I am not certified, but have been diving for almost 7 years and I am just now ready to get my certification. I found some very old tanks real cheap that held compressed air at one point I would like to convert them so that I may use them as O2 tanks as they are a bit smaller than normal. Has anyone ever done this? I also have access to empty old nitrous tanks. These can cut down considerably on cost and I may even make a buck if I can convert these. My significant other tells me it can't be done but I know better.

Im not sure I understand. You want to take a scuba tank and use it for oxygen? Do not dive with pure oxygen! It becomes toxic at around 30 feet.
Tanks are very inexpensive. They cost around $100. By the time you convert the used tanks to use safely for scuba you will be spending at least that much.

Maybe I didnt understand the question????

I understand what you said completely, and all i have to say is DON'T DO IT.

Go get you're cert using the tanks that the shop will provide till you can buy some. This is life support equipment and not to be taken ligthly. If they are not made for diving dont use them. If they are made for diving them they are probably out of vip and hydro and need to be serviced by your LDS (Local Dive Shop) if you dont know what hydro and VIP are then you really need the class first. Rebecca is correct tha tanks are pretty cheap. You can't beat the price $100.00 for a new tank.

Good luck in your OW Class and let us know how it goes.

-BadFish

Yo, Badfish is completely correct on this. Stick with getting certified and learn all there is to learn first. Good luck.

Take some scuba diving course and get certified.
Don't risk your life or the lives of others that might have to go rescue you or recover your body due to a diving accident.

You may be a good diver already but apperently you don't have all the facts if your asking questions on what type of tanks you can use for SCUBA.

Dive smart and dive safe.

You guys really want this guy in the diving world! LOL

Anyone in good health and has been properly trained is welcome to become a diver. But, there are still people that shouldn't dive. Every diver must acknowledge the inherent risks.

Before you blow your head off, let me give you a piece of advice. I live in the Florida Keys, so diving is big here. My father's friend attempted something like that, his head has olmost blown off. We also had a case down here of a guy using an old submarine tank, he ended up blowing off his leg. Don't risk it man.

First, you should not have been diving without a certification. How did you rent tanks without a c-card?

Second, once you get your cert, you will understand what a really bad idea this all will be.

Third, unless you have your own compressor, how will you get this homemade tank filled? No reputable diveshop would fill a tank that wasn't annually inspected by a certified inspector, and no certified inspector would pass your homemade tank. And I know you don't have a compressor, because you are worried about saving a few lousy bucks on tanks.

Do the diving community a favor - stay away from the water until you have your c-card.

Voob, sounds like your significant other is right, and let me be among the first to thank you for writing Dear Abyss with your question. While it is possible in some cases to change tank usage specifications, it's probably easier to insert a football into the bowels of an irate Bengal tiger, using a hot poker. Noble intentions, I'm sure; but, simply not a good idea...

Sounds like the older tanks to which you refer are steel 72's, which are a little smaller in size than today's common aluminum 80's. First, the threading will not allow an standard healthcare O2 compatible valve to be inserted into them, and besides that, before they could even be used for Nitrox blends, the current valve itself must be completely overhauled, all O2 sensitive parts, and lubricants removed and replaced with Viton and other technical stuff, and the tank tumbled, washed in solution, and dried with nitrogen, in order to prevent combustion and explosion, the most likely outcome of your experiment. On top of this, you'd have to have them inspected, both hydrostatically and visually, resulting in your eventually spending more than the old tanks are worth, or more than they cost you, which should have been about five dollars or so, since that's what they're worth. While I do not mean to belittle your diving experience, your referring to "using them for O2 tanks" has me a little concerned, as no person within the vast confines of this planetary system who knows anything about sport diving would refer to scuba cylinders as "O2 tanks."

With this said, I concur with many of the prior posts which advise you to seek certification, whereby you'll gain the knowledge necessary for you to know beyond doubt that what you are proposing is extremely dangerous. Oh, and about the nitrous tanks....don't even think about it. Too involved to explain here, but suffice to say that you'd be safer while shooting fireworks while submerged in a vat of gasoline.

Best wishes on your continued survival, and kudos to your significant other. I'd listen to her.