Aircraft Oxygen Systems and Oxygen Filling
Originally written in 2006
* last revised in 2016 *

Well, it looks like the O2 system information for -10's will be as broad as the number of O2 system vendors.  I picked up a portable (Precise Flight) system at Sun-N-Fun 2006, then upgraded it with Demand Conserver components after that, and now during OSH 2015, I purchased a new Mountain High system for the RV-10, and in 2016 another system for my RV-14. I'll explain it all below...

At present, I know people who have most every system available for our planes:

When I was originally buying my first O2 system, I didn't know which way to go, so I read as much as I could about them online.  The Mountain High stuff looks very nice, but generally cost a little (or LOT) more, depending on the configuration.  The Mountain High pulse systems conserve O2 very very well, but if you want panel-mount control it will cost a LOT of money.  The O2D2 portable 2-place boxes will help to reduce that cost drastically.  The system with O2D2 controllers will still cost you over $2000 for a 4-place system, however, if you really intend to use your O2 on long trips, you will want to spend the money and go with a DEMAND oyxgen system rather than a constant flow system. The demand systems will always cost more than the constant flow systems.

The SkyOx system looked ok, for a constant flow system too. At first I thought it might be nice to have a single adjustment knob for all 4 places....then  I read on and rationalized it a bit and realized that each person may not want/need the same amount, so there is a drawback, depending on your needs.  Personally, I use different flow rates OFTEN when flying with the family, because I want to guarantee that pilot and co-pilot have perfectly high levels of Oxygen, but if endurance comes in as a factor, I may have my rear-seat passengers flow at a slower rate to preserve oxygen for the pilot. It really depends on the system you choose.  Having a Pulse Oximeter is a real necessity anyway, and having individual controls would be nice.

The Aerox constant flow system seemed OK too.  I almost went with it, and was looking for things to nit-pick to help me decide between Precise Flight constant flow system and Aerox.  They use the same cannulas, and offered much the same stuff.  The aerox uses needle valves on the regulator.  I thought maybe that depending on what bangs into it, it might not be as durable as an inline meter.  Also,  it means the guy running the system will need to be very close to that valve, whereas if you have a flowmeter inline, you could have the flowmeter close to you but far from the bottle.  That seems like a big negative.  In the end, The Aerox was just a few bucks more, if I bought their carry case, and they only included 4 cannulas, meters, and one mask. The Aerox does have a good warranty however.

My Original Solution
From Precise Flight, my original purchase was a constant flow system to save money.  I got 4 cannulas, 4 meters, 4 masks, (1 cannula and mask was kids sized by request), and the carrying case, with an M Bottle.  The aerox was something like $631+59 for the case.   The Precise Flight was $675 for the whole thing.  The constant flow systems, however, have ugly and bulky cannulas, and waste a LOT of Oxygen. So looking to improve my Oxygen system, during OSH 2006, I added a pair of the Demand Conserver units that get attached inline to conserve O2, which at the time cost about $375-450 (ea) depending on special pricing if bought during a show.   These are supposed to save so much Oyxgen that you get about THREE TIMES, (3X) the duration on your O2 cylinder, compared to the oxysaver cannulas.   They worked so much better that at OSH 2007 I bought 2 more, so that I'd have them for all 4 seats.  The demand conservers come with their own "sensing" cannulas with 2 hoses and chambers, which are MUCH less bulky and more comfortable, as they don't need the "accumulator" bag, and only deliver you O2 during the inhale.  During my first use they worked very well and I could see that the Oxygen use was greatly reduced.  I am finding that Oxygen is a very handy thing to have in a capable cross-country cruising plane like the RV-10.   The Precise Flight warranty is 2 years, but the units are very simple and there are really not many items you have to worry about wearing out.  One huge upside to the Precise Flight demand conserver is that it does not use batteries or have any wiring needs.  If you have a device that you leave batteries in, you have multiple issues. 1) Battery leakage, 2) If you don't start the trip with fresh batteries you need to carry spare batteries, and 3) spare batteries add unnecessary weight. A small down side is that the delivery tube for the cannulas is a 2-hose bonded design, so the hoses themselves are a little thicker and heavier, up to the fork in the cannula, than the Mountain High cannulas.  One other BENEFIT to the Precise Flight system is that you manually set your altitude on the conserver dial, (or you can choose constant flow if necessary), so if you are using a pulse oximeter on your finger to check your body's Oxygen level, and want to raise or lower it, you can adjust the dial.  So if you are on an expecially long trip and your kids are requiring less O2 to keep their bodies in the 90's for % saturation, you can dial them down a bit, or dial down the co-pilot, to give the pilot the highest O2 level for the longest run time.  The added flexibility is nice.

I did download and read the Aviation Consumer article on the various O2 systems before buying.  In general, their main complaint about some of the others was the case, mounting, or individual adjustments.  They chose the Precise Flight, and I trusted that it would be a reasonable choice. If you're going with a cheap constant flow system, I don't really think it's a drastic difference between any of them, so everyone will probably be generally happy with what they have.  But I think it's well worth it to get a demand conserving system, either the Precise Flight or Mountain High.   Note that now the Precise Flight X3 Demand Conserver is sold as an STC'd system for the Cirrus and certified for use up to 25,0000 feet.

Here's a photo of the Demand Conserver

My New (2015/2016) Systems
In 2015, I was shopping at OSH and needed to buy an O2 system for my new RV-14 kit.  My first stop was to head to Precise Flight to see about getting another 2-place demand conserver system, as that worked really well for me and I already owned that type of hardware.  But, at OSH 2015 they were out of stock and didn't know when they would be back in stock, and didn't make it clear if they would still be producing them, so I gave up and went to Mountain High to check out their systems.  I had a couple friends who purchased their system but hadn't had any experience directly with it.  In July 2015, I had a long X/C flight Oxygen was my limiting factor, with 4 people using the system.  As I mentioned above, using the Precise Flight system, I flew out to Bryce Canyon UT, and then on to Yosemite N.P. in California, and then back through Yellowstone N.P. and home.  On the final 5 hour leg home, I had to reduce the amount of O2 for the kids, but they generally don't require as much to stay in the mid 90% saturation levels as we older folks do.  I also reduced the co-pilot slightly so that I would have the proper O2 saturation for as long as possible. (We were at 13,500') This allowed me to make it home with about 200psi remaining.  I was curious how the Mountain High O2D2 system would compare to the Precise Flight Demand Conserving system.  So I decided to just buy a 4-place system and see how it worked, while there was a show special.

I ended up buying a 4-place Mountain High system so that I could use it in my RV10 until the RV14 was completed.    I wanted to see if the Mountain High system was more efficient by any major measure.  So since I needed to buy at least a 2-place Oxygen system for my RV-14 project, I decided to just get a good 4-place portable system for my RV-10 and use my precise flight system in the RV-14.  What I purchased was: 8 cannulas (2 tapered and 2 standard), 2 of the O2D2 pulse units, FPR-540 4-hole regulator, 4 masks, (and 1 spare tapered cannula), and the carrying case, with an M (AL-647) 647 Litre Bottle (this bottle is very good sized, and fits between the rear seats of the RV-10.  For the RV14 that bottle is overkill (The 415 Litre bottle fits better between the RV-14 seats and is more comparable for duration), but it will EASILY provide 2 people enough Oxygen to go to California and back, in the RV-14.  The complete Mountain High system wasn't cheap, but no demand system will be.  There is no wiring to be done in the plane for the Mountain High System (I believe it's optional if you want to connect it into your audio panel), but you do need to keep fresh batteries handy.  An upside is that the cannulas are very small and light, and they even have a headset boom version if you want.  Here is MY SYSTEM, on their website.  MH Item #: 00EDS-2062-04  with full pack  Description: (2) EDS-O2D2 units with AL-647 Aluminum cylinder, FPR-540 regulator.  I did not want a built-in system due to permanent extra weight and filling hassles.  And I didn't go with a kevlar bottle due to cost...although it would be cool.  I did buy a couple of extra USB power adapters for it that you could use to power the system in an emergency, but I'd recommend planning to use batteries in it all the time, which is a disadvantage but it's the way the system works.  The Mountain High system you can set to automatically start flowing at either 5000' or 10,000' of altitude, or you can set it to flow continuously.  But, once it's activated it will start flowing if you are at or above the preset altitude and there is nothing you can do to adjust the amount of O2 delivered.  The Precise Flight has the benefit that you can tweak the O2 delivery a bit so if one person requires a bit more O2 than another, you can bump up or down the levels and not waste any more than you need to.  The other difference is the Mountain High system actually forceably "squirts" the oxygen into your nostrils...with an audible "psssst" every breath, whereas the Precise Flight is a more smooth delivery of Oxygen.  From that perspective, the Precise Flight is more comfortable and less likely to annoy you or make your kids want to rip the system off their head if you have young kids. On the other hand, the Precise Flight system will train you to inhale and exhale thru your nose, because it's your exhale in your nose that shuts off the flow of Oxygen.  So if you engage in poor breathing (NO MOUTH BREATHING ALLOWED with any Oxygen system), you may waste a slight bit more Oxygen with the Precise Flight over the Mountain High.

In mid 2016, after finishing the RV-14, I took the new Mountain High system on a 17 hour trip with a buddy of mine, and loaned my Precise Flight system to another couple on the same trip.  We flew nearly the same profile as them.  At the end of the trip, with 2 people on each system, we were within a couple hundred psi of each other for usage, so from an efficiency standpoint, the Precise Flight and the Mountain High systems are very similar, but Mountain High may have a very slight edge over the Precise Flight system.  Not significantly different.

The flight did trigger one thought for me though...
The complication is, my cannula that I used on that trip, with the Mountain High system, only works with the M.H. system, and the cannula I had been using with the Precise Flight system only worked with the Precise Flight system. This got me thinking, because that meant I needed 2 cannulas for each person in the family, and if we took 2 planes, we'd have to carry 2 cannulas for each person in case we change positions on a trip.  When I built my RV-14, I spent a lot of time and effort to make everything the SAME and interchangeable with the RV-10.  I used the same EFIS, the same COM1 Radio, Same functioning transponder, Autopilot, ADS-B system, switch layout, and almost every system and subsystem in the plane.  To bring this "universal-ness" to my Oxygen system, this would mean buying another oxygen system again, but a 2-place system.  I decided that even though I would need to carry batteries an had less flexibility to flow, I would buy a 2-place Mountain High System.  The cannulas are small and comfortable and I don't have young kids anymore who would be annoyed by the more shocking "squirt" of Oxygen into their nose.  So I now have both a 2 and a 4 place M.H. O2D2 system, and I can carry my cannulas from plane to plane.  The Precise Flight system is great and served me well, but will now have to be sold.  After buying the second system, I see they now offer the demand conservers again, but at a higher cost, but they're now STC'd for Cirrus and other planes, so selling my 4-place Demand conserving system will help pay for a 2-place Mountain High system and give the buyer a great deal as well.

Using the Oxygen

I've been very impressed with how much utility flying with Oxygen can bring.  There will be trips that I stay low, to avoid worry about Oxygen, but as a general rule, I use it on many of my longer X/C Trips, for sure all trips West of the Rockies.  (Usually I do not bring it to the Bahamas or Florida, due to weight and space constraints).  For one thing, I think it's easier for me to run Lean of Peak when at altitudes of about 8500' or greater, so using Oxygen will help guarantee I get into that altitude range, but it can also help you avoid ice in the winter, or clouds in the summer.  I've also found it necessary on our Yellowstone trips, and other trips out West, to cross the Little Bighorns with plenty of altitude margin to spare.


I don't have an installed system myself, I use mine portably, so there are better "experts" than myself to look to for permanent systems. Randy did a Mountain High Pulse system, fully installed.  Russ Daves has his system semi-permanent. There are many variations of methods that RV10 builders will install their systems.  For me, if I had an overhead console, I'd have gone with a semi-permanent install where the plumbing stays in the plane, but the bottle is removed after flight.  But, a huge benefit, and one of the reasons I went portable is to save weight, and and it is easier to ditch the bottle when you're not using it.  The 647 Litre bottle fits nicely between the rear seats of the RV-10, or can be hung in it's bag from a seatback. In the RV-14, I found the 647 Litre bottle worked, but it's best mounting location is in front of the flap motor which is right between the pilot/co-piltot's shoulders, so to save some space the 415 Litre bottle works better in that location, and also gives the option to lay it on the tunnel floor between the seats. The 647 Litre bottle is too big to lay on the tunnel in the RV-14.  If you're a builder who will likely use their Oxygen system all the time, I'd suggest going with a Kevlar cylinder and permanent mounting it.

Randy's Mountain
        High Install
Click the photo to jump to photos of Randy's install

Pulse Oximeters
One thing you don't want to skip is a pulse oximeter.  It's the only way to truly know when you need Oxygen, and how much you are getting.  You should check your level every 15-30 minutes in flight.  They're simple to use...just clip them on your finger and wait a few seconds to read the numbers.  They read your pulse, and Oxygen saturation level.  You'll want that level to be in the 90's as much as possible, and hopefully at 94 or more.  You'll notice many things as you get into the 80's.  I myself start to get a fast heart rate and get generally more paranoid about little things.  You'll also feel more energized after a flight with Oxygen....not that it's energizing you, but it's keeping down your fatigue a bit.   For a great article on these things, check here:

I previously used the Nonin Sportstat. Read the next paragraph for my update.    Also made by the same company, and more commonly found at aviation suppliers is the Nonin Flightstat.  These 2 units are identical, except the sportstat comes with a lanyard attached.  The sportstat targets Hikers and Climbers, whereas the Flightstat targets pilots.  They are also functionally identical to the Nonin 9500, a medical version.  at the time of the original writing of this section, the best one currently out was the Nonin 9550, which gives better battery life.  But by 2015 there are many more models available and they cost far less than my original Nonin.  My original Nonin succomed to leaky batteries, prompting me to ever use anything but Duracell Batteries in the devices in the plane.  I *think* duracell will cover the repair or replacement of any device wrecked by their batteries leaking.  I've had far too many things wrecked by leaky batteries.

To shop for pulse oximeters, my suggestion is to check out Amazon and search for "Pulse Oximeter". You can read lots of reviews there and make your choice.  For the ones I'm currently using, I got them after my donation to the Matronics List (I donate yearly and donate enough to get a good gift, so I chose the Oximeter and it works very well.  Now days you don't have to pay more than $35 to get a good one, whereas the Nonin's I speak of above used to cost me $200 or more.

Oxygen Filling

First of all, I'd highly recommend reading the article "Getting High on Welders Oxygen" available on AvWeb at

For my background:  I owned a SCUBA store for many years, filling thousands of cylinders over those years.  Sure, SCUBA uses air, but....    I was one of the earlier adopters of Trimix gas mixing in SCUBA diving.  We used Argon in our drysuits for insulation, and we breathed anything from 100% Oxygen for decompression, to mixtures of Helium + Oxygen + Air (O2 + N2) to do extremely deep "Technical" dives.   I spent a great deal of time filling cylinders for all of these gasses as well, and owned more than 2 dozen large sized cylinders, some used for Oxygen, Air, and Helium. Filling Oxygen isn't 100% risk free, but neither is filling air, or even hauling your Oxygen bottle.  Done safely, there are no issues that you can't overcome and you shouldn't be very uncomfortable with the filling practice.  The biggest thing with Oxygen is using Oxygen compatible materials, and ensuring they're Oxygen clean. This means no rubber o-rings, and no silicone or petroleum greases, only Viton or O2 compatible o-rings, and Halocarbon greases.  Also, the biggest issue you can cause beyond non-clean and compatible components is being careless in how you open and close your valves.  Always open the valves slowly and allow the lines to pressurize slowly.  When any gas, including air, is suddenly compressed, it can cause "adiabatic compression" that will heat the air greatly, and instantly.  I've felt this myself, and used to demonstrate it to people by turning on air cylinders and feeling the output of a 1/4" O.D. pigtail line made of stainless steel.  The instant you sharply turn the flow on, you get a sudden hot rise in temperature of the air coming out, and the tubing around it.  It only lasts a microsecond it seems.   The problem is, if there is hydrocarbon contamination in the system, that heat can cause spontaneous ignition of the hydrocarbon.  The solution is to use non-hydrocarbon lubes, and compatible and clean materials, and then you will have nothing that can burn. It can also ignite any particles that flow fast and hit a sintered filter in a system, so preventing particles racing thru the system at hundreds of miles per hour will help prevent any issues you may have.  Once you have a spark you can have a fire, and even steel will burn if it starts, as the fire will be fed by all the oxygen it needs.  I've seen an oxygen fire from adiabatic compression first hand, so I know how fast and how bad it can get...but for your normal transfilling situation, this should be very easy to avoid.

Below are some photos of my personal filling system.  I happened to own 4 cylinders.  Of the ones in the photos below, I own them all, and they are the larger 300cu.ft. bottles, the smaller one came from a very angry situation where I sent my bottles out for hydrostatic retest, and despite me labeling my bottles, they "lost" one, and had to give me one of theirs.  Makes me very angry but nothing I can do now.  Hydro retests are done every 5 years.  These cylinders can be leased from most any gas supplier, on a long-term lease, which is very affordable.  If you had 2 or 3 bottles (2 works fine, 3 is much better, 4 is overkill for most people), you will likely get years worth of fills depending on how often you use your Oxygen system.  If you are filling oxygen bottles for 2 or 3 pilots, and have a 3 or 4 bottle system, and you use Oxygen regularly, you can almost definitely save money filling yourself.  In my situation, where I already own the cylinders, it's a no brainer.  Aviation Oxygen fills are $35-75 when I travel, and they're not available on my home field, and that's for just tiny cylinder full.  In comparison, I think the Oxygen fill for one of these 300cu.ft. bottles is about the same price...or maybe a couple bucks more, and it can fill many small bottles.  I also have to pay the $20-30 retest fee per bottle every 5 years, so there is that minor cost.  If you lease, you usually won't pay that cost, just the price of the lease, which is usually a 5 year lease.   I will price out the transfiller hose at the bottom of the page.

To fill an O2 cylinder, you would then use a "cascade" method.  Filling from the first cylinder to provide the bulk of the Oxygen, then moving to the 2nd to bring the pressure higher, and then the 3rd to bring it to the top. After cylinder #1, each other cylinder provides progressively less oxygen, but retains it's higher supply pressure, allowing you to fill your bottle close to capacity.  Having 2 source bottles will get you pretty full for a low cost, but you will likely not be able to fill your cylinder to full capacity more than a few times.  Adding a 3rd bottle will exponentially give you full fills for many more fills.  Adding a 4th and that number goes way up again.  You don't swap out the first bottle until it gives you maybe less than 1000psi of fill of your can even go longer, down to maybe 500psi, before you swap it out, especially if you have 4 bottles.  Once you get that first bottle not filling a bulk of your fill, you just remove it and rotate your bottles down a number, have that one filled, and put that in the #4 position (or 3 in a 3 bottle system).   For my uses right now,  I have 4 bottles, but really only need to maintain a 3 cylinder Cascade system to get the fills that I want.  But since I own them, I'll keep draining cylinder #1 and #2, and #3, and then when cylinder #4 is not able to completely fill the portable cylinder, I will probably remove bottles #1 and #2 and have them re-tested and filled, then shift them down and make them #3 and #4.  For my uses, that will probably give me 3 or 4 years worth of Oyxgen at least at that point....maybe even 5-10 years.  The cascade method maximizes your use as good as possible without an oxygen booster.

A Booster pump runs on regular compressor air, and pumps the air in the storage cylinder up in pressure to use it down to about 300psi, but still get 2200psi output for filling your portable.  It's the most economical way to go if you did tons of fills and happen to have an expensive oxygen booster pump on hand, but would be impractical for most anyone but an FBO.  For more info on boosters, go here: and check out model 3G-SS-20-O.  The booster pumps also add a layer of complexity, danger, and maintenance.  The oxygen fire I had seen previously was in an Oxygen booster system.

Connecting and filling the cylinder is also easy.  I installed handwheel nuts on my fill whip, so you just run them down snug.  The nipples have a flexible tip to help it seal easily.  Then, you make sure the bleed valve is closed, and you open the valve on the portable cylinder.  Now you'll be able to read the pressure in the portable.  Without a gauge on the large cylinder, you will have to keep track of what pressure you left it at after the last fill.  If you have more pressure in the portable, it can backfill into the large cylinder.  This can be prevented by using an inline checkvalve, if you wish.   If the storage pressure is higher than the portable, then fill away...just open both valves slowly and let the pressure equalize over a couple minutes.  The portable bottle will get hot, if you don't go slow enough.  This probably it's much of a problem, but as the bottle cools, the pressure will drop and you will not end up with a full fill. In the SCUBA world, they fill cylinders in a bath of water, just to prevent them from heating up too much. When the pressure has equalized, shut both valves, and then open the bleed valve to remove pressure from the line.  You need to do this or you can't remove the hose easily.   If the portable still isn't filled, then just close the bleed valve again and move on to the next cylinder and repeat.  It's very easy.  Make sure you check your portable bottles stamp so you don't exceed the rated pressure during filling.


Pricing the Transfiller

I bought my Transfiller parts unassembled at the local Airgas store.  The parts are made by Western, and are readily available at most gas/welding supply outlets.  Here is what I bought:

Western Parts

Quan Part Description Price Total
1 PF2-4-48 Teflon/Stainless braid HP Hose - 48" $33.00 $33.00
2 WE 662P Handwheel Nut - CGA 540 $13.00 $26.00
2 WE 663 Soft tipped Nipple - CGA 540 $10.00 $20.00
1 WE 663-KPT Spare Nipple Tip $5.00 $5.00
1 BFT-4HP HP Brass Female T fitting $10.00 $10.00
2 B-4HP Brass 1/4" Male NPT to 1/4" Male NPT coupler $1.50 $3.00
1 217 or 211 valve 1/4" NPT Brass valve (can use others like Hoke 3712M4B) ~$20.00 ~$20.00