Do nitrogen-filled tires lose pressure more slowly?
This seems to be the main selling point for nitrogen vendors, i.e. you dont have to check/top-off your tire pressures as frequently as you do with air. N2 vendors claim that N2 leaks out anywhere from 3 to 6 times slower than air. At first glance this seems incredible, since air is about 78% nitrogen. But then again, there may be something to it. There are two commonly used techniques for separating nitrogen and oxygen from atmospheric air. One is cryogenic: you literally cool the air down until the oxygen condenses into a liquid, while the nitrogen remains a gas. The other technique is membrane technology, explained here. Interestingly enough, this is one of the ways that tire shops obtain nitrogen: they run compressed air through an on-site membrane tube bank (click here, see page 4). The only way this technology works is if O2 permeates through a polymer membrane a lot faster than N2 does. Molecule size is one factor (N2, atomic radius = 75 pm, diatomic bond length = 110 pm; O2, ato
This seems to be the main selling point for nitrogen vendors, i.e. you dont have to check/top-off your tire pressures as frequently as you do with air. N2 vendors claim that N2 leaks out anywhere from 3 to 6 times slower than air. At first glance this seems incredible, since air is about 78% nitrogen. But then again, there may be something to it. The Theory There are two commonly used techniques for separating nitrogen and oxygen from atmospheric air. One is cryogenic: you literally cool the air down until the oxygen condenses into a liquid, while the nitrogen remains a gas. The other technique is membrane technology, explained here. Interestingly enough, this is one of the ways that tire shops obtain nitrogen: they run compressed air through an on-site membrane tube bank (click here, see page 4). The only way this technology works is if O2 permeates through a polymer membrane a lot faster than N2 does. Molecule size is one factor (N2, atomic radius = 75 pm, diatomic bond length = 110
