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Old 11-24-13, 05:19 PM   #1
Drumnagorrach
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Nitrogen build up in tires

It occurred to me that as nitrogen has larger molecules than oxygen and carbon dioxide,and that inner tubes leak the smaller molecules out through the rubber,that as the inner tube is re inflated over an extended period then the ratio of nitrogen ,to other gasses found in normal air, will increase and the larger nitrogen molecules don't pass freely through the inner tube wall.
To that end,does it seem to you cyclists out there ,that the longer an inner tube is in use ,the less frequently it needs to be re inflated ?
It may be my imagination ,but unless I have a faulty valve ,after the first few times I pump up my tires they seem to stay up almost indefinitely.
.
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Old 11-24-13, 05:23 PM   #2
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hair∑split∑ting (h‚rspltng)
n.
The making of unreasonably fine distinctions.
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Old 11-24-13, 05:40 PM   #3
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Quote:
Originally Posted by Drumnagorrach View Post
It occurred to me that as nitrogen has larger molecules than oxygen and carbon dioxide,and that inner tubes leak the smaller molecules out through the rubber,that as the inner tube is re inflated over an extended period then the ratio of nitrogen ,to other gasses found in normal air, will increase and the larger nitrogen molecules don't pass freely through the inner tube wall.
To that end,does it seem to you cyclists out there ,that the longer an inner tube is in use ,the less frequently it needs to be re inflated ?
It may be my imagination ,but unless I have a faulty valve ,after the first few times I pump up my tires they seem to stay up almost indefinitely.
.
Filling tires with nitrogen gas was a retail tire chain scam. The so called better air contention is rediculous
If the air container being the tire and the sealed wheel has integrity it is not going to leak signifigantly no matter what kinda air is in the tire. There has been studies that support this,,that is why you see less and less of nitrogen filling being promoted.
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Old 11-24-13, 05:48 PM   #4
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Originally Posted by Drumnagorrach View Post
It occurred to me that as nitrogen has larger molecules than oxygen and carbon dioxide,and that inner tubes leak the smaller molecules out through the rubber,that as the inner tube is re inflated over an extended period then the ratio of nitrogen ,to other gasses found in normal air, will increase and the larger nitrogen molecules don't pass freely through the inner tube wall.
To that end,does it seem to you cyclists out there ,that the longer an inner tube is in use ,the less frequently it needs to be re inflated ?
It may be my imagination ,but unless I have a faulty valve ,after the first few times I pump up my tires they seem to stay up almost indefinitely.
.
Nice.....
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Old 11-24-13, 07:04 PM   #5
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The high concentration of nitrogen is the reason I never use my bicycle wheels for supplementary air while scuba diving.
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Old 11-24-13, 08:25 PM   #6
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Semi-permeable membrane. The theory is spot on, the actual is not.
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Old 11-24-13, 08:38 PM   #7
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Semi-permeable membrane. The theory is spot on, the actual is not.
Agreed. Yes, N2 diffuses through tubes a little slower than O2, but the difference is small and air is 78% nitrogen anyway so the effect is negligible. BTW, the difference is not due to size but rather that oxygen is more reactive with the hydrocarbon molecules of rubber and therefore tends to stick to the inner surface of the tube and then gradually diffuses through it - CO2 clings even more and diffuses much faster despite being a larger molecule.

Last edited by prathmann; 11-25-13 at 09:12 AM.
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Old 11-24-13, 09:21 PM   #8
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What the heck . . . I might as well throw this out there

If CO2 diffuses through an inner tube the fastest and N2 the slowest of the common gases, then why don't we use nitrogen cartridges in our inflators? The technology is readily available and they already make such cartridges for the food and beverage industry. When you look online the N2 cartridges are very expensive but remember that they must pass food grade standards and are a specialty item. If you wanted to produce bulk numbers of nitrogen cartridges for bike tire inflators, you could fill the same cartridges as we use for CO2 with industrial N2 for about the same price.

Last edited by Myosmith; 11-24-13 at 09:28 PM.
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Old 11-24-13, 09:48 PM   #9
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The only advantage to using pure nitrogen instead of air is nitrogen is dry. Straight air still has water vapor in it, and that can build up in auto tires causing corroded rims and changes in tire pressure as the vapor heats up while driving. Same thing in bicycle tires.


Carbon Dioxide cartridges - Carbon dioxide is one of those odd gases that goes into liquid under (relatively) low pressure (like refrigerant gases, propane, ammonia), so its easy to put enough into a small cylinder to fill a bike tire. Try putting the same amount of nitrogen in one of those small cylinders and it would be under astounding pressure, making it somewhat dangerous for the average rider to use.
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Old 11-25-13, 07:18 AM   #10
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I would use helium to make the bike lighter

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Old 11-25-13, 10:08 AM   #11
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Now see - it's threads like this one that make me glad I'm a retro grouch. One more thing that I don't worry or even think about.
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Old 11-25-13, 10:32 AM   #12
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It's been suggested that permeability declines with the age of rubber, so maybe your tubes are just getting old. But the downside to that is it gets brittle so that's probably not it

Yet I was just thinking about it last week, and it seems to me that a patch is going to be more air-tight than the bare tube, being thicker and with the vulcanizing. So the more the tube is patched, the better it will hold air - eventually my tube will be covered entirely and I might never have to add air.
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Old 11-25-13, 11:25 AM   #13
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Makes sense-sound theory
doesn't matter
because the increase in concentration and the actual difference in loss N VS O2 is TINY
Guessing lots of the actual loss is from "holes" and faulty valves big enough to pass either molecule easily enough

Besides the N2 is slightly less massive than O2-
so it is going faster-which means it might strike the inner tube"holes" more often(this is an off the cuff guess-so maybe wrong)

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Old 11-25-13, 12:50 PM   #14
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at 250+mph maybe oxygen deprived tires wont catch fire..
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Old 11-25-13, 02:19 PM   #15
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Quote:
Originally Posted by Drumnagorrach View Post
It occurred to me that as nitrogen has larger molecules than oxygen and carbon dioxide,and that inner tubes leak the smaller molecules out through the rubber,that as the inner tube is re inflated over an extended period then the ratio of nitrogen ,to other gasses found in normal air, will increase and the larger nitrogen molecules don't pass freely through the inner tube wall.
To that end,does it seem to you cyclists out there ,that the longer an inner tube is in use ,the less frequently it needs to be re inflated ?
It may be my imagination ,but unless I have a faulty valve ,after the first few times I pump up my tires they seem to stay up almost indefinitely.
If you were to fill the tube with equal amounts of nitrogen and oxygen, the oxygen would diffuse out faster than the N2. But the problem is that, in an atmospheric mixture of O2 and N2, you have a partial pressure of N2 that is almost 4 times that of O2. The nitrogen's diffusion rate is slower but it is the driving force behind the diffusion. The loss of N2 is about equal to the loss of O2 in this polymer.

When you fill the tube entirely with carbon dioxide, the diffusion rate of the CO2 is very high and it is the only gas present in the rubber. Thus the CO2 diffuses out very quickly. In an atmospheric mixture the amount of CO2 is exceedingly tiny and has no effect on the diffusion of the gas out of the tube.



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What the heck . . . I might as well throw this out there

If CO2 diffuses through an inner tube the fastest and N2 the slowest of the common gases, then why don't we use nitrogen cartridges in our inflators? The technology is readily available and they already make such cartridges for the food and beverage industry. When you look online the N2 cartridges are very expensive but remember that they must pass food grade standards and are a specialty item. If you wanted to produce bulk numbers of nitrogen cartridges for bike tire inflators, you could fill the same cartridges as we use for CO2 with industrial N2 for about the same price.
The "nitrogen" cartridges for the food industry aren't nitrogen. They are nitrous oxide or N2O. N2 can be made into a liquid form and will remain a liquid if kept cold but warm it up a little and it boils off. You can't compress enough N2 gas to put it in a tiny little cylinder like we use for bikes. CO2 can be compressed into a liquid and kept there at room temperature (and somewhat above) without refrigeration so you can put it into the little cylinders.

You don't want to be using nitrous oxide for much of anything, by the way. I sure that the "nitrogen" cartridges used in the food industry are low pressure since you don't want to blow out the foam too quickly. Nitrous oxide is a hell of an oxidizer as well. You can make a natural gas or just about any hydrocarbon gas burn much more intensely with N2O. It packs a wallop.
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Old 11-25-13, 02:34 PM   #16
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They use it for truck tires to run cooler?
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Old 11-25-13, 02:47 PM   #17
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I would use helium to make the bike lighter

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Better buy now. We're having a helium shortage.
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Old 11-25-13, 03:33 PM   #18
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I like pie!!!
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Old 11-25-13, 06:52 PM   #19
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I like pie!!!
Nitrous oxide propels the whipped cream onto your pie........................
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Old 11-25-13, 06:56 PM   #20
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You people are too smart for your own good.
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Old 11-25-13, 08:30 PM   #21
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Type Permeability of Rubber to Air in GOOGLE and check what shows up.
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Old 11-29-13, 07:29 PM   #22
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Thanks for the good information. I should have remembered that the food dispensing cartridges were N2O as I can remember stories about kids huffing the gas off of canned whipped cream.

http://www.press-citizen.com/article...S01/104260311/

http://abcnews.go.com/Blotter/danger...ry?id=16006130
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Old 12-02-13, 01:00 PM   #23
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Well that was interesting,it all started when out on a club run,I find that pedaling hard frees off my mind ,lets it explore and inquire about trivial stuff ,like " do my tires act like nitrogen generators?. So I guess the answer is NO?
I used to be a maintenance engineer in a food factory,there was a nitrogen generator in one of the plant rooms,we found that as it exhausted the waste gas into the room ,then a gas meter( something we used to check for flammability and breath-ability in the local atmosphere )would often show O2 at over the normal 20.9 % In the initial briefing on the generator ,I was told by the makers that it worked on the principle of N2 molecules not passing out through a membrane,all the other gasses did ,the remaining N2 was then pumped out to a receiver and the cycle began again. Thats what started that chain of thought.
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Old 12-08-13, 10:45 AM   #24
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The only advantage to using pure nitrogen instead of air is nitrogen is dry. Straight air still has water vapor in it, and that can build up in auto tires causing corroded rims and changes in tire pressure as the vapor heats up while driving. Same thing in bicycle tires.
Reason we use it in airplane tires and shock struts.
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Old 12-08-13, 11:46 AM   #25
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I am not cycling at 3 miles up. in the jetstream..
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