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-   -   Frost build-up on a Powertank regulator (http://www.expeditionexchange.com/forums/showthread.php?t=1309)

DougG September 4th, 2009 07:07 AM

Frost build-up on a Powertank regulator
How much is too much? Should I have any at all? I bought my Powertank a year ago, and have used it 4-5 times, and each time, I get a lot of frost on the regulator, and the hose. The last time this happened, I had trouble turning the regulator knob. What is considered normal?

marc olivares September 5th, 2009 11:55 AM


DougG September 5th, 2009 06:50 PM


johnlee September 5th, 2009 07:22 PM

My very limited understanding of CO2 is that the cold comes from the CO2 going from liquid to air inside the tank. When the CO2 is pressurized inside the tank, it is in liquid form, like the propane in a cigarette lighter. That's why you can store a Power Tank any which way you like, but the tank has to be upright during use. That is, you don't want liquid CO2 going through the regulator and hose.

My very limited understanding is that the cold effect comes from the liquid turning into air. It's sort of like water on your body evaporating into the atmosphere. It feels cool when this happens, because you are actually getting cooled by that evaporation. Same thing happens inside the tank. Think of the liquid CO2 "evaporating" into the top of the tank.

I'm sure all of this is incorrect from a physics standpoint. I was never interested enough in the matter to do any research on it. The liquid CO2 might be boiling into the top of the tank rather than evaporating. I have no real clue.

But the tank gets cold during use. And this is normal. I think paintball guns (which use CO2 as propellant) freeze up if they are fired too quickly.

hochung September 6th, 2009 01:33 PM

Aside from the cooling effect John describes, there's another cooling effect that takes place right at the regulator. The Joule-Thomson effect.

This effect is the drop in temperature of a gas as it expands from inside the tank (800 - 1000 psi) to the open atmosphere through a small opening.

CO2 has a particularly high Joule-Thomson coefficient, so the cooling effect is greater.

for comparison, Nitrogen's JT coefficient isn't as high, so you wouldn't see the same amount of "freezing" on the regulator under similar conditions.

I believe this is the principle behind refrigerators and automotive A/C systems that use CFC gases, with unusually high JT coefficients.

For info, look up Boyle's Law and Joule's Laws, and you'll better understand how your Power Tank works. :)

DougG September 6th, 2009 07:02 PM

In other words, a frosty Power Tank is normal, and doesn't indicate leaking seals at the regulator.

marc olivares September 7th, 2009 09:58 AM


DougG September 7th, 2009 04:55 PM

Thank you.

Keith Armstrong September 9th, 2009 10:00 AM

Surely we all remember PV = nRT ?


Hey, if either P(ressure) or V(olume) decrease.... i.e., letting gas outta the tank...T(emp) is going to drop too.

...might have capitalization errors there, but you get the idea...

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