OxygenTalk® How many fills will I get from one 125 cu. ft. "M" tank to a "D" tank?

[tigers2007]

I'm too cheap to get more than one 125 cubic foot tank ($270 ish from Praxair). Yeah, i can find a used one for much cheaper too. How many fills should I get for my regular "D" size tank (15 cu. ft.)?

[Steve W]

Let's do math!

Assuming your D tank is full at 2000 PSI, and your 125 cubic foot tank is full at 2200.

if we take 15 cubic feet out of the 125 then we have 2200*(110/125) which means once filled your big tank will be at 1936 PSI.

So, you get one full fill since it can no longer fill the D tank to the full 2000 PSI.

If you're ok with only 1500 PSI, then: 125*(1500/2200) means the big tank will have 85 CF when it hits 1500 and you will have taken out 40 CF.

Your D tank will hold 11.25 CF at 1500 PSI, so, about 3-4 'fills' to 3/4 capacity.

Math may be wrong, I blame the fact that I did this in between yard work.

Edited to add:

And the thing I forgot is that the small tank will probably not be empty that often, so really it's best to think about that you have 40(ish) usable cubic feet in the big tank and figure that against how much you use per trip, provided a trip doesn't ever need more than 3/4 of the small tank(being sure to include some margin for unexpected problems)

 

 

Edited August 4, 2019 by Steve W

[tigers2007]

Wow thank you Steve W. No way I would have figured that out. With my Oxysaver pendant at 4 LPM for the first 2 hrs (first leg) and then 2 LPM for the next 2 hrs (trip home) I think I burned up 2/3 to 3/4 of the D tank. Not bad in my opinion. It was the first time I've ever used it. Wow what a difference it made in how I felt after the flight. I'll just use 2 LPM from now on or maybe 1 LPM. I'm using a finger style pulse oximeter. 11,500 to 13,500 cruising altitude to overfly Lake Michigan.

[carusoam]

Looking at it from another direction... not using the ideal gas law... PV=nRT which would be better.... P1V1=P2V2...

there are 8 refills available from the large tank for the small tank.... based on actual volume comparison of the amount of O2 that is in a filled tank...

But... the pressure is always decreasing, making it impossible to get the full fill each time...

Over the eight refills... a stab in the dark.... 7/8 full, 6/8, 5/8...

You will get many refills at first... then there will be a time where you just go refill the large tank and start over...

And then look for another large tank and some plumbing to match....

Best regards,

-a-

[DonMuncy]

I'm not smart enough to confirm or refute Steve W's math, but I agree with his conclusion. If you can live with about 1500 psi, you can get about 3 "fills".

[tigers2007]

Before I spend the $$$ on a tank and transfill adapter, does anyone use a home oxygen concentrator to fill their bottles?

I just watched this video and the guy says it takes only a few hours to fill the D sized tank. I’ve seen these machines on Craigslist quite cheap as families try to get rid of them when folks pass on. $200 or so.

Obviously the transfill is less likely to break down or need servicing besides swapping the tank out.



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[carusoam]

Expect that there is an expensive and noisy compressor in there... to go along with the O2 concentrator...

Sounds like a better idea, and more reliable, than trying to use a concentrator in flight...

See if you can find how concentrated the O2 is that ends up in the tank... in the event that it isn’t 100% you would want to take that into account with your flow rate...

Interesting find...

PP thoughts only, no medical advice be given...

Best regards,

-a-

[Yooper Rocketman]

21 hours ago, tigers2007 said:

I'm too cheap to get more than one 125 cubic foot tank ($270 ish from Praxair). Yeah, i can find a used one for much cheaper too. How many fills should I get for my regular "D" size tank (15 cu. ft.)?

So how much you saving keeping that plane somewhere else besides KIMT?  I used to fill my Mooney with a fresh topped off bottle every time (taken out of my stock bottle supply at my dealership).  Probably only uses a couple bucks worth the O2.  If you're working at the VA in IMT, we could work out a pretty simple arrangement...... and I have the filling equipment at my hangar.

Tom

[tigers2007]

Tom I might have to take you up on that offer. You’ve always been more than helpful. I’ll be in touch.


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[druidjaidan]

On 8/4/2019 at 1:56 PM, Steve W said:

Let's do math!

Assuming your D tank is full at 2000 PSI, and your 125 cubic foot tank is full at 2200.

if we take 15 cubic feet out of the 125 then we have 2200*(110/125) which means once filled your big tank will be at 1936 PSI.

So, you get one full fill since it can no longer fill the D tank to the full 2000 PSI.

If you're ok with only 1500 PSI, then: 125*(1500/2200) means the big tank will have 85 CF when it hits 1500 and you will have taken out 40 CF.

Your D tank will hold 11.25 CF at 1500 PSI, so, about 3-4 'fills' to 3/4 capacity.

Math may be wrong, I blame the fact that I did this in between yard work.

Edited to add:

And the thing I forgot is that the small tank will probably not be empty that often, so really it's best to think about that you have 40(ish) usable cubic feet in the big tank and figure that against how much you use per trip, provided a trip doesn't ever need more than 3/4 of the small tank(being sure to include some margin for unexpected problems)

 

 

And this math right here is why people use cascade fill systems.  You get a lot more fills out of each bottle that way since you're only using a tiny fraction at the high pressure end.

[DonMuncy]

A cascade system is far better, if you can afford, or otherwise come up with an extra tank. Three or more is even better, but the addition of the extra one helps a lot. A pilot ought to do some calculations as to how much flight time he will have at altitude, against the expense of setting up a system, against what the various FBOs charge for a fill. But the convenience is a huge factor to me. Plus the fact that I already had two welding O2 bottles. 

[thinwing]

Ok my thoughts...1 115 composite bottle....I last filled it to 1330 and after using it to KOSH and back its 1000 

[tigers2007]

Maybe I can donate a full tank to Yooper Rocketman's setup and make it a Cascade Club. I remember cascades from filling SCBA's in the fire service. I still want to take a look at those home medical devices that fill tanks for the old farts so they can drag the tanks around casinos.

[Yooper Rocketman]

10 hours ago, tigers2007 said:

Maybe I can donate a full tank to Yooper Rocketman's setup and make it a Cascade Club. I remember cascades from filling SCBA's in the fire service. I still want to take a look at those home medical devices that fill tanks for the old farts so they can drag the tanks around casinos.

You don't need to (Cascade).  I drag a full bottle out to the airport every time I need to fill.  I'm lucky if my big industrial tanks drop 100 pounds during a fill (and those bottles are always filled 1,800 to 2,000 when I grab them).  I take them back to the fab shop at my dealership and they use them until they are empty.  They go through 2-3 bottles a week, and I usually have 3 full ones in the rack.  I DO have oxygen in the Lancair so would top that off anytime I have a bottle out there.

When Chad was a smaller shop, he was using my O2 system.  As he got larger, he wanted genuine "Aviators Oxygen" so offered to buy my filling equipment.  He really didn't buy it, he gave me 5 free fills (which turned out to be 3 instead of 5), then was going to fill me for $25 from then on.  A few years later my fills went to $50, and their "Cascade System of 4-5 bottles" was only topping me off to 1600.  In all fairness, it was his guys not meeting our agreement, he was super busy with the growth of his business, going from 3-4 employees to probably over 30 now. 

I made up my own equipment again and decided instead of keeping two bottles at my hangar (with the associated lease costs) I would just grab a full bottle from work and return it after filling.  It worked fine with the Rocket.  Don't need it nearly as much with the pressurized bird.

Tom

[Tom]

On 8/5/2019 at 10:08 AM, carusoam said:

Expect that there is an expensive and noisy compressor in there... to go along with the O2 concentrator...

Sounds like a better idea, and more reliable, than trying to use a concentrator in flight...

FWIW I use a portable concentrator which has been completely reliable (have not taken it above 16k but supposedly should be good up to 18k).   Was a Craigslist find for $800 or 900 with three batteries (in my purchase anyway) plus ac charger plus cigarette lighter adapter. Uses regular disposable medical nasal cannulas. 

Only good for one person but the convenience can’t be beat. I’m healthy but I can tell a difference in post flight fatigue after a couple few hours over 7k; I use it on practically every cross country.

[tigers2007]

Ah hah that is the anecdote I’ve been looking for. I’ve seen those “Inogen One” TV commercials and have seen them on Craigslist.

 

I’m guessing you’re watching yourself with a pulse oximeter. What are your sat’s at FL170? How many litres per min? Pendant cannula?

 

Edit: looks like a vendor sells Inogen just for this purpose, “Inogen Aviator”. They even have a Mooney on their website.

 

http://www.inogenaviator.com/aboutus.html

 

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[Tom]

10 minutes ago, tigers2007 said:

Ah hah that is the anecdote I’ve been looking for. I’ve seen those “Inogen One” TV commercials and have seen them on Craigslist.

 

I’m guessing you’re watching yourself with a pulse oximeter. What are your sat’s at FL170? How many litres per min? Pendant cannula?

 

Edit: looks like a vendor sells Inogen just for this purpose, “Inogen Aviator”. They even have a Mooney on their website.

 

http://www.inogenaviator.com/aboutus.html

 

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Mine is a G2. I keeps sats over 95 regardless of altitude. Yes to the fingertip pulseox.  The G2 has flow settings of 1 (low) to 5 (high); it’s a smart sensing pulse-demand system and I’m not sure what the technical flow (LPM) rate is.  I’ve only been to 16k and have only gone up to the 4 setting. Most of the time I’m between 8 and 12k using setting 2 or 3.  Once you get used to feeling not fatigued after a flight it’s hard to not use it all the time, particularly when it’s no muss no fuss.  Can’t hurt human factors performance either.

I’d ignore the Inogen aviator people unless you want to spend more for exactly the same unit. If you parse the verbiage on their website the FAA approval pertains to RF, while the “meets FAA supp 02 requirement” isn’t a performance designation that they earned. Rather CAMI accepts the devices as legit. 

I only use medical cannulas...disposable type that wraps around the ears. Call me Mr bad hygiene but I’m only on my second one in three years.  

If seriously interested in one of these devices but are unsure if it’ll work for you, consider stopping in a local medical supply store. Many places will rent these, +/- needing a script from a doc.   If you tell them it’s just for a weekend trial for flying you might not need a script. Offer to take them up and the trial might be free (avoiding a deposit and such). 

[carusoam]

There is a thread around here regarding use of the inogen portables... the biggest challenges were the efficiency at higher altitudes and the number of people that it could supply...

Probably works well for one person close to 12.5k’...

Find the thread, it had some real experience.

As far as marketing and names goes... ‘Aviator’ I’m not sure that it’s related to GA....

http://www.aviationconsumer.com/issues/49_6/accessories/O2-Concentrators-Inogen-Aviator-Is-Tops_7069-1.html

Oxygen is one of those things... the more complex, the equipment, the bigger the probability of failure is... 

Running out of O2 can be hard to notice.

A good electrical system connection, would be better than batteries or cigarette lighter plugs...

PP thoughts only, ran out of O2 once... 

Best regards,

-a-

[tigers2007]

Well I see the price of Medtronic LifePak 12's has fallen on eBay. Maybe I can setup my own airborne ICU to monitor my health and shoot telemetry to one of my Dr. friends to monitor in real time. When I used to work as a medic I should have grabbed more cannulas and those expensive tape-style pulse ox sensors that plug into the monitor. I'm sure I could make it trigger a loud piezo if it dropped before a certain level.

[carusoam]

Hard to fly solo and operate the lifepak... 

https://www.aedmarket.com/collections/physio-control-lifepak-12?gclid=CjwKCAjwyqTqBRAyEiwA8K_4OxQhT-OYT0pNPPJfWAub21d4ZUlQQLJBSFlCjB6bKrF9tw3UYwC3ixoCb8cQAvD_BwE

With some seriousness... we (the world?) lost a Mooney a couple of years back because of a simple O2 delivery problem... climbed to 25k’ or so and stopped responding on the radio... landed off the coast of Atlantic City...

Pilot was on his way to a MAPA PPP class...

Fuzzy memory of a PP...

Best regards,

-a-

[Tom]

10 hours ago, tigers2007 said:

Well I see the price of Medtronic LifePak 12's has fallen on eBay. Maybe I can setup my own airborne ICU to monitor my health and shoot telemetry to one of my Dr. friends to monitor in real time. When I used to work as a medic I should have grabbed more cannulas and those expensive tape-style pulse ox sensors that plug into the monitor. I'm sure I could make it trigger a loud piezo if it dropped before a certain level.

Not selling anything, rather sharing observations.

FWIW a good number of Ebay sellers of this type of equipment are simply reselling equipment that they purchased from government auctions...and for a significant mark-up (you can see this if you 'check all items by this seller' and note a bunch of clearly ex-military items).  You can bid/buy this stuff yourself from govdeals.com. Here's a pulse-ox currently at $100...this unit doesn't have an audible alarm but can be used with disposable (~$1 per flight) tape-on sensors for continuous monitoring...lower profile than the ~bulky $20 Walmart units such that you can wear the monitor the entire flight with minimal inconvenience. 

I don't mean to promote the portable concentrator over a tank.  The latter is less expensive and can be shared continuously by multiple people (while the concentrator serves only one at a time).  Just that for solo flights <18k the device is incredibly convenient, making using routine supplemental O2 use, even at lower altitude, a no-brainer.  Over 18k without pressurization is a life risk I'll never involve myself but tanks are clearly required in the flight levels.

Regarding reliability...it's worth noting that the concentrators are used by tens if not hundreds of thousands of people outside of a medical/home environment...people who would crump/slump over if the thing failed.  They're designed to be used 7 days a week for years and are accepted to be used in austere environments like the inside of a commercial airliner (withstanding the backup O2 tanks that airlines carry).  Point being that they're incredibly reliable and are designed/tested/approved to standards arguably with higher tolerance than much/most airplane stuff (but not as simple obviously as a tank system).  At least all modern units have an audible alarm if the unit isn't able to deliver what you've asked, or if there are other onboard faults needing attention.  That said, I cannot hear the alarm on my G2 in the Mooney with my Halo buds in (I do have moderate hearing loss).