Medical Oxygen Generator for small volume Nitrox?

[Lobzilla]

Has anyone used a medical Oxygen generator (self-contained, Pressure Swing Adsorption, molecular sieve system delivering 10L/min ~ .35CFM O₂) for "home Nitrox"?
I did some rough 'back of the envelope' calculations that show this to be feasible for smaller (<4CFM) systems.

What do the experts think?

 

[Peter_C]

I am no expert, but what is the cost vs buying a used O2 tank and reg? Mixing sticks can be built for less than $100.

 

[Lobzilla]

I am no expert, but what is the cost vs buying a used O2 tank and reg? Mixing sticks can be built for less than $100.

Good point.

Sorry, I forgot to mention that the motivation is independence from O₂ refills. Think extended boat cruise .

 

[dannobee]

I looked at some for sale on craigslist a while back. But I was going to use the "big bag" method, that is, pump the oxygen into a big bag, then feed it through a valve into the nitrox stick.

After looking at the unit specs, I just decided to stick with tanked oxygen. (the 0.35 cfm is not likely 100% oxygen, but significantly lower).

It didn't seem like it was worth the hassle.

 

[Lobzilla]

I looked at some for sale on craigslist a while back. But I was going to use the "big bag" method, that is, pump the oxygen into a big bag, then feed it through a valve into the nitrox stick.

After looking at the unit specs, I just decided to stick with tanked oxygen. (the 0.35 cfm is not likely 100% oxygen, but significantly lower).

It didn't seem like it was worth the hassle.

At the higher flow rates the O₂ content drops to 90% but this is not going to make a big dent in the fill time.

I agree, if I live 2 miles from a gas supplier, which I do, the whole thing is pointless. 100 miles (~ 50 gal of diesel on my boat) from the next supplier and/or being outside the USA where they may not fill your O₂ tanks is a different story. Keep in mind that additional O₂ tanks also cost money.

 

[Scuba Duck]

This is very feasible. But you have to be able to make the oxygen at whatever rate you need to feed your air compressor. Essentially this is equivelant to a miniature membrane system. So if you have a very small HP air compressor this idea is practicable. There are a couple companies that make small oxygen generations systems that will produce 10 liters per minute (.33 cfm) of oxygen at 94% purity. This would be enough oxygen to make 40% nitrox at 1.4 cfm, 1.75 cfm at 36%, or 2.4 cfm at 32%

link is to spreadsheet with oxygen flowrates and nitrox percentages.

http://www.envirodive.com/O2 Flowrate Spreadsheet.xls

 

[CraigAClark]

Last time I built a self contained PSA system, the Rix micro-boost was around $4800.00. The rest of the components, including OEM-15 (from OGSI) l.p. air compressor, receivers, moisture separators, refrigerated dryer and misc components were all relatively cheap by comparison. These small systems can deliever 93% +/_ 3%. The rate was approx. 11 CFH to a max pressure of 2250 psi.

Craig

 

[deepstops]

It's always been my understanding the O2 concentrators remove only nitrogen and concentrate all other types of gas in regular air. Argon is 1% in the air we breathe but that means an O2 concentrator has an out of about 4% argon. I think that's the contraindication to using one to generate gas used for diving.

Someone feel free to correct this if it's not accurate.

 

[Lobzilla]

It's always been my understanding the O2 concentrators remove only nitrogen and concentrate all other types of gas in regular air. Argon is 1% in the air we breathe but that means an O2 concentrator has an out of about 4% argon. I think that's the contraindication to using one to generate gas used for diving.

Someone feel free to correct this if it's not accurate.

You are correct. The PSA unit removes Nitrogen and thereby concentrates the remaining components, i.e Oxygen and rare gases, including Argon.

Now we need a Hyperbaric MD to chime in on how much Argon is permissible before one would have to be concerned about its narcotic effects. I think that Argon is believed to be 2.3 times as narcotic as Nitrogen. Therefore, 4% Argon should not be an issue. But who knows?

 

[ianr33]

Another thing to consider would be gas absorption/deco models. Far as I know deco models don't worry about Argon as its only 1% in air. Maybe they don't need to worry about it at 4% either but who really knows?