dirty old co2 tank

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Sep 21, 2007
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I just picked up a used, full 20lb co2 tank for $50. the thing is pretty dirty, a little rust on the outside, but very full. has a cert stamp from 86 on it. no coke/pepsi stamps...

anything to be concerned about? my shop will do a hydro test for $20 but say if it is full, they are certain it will pass. what can i do to clean it up? sand it? pressure wash it?
Pressure washing would be fine. Warm water only. You don't want to end up with a 10# tank.
Are you thinking of using the CO2 inside? There are different grades of Co2, from Industrial, up to Food grade.

If the tank came from a welding, security, or paintball shop, it will likely be the industrial grade and would contain impurities that might have settled inside. Inline Co2 filters are pretty cheap, and easy to install between 1/8"NPT fittings.

Co2 tanks over 2" wide need to be hydrotested every 5 years, though they rarely fail.
the guy i bought it from served soda out of it 10 years ago.... he had one of those roach coaches that drive up to workplaces and serve lunch. he has another 20 lb tank available that is full as well if anyone in the DC area needs one.

I called Robert's Oxygen and they hydro test for $10 and give me a filled keg. they don't fill on premises so they just swamp tanks like home depot does with propane.

so, i get a 20 lb tank for $50 + $10 hyrdo test. not a bad deal i guess.

the only bad thing is my keg rig guy forgot to include my faucets/taps in my shipment so no drinking kegged beer till next week.
So, hook up the kegs and let them carbonate while you wait. Swapping is my preference, fast and no worried about testing. I suppose if I had shelled out $70-80 for a new aluminum bottle, I'd want it filled, but I only care about the contents not the bottle.
This might be redundant, but once you clean it, don't forget to repaint it with a good solid rust-resistant paint. All that fresh metal will rust like crazy.
I put mine in the bathtub, lengthwise. First I put a few shop rags in the tub. If I clean up the next tank, I'll probably put an old bathmat in the tub first. I didn't want to scratch the tub. I used laundry detergent, warm water and a scrub/scouring pad. Oxyclean could also be used. I used an old toothbrush for cleaning the valve handle and brass. When I was done, I rinsed the tank with the shower head.

I have heard that there only 2 grades of gas: Medical, and other. (And, you need a prescription for the medical). One of these days I'll call the local gas supplier and ask them.

Congratulations on your buy! When your tank is empty, maybe your gas supplier will allow you to swap it out, avoiding the hydro test. Do you know where the tank was originally bought? If you don't swap it out & do get it hydro tested, the inside of the tank s suppose to be visually inspected. Like HP_Lovecraft said, you could get a filter if you are going to us the tank as is.
HP_Lovecraft said:
Co2 tanks over 2" wide need to be hydrotested every 5 years, though they rarely fail.

Is that for both Aluminum and Steel - or do they have different Hydro requirements in years (IE SCUBA tanks Al and Steel have different dates)

i'd try to swap it after you empty it. the airgas place i go to for my CO2 doesn't look twice at the tank i bring back. it's always the tank that i got from them a few months before, but i could just as easily bring them an expired tank and they'd never know. the last time i was there i asked if they had any new tanks, and they'd just gotten a BRAND NEW 20lb tank from some other homebrewer who just swapped it out for whatever $h!tty looking tank they gave him. MORON! now i have a brand new tank that i'll be taking a few extra miles down the highway to get filled instead of swapping!

as for filtering, i haven't. i'm pretty sure that airgas doesn't fill their tanks with food grade CO2. haven't noticed any off flavors or anything. maybe i'll end up with cancer in a few years. the place i'm going to take my shiny new tank is a coke distributor, so i'm sure they'll be using food grade CO2.
I spoke with a lady at praxair last time I had my 5# tank filled, she mentioned that the ONLY difference in welding grade and beverage grade is that for beverage grade they vacuum the tank out before filling it, to clear the air out. It did not cost any more for this service. She did mention that the medical grade gas comes out of the same machine, it just goes into different bottles.
I'd hit it with a wire brush, then once over with 60 grit, then a thick coat of black rustoleum spray paint. Be sure to cover your valve at the top though.

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