co2 tank to fill with air

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bravootome
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Fri Feb 19, 2021 11:13 am

hi, i got a sh 9 on( or oz ..) co2 paintball tank ( with the gun too) . the tank is made of Al and i want to know if and to what pressure (bar) can i fill it with my hill pump - with air. ( as i know co2 is more "low pressure than air"). i can not read the markings on it as it is pretty beat off ...... It is pretty heavy for it's size so it should work with 200 bar ??
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mrfoo
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Fri Feb 19, 2021 11:48 am

Avoid beating off in public. It'll get you on a list.

Sorry, that was a cheap joke.

An aluminium tank can only, AIUI, be rated up to 3000 psi. That's around 200 bar, and the absolute maximum safe rating, tank direct from the factory, you can possibly expect. However, liquid CO2 only requires a bit more than 5 bar, so your tank may only have been rated for that. If you can't read the markings on the tank (and pressure rating should be stamped into the metal, not just painted on), either the tank is extremely beaten up, or it's intended only for liquid CO2 and has not been high pressure rated. Or quite possibly both. In any case, you can't trust it to not grenade if used for high pressure air unless you have hydrostatically tested it beforehand. This means pressurising it to some margin above the pressure at which you intend to use it, using *only* an incompressible fluid such as water - a potential failure when pressurised with water will be much less "dramatic" than the same failure using a compressible gas. This can be done "on the cheap" using, for example, a grease gun, some hydraulic line and a pressure gauge that can handle the pressures you expect, but even then I'd be very wary of a battered tank.
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bravootome
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Fri Feb 19, 2021 12:01 pm

mrfoo wrote:
Fri Feb 19, 2021 11:48 am
Avoid beating off in public. It'll get you on a list.
either the tank is extremely beaten up, or it's intended only for liquid CO2 and has not been high pressure rated.
no, the tank has some markings stampted, but i could not read them clearly .... it is very heavy for his size and aluminum material, so it must hold some pressure. i put 100 bar in a diy tank. Anyhow i shall try read what is written .....
Anyone here turned a painball gun (point zero model) into a 6 mm one ?
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Fri Feb 19, 2021 1:31 pm

CO2 tanks have a nominal pressure of about 58bar at 20°C, that's why all those paintball air regulators reduce the pressure from whatever is in the bottle to that level (850psi) so air and co2 is interchangeable.

About the max. working pressure, looking at the steel tank I have here I think the markings say 1800psi, but better look at the markings on yours and google what they mean (English isn't my first language, so I'm not sure I read that right). Here the TÜV test pressure for Co2 bottles usually is 250bar. There should be a burst disk on your bottle, maybe it's marked wiuth the burst pressure. Anyway, that is not the working pressure, just the one it didn't explode when the bottle was new.

https://www.catalinacylinders.com/faqs/ ... -cylinder/

I would be very wary to go to any limits or misuse pressure bottles, if something goes wrong, it goes seriously wrong. Fast. If an aluminum bottle is so beat of that you can't even read the stamped in markings (neck/bottom) I would really consider to not use it again. I also would be concerned about corrosion, when you fill with air you get water and oxygen into a bottle propable designed for niether of that.
With an DIY tank, I would at least hydrotest it to 1,5 of the intended working pressure (just my guess, I'm sure there are good recommendations about that around here).
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Sun Feb 21, 2021 7:24 am

Some pictures of the tank would help. You say it's heavy, are you sure it's aluminum?

Personally I wouldn't go beyond 100 bar if it's aluminum. If it's steel, you'd need to inspect it properly for corrosion.
Rumpler wrote:
Fri Feb 19, 2021 1:31 pm
I would be very wary to go to any limits or misuse pressure bottles, if something goes wrong, it goes seriously wrong. Fast. If an aluminum bottle is so beat of that you can't even read the stamped in markings (neck/bottom) I would really consider to not use it again. I also would be concerned about corrosion, when you fill with air you get water and oxygen into a bottle propable designed for niether of that.
Wise words worth heeding.
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bravootome
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Sat Feb 27, 2021 10:39 am

the bottle is actualy steel and has this marks on the bottom :
-DOT E 10776 1800 - M4580- (THOUSE are written round circle ) and in the middle : 3 .01
and at the neck is written: 9 oz CO2
on the valve there is a screw with a 3000 nr. ( it may be the burst disk)

so it is has a working pressure of 1800 psi- 124 bar....
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Sat Feb 27, 2021 12:26 pm

bravootome wrote:
Sat Feb 27, 2021 10:39 am
the bottle is actualy steel
That's a good sign. Steel is far more resilient than aluminium.
bravootome wrote:
Sat Feb 27, 2021 10:39 am
so it is has a working pressure of 1800 psi- 124 bar....
No, it *had* a rated working pressure of 1800psi, for CO2 only, in March 2001 when it was last hydrotested. Not sure what the acceptable period between hydrotests is, but I'm kinda guessing it's somewhat less than 20 years. It should have had a sticker on it somewhere with the next hydrotest date on it, but that's long gone, I suppose, and it's only utility would have been to tell you how far out of date the hydro rating is. Again a guess, but probably upwards of 15 years. I am led to believe that this dot rating tank is no longer even "supported" which would mean that a reputable gas supplier will no longer refill, or even hydrotest, it. It is, effectively, scrap. This does not mean that it will explode if you fart in its general direction, but it does mean that if you manage to get it filled with CO2 and it then does explode and blow your hand off, your options only go as far as picking up the pieces with your remaining hand and putting them in your pocket. But you're talking about air, which means you're outside its original operating parameters anyway.

If there's no obvious serious damage to the outside - big dings, corrosion, any sot of cracking, etc, and you can get to the inside to inspect for corrosion, you're probably gonna be relatively OK. I'd be very tempted to epoxy coat the inside - as Rumpler says, you will get condensation inside with air, and that will cause corrosion, and I'd still hydro test it myself before giving it any sort of high pressure gas.
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Sat Feb 27, 2021 1:14 pm

i had not taken the paintball gun apart but it looks like a shitty job. it is no way better than my diy, it is all plastic and fragile, so am not sure it will hold 100 bar, and if i use 50 bar ( enough for decent power) the tank is to small and it may take 10 or more shoots ......
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