes diffusion from the tube back to its
surroundings. If you push out all of the tube and seal it, now the
atmosphere is at a higher pressure than the tube. So it would make
sense that air would diffuse back into the tube, right?

Agree. I think the unspoken bit here is that some tubes are
'flatter' or 'rounder' than others. If you cut out the
valve, what cross section does it display? Tubes which lie
flat in that test would be less likely to expand when left
laying around I think than tubes which 'want' to be round in
cross section.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

A Muzi said:

Quoted message said:

Joe Riel said:

I notice the opposite effect, which I find curious. That is, a
completely deflated inner tube, with its valve (presta) tightly
closed, partially reinflates after several days if it is not tightly
compressed. That is, when I attempt to roll it back up I have to
again loosen the valve to let out some air. What causes this? Is it
leakage at the valve? This occurs on more than one brand of butyl
inner tube.

Paul Hobson said:

Tubes lose air because they are under high pressure relative to the
atmosphere, which causes diffusion from the tube back to its
surroundings. If you push out all of the tube and seal it, now the
atmosphere is at a higher pressure than the tube. So it would make
sense that air would diffuse back into the tube, right?

Agree. I think the unspoken bit here is that some tubes are 'flatter'
or 'rounder' than others. If you cut out the valve, what cross section
does it display? Tubes which lie flat in that test would be less
likely to expand when left laying around I think than tubes which
'want' to be round in cross section.

Here's some idle speculation. What drives air molecules through the
rubber? Diffusion? Does the rate of gas diffusion through a material
depend on pressure?

In an inflated tube, constrained by the tire, the rubber of a properly
sized inner tube is in compression. That implies that any pores in
the rubber should be closed tighter than they would be if the tube
were not inflated. If the rate of diffusion is not dependent on the
pressure of the gas (independent of the compression), then the rate
should be slower as the pressure increases because the compression is
increasing, causing the pores to close. That would imply that the
rate is greatest with an uninflated tube.

Not sure I believe any of that...maybe someone who knows something
about this can enlighten me.

Joe Riel

Quoted message said:

Quoted message said:

Quoted message said:

Joe Riel wrote:
>I notice the opposite effect, which I find curious. That is, a
>completely deflated inner tube, with its valve (presta) tightly
>closed, partially reinflates after several days if it is not tightly
>compressed. That is, when I attempt to roll it back up I have to
>again loosen the valve to let out some air. What causes this? Is it
>leakage at the valve? This occurs on more than one brand of butyl
>inner tube.

Quoted message said:

Quoted message said:

Paul Hobson said:

Tubes lose air because they are under high pressure relative to the
atmosphere, which causes diffusion from the tube back to its
surroundings. If you push out all of the tube and seal it, now the
atmosphere is at a higher pressure than the tube. So it would make
sense that air would diffuse back into the tube, right?

Quoted message said:

A Muzi said:

Agree. I think the unspoken bit here is that some tubes are 'flatter'
or 'rounder' than others. If you cut out the valve, what cross section
does it display? Tubes which lie flat in that test would be less
likely to expand when left laying around I think than tubes which
'want' to be round in cross section.

Joe Riel said:

Here's some idle speculation. What drives air molecules through the
rubber? Diffusion? Does the rate of gas diffusion through a material
depend on pressure?

In an inflated tube, constrained by the tire, the rubber of a properly
sized inner tube is in compression. That implies that any pores in
the rubber should be closed tighter than they would be if the tube
were not inflated. If the rate of diffusion is not dependent on the
pressure of the gas (independent of the compression), then the rate
should be slower as the pressure increases because the compression is
increasing, causing the pores to close. That would imply that the
rate is greatest with an uninflated tube.

Not sure I believe any of that...maybe someone who knows something
about this can enlighten me.

Yes I believe tubes permeate air to a greater or lesser
extentwith afew variables liek material, wal thickness,
pressure.
To your comment about the tube being 'in compression', don't
you think in most cases a bigger factor is that the tube is
simply larger in use when it fills the space inside the casing?

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Someone said:

Sandy said:

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

INDEFINITE PRONOUN ALERT!

What is "its"?

Look at the the subject line of your own post 🙂

(she's referring to Le Cycle)

--
Paul M. Hobson
Georgia Institute of Technology
..:change the f to ph to reply:.

Dans le message de news:[email hidden],
Paul Hobson <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Someone said:

Sandy said:

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

INDEFINITE PRONOUN ALERT!

What is "its"?

Look at the the subject line of your own post 🙂

(she's referring to Le Cycle)

Please do not tamper with my gender !
--
Bonne route !

Sandy
Verneuil-sur-Seine FR
--
Les faits relatés ici ne sont que pure fiction, et ne sauraient être
utilisés ou rapprochés d'une situation réelle existant ou ayant
existée

Paul Hobson said:

Someone said:

Sandy said:

From its November 2005 issue :

Winner overall : Décathlon butyl (1,5€)
Loser overall : Challenge latex (10€)

INDEFINITE PRONOUN ALERT!

What is "its"?

Look at the the subject line of your own post 🙂

I also assumed that the source was Le Cycle, but the source should have
been stated in the text.

--
Tom Sherman - Fox River Valley