John McMurry said:Quoted message said:Quoted message said:The rubber cement used for patches is extremely volatile and the
solvent will slowly leak out of the crimp of the metal tube
container, hardening the cement. I don't think this varies too
much between brands.
Quoted message said:Quoted message said:Quoted message said:I choose to keep those metal tubes unopened and used only on the
roadside for emergency repairs, in case my spare tube also gets a
flat. When I get home, I patch the tube using rubber cement
contained in a screw top lid and pack the patched tube back into
my saddlebag.
Quoted message said:Quoted message said:Quoted message said:IME, once you open those small metal tubes, the life span
decreases substantially. I squeeze the container in my patch kit
about once a week to be sure it hasn't hardened.
Quoted message said:Quoted message said:It's the crimp as you said and don't let the screw top take the
blame. The smaller the remaining fluid, the less needs to
evaporate and leak out of the crimp.
Quoted message said:Good point.
Quoted message said:Quoted message said:Quoted message said:John Forester recommends carrying rubber cement in a small, screw
top jar for patches (to minimize volatile loss). It's in the
archives.
Quoted message said:Quoted message said:This is a misunderstanding of partial pressures of gases. A jar
large enough to hold a tube of rubber glue has enough volume to
take up the entire solvent in the glue tube as well as if the tube
were left out in the open. For a jar to hold such gases, it would
also need to have a metal gasket (one faced with aluminum foil for
instance).
Quoted message said:I'm not sure if I follow. Are you saying that at the top of the
bottle there will be enough volume for the solvent to separate and
therefore harden the cement because it is no longer in solution or;
are you saying the jar is incapable of containing the gas without a
metal gasket?
When the jar is sealed it essentially has a vacuum for the volatiles
in the tube, the partial pressure of that gas being zero when the jar
is capped. The next time it is opened, the evaporated solvent escapes
to be replaced by ambient air and the process repeats... it there is
any solvent left at that time.
Quoted message said:Why a metal gasket? Is it because the metal gasket is not porous?
Yes. Other gaskets (most soft materials are porous for this sort of
gas), like a mayonnaise jar with a plasticized paper gasket, leak like
a sieve for this stuff. As an example in packaging, club soda (Canada
Dry) is sold in clear plastic bottles that are porous for CO2. If a
bottle stays on the shelf for a longer time (few weeks from bottling)
it is nearly flat. Don't buys soda pop from stores with long shelf
life. I have had one liter bottles that were flat. A good manual
squeeze helps identify those.
I forgot to mention glue tube crimps when I talked to the REMA patch
guy at InterBike but then he wasn't even a bicycle guy, but from the
automotive division. I'm sure that if these tubes had a suitable
material in the tube where they are crimped, a crimp could be a solid
seal... some sort of Loctite.
Jobst Brandt
