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Help - Valve freezing with CO2

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Help - Valve freezing with CO2

Unread postAuthor: l_uk3y » Sun Apr 17, 2011 3:33 am

Hey guys.

Fairly new to all this. Either way im building my first air gun.

Im using copper pipework with a fairly basic compressed air trigger valve. At this stage im intending to use bottled CO2 as my fuel. The goal being from a Sodastream bottle or a MIG welder. (portable and easily available).

Testing at 100psi from my Air compressor it works really well (albeit lack of pressure). But my first test on the CO2 bottle (sodastream) instantly froze the trigger open as soon as I touched it.

Ive done some searching on here to find a solution. Ive found plenty to say that it is a concern. However I haven't found anything that provides a solution. Also getting a lot of condensation but the freezing trigger is the first issue to fix.

Cheers. Luke
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Unread postAuthor: Crna Legija » Sun Apr 17, 2011 3:44 am

you need a anti siphon co2 tank, or a expantion tank after the reg. a expantion tank is just any tank that can take the pressure to let liquid co2 boil off.
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Unread postAuthor: qwerty » Sun Apr 17, 2011 3:55 am

Im using copper pipework with a fairly basic compressed air trigger valve. At this stage im intending to use bottled CO2 as my fuel.



You're using copper pipe? Be carefull, CO2 can get as high as 800psi and you don't mention that you regulate it.

I wouldn't trust copper any higher than 550psi.
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Unread postAuthor: al-xg » Sun Apr 17, 2011 7:47 am

I wouldn't trust copper any higher than 550psi.


That depends on wall thickness and diameter. As an example 6mm (0.24") (0.6mm wall) British Standard half hard copper tube has a max working pressure of 13.3MPa (133bar, or 1220PSI).
22mm(0.87") (0.9mm wall) half hard copper has a working pressure of 5.1MPa (51bar, 740PSI).

However, for sizes larger than 35mm (half hard and annealed) the working pressure falls below 550psi.

This is the British Standard copper pipe spec so obviously one would need to check the rating of the type of pipe they are using.
I am off course giving working pressures not yield or burst pressures, so no need for safety factors, they are already in.

Just as Crna Legija explained, the solution to freezing is expanding the CO2 before it gets to the valve ( so it doesn't have to expand as much in one go, therefore cooling a lot less), either taking only the gas phase, or boiling off the liquid first.
The change from liquid to gas causes even more cooling.
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Re: Help - Valve freezing with CO2

Unread postAuthor: velocity3x » Sun Apr 17, 2011 1:39 pm

l_uk3y wrote:my first test on the CO2 bottle (sodastream) instantly froze the trigger open as soon as I touched it.


CO2 is nasty! Switch to Nitrogen or HPA and you wont have any problem.
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Unread postAuthor: l_uk3y » Mon Apr 18, 2011 2:51 am

Cool. Thanks guys. I would love to use HPA. Biggest problem is availability. Bottled CO2 is the simplest option for purchasing hence my desire to use that.
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