Reader John Welsh recently reached out for help with a problem that’s a hassle at remote airports, and that’s finding oxygen to fill the supply cylinder in the airplane. “Why can’t I build my own filling station,” he asks. Why not?
A while back—from our own frustration—we asked just that of Aerox—the household name for all things aviator oxygen tanks and accessories. As we suspected, sourcing O2 refills in a pinch is a growing problem because at some airports it’s the maintenance shop that provides tank refills and not the FBO. And of course maintenance shops generally don’t keep the same schedule as the FBO. Scott Ashton at Aerox told us the company is selling more transfill systems than ever as pilots struggle to find tank refillers when they need them. It’s a good solution, but only when done correctly and safely.
The simplest Aerox station consists of two standard tanks with familiar CGA-540 connections, a slow-fill restrictor, and 6 feet of braided stainless filler line to connect directly to an Aerox portable cylinder. But it’s not limited to a single tank. If you go through a lot of oxygen, you can add as many supply cylinders as you want, with some options to include an overfill regulator and a bleeder device for bleeding off the pressure before disconnecting the supply line. But remember that the majority of supply cylinders are around 2300 psi, and portable cylinders may be lower, so the ability to set the outflow pressure as a safety backstop is a plus. You don’t want to rupture a safety burst disc, which are equipped on all Aerox cylinders. Mountain High has a straightforward video on filling cylinders.
Fittings, Cascading
The first step is understanding the hardware that’s proper for safe refilling. The Aerox bottles use a standard CGA-540 fitting, or a PB-3 fitting for some variations. The PB-3 is a standard for installed systems and the CGA-540 is pretty much the standard for portable bottles. Aithre Aviation, a provider of composite cylinders and accessories, sells a 24-inch high-pressure transfill adapter line for its smaller composite cylinders when the Mountain High regulator isn’t being used. Aircraft Spruce sells the $415 FBO-1 filler station, which comes with 2 CGA-540 cylinder connectors, 6 feet of high-pressure (3000 psi) braided stainless filler line, a contents gauge, a flow restrictor, and adapters to fit Puritan-Bennett, Scott, and CGA-540 filler ports. The entire cascade kit with three bottles is $1350 through Aerox, and you can select up to five cylinders in a cascade.
Last, respect the DOT certification standard and life limits that are in place for the cylinders—it’s important—as is the date stamp on the cylinder. The aluminum cylinders have no life limitations as long as they pass the hydrostatic test every five years. Again, read the stamp. The Kevlar cylinders, which have a rigidly laminated fabric over an aluminum shell construction, are continuously expanding and contracting, which stresses the cylinder over time. There’s generally a 15-year life limit on a Kevlar cylinder for as long as it passes a hydrostatic test every five years. Thin-wall steel cylinders have a 24-year life limit with a three-year hydrostatic test cycle, and the thick-wall steel cylinders have an unlimited life cycle as long as they pass their five-year hydro. The majority of cylinders successfully pass the test, but some don’t. A good habit is storing empty tanks properly—like many other things, condensation is the enemy.
I used a system like this for a while. While my current airplane has a built in oxygen system, I stopped using it regularly and just use an oxygen concentrator. It’s much easier than refilling oxygen tanks etc. They work well up to about 15,000 feet. If you’re patient, you can buy an Inogen concentrator used online for less than $1,000.
Same here – it works great, inexpensive, and never runs out during a flight. I just put on the cannula any time I expect to go over 7500 ft – just makes me feel fresher after a long flight. I bought my inogen g5 used on an online marketplace. I think some articles on oxygen concentrators would be helpful to the avbrief audience.
This article does not cover the lousy economics of a 3+ bottle cascade nor all the safety precautions that should be taken in making and using one. Before trying this, do more homework.
The pressure swing O2 concentrators are an interesting option, Rob.
Added one of many available tutorial videos on filling safety in the article. We’ll look at the slim and limited market of O2 concentrators in an upcoming report.
Yikes! You guys didnt even touch on the grades of oxygen (8 of them) or the disastrous issues associated any greases or contamination when working with 100% O2, equipment cleaning requirements, solutions and tools used etcetc. This is not DIY stuff. Neglecting to even mention it is going to get someone killed. Theres a reason why breathing oxygen tanking is not available to the public and thats because its highly dangerous in the wrong hands and requires training and certifications. I have the certs to pump and work with 100% O2, and itll scare the bejesus out of you even when you know what youre doing . Redo your research or take the article down. Your call.
not taking it down. This is a general report on sourcing hardware, based on a question from a reader asking if it’s even possible. Pilot supply houses offer these cascading setups for DIY refilling. Since you obviously have commercial experience refilling, how about input from you on how to get the right training, for those who want to learn more?
Mountain High Staff put a similar story in this month’s Cessna Owner magazine. Too soon to link to the story.
I found that it is nearly impossible to get aviator’s breathing oxygen cylinders refilled in the greater Boston metro area. I have called ahead to FBOs that I planned on traveling to and not gotten any positive responses. I considered my own refilling system but the fire department covering my community hangar will not permit it due to the hazards of oxygen storage where fuel and oil are stored. This made me think twice about storing it in my garage. I ended up getting a military surplus Saros oxygen concentrator and recently tested it with excellent results. I am not sure why it is so difficult to get cylinders refilled in certain areas of the USA but for those areas a concentrator may be a good workable solution.
I found it refreshing to read an article about aircraft oxygen refilling without mention of the term, “Aviator’s Breathing Oxygen”. Whomever coined that expression used it to get rich selling plain old oxygen to the masses. I’ve looked and can not find that term or “requirement” anywhere in the FARs for Parts 91, 135, or 121 beyond the requirements of when oxygen must be used.
I bought a large oxygen cylinder from the local gas supplier and a transfill hose with pressure gauge from a veterinary supply house for far less than what the Aerox and Mountain High charge. When my single storage tank got down to around 500 psi, I simply returned it to the supplier and they swapped it out for a fresh tank for under $50. They handled hydrostatic requirements. Of course the small aluminum cylinder was my responsibility. A single large tank generally lasted for a year of flying my glider at altitudes between 16-18,000 ft MSL, or around 100 hours. I turned on the oxygen on the ground at sea level setting before takeoff from the 6,200′ elevation airport.
I am aware of the dangers of using O2 and petroleum products in close proximity to each other and kept them widely separated in the hangar. I had one wrench dedicated to the CGA-540 connectors on both tanks to avoid contamination. The Mountain High regulator had an o-ring seal and so was hand tight only.
Pelican’s Perch #13 by Capt John Deakin has a good article just about this very thing. All his articles are great reading.
GA recreational flying mostly stays below FL180. Some pilots think diver or vet oxygen is good enough, but the numbers don’t back that up. On a standard day, air cools about 2 °C per thousand feet. By 10,000 to 15,000 feet it’s already between –5 °C and –15 °C, the same range as the dew point of diver and vet oxygen, which runs around –10 °C to –20 °C. Moisture in that gas can freeze in valves or lines and stop the flow when you need oxygen most.
In small piston aircraft, portable tanks ride in the warm cabin. In higher-performance and pressurized aircraft, oxygen tanks sit in unheated compartments, so the only protection against freezing is the dryness of Aviator’s Breathing Oxygen itself. That’s why diver or vet oxygen, with dew points near –10 °C to –20 °C, is unsafe for aviation. Those unheated tanks and lines can easily reach –30 °C at 15,000 feet. I’ll stick to ABO. It’s made for altitude and tested for dryness.