I’m considering to start DIY refilling my CFFC-048 O2 cylinder using a large rented storage cylinder.
From Peters writeup I understand that he is using a single storage cylinder with a filling hose using pressure difference to fill the aviation cylinder.
I’ve done some calculation and it seems to me that with the largest storage cylinder I can get (10.8 m3 gas Volume) I can do about 5 or 6 full refills before the pressure in the source cylinder drops below the typical pressure of the aviation cylinder (127 bar).
Does this seem about right?
Yes that is probably mostly right. The big BOC source cylinder is filled to 200 bar (3000psi) while the aircraft cylinder is normally (Aerox, MH) redlined at 150 bar (2250psi) and that difference gives you a slight advantage.
An additional and unexpected advantage of the bigger “48 cu ft” composite cylinders is that they remain usable even when say only half filled 
Currently, my BOC cylinder is down to about 70bar which fills the aircraft cylinder to halfway short of the redline (which is 150bar on aviation cylinders I have seen – ones sold into the scuba scene are normally redlined at 200bar), and this is still entirely useful and I fly with it. So now I am looking for two strong men with a van so I can get a replacement cylinder 
It’s great if you can get big O2 cylinders at 200 bars – usually they fill it up to 170-180. Volume-wise there are 40 or 50 liters cylinders which gives you somewhere between 7000 and 9000 liters of oxygen. Anyhow, yes you can get 5 to 6 fills.
You should use two cylinders too fill one, to get the most out of your bottles.
But then you pay two lots of rental charges which here are 100 quid a year per cylinder. Swapping a cylinder for a new one is just 25 quid. And this is the biggest cylinder available (from the welding gas depots which is what I always use because they don’t ask any questions).
You can create a bank of 12 cylnders or more but I don’t think it makes sense.
Lenthamen: the Dutch shop where I bought my MH set from could provide a O2 filling service. I have no connection with them except that he helped me properly with selling the MH set : http://www.glider-equipment.nl
Maybe this saves you some hassle?
Hi Niner Mike, we currently use a scuba diving shop for O2 refills. It works well, they’re cheap (I pay 10-20€ for a refill) but we’re fully depending on them for O2 supply.
There are some maintenance shops here at EHLE that offer O2, but they charge in the order of 100-150€ for a refill, which is ridiculous.
There is another guy in our group who’s buying his own O2 set, so I was thinking about starting DIY refilling so we have it in our own hands.
With 6 refills from a large cylinder before it needs to be swapped it seems to be much more expensive than our current solution via the scuba shop.
The scuba shop has multiple cylinders cascaded and a booster pump so theu are able to sell almost the full content of their cylinders.
I will keep the DIY refill option as a backup plan just in case we need it. Like Jesse said; to do it well you need to use multiple cascaded cylinders, preferably with a booster pump. But that will be too expensive for private usage…
Would one be able to use 300bar scuba diving tanks for refils? (I’ve never used O2 on an aircraft)
Something like this?
http://www.diverswarehouse.co.uk/index.php/cPath/12_1640_1642_1655?osCsid=7h5td7khcfutodqebf5qjqimo1
They should be easier to handle than a large 40 liter 200bar tank.
With 6 refills from a large cylinder before it needs to be swapped it seems to be much more expensive than our current solution via the scuba shop.
Remember the six refills (actually it’s more – see above) are into a 48 cu ft cylinder which is HUGE.
To illustrate it: I did the whole Corsica-Greece this year on about 1/3 of this cylinder, and there were 3 on the way out, up to FL190 (one with a mask, due to a partly blocked nose), and 2 on other routes. Only the last 2 were just me. All using the O2D2 demand regs. This is totally different to my “previous life” on the little Aerox aluminium cylinders and oximiser cannulas… one trip 2-up across the Alps would empty the cylinder and then you are looking for a scuba shop (in southern Europe – good luck with that ).
I agree the 100 quid rental I pay is not cheap but it removes the hassle. Then I think the same as you when my local scuba shop is willing (again) to refill but I also know that the next 12 year old shop assistant will ask me for an “oxygen certificate” and start hissing something between his teeth about not having insurance for aviation
and a booster pump so theu are able to sell almost the full content of their cylinders.
Yeah, I looked at a booster pump too. You can find them on Ebay sometimes, for a few k. Not worth it at all.
Would one be able to use 300bar scuba diving tanks for refils?
Not sure where one would get O2 at 300 bar.
