Homebrew Nitrox?

[Rhone Man]

I live on an island where it is very difficult to source Nitrox.

However, oxygen is relatively easy to source on island, and I was reading Gary Gentile's Technical Diving Handbook, and he certainly implies that homebrew Nitrox is well within the skill set of most mortals (oxygen clean your cylinders, fill with 02 to desired partial pressure, go to LDS and top up with air, analyse gas before using), and that it used to be done pretty regularly by technical divers before Nitrox fills became widely available at your nearest LDS.

Of course that is fine on paper, but if I blow up the shed (particularly with me in it), I'll never hear the end of it from my wife. Does anyone have any experience of home brewing Nitrox? I only found one related post on SB ( http://www.scubaboard.com/forums/ask-dr-decompression/26363-nitrox-after-45-a-3.html ) and that was from 5 years back, but it certainly implied: "it's not difficult, but be very careful".

 

[pescador775]

There are several threads which deal with Nitrox and DIY blenders. Most of these folks got their design concept from books like Oxygen Hackers Companion. You will need some stuff; two inch PVC pipe, end fittings, small barbs, steel abrasive pads (stainless ribbon, Gottschalk steel sponge), Oxygen analyzer, oxygen regulator flexible plastic tubing, some kind of small intake filter or dacron felt pads. You will figure it out when you read up on it. The books call for a more complicated approach than mine. The main difference is that, instead of wads of spun ribbon, the book calls for some intricate series of cut plates (baffles). I find that very baffling (heh) so just stuffed the pads inside the stik. The oxygen is fed in near the top of the pipe through the small barb. The sensor for the analyzer should be located near the bottom. The tough part is shopping for all the little bits and pieces, I hate that. I threw together a couple of Nitrox sticks in less time than the shopping trip. The actual mixing is fun but also tense. The average compressor output cfm on my machine drifts a little, dropping at higher press, so I have to keep an eye on the analyzer.
http://www.scubaboard.com/forums/search.php?searchid=7142948

 

[JeffG]

There are several threads which deal with Nitrox and DIY blenders. Most of these folks got their design concept from books like Oxygen Hackers Companion. You will need some stuff; two inch PVC pipe, end fittings, small barbs, steel abrasive pads (stainless ribbon), Oxygen analyzer, oxygen regulator soft plastic tubing, some kind of small intake filter or dacron felt pads. You will figure it out when you read up on it. The books call for a more complicated approach than mine. The main difference is that, instead of wads of spun ribbon, the book calls for some intricate series of cut plates (baffles). I find that very baffling (heh) so just stuffed the pads inside the stik. The oxygen is fed in near the top of the pipe through the small barb. The sensor for the analyzer should be located near the bottom. The tough part is shopping for all the little bits and pieces, I hate that. I threw together a couple of Nitrox sticks in less time than the shopping trip. The actual mixing is fun but also tense. The average compressor output cfm drifts a little, dropping at higher press, so I have to keep an eye on the analyzer.
http://www.scubaboard.com/forums/search.php?searchid=7142948

Ummmmm...Did you read his post? He doesn't have a compressor.

 

[mike_s]

oxygen clean your cylinders, fill with 02 to desired partial pressure, go to LDS and top up with air, analyse gas before using), .

Taking your cylinder that is clean, filled with o2, down to your LDS which might not have proper filtration and have lots of hydrocarbons in their air/compressor system might just blow up the shed you're talking about.

Your solution is two part. The first part is fine if you've got everything o2 clean, but if you're 2nd part of LDS air is not clean, then you're skirting danger with pure o2 in your tank when you hook up to a non-clean source.

 

[JeffG]

I live on an island where it is very difficult to source Nitrox.

However, oxygen is relatively easy to source on island, and I was reading Gary Gentile's Technical Diving Handbook, and he certainly implies that homebrew Nitrox is well within the skill set of most mortals (oxygen clean your cylinders, fill with 02 to desired partial pressure, go to LDS and top up with air, analyse gas before using), and that it used to be done pretty regularly by technical divers before Nitrox fills became widely available at your nearest LDS.

Of course that is fine on paper, but if I blow up the shed (particularly with me in it), I'll never hear the end of it from my wife. Does anyone have any experience of home brewing Nitrox? I only found one related post on SB ( http://www.scubaboard.com/forums/ask-dr-decompression/26363-nitrox-after-45-a-3.html ) and that was from 5 years back, but it certainly implied: "it's not difficult, but be very careful".

Its easy, but I would first find an LDS that will fill your tanks that have 100% O2 in them.

 

[pescador775]

OK, I get it, and the question (is there a question?) is fairly simple. Clean and dry the inside of the tank. Disassemble and clean the valve. Partial pressure fill the tank slowly with oxygen using oxygen safe fill whip. Starting from empty, use this formula:

(FO2 mix - FO2 air)/FN2 air X final press = psi O2

IOW, percent mix minus percent air (21%) divided by percent nitrogen(79%) multiplied by final press.

(32%-21%)/79% = 13.9, 13.9 X 3000 = 417 psi

Inject tank with 417 psi oxygen and top off with air.

To answer your question, yes, be careful, no smoking or drinking whilst doing partial pressure filling.

 

[tlawler]

I've thought of going this route also since access to O2 is easy. I'm a little leary of taking a tank to my LDS to get it topped off. If you tell them there is pure O2 in it, are they not likely to top it off for you? If you don't tell them and something happens, are you liable? And lastly what is the likelyhood of anything actually occuring (read:BOOM!) when topping a tank to scuba pressures that starts off with pure O2 in it.

Mike S brings up a good point that as soon as Grade E air is used to top off your O2 cleaned tanks, they are no longer O2 clean.

I suppose you could ask for them to be topped off with O2 compatible air, but if they have to go to all that trouble, they may want to charge you the equivalent of a nitrox fill.

 

[JeffG]

be careful, no drinking whilst doing partial pressure filling.

Thats a load of bunk.

Beer goes quite well with mixing.

 

[pescador775]

I think it was mike, not me, that was talking about "dirty" compressors. I would not hesitate to top off a tank at a reputable shop so long as the concern is restricted to equipment. Most shops use banked air which are supplied by competent compressor systems. The storage cylinders are a line of defense against oil vapor, the major concern with PP filling. There are other possible technical issues, I mean there are any number of nitpickers out there, but your average shop air should be OK. Grade E is a minimum standard these days, but I have opined here and yon that most commercial air in the USA and Europe is very probably better than that in the crucial area of oil. I can't speak to specific situations, in the islands and soforth. We occasionally read these scare stories in the "accidents" room.

 

[mike_s]

I'd say a lot of shops are reputable and have decent compressor systems with Grade E air...


I've also seen other shops that have Ebay or WWII surplus compressors that just leak oil on the floor and sometimes in the lines also. Or even have oil in your tank after your fill. ...... I'd definately be leary of taking any shop that operates like this a tank with pure o2 in it to "top off"