Oxygen concentrators and nitrox sticks

[estresao]

Hi,

I'm struggling getting a place nearby where I can buy oxygen to be used with my nitrox stick, but so far I have not been pretty lucky, so I'm still finding out how I'll do.

Investigating I've seen for some sickness there are people who uses potable oxygen concentrators and I was just wondering whether could be used on of this to inject O2 to the nitrox stick?

I'm not sure how many litres per minute is enough for this purpose, but there are concentrator able to provide 10+ litres per minute.... and they can be found second hand.

What you think? Is there any one already using a flow meter with the nitrox stick who can provide some numbers?

 

[estresao]

I was thinking about that and I guess there are some number I need to bear in mind:
- My compressor is a Bauer PE 100, able to do 100 litres/minutes (effective flow)
- I want to get Nx32 so I need to add 11% to air

11% of 100 litres are 11 l/m, so I guess an oxygen concetrator able to provide over 11 L/m could work in my case.

 

[OMyMyOHellYes]

What kind of O2 are you trying to obtain?

Would welding or aviation O2 work? Must it be medical O2?

Older thoughts on the subject found after original post:

Welding versus Medical O2?

I asked this question in another thread I started, after getting an answer to the original question, but thought I would post a thread about it to get some more people to see it. I have 3 locations locally that can handle O2. One is strictly welding, another was medical but was forced to drop...

scubaboard.com

 

[Gone for diving]

I use an o2 concentrator and have a medical tank filler
I fill my own torch tanks,
It's very slow 2lpm I think. But works well, don't notice anything when torching... its around 90+ %

 

[grantctobin]

@tbone1004 has some solid options. Argon is the real annoyance, so I would advise against using it for CCR bottles

 

[estresao]

I use an o2 concentrator and have a medical tank filler
I fill my own torch tanks,
It's very slow 2lpm I think. But works well, don't notice anything when torching... its around 90+ %

Problem is that medical tank filler I've found here are around 4000€ (HomeFill II).... that's painfull

 

[tbone1004]

math is a little wrong since the compressor will still only take 100lpm so it's effectively 90+10 vs 100+11.

It is also important to note that when these things are up at their full flow rate the fO2 can drop to around 80% so you may come up a bit short. This is one of those times that having a VFD on the compressor is clutch because you can slow them down a little bit to match what is incoming. You can use a pair of these concentrators in parallel so long as you have enough power as they're a bit of a pig when it comes to power consumption.

as @grantctobin said, these are really only removing the N2 from the atmospheric gas and you're left with all of the trace gases with Argon being the primary offender. If you're diving OC then you have nothing to worry about and just pretend it doesn't exist. If using it as a "100% O2" deco bottle, you're still creating a near pure gradient on the issues for the N2 and/or He to come out, you're just pushing some Ar in but it's not really significant. If using that gas for the O2 bottle on a CCR then the Ar accumulates and as it is both very dense and extremely narcotic then you want to dil flush fairly regularly to prevent it from building up, every ~10-15mins or so seems to be an accepted interval but if you're on OC it truly doesn't matter.

 

[broncobowsher]

How you need it also matters. The Argon buildup on a rebreather really sucks. But open circuit it really doesn't matter. Since I see you are after Nitrox32, open circuit, fine. So you end up with ~1½% Argon instead of the normal 1% in air. Being Nitrox32 there is enough depth limitation that it isn't anything to worry about.

New oxygen concentrators are expensive. Used ones are often cheap. Since they are often used by the elderly, and the elderly die. The estate is left to clear out all the old stuff. Sell it cheap, get it gone.
The less expensive version just makes O2, and the more expensive version will fill portable O2 bottles. At least that is how things are in the states. I can't speak for what happens in Spain.

If you can get one that fills medical O2 bottles, it will be like you are doing now with O2 bottles. Fill the medical at a separate time from running the dive compressor. You are your own oxygen provider.

If you get one that doesn't make pressurized O2, just (near) atmospheric pressure, that will work as well. You will need to look at flow rates, do math. You could put a flow regulator on the output of the compressor and feed that back into the Nitrox stick. Compressor moves 100LPM, you give it 90 air and 10 O2. But if you only have 5 O2 you would need to limit the compressor to 50 LPM total output. If you sent 50 (of the 100) back into the compressor again your real intake would be 5 O2 + 45 air (and 50 or through the compressor) to get the same as 10 + 90. Just inefficient as you are only getting half the output from the compressor while taking 100% of the power. But it could be done, just a hack way of doing it (my numbers are probably greatly simplified from reality)

 

[tbone1004]

@broncobowsher throttling the compressor can only be done within a very narrow range since most of the small pumps are splash lubricated. You definitely can't slow them to 50% RPM, 60-70 bare minimum on most of them. Definitely better to get a second concentrator than risk causing issues with the lubrication system.

 

[estresao]

My compressoor doesn't have any option to slow it down... probably hacking it, buy I don't want to tink with a brand new compressor which is sill under guaranty.

I was thinking as well about using two concentrators but, even if I get two used ones, they could reach the price of one ablenro refill tanks.

Here there are also many of them on sales second hand (for some reason ) but nlmost of them produce under 5 L/m.

The perfect solution I think is one of those which can refill tanks. These ones are not very popular in Spain (I think) and they are no easy to find 2nd hand.

I'll keep searching alternatives.

BTW, it's for OC... mainly Nx32 and, in a future, trimix also on OC.