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post #1 of (permalink) Old 12-23-2000, 04:15 PM
brendan
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scuba tank for on-board air?

I'm wondering if an old aluminium scuba tank is a worthy candidate for an onbord air tank. I scavenged it at the dump. The valve body is busted, the hose outlet is broken off. I imagine that this is why it was in the dump. I intend to have it pressure tested, as it is going to be mounted behind the passenger seat. I was just wondering what sort of pressure they were originally designed for. I'd imagine they're quite stout, but I figured that there are plenty of divers on the board who can answer this for me so i don't accidently blow anyone's crapper off. Thanks again Brendan

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post #2 of (permalink) Old 12-23-2000, 05:34 PM
 
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Re: scuba tank for on-board air?

The tank your reffering to should be an Aluminum 80. That is, it holds 80 cubic feet of air at 3000psi. They are not a good choice for a truck's air tank since they dont hold up well to a rough environment. I'd be pretty surprised if it passes the pressure check (ask to stick around so you can feel the explosion in the water-tank if/when that puppy goes off) About the only thing worse is using PVC pipe....

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post #3 of (permalink) Old 12-23-2000, 05:46 PM
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Re: scuba tank for on-board air?

You'll have to make your own decision about using a SCUBA tank for air or not, but I can fill you in about tanks in general. If what you have is indeed a Scuba tank it is most likely an 80 cubic foot tank as these are by far the most common. This volume is what the tank will hold when filled to its maximum working pressure of 3000 psi. Now for the good stuff. These high pressure cylinders when used in the SCUBA word must undergo hyrostatic testing every 5 years. Additionally, an internal and external visual inspection is performed annually. If no stamp for the hydro and no sticker for the annual, then no air from the dive shop. Also, unless you have a certification card you'll have a hard time getting it filled. All this is compliments of our law suit happy society. Now, if you have access to a compressor to fill your own tank, there are no rules. You fill it, you take the risk. If you found this tank in the dump I would suspect that it did not pass the inspections or for some reason was pulled form service. For example, if exposed to heat in excess of about 350 degrees the tank is automaticly condemed. Certain tanks made by Luxfer are the subject of much concern due to cracks in the neck area. The big concern is that cracks=exposions. My advice would be to take it to your local Dive shop and have it checked out. Most of these guys are proffesionals and won't steer you wrong. Good luck

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post #4 of (permalink) Old 12-23-2000, 05:56 PM
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Re: scuba tank for on-board air?

Oh, I forgot to cover durability. Aluminum tanks are a lot more durable than you would think. Take a look at the tanks used by Cave or wreck divers. These are constantly being banged, gouged, and scraped on rocks and twisted metal. If you really want to see abuse, go watch what a rental tank goes through. Its almost as bad as a rental car. The main thing about using a SCUBA tank is making sure its secure and protecting the valve. I've been diving since 1981 and an instructor for 16 of those years so I've seen tanks take a real beating and still be ok.

post #5 of (permalink) Old 12-23-2000, 06:02 PM
 
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Re: scuba tank for on-board air?

it take a special compressor to fill those to 3000 psi, so Ill assume youll fill it with a normal air source like 120 psi?

if it was designed for 3000, and fell out of certification, its probably going to be ok at 120 psi, even thouhg its unsafe at 3000.

just plumb it for an air chuck, wrap it in a thick blanket, and fill it to 120 psi from a distance to see if it busts, or leaks down.
just think shrapnel and be careful.


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post #6 of (permalink) Old 12-23-2000, 06:14 PM
 
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Re: scuba tank for on-board air?

If you do decide to use it, I highly suggest wrapping it in a "space blanket" which isn't too tough to find in outdoor equipment catalogs. It will block direct sunlight from heating it up and putting even more pressure on things.

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post #7 of (permalink) Old 12-23-2000, 08:28 PM
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Re: scuba tank for on-board air?

IMHO, Forget the dive shops. Most will overcharge you and probably won't understand what you are attempting. In my experience with the diving community, this usually can equated this way... It's no good if I didn't think of it."

The tank should have stampings near the top. One HAS TO SAY "DOT" with some numbers after it. If it doesn't have this, chuck it!! It will also have the max pressure stamped in. If it is an Aluminum 80, this will be "3000" AKA 3000 psi. It will also have a hydrostatic testing mark, with the month & date stamped in. Between these numbers, is usually some small symbol, I believe a trademark of the test facility. If there is more than one, the oldest will give you some idea of the tanks age.

For reference, I have one of these tanks from 1972, which passed hydro and visual this summer. This tank has seen hundreds of refills, slammed around on countless boats and dragged up & down miles of beach. I dropped it out of a van once, right onto the valve with no harm.

These tanks are very durable. Keep in mind they were designed to be life support equipment that will be strapped to your back, used in a salt water environment, on rolling boats, sandy beaches and in a wide range of temperatures. The scuba tank is almost certainly overengineered to a far higher degree than any other storage tanks you might buy for the jeep.

Again, forget the dive shop, take the tank to your local Fire Dept, and ask them where they have their air tanks serviced. These facilities are the real pros, and will do a better job for less money in my experience. Ask them to hydro the tank, (even if it shows a current hydro!!). If they give you the tank back, you can rest easy it's safe. They can fill for you too. This cost me about $22, in the NY area, I think.

After that, a scuba regulator knocks the tank pressure down to about 150 psi. I have used my tanks to run a sandblaster, an air hammer, air ratchet etc. I always seem to be airing up tires with them.
If you can't fill to max, use this formula to determine the contents:

Tanks Max capacity / Max working pressure x actual working pressure = Actual cubic footage

or
80 (Cubic Feet) / 3000 (Max pressure) x 1000 (arbitrary pressure) = 26.6 Cubic feet


If you go with this, I would make absolutely sure the mounting is rock solid. If one of those tanks gets loose, the weigh enough to do a lot of damage, and if the valve were to take a good shot, things could get REALLY ugly!.

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post #8 of (permalink) Old 12-23-2000, 10:22 PM
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Re: scuba tank for on-board air?

Still, for airing up tires, I'd just go with the standard psi, a lot of run-of-the-mill air compressors (plug in style) claim to go to 250 psi. It'd cost virtually nothing to run, and would still do the job. At 3,000 psi, I'd be damn careful about wheeling with it. Down there, Johnson's Sporting Goods refills tanks, but unless you're a diver, and with the other restrictions mentioned, forget it. You might have better luck with the local fire department, I know a few guys on the crew, but they take the tanks to Thomaston to get them filled, they don't have the cascade system required there. Most of their systems are for "breathing" air, which isn't what you need, you can use, but you're going to pay to fill it each time. Maine Oxy or Rockland Welding might fill it, but I seriously doubt it, they're sticklers when it comes to tanks. I have an air tank I use as a "pig", and will be mounting it under the Scrambler. I'll also plumb it in for the onboard air.

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post #9 of (permalink) Old 12-25-2000, 08:50 AM
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Re: scuba tank for on-board air?

Thanks a lot,guys. I didn't expect such a thorough group of responses. I have no intention of putting 3000 pounds of pressure in it. I'm only intending to use it as the storage tank for my York onboard system. I'm going to try ozarkjeep's no buck pressure check first--plumb it for a chuck and hook it up to a compressor. Stand at a distance w/ the thing wrapped in something to slow down shrapnel. I'm thinking that i'll just pressurize it and wait for the compressor to kick on again. If it's leaking, it should kick back on in less than a half hour, I'm supposing. According to be stamping, it was last hydro'd in july of 93 and the stcker shows that it passed the visual in 93 also. not that it counts for anything, but it looks fine to me. The paint is almost perfect, excepting the bottom surface where the paint has been chipped. It shows no evidence of repainting. This tank was manufactured by Luxfer who garyl is concerned about. Are the cracks caused by poor quality casting or just fatigue? Is a tank from 93 one of their poor quality units, or are all luxfer tanks junk? Thanks again for putting up with me. Brendan

post #10 of (permalink) Old 12-25-2000, 11:34 PM
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Re: scuba tank for on-board air?

Hey Brendan,
Any hydro, current or otherwise, is useless if you don't know the tanks history. As for the bad lots of tanks, there are more stories than the Empire State Building right now. Industry is pointing to the older Aluminum alloys not being resilient enough, and, Ha Ha, the manufacturer says it's the diver's fault. Cracks around the inside of the neck are the sorest point with these tanks.

If you aren't planning to use it to max pressure, you should consider testing the tank to a point far beyond it's intended use anyway. For example if you're plumbing it into a system that's set for 150 psi, it would be a comfort to know the tank had withstood a 300 or even a 450psi test.





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