On Tue, 11 Nov 2014 07:30:07 -0800, "Jeff Strickland"
wrote:


"dpb" wrote in message ...
On 11/10/2014 10:03 AM, dpb wrote:
On 11/10/2014 9:36 AM, Jeff Strickland wrote:
"dpb" wrote in message ...
...

That's still atmospheric pressure of this nasty, wet air everybody's
so concerned about...
...
But the ratio is so low that it's kinda like the heat in your freezer
when you put a candle inside. I'm all but certain the candle makes heat,
but the ice cubes are not going to melt, so the freezer is still a
freezer.

Are you certain...have you calculated the actual fill percentage and
compared that to the 95% claimed needed to be effective? I've not taken
(nor am I going to) the time but it's the underlying question.
...

Actually, it's not that tough to get pretty good estimate...

14.7/(14.7+30) = 0.33 -- 33% air by fraction of total pressures. So w/o
purge you're only going to be 2/3rds or so N...

--

That cannot be right, but I have no idea the formula that is needed.

An "empty tire", one with 1 atmosphere of air inside will not pollute with
any significance the contents it takes to bring that tire to 30+ psi. The
empty tire will contain air, no doubt. But filling the tire to 30 psi will
most certainly result in a dillution of the "empty" contents to far less
than 1/3. Surely the anology of a candle in the freezer has to be pretty
accurate, even if not the same type of thing.

An "empty," balloon has air inside, and filling it with helium still results
in a balloon that floats.

An "empty" balloon has virtually no air because it is "flat" The same
can be said for a tube, but not a tire. A tire has it's full volume of
air at 1 atmosphere. That 1 apmosphere is roughly 80% nitrogen.
Inflate to 3 atmospheres is 3 times the mass - correct? So 2 thirds of
the volume is 96-98% nitrogen and 1 third is 80% nitrogen. Lets say
the nitrogen fill is 98%., so 98+98+80/3=92%.

Close enough anyway, unless it takes the addition of more than twice
the volume of the tire to raise the pressure to 3 atmospheres from 1.