Key step #1 – Purge the moisture from the tire!
Moisture is a tire’s worst enemy. It will:
• Fluctuate tire pressure by expanding and contracting
more than dry air.
• Corrode and damage rims, steel belts, and some
TPMS sensors.
• Carry contaminants that clog valve hardware
How do I remove all the moisture from a tire?
• Deflate each tire an average of two times to 3psi
depending on the method or device used.
Starting
Purity in
Tank
O2(9.8ps
i)
O2(3.1p
Deflate to 3psi
and fill
one time
98%
Deflate to 3psi
and fill
two times
78% Nitrogen
The best case for passenger tires (32 PSI target) occurs
with an inside composition of ~6.6% O2 / ~93.4% N2*;
that’s where the partial pressure of O2 inside and outside
equalize, so there is no driving force for permeation.
*Outside oxygen partial pressure is about 3 psi. Optimally, you’d want
6.6% oxygen in the tire, or 93.4% Nitrogen inside of a 32 psi tire.
Method used Final Purity
to fill tire
in tire
99%
si)
Key step #2 – Balance the oxygen inside pressure
with the air outside the tire.
Any gas in a tire permeates to equalize with its partial
pressure outside of the tire. If nitrogen is “too pure”, oxygen
actually permeates back into the tire if the oxygen partial
pressure is lower inside the tire than outside.
Minimal
91.5%
95.4%
psi)
95%
i)
(3.1ps
2
O
i)
0.9ps
2(
O
98% Nitrogen
O2(3.1psi)
Dry
O2(3.1psi)
But not enough
dry 02 to balance
tire to outside air
Greatest!
i)
(2.3ps
2
95% Nitrogen
Moisture present
More
O2 (3.1
O
Benefit to
Customer
Deflate to 3psi
and fill
two times
93.1%
Now the dry 02 is
balance with the
outside air
Plus or Minus
Not Good
Not good for the customer
Not good for the dealer
Better
Good for the customer but
expensive for the dealer
Best
Optimal for customer and
dealer has lower cost and
can produce more N2
The truth about nitrogen in Tires:
Special caps will self seal and lock in nitrogen – False.
According to Bridgestone / Firestone only 10% of gasses leak through the
cap. 75% permeates through the sidewall, belt and tread and the final
15% around the tire bead (source: Tire Business 9/22/03).
You can “refine” nitrogen. False - nitrogen is nitrogen!
There is only one quality of nitrogen. Of course, purity levels may vary based
on the presence of other gasses.
Using the nitrogen generator to produce 99% instead of 95% purity will require an air-to-nitrogen-ratio of 2X to generate
an equal volume of product gas at the higher purity. Thus, compressor duty cycle will be higher (shorter life) and energy
consumption per cu ft nitrogen enriched gas produced will be higher. This is generally true irrespective of whether you are
comparing membranes or PSA, although the exact ratio comparison will be different.
93.4% Nitrogen
(Equilibrium)
Note: This document supports Dalton’s law of partial pressures for a tire previously at 32psi of normal wet air. For new tire procedures go to www.getnitrogen.org