Can I convert a medical oxygen bottle to be charged by air compressor?
March 7, 2020 5:05 AM   Subscribe

I picked up a used medical oxygen bottle for cheap and I'd like to try converting to use with my pneumatic tools. I often find an air compressor's hose or cord too short to be practical. So I want to have this bottle that I can charge with my air compressor and then hook a tool up to it and move it around without having to drag the compressor around. The bottle is rated to 2,000 PSI which is well above the pressure I'd be putting it to so I'm not worried about a failure. How would I go about doing this?
posted by Socinus to Sports, Hobbies, & Recreation (9 answers total) 2 users marked this as a favorite
Are the fittings even compatible?

Bottles for different gases are deliberately built with incompatible fittings so that you can't accidentally screw, say, a nitrogen bottle into someone's oxygen line.

I don't know what it would take to refit the bottle, but I would guess that it costs more than a new bottle and reputable shops will refuse to do it. Especially if your bottle is still labeled for oxygen. Where I live, the bottles are color-coded, so you'd have to sand off all the paint to relabel a bottle. And then you'd definitely want to get the bottle re-proofed after all that.

I don't think this is a good plan.
posted by meaty shoe puppet at 6:41 AM on March 7, 2020 [1 favorite]

This is a bad idea for several reasons. One is cost: you can get an 11-gallon air tank at Harbor Freight for $40. . One of those charged up should run a small air nailer for a least a hundred shots. Another problem is safety. A tank with 2000 PSI inside it is a lot of potential energy to be dragging around the jobsite, and accidentally breaking off the regulator on a 2000 PSI tank is a lot more dangerous than a 125 PSI tank. Regulators that can step down that kind of PSI to useable levels for air tools aren't cheap either.
posted by cosmicbandito at 8:03 AM on March 7, 2020 [4 favorites]

Unless I have misunderstood, the OP is talking about taking an EMPTY oxygen tank rated for 2000psi and then filling it with compressed air from a standard air compressor at perhaps 100psi or so. If you can remove the existing valve and use threaded adaptors to make the transition to air fittings it should work, but the tank will be far heavier than one of the inexpensive off the shelf air tanks like the one the above poster mentioned. It's kind of a "yes you could, but why?"-unless you live in a place where it's really hard to get air tanks, I'd skip this project.
posted by Larry David Syndrome at 9:42 AM on March 7, 2020 [6 favorites]

There's also no mention of size. Maybe this is a small personal sized oxygen tank and the OP is only talking about something enough to fix a flat or blow the dust out of a computer on the porch. If it's small and enough for intended use then it might be worth it. The only thing I'd possibly worry about is that the oxygen tank might not like holding damp air. You can probably find a small lighter air tank easier than you can make one out of the oxygen tank.
posted by zengargoyle at 10:36 AM on March 7, 2020

You can certainly purchase the correct parts from McMaster-Carr.

High pressure air is very dangerous and the various rules, labels, and restrictions have been written in blood. If I saw a bodged up bottle such as you are describing I would leave the area immediately. No shop would fill such a thing.

I'd drill a hole in the bottles, sell them for scrap, and buy a 5 gallon bottle as linked above.
posted by pdoege at 11:08 AM on March 7, 2020 [2 favorites]

Like others, I think the big problems are:

1. Compared to a "real" air tank it would be considerably heavier for the same volume of air, and if it's on the small side it may not hold a useful volume when charged to the max pressure your compressor can produce. You can probably do the math on this one if you're curious.
2. You'll probably need to buy fittings and adapters, which may actually come within spitting distance of the price of a cheap air tank.
3. After you assemble it, it sounds like it won't be safe to use. My specific concern would be that it would be less stable than an air tank designed for this sort of application. Medical oxygen bottles tend to be tall and skinny, and unless you also have a cart or stand, attaching an air hose to it will tend to pull it over if upright or roll/drag it around if laid on its side, both of which seem like they'd pose significant risk of (explosively) popping off your ad hoc fittings. Compressed air tanks tend to be stubby, horizontally oriented, and stable, and usually sport little feet and a handle. That is, they're designed to be dragged around a garage or job site without posing danger to their users.
posted by pullayup at 1:02 PM on March 7, 2020 [2 favorites]

I often find an air compressor's hose or cord too short to be practical.

Um, along the lines of "Maybe you could, but why?", you can totally buy longer hoses & hose extensions and electrical extension cords - 25 ft airhose from Harbor Freight for $15 bucks.

Honestly, unless there's complications or limitations you haven't told us about, it seems like buying that oxygen bottle for cheap has put the idea in your head that the best/cheapest thing to do is to MacGyver a solution out of it, and you've lost sight of the very likely possibility that it would be much simpler and quite possibly cheaper to just . . . get the right stuff in the first place - like a portable air tank meant for compressors, or extension hoses and/or electrical cords.
posted by soundguy99 at 1:17 PM on March 7, 2020 [1 favorite]

For all the reasons (safety, cost, practicality) the answer to your question is really no. If you had a scuba tank and access to a dive shop that could charge it for you maybe but with a home compressor not really. To give you an idea the 5 gallon air tank someone linked is barely adequate to fill a standard car tire. A home oxygen tank has much less capacity.

If the appeal of the O2 tank is the small size you might be interested in a CO2 tank instead (EG: Powertank). All the compact size of the O2 cylinder with substantial capacity (orders of magnitude more than you'll be able to achieve with an O2 tank at 125psi) because the CO2 is liquified.

CO2 is available at any welding shop.
posted by Mitheral at 6:18 PM on March 7, 2020

Air compressors compress... air. Which is partly water vapor. The air stored in your compressor's tank contains a surprising amount of water. This is why your air compressor has a drain on the bottom of the tank (you're opening that every single time you're finished using your compressor, right?) to allow the collected water to drain out of the tank. This oxygen bottle does not. By storing compressed air in this bottle, you are encouraging rust development, weakening the integrity of this pressure vessel.

If you haven't opened the drain valve on your air compressor in a while, do it now, if you can get it open. You'll probably be surprised at how much rusty water comes out. I hope your tank doesn't rupture on you, I really do. But I've seen it happen from rusting out, and it is terrifying to witness.

I love air tools. I have a large 50-gallon compressor in the shop. It's sort of loud, so it lives in the corner far from where I work. I have many air lines of different lengths, and if I need to work outside, it's easy enough to string a couple lines together.
posted by xedrik at 10:18 AM on March 8, 2020 [1 favorite]

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