Originally Posted By: CapriRacer
Originally Posted By: bchannell
OK, I'll take a stab at this one, and if you think I'm wrong, please speak up, contrary to current wisdom, I DON'T know it all. ......
Good to know.
Originally Posted By: bchannell
...... No matter what the constituents of either container are, as long as it will hold pressure, then there can be no migration of the lower pressure to the higher pressure. Air can't infiltrate the tire when it's pressure is higher. In that instance total pressure is what matters. ....
Sorry, but that isn't the way it works - and it has been demonstrated.
I can not remember how long ago it was, but a colleague of mine repeatedly filled a tire with N2, then deflated it, coming to the point where there was very little N2 (percentage wise) in the tire. He then put in an O2 monitor and recorded the rise in O2 percentage over time. He presented this at a tire conference and I didn't get a copy of the paper. Basically he proved the Partial Pressure of Gases Law works everywhere.
Yup, and it's a good thing that it does as that's the principal by which our lungs work. Gasses equalizing partial pressures across a permeable membrane, even against blood pressure.
The migration of gasses across a leak has been demonstrated at a 50,000 psi differential. individual molecules know nothing of pressure. Any time there is a path for molecules to move, they will. In reference to tires; that means through the rubber, leaky valve core, imperfect bead seal, or wheel porosity. With a nitrogen fill oxygen is happily leaking in and "extra" nitrogen is happily leaking out.
I think that the fact that people see lower leakage is that a nitrogen fill usually comes with replacement of the cheesy plastic valve caps with quality ones with an o-ring seal.
Ed
