Innertube Porosity?

Steve Sr. writes:

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.

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 ,
a
réfléchi, et puis a déclaré :
Steve Sr. writes:

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.

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

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.

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?

Leo Lichtman wrote:
"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 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.

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 wrote:
Leo Lichtman wrote:

"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[

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 wrote:

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"
wrote:


Sandy wrote:

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.
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Words processed in a facility that contains nuts.