@Peter – Which oxygen bottle do you have?
Presumable the CFFC-048? Do you fill to the maximum 3000psi with the BOC?
https://peter2000.co.uk/aviation/oxygen/index.html ?
If so what BOC do you order on the refill per month programme?
https://www.boconline.co.uk/shop/en/uk/gas-a-z/oxygen/breathing-oxygen-123
Yes.
Yes.
I swap it for a full one at the local welding gas / steel fabrication depot, roughly every 2 years. Very well organised.
At what pressure do you exchange the cylinder? Is it the BOC W cylinder you have?
I’ve tried some back of the envelope calculations, but not sure they make sense:
BOC W cylinder (external dimensions 146cm tall by 23cm diameter) holds 11.09 m^3 according to their website. (I have presumed that is at 1 bar and at room temperature). I think that is about 450 moles of oxygen.
The Mountain High CFFC-048 cylinder can be filled to 2216 psi (~ 150 bar). Its (external) dimensions are 50cm high x 17.2cm diameter. Assuming the internal dimensions are about 45cm x 15.5cm, that is a volume of 0.0085 m^3 which implies it can hold (at room temperature) about 53 moles of oxygen. The minimum pressure at which it should be refilled is I believe 35 bar. I think that means about 12-13 moles left in the cylinder.
Quantity of gas (in moles) is linear in the pressure (assuming constant temperature and volume of cylinder), so using the main BOC cylinder from 300 to 150 bar will use up half the oxygen. So roughly, I’d expect you would get 225 moles out of it and be able to fill your MH cylinder 5.5 times (from 35 bar) before resorting to only partially filling the MH cylinder.
I presume you don’t wait until your MH cylinder is empty to refill it, but do these numbers sound about right?
I change the BOC cylinder when there is not enough gas left to pressurise the portable cylinder to about 50% on the gauge (which as you say is 150 bar; the BOC one is 200 bar, or actually 3000psi, when full).
This policy is enabled by the portable cylinder being quite big, so a half full one is also very useful.
To get much better you would need an oxygen pump.
The biggest job is to get the BOC one swapped. One needs an estate car, at least, and 1 or 2 strong people. I can’t do it myself.
If you really want to fill the portable cylinder to its maximum pressure, you can also get two oxygen cylinders. You use the first cylinder to fill the bulk of the bottle and the second one just to top up when required.
This works best if you refill portable cylinder when it is empty, and if you really need it full.
if you only top up when you really have to, the second cylinder lasts forever.
That’s clever 
I have found that since I went to the 48 cu ft cylinders about 10 years ago, I have not needed them anywhere near full. A trip to Greece and back with 2 people, at European IFR levels, say FL100-170, uses up maybe 1/3 of it.
The size is the key. When I used to fly with smaller cylinders, like the Aerox aluminum ones, I was constantly running around to find refills. I’ve posted previously about the comical situations in say Greece, where the brother of a friend of a scuba shop owner had a gas factory where we spent half a day, eventually getting an invoice for peanuts. And the hassles with UK scuba shops where some anally retarded dickhead decides you are not a real scuba diver and aviation is risky…
So just looking at the maths. The CFFC-048 will give me 40.5hrs with 2216 psi with an EDS. So I am looking at two adults getting 20 hours of oxygen at FL150 where I am likely to cruise at for Euro Touring (Give or take) which would cover the range of a return journey in Europe.
Do I go for the CGA-540 or the DIN447?
Does the CFFC-048 fill to 3000psi?
Peter wrote:
To get much better you would need an oxygen pump.
Which leads me to my next question. If I have one of those BOC bottles, how many refills would I get with an oxygen pump? How much is the oxygen pump? I want to do a similar setup to you but refill the bottle to full at least 5-6 times per year. Maybe 9-10 times.
Peter wrote:
The biggest job is to get the BOC one swapped. One needs an estate car, at least, and 1 or 2 strong people. I can’t do it myself.
Do BOC not come and replace it for you? I can drive, but don’t have a car. (Zone 1 London).
Peter wrote:
running around to find refills.
I have a Scuba centre on the North circular that I go refill at, which is near to Stapleford and 1hr journey from home. That set’s me back £15 refill. Hence why I think if I get this bottle I’ll want to have a setup at the back of the parking stand we have.
Here is a UK oxygen pump listing (HIHP-20648 Cylinder-Mounted Oxygen Booster). Claims you can still get over 2000psi when the cylinder pressure is as low as 300psi. Can be pumped by hand too. No price listed though.
derek wrote:
Here is a UK oxygen pump listing (HIHP-20648 Cylinder-Mounted Oxygen Booster). Claims you can still get over 2000psi when the cylinder pressure is as low as 300psi. Can be pumped by hand too. No price listed though.
I bet that’s expensive. I’ll email them when I get around to it for a quote.
Does it have to be aviation oxygen in the bottles or can you fill up with any old oxygen? Which BOC one is best?
