Why nitrogen?

On Sep 15, 6:20*pm, a wrote:
On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.

On Sep 16, 8:25*am, a wrote:
On Sep 15, 6:20*pm, a wrote:





On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.- Hide quoted text -

Dont see why it would reduce water vapour, dry air has no more water
than dry nitrogen. and migration or porosity is a function of
molecular size. There is not much difference between nitrogen MW 28
and Oxygen MW 32.
Terry

On Sep 16, 6:39*pm, terry wrote:
On Sep 16, 8:25*am, a wrote:



On Sep 15, 6:20*pm, a wrote:

On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.- Hide quoted text -

Dont see why it would reduce water vapour, dry air has no more water
than dry nitrogen. and migration or porosity is a function of
molecular size. *There is not much difference between nitrogen MW 28
and Oxygen MW 32.
Terry- Hide quoted text -

- Show quoted text -

OK , I will stand corrected, on the porosity, the proper word was
permeation and nitrogen is actuallly a larger molecule than oxygen
despite its lower molecular weight. Attached link is a really good
explanation ..from an expert. oxygen does permeate 3 to 4 times
faster through rubber. I guess leakage through the tire would occur
even faster in an aircraft tire at altitude due to the driving force
of the pressure differential. But still not convinced if its the
primary reason.. I think I am leaning towards the fire risk. Anyways
its a very interesting aviation topic.
Terry
http://www.getnitrogen.org/pdf/graham.pdf

a wrote:
On Sep 15, 6:20 pm, a wrote:
On Sep 15, 6:09 pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.
Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.
I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.
The legend is that the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.

We bought a new Toyota and the salesman stated the tires were filled
with N2 since the molecule was larger and less corrosive than air which
contained O2. Now, how easy is it to find N2 around town. I can take it
to the airport where the mechanic has a tank. But, all the years of
owning a car, I never seem to really have a problem with tires going
down that quick. At the 3K oil changes they top them off anyway. I did
buy a small compressor for the hangar, but never really used it that
much. I have a couple of bikes that I have to air up before each ride.
Those tires really loose pressure. I brought the compressor home.

--

Regards, Ross
C-172F 180HP
KSWI

On Mon, 15 Sep 2008 15:25:21 -0700 (PDT), a wrote:

On Sep 15, 6:20*pm, a wrote:
On Sep 15, 6:09*pm, "Viperdoc" wrote:

The thread on brakes raised a question from the past- why nitrogen in the
tires of big jets and heavies? Air is around 78% nitrogen anyway, and the
coefficient of expansion of the remaining 20% that's oxygen can't make that
much difference in volume.

Why not just use dry air? I couldn't imagine that dry air or dry nitrogen
could make that much difference in corrosion, either.

I seem to recall someone giving me the rationale for this a long time ago,
but also seem to remember thinking it didn't make that much sense at the
time.

The legend is that *the oxygen is reacting with the rubber. Even
though compressed air has the same fraction of oxygen as does the
atmosphere, the fact that it's compressed, it's been argued, increases
its reactivity. I can't validate the legend.

I got curious, did a quick check. The process also reduces water
vapor, and N2 does not migrate through the rubber as fast as does O2,
so pressure stays more predictable. So it's more consistent tire
pressure, less corrosion.

Howevwer even in air the % of O2 is considerably smaller than N2. I
practice I've never been able to see a difference. Possibly with the
old style "natural rubber" innertubes in aircrat tires it would make a
difference, but I doubt any of us would see any difference in todays
car and aircraft tires. I've not had to put air in the tires on
either car in over two years. It's been over a year on the Debonair
and the mains are still up to pressure. The nose gear which still has
the old Natural Rubber has to be filled about every two to three
months. OTOH I've nver tried N2 in it.


Technically O2 leaks about 3 times as fast in Natural Rubber as does
N2. However it that proved out in practice we'd actually be purifying
the N2 in the tires and after refilling them 3 or 4 times there would
be almost no O2 left.



Roger (K8RI) ARRL Life Member
N833R (World's oldest Debonair)
www.rogerhalstead.com