What equipment is needed to fill an appropriate cylinder with oxygen generated by the electrolysis of water?

Update: I need someone that has experience with gas cylinders to point out potential dangers that would be present by filling this way, We've already discussed water vapor and oil potentially making its way inside. That doesn't sound good to me so I need certainty that its safe or those can be eliminated or reduced to safe levels.

Right now I would really like to know what I need so I can refill tanks myself. I'm guessing its a special adapter or replacement valve, but I don't know where to start

Would it be possible to fill an appropriate oxygen tank with the right adapters/compression system with the oxygen generated by electrolyzing water and what kind of equipment would be needed? I know for propane you can buy adapters and refill/transfer from one to another, but obviously this is completely different, and I don't know anything about oxygen valves/adapters or compression systems. Yes I know this could potentially be very dangerous and also have no interest in collecting the hydrogen.

Just to clarify we are talking about commercial grade tanks, not a 2 liter soda bottle. Also, if possible how high of purity would be expected using optimal electrodes and electrolytes to prevent corrosion and impurities. Any information at all would be very helpful.

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NathanE31 (author) 10 months ago

I finally found some info how to refill oxygen tanks from each other. Might not have anything to do with the question, but I wanted to know. 3rd post down


and found a pump that doesn't cost thousands


would that work?

iceng10 months ago

You will need a special compressor.

Specifically one that does not allow oil to pass into the cylinder.

This is assuming you are going to breath the O2.

Oil in air is much worse then two life times smoking in one tank used.

NathanE31 (author)  iceng10 months ago

These oxygen tanks would be for torches. Propane/MAAP gas. I have a few of the bernzomatic 1.4 oz oxygen tanks and they're expensive and don't last long at all. Thinking about getting a bigger one after I do some research.

why would I need a compressor that doesn't allow oil? I can see how that would be bad for breathing and extremely dangerous when used with a flame but is that oil coming from the compressor or trace amounts that get in?

This is mainly for my amusement, to be able to do it I guess. if its cheaper than buying oxygen then that's just icing. Safety is obviously most important when doing this, and would need absolute 100% certainty it wouldn't be dangerous.

I'm starting to think this might cost too much to be possible or if the tanks would even be able to be refilled. But I guess that's why I'm here. To find out if nothing will explode and if minor impurities wouldn't effect the cylinder in any way. Would I even get 99%+ oxygen with a perfect electrolytic setup ?

iceng Quadrifoglio10 months ago

O2 likes to burn lots of things but I don't believe the air fuel ratio in even in a cheep over lubed compressor is in the explosive stoichiometric mixture range.

Did I ever mention that I worked for Bill Lear and his STEAM BUS and had a grand education on formulating burning mixtures to boil water (1200 PSI) known as the working fluid it was called Learium....
Bill Lear searched long and hard for a suitable replacement for H2O as
the working fluid in the steam bus. Because Water freezes.

Named Learium but ultimately came to be known as unobtainium.
Some fluids were poisonous and an explosive decompression would
coat every internal surface with Teflon. The antidote for inhaling the
Learium de jour vapors was alcohol, ergo all employees were supplied
a half gallon of JB Scotch to be kept in their desk drawer.
It wasn't often but on a tiring Friday afternoon it wasn't unusual to have
a steam engineer smell a vapor leak and we would all take some of
the antidote (several shots to be sure ;-)

steveastrouk iceng10 months ago

Its not to do with vapours. Oil in O2 lines is verboten

As is oil on connections or connection threads. That will get you fired, immediately.

Fired...thermally, or employment-ly ...or both.

Another funny one if running Copper lines with acetylene gas in them....forms a very unstable explosive layer internally !

iceng NathanE3110 months ago

Most piston compressors have trace lubricating oil.. That oil does not matter for torches and helps downstream machines but is deadly if being inhaled at 30 feet (two atmospheres pressure) under water == instant hard to cure pneumonia.

Most $99 Harbor Freight compressors can deliver a hundred PSI or less.

NathanE31 (author)  iceng10 months ago

Well my dad has an air compresser but how would i connect them? Wouldn't I need some type of oxygen valve and a hose that would connect the two?

NathanE31 (author)  NathanE3110 months ago

also not sure about all oxygen tanks but these tiny ones are left hand threads

rickharris10 months ago

Do you need high pressure? or just a flow of O2

Awesome, a link to the KOR! This guy makes good videos, and he's my hero, and everything I would like to be! And I mean that sincerely, with apologies to Bette Midler for stealing her song lyrics.

I am not totally sold on all his projects but most are interesting and well conceived and engineered.

My problem is I tend to remember the things I find when wondering around the internet.

What I admire, envy, most about the KOR is his ability to turn ideas into finished, attractive, project-tutorials.

In contrast, I'm full of good ideas, but I haven't upped a new project here, or anywhere, since, let's see... 2011.


Well, likely the result of too much time spent jabbering in the Answers forum.


NathanE31 (author)  rickharris10 months ago

The that's awesome. The small tanks are rated at 500 psi

I don't get it. If you knew the rated pressure of your tanks, why not mention this in your question? Why not share that info with the rest of the class? Why use all these mealy-mouthed words like "appropriate" and "commercial grade", which are pretty much meaningless compared to an actual spec for the rated pressure, e.g. 500 PSI?

I mean, just to clarify, which statement do you think is more clear?

"Just to clarify we are talking about commercial grade tanks, not a 2 liter soda bottle."

"The small tanks are rated at 500 psi."

NathanE31 (author)  rickharris10 months ago

I don't know for sure I can't find anything on how to refill oxygen tanks

iceng NathanE3110 months ago
rickharris10 months ago

Do you really need oxygen under pressure. I used to have a Map torch with force fed air which produced a flame easliy hot enough to braze with.

Jack A Lopez10 months ago

In response to some of your questions, in no particular order:

The main difference between storing room temperature liquefiable gases like {propane, or ammonia, or 1112-tetrafluoroethane} versus more gassy gases like {oxygen, nitrogen, hydrogen} is the former can be liquefied at room temperature, and at pressures that are not super high.

I mean, to sort of qualify that statement, consider a bottle of propane. The pressure inside the bottle is less than 10 atm, or 150 PSI, even on a hot day, and the stuff in the bottle is an actual liquid, with density comparable to water or petrol.

In contrast, the breathing gas in a SCUBA tank, a mixture of nitrogen and oxygen, e.g. dry air, has very high pressure, around 100 to 300 atm, but it has NOT been liquefied. In terms of density, the density is approximately what you'd expect for an ideal gas. That is to say, the density is approximately proportional to the pressure, e.g compressing dry air to 100 atm , gives a gas that is about 100 times as dense (approx 120 g/L) as that air at 1 atm (approx 1.2 g/L).

Actual, cryogenic, liquid air has a density of about 870 g/L, according to Wikipedia page titled "Liquid air".

Anyway, that's sort of the story for gases that cannot be liquefied at room temperature {e.g. oxygen, nitrogen, hydrogen}. Since they cannot be liquefied, the best way to get useful density, is to store them under very high pressure.

Oxygen from electroylsis of water tends to be wet; i.e mixed with water vapor. You might want to dry it first, before storing it, by piping it through some desiccant, or a dryer, or something.

Regarding pressurizing, I overheard that electrolysis can be used to pressurize the produced hydrogen and oxygen, to like, arbitrarily high pressures. Although I don't have an authoritative link for this claim, so please treat that as a rumor.

Regarding pumps, for producing really high pressures, I have overheard that pumps sold for pressurizing SCUBA tanks, can reach really high pressures, like 1000s of PSI, 100s of atmospheres. I am guessing there exist pumps of this kind compatible with pure, or almost pure, oxygen.

Although, I think the last time I went looking for prices for SCUBA compressors, even just like, used ones on eBay, the numbers were somewhat shocking. I dunno. I guess it is kind of a rare, high performance, thingamajig.

Also note, what qualifies as a "commercial grade", non-cryo, oxygen tank may vary widely depending on the application. I mentioned SCUBA tanks. Those are filled to pretty high pressure. There are also oxygen tanks sold for oxygen-acetylene cutting torch. There is also a cheap disposable, oxygen-propane kit, sold by Bernzomatic(r). I have also seen little, skinny, green cylinders of medical oxygen, with wheels, and a handle to push it around with.

All these are "commercial" since they're sold, but I would be very surprized if they were all filled to the same pressure. If I had to guess, I would guess the cheap Bernzomatic oxygen tank is the weakest, lowest pressure filled, and the SCUBA tank is the strongest, and highest pressure filled, and grandpa's little green cylinder with wheels on it, is filled to some pressure intermediate pressure.

See also the Wikipedia page for "Diving clyinder" for a believable description of this kind of pressure tank.

iceng Jack A Lopez10 months ago

Excellent discussion, as always.

There are 5000 PSI SCUBA tanks made of dual material (fiberglass over metal) and half size more oval. Not all dive shops are equipped to fill these super tanks.

Jack A Lopez iceng10 months ago

Yeah. Similar things are used for storing compressed hydrogen.

For example, "aluminum liner completely wrapped in epoxy resin-coated, aerospace-grade carbon fiber", uh, here:


Found that link via Google. Interestingly, the same company (Worthington, not Google) makes disposable, thin steel, low pressure tanks too. I have seen their name on disposable propane cylinders, also BalloonTime(r) disposable helium cylinders for filling party balloons.