[fehdxl]

Group,

A few question for the experts.

How much does a two bottle refill set-up cost?
Heard something about Teflon inside the hose and O2 causing a fire...true?
Any idea about how many refills you get before needing a O2 supply refill?
Anyone ever use a medical oxygen compressor that takes the O2 from the air and compresses it into a bottle?

Sorry for all the questions.

TIA,

Jim

 

[rv9av8tr]

O2 tank refill

I bought a SS hose through a welding supply outfit and refill my tanks from my O2 welding tank. Generally lasts me 2-3 years... considering I rarely weld anymore. Don't have a welding tank.... perhaps a welding friend will let you fill your tank for a few bucks. Just a thought.

 

[Greg Arehart]

I can't speak so most of these, but absolutely the teflon will not oxidize (burn). It is a material that is already so oxidized that it is impossible to oxidize further.

I would be interested in hearing about the medical thingy and whether it works - but they look pretty pricey on ebay (like, $1000 for a setup - that buys a LOT of oxygen in tanks).

greg

 

[nomocom]

mol sieves

Group,

Anyone ever use a medical oxygen compressor that takes the O2 from the air and compresses it into a bottle?

I'm not familiar with the unit that includes a compressor to fill a tank, it would likely be very expensive and relatively complicated. However, the other half of what you are talking about is common. The "oxygen concentrators" that push air through a molecular sieve and concentrate oxygen are in many houses of people that need a steady supply of supplemental oxygen.

I have wondered a few times if you could skip the bottle and just use a concentrator. AFAIK, the concentrators haven't been adapted for airplanes, though I don't see any reason they couldn't be. It would be a interesting engineering challenge. The problems would be the usual ones; weight, cost, and complexity. Just like the engine up front, there would be less and less airflow through the compressor as altitude increases, so to get the oxygen you need at altitude, you'll have to have the pump sized for that.

 

[RV7Guy]

Fire Departments

Check around your airport for the closest fire department. See if they have a cascade system they use to fill their bottles. Most will top it off for you.

Even better if you can find a fire fighter that is a pilot. Bribe them with a pizza.

The helicopter I fly is based at a fire department. They have a 5 bottle cascade system. No problem filling the bottle.

 

[Ironflight]

I used to fill mine at our firehouse on the O2 cascade. Then someone in the medical group found a service that just dropped off fa rack of full portable bottles and picked up the empties. So much for the cascade! Most of the local departments went with this service - don't know if it popular elsewhere.

I figure we'll get our own big bottle and transfill adapter when we live out in the mountains - we just don't use much oxygen here at our current sea level base....

 

[sbarger24]

Big Green tanks

Where you also asking about the big green tanks people use for welding, torching, and other oxygen supplies. The actual tanks most FBO's suppliers use. Because I would also be curious if it would be worth the investment as well? I just paid the local FBO 50 dollars to fill my small tank.

Growing up on the farm we use to exchange our oxygen tank for torching all of the time, pobably for less than 50 dollars. Just curious how many refills you would get out of a tank like this before needing to exchange it.

I realize there would be a point where the pressure would drop off and you esentially would not be completely refilling your aircraft tank. That is probably why you mentioned using two tanks?

 

[Greg Arehart]

Steve,

John Parker's shop (Thunder Mustang) has a cascade system with 6 bottles and will fill small cylinders for a donation to the coffee fund. Using a single bottle might work for a few fills, but each time you end up with less pressure (and therefore less cubic feet). Doing the calculations, for my 24 cu ft (E size) medical cylinder, I can get 6 refills out of a 125 cu. ft tank before I am down to half pressure (~1000 psi). Having said that, a half-full cylinder will easily last two of us for ~6 hours flying at 17000 ft using the oxymizer cannulas.

Let's talk this weekend at the airport. Maybe the RV group could get a two- or three-tank cascade system. The biggest advantage over using Parker's setup is being able to access it whenever needed.

cheers,
greg

 

[fehdxl]

Thanks for the input. A couple follow-up points.

How much does a two bottle refill set-up cost?

So I checked the local Linweld (they are national I think) today. Each tank is $430, then add in a cart $150, hoses $150, misc fittings $50...suddenly we're up to $1200 pretty darn quick! The actual oxygen is cheap...$30 I think.
It's about $25 per month to rent two tanks, so $860/$25=35 months to break even...assuming a resale value of zero; if you can sell the tank for something, then payback is shorter.

I just paid the local FBO 50 dollars to fill my small tank.

I too was quoted about $50 to refill a portable bottle from the FBO.

Heard something about Teflon inside the hose and O2 causing a fire...true?

The guy at Linweld showed me an example where there was a hole in a steel bradded hose...said it was oxygen and teflon reacting. I wasn't convinced. Went on to talk about fire-fighters refilling at hospitals and fires and how he would only sell me solid coper everywhere...I talked him into a compromise of copper from the fill-tanks to the T, then steel bradded from the T to the airplane bottle.

As an aside, fire-fighters breath pure oxygen from their tanks? I would have figured it was just compressed air like SCUBA tanks...must be something else to it.

Another tid-bit of information. I "didn't hear it from them" but all their oxygen is the same; welding, breathing, medical, etc. It's too costly to manage the infrastructure for each type, so they comply with the most restrictive and it's all the same. As far as moisture, I'm not concerned with it freezing in the heated cabin. Different airplane with a different set-up, then maybe so.

Thanks for all the inputs...I'm not completely convinced I want to do this. But I look at it this way...if I have oxygen in the hangar, I'll use it. If I have to go and refill at the FBO at a different airport and pay $50 each time, I won't use it as much. Using oxygen on long, high flights, even when not technically 14 CFR's required, is a decent risk mitigation technique.

Fly safe,

-Jim

 

[Walt]

I bought 2 used bottles from my local O2 store and a single fill hose from Aerox for about $450. I charge local RV'rs $25 for a re-fill and fill my own occasioanally as well. I still haven't recovered my investment but I didn't really set it up to make a profit. I did it to make it more convenient for myself and other locals.

 

[L.Adamson]

I have wondered a few times if you could skip the bottle and just use a concentrator. AFAIK, the concentrators haven't been adapted for airplanes, though I don't see any reason they couldn't be. It would be a interesting engineering challenge. The problems would be the usual ones; weight, cost, and complexity. Just like the engine up front, there would be less and less airflow through the compressor as altitude increases, so to get the oxygen you need at altitude, you'll have to have the pump sized for that.

Just like any other compressor, they put out a lot of heat...... too.

L.Adamson --- RV6A

 

[RV7ator]

If you can't use someone's cascade system for cheap, ask around local weld shops if you can fill your tank off one of their full bottles. That's what I do, and tip 'em $5 or $10 for their trouble. What gas you'll consume is lost in the noise of daily operations. All you need is a transfer hose and Mountain High, Precision and their ilk sell them for less than $100. The industry suppliers around here are more worried about liability, a non-medical bottle, and you being in the way than your pittance of business.

How often you refill depends on a ton of variables you need to know about if you're going to use oxygen.

John Siebold

 

[fehdxl]

Check around your airport for the closest fire department. See if they have a cascade system they use to fill their bottles. Most will top it off for you.

The helicopter I fly is based at a fire department. They have a 5 bottle cascade system. No problem filling the bottle.

The guys at Linweld, where I bought my tanks just now, were telling me that firefighters use compressed air, not compressed oxygen. That seems to make sense to me...not sure I'd want a bottle of fire enabling oxygen on my back fighting a fire. However, I would want clean air To breath rather than smoke. Just like traditional SCUBA tanks which are just compressed air (nitrogen, oxygen, etc).

Do we have firefighters in the group that can clarify?

Thanks!

Jim

 

[Mike S]

Firefighter SCBA's use compressed air. Well filtered, but no oxygen other than what is there naturally.

Many if not all fire engines also carry oxygen for medical aid calls, but it is not used for firefighting.

 

[flion]

I can't speak so most of these, but absolutely the teflon will not oxidize (burn). It is a material that is already so oxidized that it is impossible to oxidize further.

Sorry, and this is sideways to the discussion here, but I have to totally disagree. As the Apollo disaster showed, oxygen is extremely dangerous; it supports combustion for any material. This NASA study specifically speaks to Teflon and a few other non-metallic materials and their combustibility characteristics in various concentration of oxygen. As you can see, Teflon will ignite given the proper temperature and oxygen concentration. I can't speak to the equivalent concentration for an oxy system like ours but I doubt we'll hit those temperatures; if we do, we have other worries.

My gut feeling is that Teflon should be fine for our O2 systems; it's more important to be diligent in our construction and inspection practices and also be extremely careful handling the stuff.

 

[rchrds]

So this is a pretty involved thread for something that should be pretty simple. I do a lot of cave diving and probably burn through 2-3 Ts (304cf) bottles a month for my decompression and rebreather gasses. I pay -at most- (and it varies a lot) $28 a bottle for just the gas. The slightly smaller K (228cf) bottles run $14-18 for the gas. If you don't want to f with owning a bottle (periodic hydro, etc) just rent the bottle annually from praxair or similar welding house, maybe $60-100 a year depending on who you are working with. I have 15 Ts for banking other gasses I own, but it is easier to rent the 3 helium and 3 oxygen from the gas house, and the swap is immediate instead of waiting to get my bottle back from the warehouse where they fill them. As for fittings, everything is available from McMaster-Carr. Haven't priced it out lately, but a full set of brass fittings for a gas bottle is probably less than $20, only two parts, the nipple and sleeve. You need a pressure gauge, doesn't need to be fancy as you aren't mixing gasses, and a hose. Arguments here are deep about the hose, best practice is an oxygen compatible braided stainless, but those are stupid expensive. Standard high pressure hose works just fine, with caveats. I cant guess at the fitting for whatever bottle you have in the plane, but medical fittings with an npt thread are cheap on eBay. Slap it together, use teflon tape to seal the npt threads and don't worry about it.

Caveats- here is the argument about the hose. Welders get excited about oxygen cleanliness for a reason. Know where your stuff is coming from. Don't put your oxygen service stuff in the same box as your oil pump plumbing or anything remotely to do with the engine. If you want to go whole hog, you can scrub and flush the parts and hose innards with a simple green solution to remove oils, but if you start with clean parts you aren't likely to have problems, if you keep things separate. Also- cross filling creates adabiatic heat through compression, so you have to go slow. The little sharp parts inside the fittings can get cherry hot. I've burnt down fill whips doing this and not paying attention. You should be able to hear the gas transfer, but still touch all the parts of your whip.

Also, lots of welding oxygen being used here, and I use the same for diving, because the price is right, and I've never had issues in 20 years of doing it. However, different companies have different standards for their medical and aviation gasses, most of which comply with CGA standards. Generally, medical oxygen has a vacuum drawn on the cylinder prior to filling, to up the purity of the gas, or really to remove other gasses when the user lets the tank empty completely and leaves the valve open, and aviation oxygen is run through a moisture separator to lower the water vapor, which keeps the gas from freezing the regulator at altitude. At the altitudes we fly, and the fact that most RV people probably have the bottle in the cabin with the heat, this shouldn't be an issue.

 

[Carl Froehlich]

I'm in a group of three aircraft owners that share an Oxygen charging station. It uses this to transfer: http://www.mhoxygen.com/index.php/ground-support-equip

We each own a bottle from the local welding supply shop ($140). It comes full. Refill is $40 (you just exchange the bottle). The three bottles are in series so that we charge from the lowest bottle first, and top off with the highest bottle.

Total cost to me is less than $40 a year to always have a full bottle in the plane. I use the AL-682 cylinder from Mountain high. A cross country trip for two people is just about half a bottle (typical cruise is 12K'). The bottle, in the provided pouch from Mountain High, straps to the top of the tunnel between the rear seats in the RV-10.

Carl

 

[LettersFromFlyoverCountry]

I just paid the local FBO 50 dollars to fill my small tank.

Ouch. Just paid $25 to Wipaire to fill a 13 cu. ft. bottle.

 

[BillL]

I'm in a group of three aircraft owners that share an Oxygen charging station. It uses this to transfer: http://www.mhoxygen.com/index.php/ground-support-equip

We each own a bottle from the local welding supply shop ($140). It comes full. Refill is $40 (you just exchange the bottle). The three bottles are in series so that we charge from the lowest bottle first, and top off with the highest bottle.

Total cost to me is less than $40 a year to always have a full bottle in the plane. I use the AL-682 cylinder from Mountain high. A cross country trip for two people is just about half a bottle (typical cruise is 12K'). The bottle, in the provided pouch from Mountain High, straps to the top of the tunnel between the rear seats in the RV-10.

Carl

People should note that a 3 bottle fill system, with hardware is about $1300 investment assuming new hardware from MH and Praxair local quotes. It takes 42 80% fills (more or less) to pay break even with a $25 (JD) bottle fill. Cost per incremental bottle+hardware is lower than one. It extends the payoff, but provides a higher practical % fill and lowers the variable costs further. An oxygen pump to get all the gas from a bottle is ~$5000 so not in the range of practical for mere mortals. Maybe for a business, but bottle rotations with an 8 bottle manifold still beats a pump.

If you want 100% fill it will be more. Granted the variable cost per fill is less than $2 so a larger bottle would be cheaper than smaller at 100% overall. My conclusion for now is a $25/JD bottle fill. Economics are one thing, time, travel and pain are another factors that can sway the decision. All decisions are valid.

If someone gets serious about the technical details and economics, let me know. All this is in a spreadsheet. Local costs will vary.

 

[catmandu]

You just need to hunt for free O2, it is not usually that hard. I am probably about to enter hunting season again, as my free source just upgraded his Mooney to a Meridian. for me, for him!

 

[scsmith]

stainless braided hose and O2

I can speak somewhat intelligently about this from practical experience on both sides.

The key is to use aircraft-quality stainless braided hose. You would never know it, but the teflon liner has a spiderweb net of carbon threads laced through it. This allows static charge to dissipate lengthwise through the hose and dissipate at fittings or ground points. This is important. Without it, it is possible to build up enough static charge in the hose to eventually get a discharge, at which point the teflon, plus any elastomeric seals in any valves or other fittings (including o-rings) can and will burn very fast and very hot.

It happened to another glider pilot at my gliderport. Unknown to us, the club put together our O2 cascade system at the gliderport with cheaper automotive stainless hose that did not have the static-discharge carbon threads in it. It was in service for a long time before the bad luck of the right circumstances caused an internal discharge inside the hose, with a 'bang' that could be heard all the way across the airport, and a pretty serious fire with hot chards of stainless fragments added as shrapnel flying about. My friend was fortunately not hurt. And IIRC no damage to expensive carbon-fiber composite structures either, but it could have been very bad.