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Portable Oxygen Bottle Refill

Tankerpilot75

Well Known Member
I’m sure I’m not the only RV’er to be frustrated by this but I’m having a heck of a time trying to get my portable oxygen bottle refilled at a reasonable price. It’s a small Mountain High AL-415 cylinder 14.7 cubic feet of oxygen at 2000 psi.

In the past a friend of mine generously filled it but his oxygen tanks are now low enough that the pressure output is insufficient to bring my tank to the full psi level. Using a medical oxygen refill station requires a prescription I’m told. Local welding oxygen suppliers won’t touch refilling an oxygen bottle used for breathing. FBO’s near me don’t have oxygen refill capability. The nearest place I’ve found is an airport maintenance shop about a 45 minute drive away and they want at least $50 to refill the small bottle. The drive plus recurring $50 refill cost every time I want to top my bottle off just seems like too much trouble.

Now I don’t use oxygen very often in my RV but I like to keep the bottle full for the unexpected trip. Due to age and an elevated diaphragm on one side, I tend to monitor my oxygen levels anytime I fly above 8000 feet and usually start supplementing my breathing with cannula oxygen around 8,500 feet.

Does anyone have a suggestion for a small oxygen bottle refill system that’s relatively inexpensive to purchase?
 
In the past a friend of mine generously filled it but his oxygen tanks are now low enough that the pressure output is insufficient to bring my tank to the full psi level.

Get your buddy's tanks filled----offer to split the cost, or just pay it yourself.

Methinks he will appreciate it and you will most likely save $$ in the long run compared to the $50 each refill at the airport.
 
Refills

I faced largely the same problems until I discovered my local scuba store would fill mine cheaply ($10?). I use an O2D2 which stretches tanks for a looooong time, and haven’t been able to justify buying my own refill setup.
 
Get your buddy's tanks filled----offer to split the cost, or just pay it yourself.

Methinks he will appreciate it and you will most likely save $$ in the long run compared to the $50 each refill at the airport.


This is the way. Take his tank to a local gas supply place and they’ll swap it out for a full one for not a lot of money.
 
Get your buddy's tanks filled----offer to split the cost, or just pay it yourself.

Methinks he will appreciate it and you will most likely save $$ in the long run compared to the $50 each refill at the airport.

We discussed this but he is a wealthy gentleman and was sued not long ago by someone seriously hurt while they were illegally on his property stealing. Of course he won the law suit but his legal costs weren’t cheap. His attorney has suggested he not loan tools nor help others with parts, supplies or assistance as he has done in the past. It’s just too easy to sue someone with deep pockets.

It’s situations like this that are causing a lot of people to rethink how they operate. I’m sure if I truly needed his help he would provide it but I’d rather not ask now that I know more of his reasoning.

But that takes me back to the original one of how to reasonably refill a small oxygen tank. It seems there aren’t many fbo’s with this capability and don’t want to get into this line of service.
 
In case anyone's wondering, the company that resells the Inogen oxygen concentrator in a pilot-friendly configuration (Windblade) is out of stock and unable to get more inventory for the moment. Actually, this has been a problem for them for about 18 months now.

Supply chain disruptions aren't just for auto manufacturers, box stores, farmers and petroleum refiners anymore. If you were planning on a concentrator instead of a tank, might want to look carefully at your options for the near-term.
 
As someone else mentioned, local scuba shops will often do this for a very fair price. But you might have to show up with a fitting to adapt your tank’s fitting to their’s. Are there any scuba shops in OK?
 
I recently solved this for myself, but it will cost you a couple of bucks. Buy 2 or 3 large oxygen bottles from Craigslist, get them refilled or exchanged, buy the “FBO cascade fill” system, and you can fill your own or buddies for pennies.
 
Oxygen filling

Like what’s been said- just did this. Unable to find good used locally. Bought new from Gas Cylinder Source online 2- 150cuft cylinders, had them filled locally both for $50. Bought transfill assembly eBay from Branton veterinary. Mark one cylinder “low” one cylinder “high”. Fill your cylinder first from low, then close valve and top your cylinder from high. You won’t reach 2000 , but close.
 
I’m sure I’m not the only RV’er to be frustrated by this but I’m having a heck of a time trying to get my portable oxygen bottle refilled at a reasonable price.

I use my local technical diving store (SCUBA). They have rows of giant ABO tanks, and a "jammer" to increase O2 pressure when needed. I pay $6 to $8 to fill my portable tank.

I needed an adapter to go from their SCUBA interface to my portable tank. For about $90 to thescubadiverstore.com I bought a Global GCA 540 Oxygen 2" Nipple/nut and a Global 45021ox Scuba Port converter Block (Viton O-ring O2 version).

I have two portable tanks that I rotate. I offset the hydro inspection dates so I'm never without a tank in the plane.
 

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Call your local scuba shop. They are used to filling small O2 bottles and are usually cheap. Mine is $8 for a fill and will do it on the spot.
 
Bought the transfill hose from mountain high and my own large O2 bottle from the local PraxAir store. Love to eventually buy another bottle for $350ish, but as it is I exchange a mostly full bottle after multiple refills a of my AL-647 for $30ish every other year I haven’t yet.
 
Bought the transfill hose from mountain high and my own large O2 bottle from the local PraxAir store. Love to eventually buy another bottle for $350ish, but as it is I exchange a mostly full bottle after multiple refills a of my AL-647 for $30ish every other year I haven’t yet.

I bought 3 large O2 bottles from Craig’s list for $50 to $75 each. Since they had an old Praxair sticker, the local praxair guys traded them out for new ones, no hydro charge since they already had prax stickers!
 
Preece Precision LLC - transfill station

Buy some oxygen tanks off Craigslist, preferably the largest you can easily transport. I got (2) 330cf tanks for $150 each. If the neck ring is stamped with a suppliers name on it they are the only ones who will exchange it. It the neck does not have a supply house name on it then it is a "customer owned tank" and anyone will fill or exchange it. Just make sure if they exchange it they give you a clean necked bottle again or now you are committed to them for the future. Preece Precision LLC sells a 2 tank cga540 cascade system $109.95 shipped. Add $50 for each additional tank you want to add to the system. A single tank fill setup with bleed valve and gauge is $59.95 shipped. They shipped quick too. Nothing beats leaving the hangar with a full bottle EVERY flight.
 
Welding shop

Buy a transfill hose and make friends with your local welding shop. They should always have a full oxygen tank on site. A case of beer, box of donuts or a $20 should do the trick
 
Buy some oxygen tanks off Craigslist, preferably the largest you can easily transport. I got (2) 330cf tanks for $150 each. If the neck ring is stamped with a suppliers name on it they are the only ones who will exchange it. It the neck does not have a supply house name on it then it is a "customer owned tank" and anyone will fill or exchange it. Just make sure if they exchange it they give you a clean necked bottle again or now you are committed to them for the future. Preece Precision LLC sells a 2 tank cga540 cascade system $109.95 shipped. Add $50 for each additional tank you want to add to the system. A single tank fill setup with bleed valve and gauge is $59.95 shipped. They shipped quick too. Nothing beats leaving the hangar with a full bottle EVERY flight.

And if they are marked on the neck, that’s nothing a flap disk and sand paper can’t convert to a clean neck! (So I’ve heard)
 
Preece

Buy some oxygen tanks off Craigslist, preferably the largest you can easily transport. I got (2) 330cf tanks for $150 each. If the neck ring is stamped with a suppliers name on it they are the only ones who will exchange it. It the neck does not have a supply house name on it then it is a "customer owned tank" and anyone will fill or exchange it. Just make sure if they exchange it they give you a clean necked bottle again or now you are committed to them for the future. Preece Precision LLC sells a 2 tank cga540 cascade system $109.95 shipped. Add $50 for each additional tank you want to add to the system. A single tank fill setup with bleed valve and gauge is $59.95 shipped. They shipped quick too. Nothing beats leaving the hangar with a full bottle EVERY flight.

Any chance you could post the links to the products. I searched and no hits on CGA 540
 
Any chance you could post the links to the products. I searched and no hits on CGA 540

Preece did not list specifically what I wanted so I emailed them and asked if they could supply a cascading system. I found the company through flea-bay where they listed a single tank cga-540 transfill. I'm rather happy with the product they provided.

Looks like they now sell a "2 to 1 Oxygen Transfill Manifold Adaptor CGA540 Aviation Veterinary Medical" after putting one together for me.

2 to 1 Oxygen Transfill Manifold Adaptor CGA540 Aviation Veterinary Medical | eBay
https://www.ebay.com/itm/194163183541

Preece Precision LLC
19466 stafford loop Bend, OR 97702 US
[email protected]
 
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I use my local technical diving store (SCUBA). They have rows of giant ABO tanks, and a "jammer" to increase O2 pressure when needed. I pay $6 to $8 to fill my portable tank.

I needed an adapter to go from their SCUBA interface to my portable tank. For about $90 to thescubadiverstore.com I bought a Global GCA 540 Oxygen 2" Nipple/nut and a Global 45021ox Scuba Port converter Block (Viton O-ring O2 version).

I have two portable tanks that I rotate. I offset the hydro inspection dates so I'm never without a tank in the plane.

I think this taps into the issue that we face on a cross country across the mountains. I'd like the ability to take a courtesy car into town and find a weld shop or a scuba shop that will fill the bottle. Specifically, what is the adapter from the aviation O2 bottle to what they have in a weld/scuba shop?

Aviation O2 bottle fitting (Medical O2), CGA870?
to
Weld/Scuba O2 fitting (industrial bottle), CGA540?
 
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RV-4 O2 bottle placement....

I bought 3 large O2 bottles from Craig’s list for $50 to $75 each. Since they had an old Praxair sticker, the local praxair guys traded them out for new ones, no hydro charge since they already had prax stickers!

Going back to that discussion in October I was wondering what O2 system you use and where you mount it in your RV-4.

Thanks!
 
Oxygen

Inogen oxygen concentrator with an extra battery and Cigarette lighter adaptor off Craigslist for $450.00 with only 180 hours of use. No more refills. Works for two people and just plane works.
You may not find that good a deal, But, they are out there if you look. People get old and need them then the day comes they don't.
I found three of them and bought the youngest. That was two or so years ago.
Art
 
I went to a local welding supply store and they filled it for $22. no hassle, no questions. It's not an illegal gas for industry.
 
O2 refill North Tampa

Any recommendations for Oxygen refill north Tampa to Brooksville area? Seems AirGas can’t do it any longer.
 
If you are ok with having your own filling station you can lease 2 bottles of aviators oxygen from airgas for a super small fee considering how many refills you get from it. I did this and use a eBay supplied oxygen line that connects both bottles to a refill nozzle that threads onto my aviation bottles. I can refill a D bottle for less than $10 after accounting for the lease and cost of oxygen.
 
Any recommendations for Oxygen refill north Tampa to Brooksville area? Seems AirGas can’t do it any longer.

I use Crumpton’s in Tampa for my welding gases. https://crumptonws.com/ They also have a Brooksville location. Disclaimer: I’ve never used them for O2 as I just got my MH system back at Osh and haven’t reached the point for a refill. However I do know they offer O2. Very interested in hearing your experience if you opt to use them.
 
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Any recommendations for Oxygen refill north Tampa to Brooksville area? Seems AirGas can’t do it any longer.

Call a local scuba shop that caters to technical divers. They have 100% aviators o2 and are usually happy to provide a fill for under $10.
 
…. Using a medical oxygen refill station requires a prescription I’m told.


True, but most/many/some physicians will write a prescription for supplemental oxygen, or even an oxygen concentrator for aviation purposes. The diagnosis coding might get a little tricky if he/she doesn’t code it specifically as something like “hypoxia at altitude” or some such (can’t remember the specific code). If left to hospital or clinic coders, it might end up as some kind of COPD diagnosis which in turn might lead to some questions at your next Class I, II, or III medical exam. Unlikely to be an issue if your doctor documents that the prescription is for unpressurized aviation above 10,000 feet. Usually the set of vital signs that the nurse takes when you arrive for the visit includes oxygen saturation.

I don’t know if such a prescription would successfully result in insurance or Medicare paying for the fills and/or the equipment.

Certainly a SCUBA or welding shop would be easier, if available. The oxygen…aviation, welding, or medical…is all the same. Only difference is how the tanks are filled.
 
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O2 refill

Thanks, I'll check with Crumpton’s, it was too late to call them today. Called 3 dive shops in the area and 2 industrial gas houses. The later seem to only fill at their home base in the larger cities (both claimed they use to direct fill) and now only exchange bottles. One wanted to look at my bottle (MH with a CGA 540 male) and said he doesn't think the filling station in Tampa could fill that fitting. The dive shops seem very willing to fill but they did not seem to know what fittings they could fill unless they looked at it. 2 said they do not use pure O2 but a mixture now. The one I went to did not have the fitting to fill my tank. It appears I need a female-to-female CGA 540 fitting to fill at the dive shop I went to today. (On order) There's another large dive shop I'll visit on Friday to try and understand better fittings they use. Most likely I'll need to purchase a larger bottle and do the swap an MT for full one technique at one of the industrial satellite facilities in the area.
 
True, but most/many/some physicians will write a prescription for supplemental oxygen, or even an oxygen concentrator for aviation purposes. The diagnosis coding might get a little tricky if he/she doesn’t code it specifically as something like “hypoxia at altitude” or some such (can’t remember the specific code). If left to hospital or clinic coders, it might end up as some kind of COPD diagnosis which in turn might lead to some questions at your next Class I, II, or III medical exam. Unlikely to be an issue if your doctor documents that the prescription is for unpressurized aviation above 10,000 feet. Usually the set of vital signs that the nurse takes when you arrive for the visit includes oxygen saturation.

I don’t know if such a prescription would successfully result in insurance or Medicare paying for the fills and/or the equipment.

Certainly a SCUBA or welding shop would be easier, if available. The oxygen…aviation, welding, or medical…is all the same. Only difference is how the tanks are filled.

I can confirm some Drs won’t do it. Got a good Dr for my BasicMed so I asked about O2 and he said he would get back to me. Called 2 weeks later and said no because he could lose his license. I’m betting it had more to do with insurance.

One of these summers I’m going to either fly around asking Drs until I find one that will write the script or just buy my own welding tanks and trans fill. :)
 
I can confirm some Drs won’t do it. Got a good Dr for my BasicMed so I asked about O2 and he said he would get back to me. Called 2 weeks later and said no because he could lose his license. I’m betting it had more to do with insurance.

One of these summers I’m going to either fly around asking Drs until I find one that will write the script or just buy my own welding tanks and trans fill. :)

Seems a bit of an extreme assumption on his part...doctors write off-label prescriptions routinely. It's hard to imagine how his license would be in jeopardy. If he's that concerned, a 10-minute office visit with subsequent documentation in your record would keep him safe from any license action. I would have ZERO concern, although I concede that not all doctors feel the same. Some doctors have the same misconstrued fears about licensing or liability issues if they perform Basic Med exams, for example.
 
Ok,

Could some one clearify some things for me?

I might be misunderstanding but I was under the impression that Medical/aviation oxygen was pure or rather much higher then 21% vs compressed atmospheric. As being a Medic-vol Fireman the point of medical oxygen is to increase the percentage getting to the blood stream. Breathing compressed atmospheric air is useless in that regard. I would think even breathing a standard 21% mix at altitude the immediate low-pressure difference will diffuse enough through a canola negating any real benefits. Don't get me wrong it will raise the amount breathed in a few % points but not much. At least that is how I imagine it.

Heck if I'm wrong then if just getting compressed breathable air is all that is needed look into your local VOL fire department. They may already have the adapter to fill it.

Happy Thanks-Giving you all glorious people.
 
Ok,

Could some one clearify some things for me?

I might be misunderstanding but I was under the impression that Medical/aviation oxygen was pure or rather much higher then 21% vs compressed atmospheric. As being a Medic-vol Fireman the point of medical oxygen is to increase the percentage getting to the blood stream. Breathing compressed atmospheric air is useless in that regard. I would think even breathing a standard 21% mix at altitude the immediate low-pressure difference will diffuse enough through a canola negating any real benefits. Don't get me wrong it will raise the amount breathed in a few % points but not much. At least that is how I imagine it.

Heck if I'm wrong then if just getting compressed breathable air is all that is needed look into your local VOL fire department. They may already have the adapter to fill it.

Happy Thanks-Giving you all glorious people.

You’re correct. The aviation requirement is straight O2, not compressed air. That’s why not all dive shops can support filing an aviation bottle but a medical or welding gas suppler can.
 
Ok,

Could some one clearify some things for me?

I might be misunderstanding but I was under the impression that Medical/aviation oxygen was pure or rather much higher then 21% vs compressed atmospheric. As being a Medic-vol Fireman the point of medical oxygen is to increase the percentage getting to the blood stream. Breathing compressed atmospheric air is useless in that regard. I would think even breathing a standard 21% mix at altitude the immediate low-pressure difference will diffuse enough through a canola negating any real benefits. Don't get me wrong it will raise the amount breathed in a few % points but not much. At least that is how I imagine it.

Heck if I'm wrong then if just getting compressed breathable air is all that is needed look into your local VOL fire department. They may already have the adapter to fill it.

Happy Thanks-Giving you all glorious people.

Medical oxygen, aviation oxygen, and welding oxygen are all the same stuff these days. Only difference is that medical oxygen cylinders are filled (supposedly) only after completely emptying them, theoretically to “purge” contaminants that might have gotten into the tank as it was sitting around empty with the valve open. In the old days, aviation oxygen was (supposedly) “dried” to avoid freezing up of flow regulators.

When delivered to the lungs under pressure, oxygen is toxic and can be deadly, which is why SCUBA tanks are only compressed air (21% oxygen). As you go deeper underwater, it takes more pressure to expand the lungs and you don’t have to go very deep before that pressure is high enough to cause oxygen toxicity if the percentage of oxygen is too high. There is Nitrox for SCUBA diving, which is a percentage O2 that is greater than 21% but less than 100%. Other medical situations can cause O2 toxicity for patients under the care of an unwary respiratory therapist. Note that that’s for O2 delivered under pressure. As altitude increases, atmospheric pressure decreases so oxygen toxicity is not a thing in an airplane, especially when breathed through a mask or cannula.
 
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Medical oxygen, aviation oxygen, and welding oxygen are all the same stuff these days. Only difference is that medical oxygen cylinders are filled (supposedly) only after completely emptying them, theoretically to “purge” contaminants that might have gotten into the tank as it was sitting around empty with the valve open. In the old days, aviation oxygen was (supposedly) “dried” to avoid freezing up of flow regulators.

When delivered to the lungs under pressure, oxygen is toxic and can be deadly, which is why SCUBA tanks are only compressed air (21% oxygen). As you go deeper underwater, it takes more pressure to expand the lungs and you don’t have to go very deep before that pressure is high enough to cause oxygen toxicity if the percentage of oxygen is too high. There is Nitrox for SCUBA diving, which is a percentage O2 that is greater than 21% but less than 100%. Other medical situations can cause O2 toxicity for patients under the care of an unwary respiratory therapist. Note that that’s for O2 delivered under pressure. As altitude increases, atmospheric pressure decreases so oxygen toxicity is not a thing in an airplane, especially when breathed through a mask or cannula.

I'm pretty versed in the subject of oxygen toxicity. Hense my confusion on why there was suggestions on filling at a scuba shop.. I was un-aware of there being pure O2 offered for diving.
 
I'm pretty versed in the subject of oxygen toxicity. Hense my confusion on why there was suggestions on filling at a scuba shop.. I was un-aware of there being pure O2 offered for diving.

Saturation diving and Technical diving (simplistically diving to depths greater than normal recreational diving) uses breathing gas mixtures other than compressed air such as NITROX or HELIOX. Pure O2 isn’t used by itself, but you need it to create the desired mixture.
 
I'm pretty versed in the subject of oxygen toxicity. Hense my confusion on why there was suggestions on filling at a scuba shop.. I was un-aware of there being pure O2 offered for diving.

There really isn't, 40% oxygen is about the max that any responsible dive shop will mix for you for recreational diving, and they're the shops that are likely to have O2 cylinders for filling. Most other shops buy a Nitrox pre-mix..usually 32%....and all will require that you have Nitrox certification before they'll put it into your dive tank. If they have pure O2 on the premises, they "might" fill your airplane O2 cylinder as long as it's not a SCUBA cylinder.
 
Seems a bit of an extreme assumption on his part...doctors write off-label prescriptions routinely. It's hard to imagine how his license would be in jeopardy. If he's that concerned, a 10-minute office visit with subsequent documentation in your record would keep him safe from any license action. I would have ZERO concern, although I concede that not all doctors feel the same. Some doctors have the same misconstrued fears about licensing or liability issues if they perform Basic Med exams, for example.

Ya the response seemed a bit weird. He is usually a pretty chill guy so it surprised me when he said no. I do remember during the exam he mentioned there was a difference between the O2 types (which we all know is not true anymore). I tried to explain it to him.

Always found it extremely stupid that I can get aviator oxygen with no hassle but medical needs a prescription...
 
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Always found it extremely stupid that I can get aviator oxygen with no hassle but medical needs a prescription...[/QUOTE

With a bit over 4 decades in that business, I'll take a swing at that one.
The moment a gas company puts a "Medical Oxygen" label on a cylinder, the product becomes a drug, regulated by the Federal Food & Drug Administration and is subject to all the regulations thereof. It's been more than 20 years, but I still remember that they're in Rockville, Md. The guys at the welding supply can no more sell you a cylinder of Medical Oxygen, without a prescription than a pharmacist can sell you a bottle of your favorite medication, without a script. It's just that simple or complicated, depending on your outlook.
Aviator Breathing Oxygen is not considered or regulated as a Drug, but rather Oxygen certified to meet the specs, originally determined by the Military. It's perfectly legal for anyone to buy or use ABO without any proven requirement.
As to the suggestion that "all Oxygen is the same", well not exactly. My company had bulk storage of 6,200 gallons of liquid Oxygen and we filled lots of commercial and some medical Oxygen. We sold a fair amount of ABO, but couldn't fill the cylinders. The liquid Oxygen we bought was produced at liquefaction facilities in the deep South, among a lot of chemical plants. The specs for ABO called out maximum hydrocarbon levels. The LOX produced in our part of the country couldn't meet that requirement. The ABO that we sold was filled from LOX produced at an air separation facility "somewhere in the Northeast". It was just Oxygen, but not quite the same as ours. It was kinda pricey!
Keeping on the subject of "all Oxygen is the same", much of the difference is the handling of the cylinders. Any reputable gas plant will use new, virgin cylinders for Medical or ABO product. Those have no contamination of any type. Commercial oxygen cylinders can and sometimes do have contaminants. "What kind of contaminants?" you say... Under the right circumstances, a plugged welding tip can allow a full cylinder of Acetylene to produce some backflow into a nearly empty Oxygen cylinder. "Oh, THAT can't happen! Torches have check valves!" Want to bet? Not common, but I've seen it a lot of times over the years. I've seen cylinders with muddy water and who knows what, in them, because they were dropped in the mud when the full was hooked up. The worker, filling the cylinders, is supposed to "Sniff Test" each cylinder, before hooking up the fill lines. He's also supposed to vacuum the cylinders before fill. I wouldn't bet my life on it, though. If you were unlucky enough to get an oxygen cylinder that was contaminated, to fill your little MH cylinder, imagine the shock of that first hit of stinky gas! It's a good idea to breathe a bit on the ground, after a fill. If I were setting up a transfill for such, I'd definitely get a couple of cylinders of ABO.
After requalification (Hydro test) the cylinders are flushed and dried out, so the "clean" part starts over.
Anyone who's read this far is no doubt bored to tears, so I'll leave you with an interesting tidbit. In the US, industrial gas specifications are mostly administered by the CGA, thus the standard oxygen connection being CGA 540. While there are several CGA grades of Oxygen, most are not germane to this conversation. The purity requirement for Medical Oxygen (the drug that you breathe) is 99.0% pure Oxygen. The purity requirement for Commercial Oxygen (what you use in your cutting torch) is 99.5% pure Oxygen. Chew on that one a while! And before someone jumps in and proclaims that the 99% purity thing isn't the ONLY requirement, yeah, I know. Remember I specified "Purity Requirement"...

Now, about that Nitrogen in your tires! :)
 
Found O2

Found a dive shop just north of Tampa (Scuba West) that had O2 to fill my bottle, was not easy. Calling around the dive shops don't know a CGA fitting from a PPE. It's ok they just were not trained to understand the different fittings they use. Yes, they keep pure O2 in stock and yes, it's poisonous below 30 ft. Why, to mix with Nitrogen and sometimes Helium for specialized deep-sea diving. Also, if they need to give a diver an added O2 hit use on the dive boats or so I am told. If you go there with your CGA540 tank look for the gang of O2 bottles and ask to look at the hose fittings they are hooked together with. After closing the tank valves and uncoupling a hose it's a CGA female that fits on top of your tank albeit there is no O-ring on their fitting, so you need to tighten the fitting with a wrench o so slightly. Cost to fill about 10 bucks a tank. (I have 2 of the Kevlar 11 cu ft tanks so smaller than normal)
 
Off topic

I did ask the tank filler where did the mixture of O2/Nitrogen (Air) that was inside my tank go? He said the tank was empty, so it did not go anywhere. I said I'm pretty sure the tank was not under vacuum and at that point we talked about the dilution of the O2 in his tanks the O2 must have achieved. I guess the numbers works out that his tanks where at 2,500 psi and mine was at 14.7 psi so if he used all of the O2 in his tanks (eventually) his tanks would have been diluted 14.7*.80/2,500 or ~ 0.5%??
 
Always found it extremely stupid that I can get aviator oxygen with no hassle but medical needs a prescription...[/QUOTE

With a bit over 4 decades in that business, I'll take a swing at that one.
The moment a gas company puts a "Medical Oxygen" label on a cylinder, the product becomes a drug, regulated by the Federal Food & Drug Administration and is subject to all the regulations thereof. It's been more than 20 years, but I still remember that they're in Rockville, Md. The guys at the welding supply can no more sell you a cylinder of Medical Oxygen, without a prescription than a pharmacist can sell you a bottle of your favorite medication, without a script. It's just that simple or complicated, depending on your outlook.
Aviator Breathing Oxygen is not considered or regulated as a Drug, but rather Oxygen certified to meet the specs, originally determined by the Military. It's perfectly legal for anyone to buy or use ABO without any proven requirement.
As to the suggestion that "all Oxygen is the same", well not exactly. My company had bulk storage of 6,200 gallons of liquid Oxygen and we filled lots of commercial and some medical Oxygen. We sold a fair amount of ABO, but couldn't fill the cylinders. The liquid Oxygen we bought was produced at liquefaction facilities in the deep South, among a lot of chemical plants. The specs for ABO called out maximum hydrocarbon levels. The LOX produced in our part of the country couldn't meet that requirement. The ABO that we sold was filled from LOX produced at an air separation facility "somewhere in the Northeast". It was just Oxygen, but not quite the same as ours. It was kinda pricey!
Keeping on the subject of "all Oxygen is the same", much of the difference is the handling of the cylinders. Any reputable gas plant will use new, virgin cylinders for Medical or ABO product. Those have no contamination of any type. Commercial oxygen cylinders can and sometimes do have contaminants. "What kind of contaminants?" you say... Under the right circumstances, a plugged welding tip can allow a full cylinder of Acetylene to produce some backflow into a nearly empty Oxygen cylinder. "Oh, THAT can't happen! Torches have check valves!" Want to bet? Not common, but I've seen it a lot of times over the years. I've seen cylinders with muddy water and who knows what, in them, because they were dropped in the mud when the full was hooked up. The worker, filling the cylinders, is supposed to "Sniff Test" each cylinder, before hooking up the fill lines. He's also supposed to vacuum the cylinders before fill. I wouldn't bet my life on it, though. If you were unlucky enough to get an oxygen cylinder that was contaminated, to fill your little MH cylinder, imagine the shock of that first hit of stinky gas! It's a good idea to breathe a bit on the ground, after a fill. If I were setting up a transfill for such, I'd definitely get a couple of cylinders of ABO.
After requalification (Hydro test) the cylinders are flushed and dried out, so the "clean" part starts over.
Anyone who's read this far is no doubt bored to tears, so I'll leave you with an interesting tidbit. In the US, industrial gas specifications are mostly administered by the CGA, thus the standard oxygen connection being CGA 540. While there are several CGA grades of Oxygen, most are not germane to this conversation. The purity requirement for Medical Oxygen (the drug that you breathe) is 99.0% pure Oxygen. The purity requirement for Commercial Oxygen (what you use in your cutting torch) is 99.5% pure Oxygen. Chew on that one a while! And before someone jumps in and proclaims that the 99% purity thing isn't the ONLY requirement, yeah, I know. Remember I specified "Purity Requirement"...

Now, about that Nitrogen in your tires! :)

Thanks for your expertise Bill. Lots to think about on that one. Kind of confirms my thinking on the different types of oxygen and how either spec wouldn't concern me. Interesting about the tanks being contaminated though. If I do trans-fill I'll take a gander at ABO prices at that time. In the end I might just fish out a Dr. willing to write medical. Then I can just drop an empty off and pick up a new! :)
 
I did ask the tank filler where did the mixture of O2/Nitrogen (Air) that was inside my tank go? He said the tank was empty, so it did not go anywhere. I said I'm pretty sure the tank was not under vacuum and at that point we talked about the dilution of the O2 in his tanks the O2 must have achieved. I guess the numbers works out that his tanks where at 2,500 psi and mine was at 14.7 psi so if he used all of the O2 in his tanks (eventually) his tanks would have been diluted 14.7*.80/2,500 or ~ 0.5%??

When I fill my bottle, I purge the line by attaching it to the bottle, then cracking the supply bottles a little before tightening the last connection. I asked the FBO if they purge the line and they looked at me like a dog watching TV.. I don’t know if nitrogen settled out, but since it’s lighter than oxygen. Perhaps allowing the bottle to stand up a few days then purging off the top may get rid of it? Probably not though.
 
Medical oxygen tanks are purged before refill because of the theoretical possibility that ambient contaminants in the air may have gotten into the tank while it was sitting around empty. Nothing to do with nitrogen from the air that’s in the empty tank.

If using a nasal cannula or non-rebreather mask, in an airplane or in a hospital bed, the fraction of inspired oxygen that actually gets into the lungs is going to be about 30% at 2 liters/min (as opposed to 21% breathing room air). Crank the flow up to 6 liters/min and you might get an FIO2 of 50%, probably less. Being concerned about minimal residual air in the tank at the time of filling (not that anyone here is) is probably unnecessary.
 
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