Blend your own nitrox?

[BarryNL]

Is it conceivable to rent/buy a big tank of oxygen from a gas company and use it to blend your own nitrox, or are the regulations so restrictive (or the tanks so expensive) that it's simply not practical to do this.

I was thinking, I could stick a tank of O2 in the shed, use it to part fill a tank, then take it to the air-only LDS to top off with air. Are those "personal filters" good enough that the tank would stay O2 clean?

 

[Dive-aholic]

First, buy this book and read it. Cost effective for a few fills, it is not. Taking the tank to the air only LDS is a bad idea. The compressor they use is not likely to be hydrocarbon free and could cause problems for the LDS. I'm not sure what the regulations in the Netherlands are.

 

[BarryNL]

Cost effective for a few fills, it is not.

Well, it currently costs me about €17 including petrol money to get a nitrox fill... it may well be more cost effective than you'd think

Taking the tank to the air only LDS is a bad idea. The compressor they use is not likely to be hydrocarbon free and could cause problems for the LDS.

Hence the "personal filter" bit...

 

[mike_s]

As long as you do it safely and correctly, you should be able to do it yourself.


Don't do it safely and this will happen
http://www.irishmansoftware.com/fill_your_own_tanks.htm

 

[loosebits]

If you can find a shop to top you off with oxygen compatible air (make sure they know you've got pure O2 in there), it makes financial sense to blend your own. A transfill whip from an O2 bottle to a scuba tank will run anywhere between $150 at $600 depending on what bells and whistles you want. I get my O2 for $18 for 300 cuft (or maybe its 250, don't remember) and the tank rental is $5/mo per tank.

If you can't find a shop for topoffs, that means you'll need a compressor. There is no way you'll ever make your money back filling nitrox having bought a compressor. Me and my buddy bought a newly rebuilt 3.8 CFM Bauer compressor for $800 with a 7 HP gasoline engine and a small filter stack. Add about $500 for a 5HP electric motor (gasoline engines are loud and dirty), switch and pulley, $350 for a tall filter stack (we got a hell of a deal on it, retail is a bit over $1K) and then another $750for all the stuff needed to plumb the damn thing (yes, $750for valves, gauges, fittings, HP stainless steel tubing, etc) and then throw in the actual filters and you're looking at around $2500 (and don't forget that $250 transfill whip for the O2/He)

Now, start blending your own trimix and you might be able to dig yourself out of the hole someday but for nitrox, it will never happen.

 

[mike_s]

Well, it currently costs me about €17 including petrol money to get a nitrox fill... it may well be more cost effective than you'd think

17Euro runs about $22 US dollars. yep. that's not a cheap nitrox fill (by the rates where I live).

Most places here will give you a standard nitrox fill for $10-$12 USD.
My LDS charges $10/fill (for up to 40%), but you can buy "Nitrox Fill Cards" in bulk and get the costs down to about $7.50/fill, which is pretty dang cheap. (in my opinion).

In south Florida, you might even get better rates. For exmple, at Fill Express they sell 32/36% banked at $.08 US cents per cubic foot. So to fill a 3000psi AL80 from 500psi to 3000psi would be about 65 cubic feet, which equated to about $5.20 USD (by my math, but their website says the typical nitrox fill costs $4.75 USD. I guess thats for people who don't drain their tanks down to 500psi.)


I think having my own compressor and nitrox blending station would "be cool", but it's just not cost effective either.(for me).

 

[BarryNL]

I think having my own compressor and nitrox blending station would "be cool", but it's just not cost effective either.(for me).

On the other hand, if you could get a few friends together...

An entry level compressor comes in at about €3,000. If you share that cost between 10 people over five years and the O2 costs about €1 per fill you suddenly have nitrox for about €2 a fill if everyone dives once a week...

Hmm, if only I had 9 friends.

 

[loosebits]

In the US, you can get a 3.5 CFM compressor new for about $3K. Now add on the stacks for oxygen clean air and all the plumbing you're going to need, you're looking at about $5K to get up and running. What I did was start diving trimix so I could show my wife how much money it was saving me

 

[grazie42]

Barry, I don´t know about Holland but up here membrane-systems are starting to appear, filling up to 40% is no more expensive than the equivalent airfill...If you invest in that compressor you may find that your LDS has installed one within the next year, that would really suck...

Of course He is 0,02€/liter here so that may be worth the effort...

 

[loosebits]

Personally I don't see the advantage to membrane over stick. With O2 being so cheap, stick seems the way to go (we're not doing stick since the compressor is so old, anything with more than 21% O2 in that thing and we might have a mess). Now, you can spend $1000 on a comercial stick or you can make your own out of PVC tube and some sheet metal for the baffels for about $30.