I reviewed a compressor a couple of years ago that gets a ST front tire from 0 to 42 PSI in under three minutes. The Slime compressor and its ilk always impressed me as being a little on the wheezy side but adequate if you're willing to wait for it to do its job.
It's all about how much air you pack into how much space. Boyle's law says that P1 x V1 = P2 x V2, where P is pressure and V is volume. If you know the interior volume of the larger of your tires, its inflation pressure and the volume of any tank you propose to hold compressed air, that would be enough to figure out the minimum pressure the tank should hold. I'd actually double whatever number you come up with for that to account for leakage and so you have enough oomph to get the tire completely filled quickly.
its in post #8
From what I can gather, his 20oz tank should hold close to 1 liter, and 20oz of liquid CO2 is about 0.5 liter. If that's the case, then 0.5 liter of gas at 1000psi should be enough to fill the tire with existing gas in the tank at ambient temperature. As that gas is expelled, then the expansion cooling will begin for the newly formed gas, so it may be a little cooler than ambient, but I doubt it would get seriously cold. Then subsequent fills would have proportionally more gas, less liquid, as more fills are performed, so it will be less affected by expansion cooling as it empties over multiple uses. Just to be safe, I'd ride a short time and as the tire warms up take another pressure reading, and bleed off any excess pressure that might have occurred as the cold gas warmed.It will get very cold as the CO2 vaporizes, as it may not be designed for fast discharge. That may slow down the fill, but an interesting prospect nonetheless. If someone gets one, I'd love to hear how it worked for you on a flat tire.
Oh yeah, I forgot about the fact that the expanding gas from 1000psi to 50 psi will also cool, just like the expanding liquid to gas will cool, duh. But it is true that the intermediate gas will acclimate to the ambient temperature around the cylinder, so there is some temperature equalization in the process (assuming the cylinder is sitting around long enough to temperature equalize before expelling the gas, which is reasonable). This is a topic I'm not too familiar with, how does the temperature drop from liquid to gas compare to the temperature drop going from 1000psi to 50?
co2 will expand when it gets hot, used to paintball and if you left you tank in the sun it would eventually blow the safety valve. How safe would that be in your tires ??? an expanding gas sound like a recipe for disaster!! Just keep a can of fix a flat for emergency. Paintball compressed air tanks are over $100 more like 150 , need to be tested ($30) 3-5 years and a safety cover($25). but you can get a small bottle 45cu in @4500 psi... fix a flat $5.99
all gases expand at basically the same rate, so CO2 is no different than plain air in that regard. Also, CO2 contains no water vapor, like pure Nitrogen (which some racers prefer), that would be the only difference. As has been previously mentioned, the initial temperature of the CO2 inside the tire might be a bit cold from the expansion, so you'd get an initial pressure rise as it warmed back to ambient temp. After that its no different than air.
if all gasses expand equally why not use 134a ?? ///
Interesting idea, do they still sell those can piercing devices with a hose and a schrader valve like back in the R-12 era? I see the cans of r134a are available online, so maybe that's another option.
show me the mathematical reasoning. 90F = 90 psi doesn't make any sense unless you put it in a mathematical context. In a gaseous state, all gases will have the same temp/pressure relationship based on pV = nRT, where the T (temperature) is in absolute temperature units, either Kelvin or Rankine, not Fahrenheit, so the fact that you're saying psi and degrees F are proportional is suspect. To raise the pressure by 10%, requires a temperature increase of 10%, in degrees Rankine, which is about a 50 degree F increase at ambient temperature levels. Got a link to explain the calculations behind your claim? Also, the pressure inside an A/C system with an active compressor/evaporator isn't necessarily comparable to the same gas being used inside a tire. Please explain your figures.
