"Transfilling" your Suplemental Oxygen

[patterson]

I have been flying my new RV-4 for 3+ months and 90+ hours...what a fantastic airplane Van designed. I love it.

However, now that I CAN climb to 11,500 and 12,500 routinely, I find I need supplemental Oxygen to arrive fresh after 2 or so hours up there. So, I bought an Aerox system and it works great.....just needs filling every 8-12 hours of flying. So I went to buy a large cylinder to store enough that I could do my own filling. I bought a 150 cubic foot tank...brand new. That's where it gets weird. The companies that have these products to sell (fittings etc) don't want the liability / risk, so they won't sell you the parts to "transfil" your own tank (since you admitted that was your intention).

I researched what I could about the safety concerns with pressurized O2...it's significant. I still think that it could be learned and safely done at the hanger with proper technique. I bought the FBO Filling Station from Aerox today, and they assured me it's safe to do the filling one's self. I wonder who is right...? I now have the large full tank, and I have the hardware coming to transfer O2 via UPS from Aerox, but am significantly confused about the advisability of this practice. So, I'm curious...what do the rest of you do about this?

Appreciate any thoughts and suggestions for safely transfilling myself.
Ron
N8ZD@yahoo.com

[gvgoff99]

Sorry, I do not know much about transferring the O2.

I do know that the supplier of O2 for aviation grade, medical grade, and welder?s grade O2 get it all from the same tank. There is no difference in the product only in the paperwork and cost to fill out that paperwork. So buying a tank of welders O2 is the same as buying a tank of Medical grade or aviation grade O2. There is a difference in the cost though.

I think that this is pretty common knowledge but when I bring it up someone always gasps. Please don't flame me until you do as I did and go to an actual supplier of the O2 and talk to the fellow that actually dispenses the O2. There is no separate source for the so called various O2 types. It all comes from the same source. It is a pretty dangerous gas because it supports combustion and will cause oils to spontaneously combust. So even the welders O2 is handled by the supplier with the same care as "aviation O2."

It is not something one can get sloppy using. There has been more than one welder killed when they used O2 to check for leaks in pipe welds. Any Oil in the pipe will combust/explode.

[William Slaughter]

Really only two issues, and they're not unique to "transfilling":
1) It's a big tank full of really high pressure gas. Don't knock off the valve thus creating a large and energetic missile. I have an oxygen cylinder in the garage for welding, and keep the cap on except when in use, and make darn sure I don't knock it over when it is in use. Strapped to the wall or laying on it's side work fine.
2) Oxygen does facilitate combustition to a remarkable degree. Back in the day, I was an engineer at a company which produced welding equipment and regulators, and I saw demo's that were pretty astonishing. A t-shirt well saturated with O2 will burn like gunpowder. So, don't let the O2 leak out and create a hazardous atmosphere.
I wouldn't be concerned about the transfilling, just treat things with the respect they deserve.

[ddurakovich]

Another aspect of refilling your own cylinders is the pressure drop you will experience. Commercial operations use a "cascading" arrangement, filling from the lowest pressure source, and then moving up the line in order to get the maximum pressure in your cylinder. I think that most operations use a minimum of three cylinders, but I could be wrong.....

Having said this, if you can live with half full cylinders each time you leave, it may not be a problem at all until you source cylinder drops below that level.

[Davepar]

Tim Olsen has a whole write up on his site:
http://www.myrv10.com/tips/accessori...gen/index.html

[ptrotter]

The posts above give a good review on transfilling O2 tanks. It is not very difficult but to get maximum pressure in your tank you will need several large tanks to fill from.

While filling tanks is easy to do, handling O2 is extremely dangerous and there are some things you need to understand before you try it.

You cannot under any circumstances let any hydocarbon based material like oil or grease come in contact with high pressure O2. This will cause a fire or even an explosion. All equipment such as valves, hoses, etc. must be properly cleaned to remove any traces of hyrocarbons. Valves, O-rings (which should be viton) and anything else that need lubrication must be lubed with O2 compatible lubricants. This is very important. Do not assume that any parts you buy new will be properly cleaned.

Also remember that this is much higher pressure than you are used to. A normal air compressor puts out about 125-150 PSI max. These tanks are 2000+ PSI so be careful when opening valves.

With the proper care you shuold have no problem transfilling your tanks.

[N91CZ]

Ron,
Mountain High http://www.mountainhighoxygen.com/ has various flavors of transfilling hose assemblies available. I have been using their simplest model for the last 8 years.
Chris

[gmcjetpilot]

If you really are going thru O2 you can buy, rent or lease a full size O2 bottle from welding supplies. You know those BIG green ones, 220-250 cu-ft. When it's empty you trade it in for a full one, $20! Where $50 can be charged to fill a small aviation bottle. You make your back money in a few refills. I like your idea of using O2 at 12,500 ft, you do feel better. I flew above 10,000 ft once with out O2 and had a raging headache. You may be able to go thru medical supply but I think they are more particular. Of course don't tell the welder supply house what you are doing with it, oxygen acetylene torch right.

Buy the hose to transfer and you are good to go. The article is on Avweb.com "Pelican's Perch #13:
Getting High on Welder's Oxygen". You can register for free to read the article. The article addresses the "dirty welder Ox" v. Medical Ox.

As far as transferring and filling, as long as bottles are tested safe and you don't overpressure, there's little if any danger. Of course O2 is a great oxidizer and can feed a fire; Just make sure nothing can fall on them or they fall over. Overall unless you do something weird its pretty benign.

Here is some nice info from RV builder, vendors at bottom of page:
http://www.fdatasystems.com/chuck/oxygen.html

and

Consumer report article:
http://www.nelsonoxygen.com/aviation8-01.pdf


Vendors with transfill hoses:

http://www.mountainhighoxygen.com/in...earchtext=fill
http://www.aviationoxygen.com/refill_stations.html
http://www.aerox.com/

good general O2 use info
http://www.c-f-c.com/supportdocs/abo1.htm
http://www.dr-amy.com/rich/oxygen/

[JeffD]

Experienced scuba divers to it quite frequently. Look for an "O2 Whip" http://www.magnificentrelief.com/nitrox.htm I believe. Scuba tanks are usually around 3,000 psi and they "mix" the gas up to 40% O2 60% N2, going 100% should be fairly similar except extra precautions. I've never dealt with aviation O2 systems but scuba tank pressures should never get below 200psi or a tank inspection is required; I assume its similar for the O2 bottles on aircraft.

And about cascading tanks etc. *warning Math ahead*

PV=NrT : Pressure is inversely proportional to the volume.

If you transfer 8cf of gas out of a 150cf cylinder then the pressure is going to drop by ~ 5.3% each time you "fill up". And each time your 8cf tank is going to be getting short filled until you fill up the main tank again.

So "Full" fills will probably go on the order of (assuming 3000psi operating pressure):
2800psi (7.5cf)
2600psi (6.9cf)
2400psi etc.(6.4cf)

Now if you cascade two tanks (put two 150cf tanks in parallel) then your main gas now becomes 300cf and 8/300 = 2.6% drop on each fill.
2920(7.8cf)
2840(7.6cf)
2760(7.4cf)

3, 4, 5, tanks will just keep making that % drop number smaller and smaller and lengthen the time between MAIN system refills.

Side note: Most scuba shops use 400cf tanks and I have seen them have a 5 cylinder cascade up to about 15.

[brianwallis]

The only thing I really need to say... is if you transfer O2.... make sure you have a seperate wrench that is only used for this... DO NOT.. DO NOT DO NOT IN ANY SHAPE OR FORM USE A DIRTY WRENCH TO WORK ON O2 FITTINGS WITH... IT WILL BURN!!!!!!!!!!!! ALL THE MECHANICS I KNOW THAT SERVICE O2 HAVE A COMPLETELY DIFFERENT SET OF WRENCHES FOR IT... AND THEY ARE CLEANED BEFORE AND AFTER....!!!!!!!!!
Good Luck,
Brian