Scuba tank to CO2

[Ric]

hey guys, a buddy got a scuba tank, and was wanting to know how to set it up as CO2 I know head will need to change is there anything else he should look at, watch out for ?
where could he get the proper fitting for airing up ?

thankx for any help

[SacRunner]

DON'T DO IT

Scuba tanks are designed for ~150psi of compressed air (a gas), CO2 tanks are designed to withstand 3,000psi of LIQUID CO2.

tank ratings aside the regulator fittings and tank threads don't match.

I went through the same thought process last May while trying to find a cheap CO2 tank for some CO2 beverage pumps. I called a couple of scuba shops, and after they quit laughing I got some really good advice from them (about tank ratings and regulator fittings). Called a couple welding supply and gas supply places just to confirm.

[Ric]

thankx man, Ill pass this along

[MTL_4runner]

DON'T DO IT

Scuba tanks are designed for ~150psi of compressed air (a gas), CO2 tanks are designed to withstand 3,000psi of LIQUID CO2.

The scuba tank itself is designed to hold 3,000 psi with an aluminum tank (some even as high as 4,500 psi with a steel or composite carbon fiber tank!) of air as well. I'm not sure if maybe you got confused when they started talking about stepping down the pressure for the regulator in regards to the 150 psi. The paintball industry has been filling Scuba tanks with CO2 or nitrogen for a long time now. Not to mention that CO2, N2 and air are all gasses and it doesn't matter what state they are in compression. The fittings are all available for retrofitting scuba tanks for other hookups. Also air is 79% nitrogen so at the very least you could refill a scuba tank with compressed nitrogen quite safely and cheaply.

Here's a few good threads on that subject:
http://www.scubatoys.com/store/Paint.../whichtank.asp
http://www.ottersccustoms.com/filling.html
http://kegman.net/paintball/pbrefiller.html

[Bighead]

Whatever he gets make sure it has a current hydrostatic test date or he can expect to spend a little bit more money getting it done.

[mastacox]

DON'T DO IT

Scuba tanks are designed for ~150psi of compressed air (a gas), CO2 tanks are designed to withstand 3,000psi of LIQUID CO2.

You are quite incorrect; but then, I suspect it's because you are not SCUBA certified and don't have a good grasp of phase changes.

Most SCUBA tanks hold about 3000psi, and like MTL said, some can hold upwards of 4500psi. As for the difference between gas and liquid, it really doesn't matter; pressure is pressure. 150 psi is the intermediate line pressure between the regulator on the top of the tank and your breathing regulator, NOT the max pressure in the tank. You wouldn't get more than 10 or so breaths out of a SCUBA tank filled to 150 psi, at 100 feet, you'd get about 2. It's actually quite convenient CO2 turns into a liquid at medium-high pressures, because you can hold much more mass in the same tank. Translation- a CO2 tank at 3000 psi will fill a lot more tires than an air tank (or Nitrogen) at 3000psi. And when I say a lot more, I'm talking factor of 5 more.

EDIT- Actually, looking into it further it turns out a CO2 tank full of saturated liquid CO2 at 75F will only be at about 900psi, far below the max rating of a SCUBA tank. When the tank is heated to above 87F (in a car in the sun for example), the CO2 goes "supercritical" (turns back into all gas) and the pressure raises dramatically. If it is heated enough, and the pressure in the tank could go to or above 3000psi (necessitating a blow-off valve if this occurs). For lower temps, say 20F, the pressure in the tank would be around 430 psi. The max pressure a liquid-gas mixture of CO2 will see is about 1060psi (at 87 F). After that it gets more complicated, but suffice to say you wouldn't want to go much over 100-110F.

As was said, I suspect as long as you are able to get the correct regulators and fittings, and the tank is properly hydro tested, should be fine. I suspect a SCUBA tank filled with CO2 will fill a LOT of tires, even a "little" Powertank fills about 40 sets (depending on size of course). I would be most worried about making sure the "custom" system has proper emergency safety features such as blowoff valves in case of an overheat, and is strapped down properly. Also make sure the tank will be upright, not lying on its side.

Engineering nerdiness triumphs again!!!

[wifesaysimadumbass]

i've used my scuba tanks for years now!!!1 don't fill a scuba tank with co2 especially since an air fill is like 4 bucks and a co2 fill is like 20... i bought a cheap reg used at the swap meet and have been filling tires for years with it

[crolison]

Whatever he gets make sure it has a current hydrostatic test date or he can expect to spend a little bit more money getting it done.

Ditto, and scuba places wont fill without it tested.

And yes, this is from a scuba diver, 3000 is very normal, 3500 is also very normal. 4000 your high as you want to go. thats in the steel tanks i have been using

[Crozhawk]

Whatever he gets make sure it has a current hydrostatic test date or he can expect to spend a little bit more money getting it done.

Ditto, and scuba places wont fill without it tested.



And yes, this is from a scuba diver, 3000 is very normal, 3500 is also very normal. 4000 your high as you want to go. thats in the steel tanks i have been using

i've used my scuba tanks for years now!!!1 don't fill a scuba tank with co2 especially since an air fill is like 4 bucks and a co2 fill is like 20... i bought a cheap reg used at the swap meet and have been filling tires for years with it

i've used my scuba tanks for years now!!!1 don't fill a scuba tank with co2 especially since an air fill is like 4 bucks and a co2 fill is like 20... i bought a cheap reg used at the swap meet and have been filling tires for years with it

I did the same thing with an aluminum 100. The 20lb bracket from wheelers fits perfect and I have it mounted up high underneath the truck above the rear axle. I've been wheeling with it up there for about 8 months with no issues. Just make sure the valve isn't in a vulnerable spot and keep it a SCUBA tank for air. With air you also don't have to deal with some of the freezing/temp issues as much as CO2. I'm a veteran Navy Diver so I had all the equipment lying around thanks to Uncle Sugar.

[wifesaysimadumbass]

oh cool i never thought of mounting the tank under the truck you got any pics of that?