Bike Forums - Nitrogen Test Cartridge instead of CO2?

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If moisture is that key to tire pressure and temperature fluctuations, you should probably fill your ties from a commercial air compressor. A commercial air compressor, such as at a large gas station with repair stalls and a lot of air operated tools, those air compressors usually pump up to well over 100 psi. When you compress air that high and let it sit, a lot of moisture condenses out it which is why you see drain valves on the bottom of air compressor tanks and you often see water traps on compressed air lines in the shop. When that air is partially de-compressed later, it is much drier because some water condensed out of it. But, if you are using a bike pump, the air you pump goes into the tire, moisture and all.

Commercial air comprssors where there are a lot of air tools however might have oil added to the air to lube the air tools, so you might get a bit of oil in your compressed air.

Quote:

Originally Posted by DrIsotope (Post 20734258)

Water expands as it gets hotter.

"At 212°F, 14.7 psia, liquid water has a specific volume of 0.016716 ft3/lbm and steam has a specific volume of 26.80 ft3/lbm, which is a volume ratio of ~1600 : 1 of steam:water."

When racing, we had tires running as little as 15psi, and heating to as much as 230º on the center of the carcass. So it doesn't take much moisture inside the tire to cause the pressure to raise at higher temperatures.

The other factor on this is humid air, like what comes out of a typical air compressor, is less dense than dry air. So you have water making up a greater % of the gas filling the tire meaning that the overall pressure is more dependent on the partial pressure of the water than you would with dry air.

Quote:

Originally Posted by Tourist in MSN (Post 20734511)

If moisture is that key to tire pressure and temperature fluctuations, you should probably fill your ties from a commercial air compressor. A commercial air compressor, such as at a large gas station with repair stalls and a lot of air operated tools, those air compressors usually pump up to well over 100 psi. When you compress air that high and let it sit, a lot of moisture condenses out it which is why you see drain valves on the bottom of air compressor tanks and you often see water traps on compressed air lines in the shop. When that air is partially de-compressed later, it is much drier because some water condensed out of it. But, if you are using a bike pump, the air you pump goes into the tire, moisture and all.

Commercial air compressors where there are a lot of air tools however might have oil added to the air to lube the air tools, so you might get a bit of oil in your compressed air.

Most air compressors do not have a separate air dryer and supply air saturated with water. Just compressing the air doesn't dry it, you really need to have a separate dryer to get the dewpoint down to reasonable levels. Oil is another contaminant that usually doesn't do rubber much good.

I have worked with air bearings, which require reasonably dry air. You would be amazed at what comes out of a typical air compressor. Gas stations and race tracks are unlikely to have a dryer on the output of the compressor. Our system had a dryer (cools the air) and salt desiccant systems and on a hot day, the air still had a dew point close to 60F.