patterson

patterson

Well Known Member
Patron
"Transfilling" your Supplemental Oxygen

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

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). :confused:

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
[email protected]
 
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O2 suppliers

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.
 
Oxygen safety precautions.

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.
 
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.
 
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.
 
Mo infoo

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/index.phtml?nav_id=24&curr=0&reccount=10&searchtext=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/
 
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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.

:)
 
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Danger!

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
 
Great Advice

:) Thanks everyone for these good posts! I learned alot from you and you all helped to make further research into this topic alot easier. Blue Skys....
Ron
 
Cascading tanks

Jeff,

The way to take full advantage of cascading tanks is to open them one at a time. When I worked at an FBO years ago, we would open the low cylinder first; after pressure equalized, we?d close off the first cylinder, and open up the next highest pressure. Using this technique, you can go a lot longer before you need to take your lowest cylinder in for a refill. Here?s an example:

Step 1 Step 2 Step 3
Portable Cylinder : 0 760 1557 1977
Tank #1 : 800 760 760 760
Tank #2: 1600 1600 1557 1557
Tank #3: 2000 2000 2000 1977

Assuming 150CF tanks, and 8CF cylinder,

(800*150)/158=760
((1600*150)+(8*760))/158=1557
((2000*150)+(8*1557))/158=1977

Paige Hoffart
RV-8A (Finish Kit)
Shreveport, LA
 
Paige,
Yes, that is a way to get a higher fill. Now were all the tanks hooked up together and then just opened one at a time? or did you switch main bottles every time you went to a higher pressure? Basically did you have to attach the aviation bottle once or several times to get the fill. If once then I agree, if you have to keep changing main bottles I would say its a bad idea since there is more wear on the threads, O-rings, valves, a higher chance for particulates/water to enter the bottle. I hope this made sense. *after re-reading your post it looks like you only hooked the AV bottle once. :)

Just out of curiosity, when using the O2 in the plane do you try to match 21% O2 in your breathed in air or do you go higher?
 
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If you use the multiple bottle method you usually connect all the bottles onto the fill line with t-connectors and then open and shut each bottle individually to get the fill, starting with the bottle with the lowest pressure as stated before. It takes a bit more initial plumbing to do this but it saves connecting and disconnected the bottle to be filled.

You want to fill your bottle with 100% O2 not a mixture. I suppose that technically you could use a lower O2 percentage mixture that you could calculate based on the maximum altitude you will reach, but it would not be worth the trouble.

Another good resource for O2 systems it the book "Vance Harlow's Oxygen Hacker's Companion". This is writtern primarily for diving so it talks alot about different gas mixes that don't apply to aviation, but it contains a lot of good info on O2 safety and some info on plumbing.
 
JeffD said:
Paige,
Yes, that is a way to get a higher fill. Now were all the tanks hooked up together and then just opened one at a time? or did you switch main bottles every time you went to a higher pressure? Basically did you have to attach the aviation bottle once or several times to get the fill. If once then I agree, if you have to keep changing main bottles I would say its a bad idea since there is more wear on the threads, O-rings, valves, a higher chance for particulates/water to enter the bottle. I hope this made sense. *after re-reading your post it looks like you only hooked the AV bottle once. :)

Just out of curiosity, when using the O2 in the plane do you try to match 21% O2 in your breathed in air or do you go higher?
Click to expand...
Since the gas transport across the lung membrane is based on partial pressures, I would think that the percent O2 you want while at altitude would be greater than that available at sea level atmospheric pressure. I suspect the non augmented PERCENT O2 at altitude is the roughly same as the percent O2 at sea level.

-mike
 
JeffD said:
Paige,

Just out of curiosity, when using the O2 in the plane do you try to match 21% O2 in your breathed in air or do you go higher?
Click to expand...

The O2 percentage at altitude is still 21% - that doesn't change anywhere in the atmosphere to any appreciable margin. The difference is in the pressure. As the pressure drops with altitude, the partial pressure of oxygen in the lungs will drop, even though the total mix percentage remains the same. You add pure O2 in your inhaled air to get the partial pressure back up to more normal ranges. At an altitude where air pressure is half that on the ground (around 18k??) you would need twice as much oxygen, or a 42% mix, to have the same amount of O2 available to your lungs as sea level air.
 
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Do it slow...

I transfilled out of a large O2 cylinder into my Mountain High system for almost 5 years. It helps to have a cascade system, but not necessary. You will have less and less pressure and I think I used to trade cylinders when the pressure in the large tank reached 900psi. Everyone seems to have hit the high points and certainly the links lead you to a lot of valuable information. One thing that should be mentioned and I haven't read here is that when transfilling, make sure you open the valves very slightly and very slowly. Oxygen going from a very high pressure tank to a lower pressure tank will generate considerable heat in teh line. You should just crack the O2 valve and let it take it's time filling. The instructions in the Mountain High system spell all of this out in detail. Also, never stand "in front" of the valve opening when opening or closing a valve, that's just good safety practice when working with high pressure tanks.
 
Ron, try a trip to your local fire station, they will most likely have a cascade system that they use to fill SCBA and O2 bottles.

The info that has been presented in prior posts is correct, but it will help to actually see it being done.

One other thing I did not see mentioned, is the heating effect of filling your bottle------there is a need to fill slowly, many setups also use a water bath to cool.

Last, you will need to be aware of the need to keep on top of maintance issues, and hydro testing. Again, a visit to the local Fire Dept can be of assistance.

Mike
 
Make sure you have a gauge on the transfill!

Bob Brown said:
I transfilled out of a large O2 cylinder into my Mountain High system for almost 5 years. You will have less and less pressure and I think I used to trade cylinders when the pressure in the large tank reached 900psi.

One thing that should be mentioned and I haven't read here is that when transfilling, make sure you open the valves very slightly and very slowly. Oxygen going from a very high pressure tank to a lower pressure tank will generate considerable heat in teh line. You should just crack the O2 valve and let it take it's time filling.
Click to expand...

I also have a transfiller setup and fill an aluminum medical oxygen bottle from a large steel welders bottle. The AL bottle is rated for 2000 +/- PSI and the steel bottle holds ~3500 PSI when freshly filled. That is a big pressure difference. Just so you don't blow it up...slowly fill the AL bottle over 5-10 minutes, it will heat up, and stop when your gauge reads 2000 PSI. Without a gauge you will not know the limit.

I also learned the AL bottles are hydro tested every 5 years to ~3000 PSI. They measure the expansion of the bottle to verify strength, not just the pressure. Don't try this at home. Here's the link to the excellent Welders OX article: http://www.avweb.com/news/pelican/182079-1.html

Last - the aluminum medical oxygen bottles (CGA-870) are cheap and readily available (EBay) and use regulators (aluminum with gauge) that can flow .5 - 1 LPM (you don't want anything over 5 LPM). This is a good flow rate for one or 2 occupants. Add a couple Oxymizer cannulas and tee them using plastic drip irrigation fittings.

With this setup I can do a light refill to maybe 1200 PSI and have 4-5 hours of dual OX, or 6-8 solo. All for 'free' until I need to top up the steel bottle.
 
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