I have two of the CFFC-048 cylinders. The only reason I have two is because if you are on a long trip and one leaks out, you are stuffed with regard to altitude! Otherwise, a half filled CFFC-048 with the O2D2 will do two people all the way from the UK to Greece and back. Their size is such that most refilling hassles are removed, even if you only half fill them (e.g. due to below, or because the source cylinder doesn’t have enough gas) but they are very light.
The other gotcha is the 15 year life; this allows only two tests at 5 years and 10 years and at 15 years you are supposed to scrap it. I think a lot of people don’t test them and after the 5 year point just half fill them… or delay the first test to 10 years.
I would also buy a cylinder with the pressure gauge on it so you can tell how much gas is in it, without having to attach something to it. That way you can also fill it correctly; the standard oxygen cylinder is 3000psi whereas the aviation cylinders such as the CFFC-048 are about 2200psi. If you just join the two together with the refill hose and run it until it stops flowing, the CFFC-048 will end up way beyond the red line.
The DIN versus 540 argument depends on where you refill. With scuba shops, DIN is better. With your own cylinder, or if you have a useful contact somewhere you can get an adaptor hose, then it doesn’t matter.
I vaguely recall something about the scuba oxygen certificate. It might work with a particular shop. The likely problem is that the shop guy will immediately realise you are not a diver and is likely to get anal about it. This is the biggest issue I have found with scuba shop refills: their attitude is like the UK weather 
For 1 year they might be friendly, the next year some anal twat works there and tells you all kinds of crap. I have a number of shops around here and every one of them but one would fit that description. And that’s before you get onto the other UK scuba shop scams like insisting on 2 year tests (for ground use compressed air cylinders; 5 years) on the basis that you could peel off the “ground use” sticker and dive with it
I got fed up with it pretty soon and got my own cylinder, rented from BOC, which is super but isn’t the cheapest way because the rental is rather wasteful, and the BOC cylinder is so heavy I need help to get it moved and transported to swap it for a new one. One can buy cylinders (on an exchange basis) so there is no rental but AFAICT only for stuff like argon, not oxygen.
I have no idea about regulators or gas fittings, but I have access to a BOC cylinder in work. All I know is that it has a 2-stage regulator that goes into Swagelok piping. Is that enough info to figure out what hardware would I should buy with my aviation oxygen system?
@TimR
You have it all, almost.
I’ve chosen DIN, and I refill to scuba shop easily.
Though, having this adapter has been a huge help, because they could not connect their refill station without it.
That is a DIN (one type) to DIN (another type) adapter, I think.
I’ve used sub aqua products for adapters and they will do pretty much anything for very reasonable prices. The contacts are in Peter’s article about o2. They only really work by phone though.
I got the DIN from mountain high, the cost delta is really small.
Thank you all – very helpful!
How much weight do you factor in for all the equipment assuming full tank (CFFC-048)?
The weight is much less than your extra weight if you live off UK GA airport food for a year
It isn’t like the huge steel cylinder which is found in the back of a typical turbocharged SEP, as a part of its fitted oxygen system. I know one TB21 owner (no longer flying) who spent 4 or maybe 5 figures (he was G-reg and in the EASA system that doesn’t get you very far because you have to pay a company to do expensive testing) certifying a composite cylinder to replace that steel one, for weight reasons.
I have just weighed the -048 cylinder, in the Cordura bag, full of gas, at 5.3kg, and the rest is negligible. I lost 8kg in 2 months by going mostly plant-based
I have been flying for years on supplemental oxygen using the MH O2D2 pulse regulator. I feel comfortable up to around 18.000 feet and will fly higher if needed using cannulas only. My wife is sensitive and more easily not feeling well when flying higher than 18.000 feet, so I try to not go higher than 18k and it would be the reason of switching over to a pressurized cabin aircraft. In 2014 I wrote a blog post on this topic. It can be found here.
In the latest magazine of PPL/IR there was an article published on flying on supplemental oxygen in which pilots are warned about the limitations of pulse oximeters in measuring the oxygen levels if I remember well.
That magazine is behind a paywall but fortunately a google on e.g.
pulse oximeter limitations
digs out many links e.g. this one.
I think that for a normal healthy person, not subject to inhalation of toxic gases etc, if the oximeter / oxymeter reads say 95% then you are “good”. My experience of the O2D2 for about 10 years is that it works superbly.
One option, if the desired level is not being achieved, is to run the O2D2 on one of the “mask” settings. You get a higher flow rate that way.
