I don’t know much about portable oxygen in GA, but spent a lot of time involved in certification of military role equipment – which I know is different
- but out of interest how is the crashworthiness of these cylinders considered? I’ve seen the aftermath of heavy objects flying around in an incident and it isn’t pretty
For a cylinder filled to say 150 bar (the usual pressure for aviation-marketed cylinders; the normal scuba-marketed ones are filled to 200 bar) if you lift it from sea level to outer space, the stress on the material increases by 1 part in 150 i.e. about 0.7%.
Ambient temperature is perhaps one to check because steel becomes brittle at low temps. No idea if this is relevant.
Crashworthiness I know nothing about.
What about BOC medical cylinders? They regularly deliver to where I work so I was thinking that instead of having to faff about with refilling I could have them deliver me a full one each month and take away the empty. I guess the question is how easy it would be to rig up cannulas to it? I’m guess it could be OK. The ZD and ZX cylinders look plausible for aviation use.
The data sheet is here
As I understand it Timothy is set up for feeding directy from a BOC cylinder behind the seats in his Aircraft, so there may already be some information available from him.
When I get to that point in my flying I’ll be trying to source Parts/Fittings to fill from a BOC Cylinder into the inboard tanks myself rather than paying Handling agents to do it.
What about BOC medical cylinders? They regularly deliver to where I work so I was thinking that instead of having to faff about with refilling I could have them deliver me a full one each month and take away the empty.
This would work but is not all that cheap. The cost of having a swap cylinder delivered, to a small client (not a hospital working under a bulk NHS deal) is likely to be of the order of 50-100 quid. I currently pay about 30 quid for swapping mine (largest size, almost) and that is for driving it down to the BOC welding gas depot myself. It is so heavy I have to get help to do it, plus borrow a big car. Then there is the annual rental, in the region of 100-130 quid.
So it makes sense to rent one, but swap it as infrequently as possible. Mine lasts me about 2 years, at the end of which it refills the “48 cu ft” MH cylinder to only about halfway, but because those cylinders are so big, it is still enough to fly two people to Greece and back.
Quite a lot of people get aviation refills via a hospital but I suspect in most cases when somebody is looking the other way
Yes cylinders with integral valves are actually quite expensive to rent. I guess I’ll just use the big cylinders we have here and get a hose made up for the refills with a release valve so I don’t blow myself up.
We have set up a large welding oxygen cylinder with a three way splitter (attached directly to the cylinder, which has its own regulator) then 4mm tubing to each of three O2D2 units. WE built the splitter from parts and I can post the spec, if anyone wants.
The regulator has a gauge marked in bars, and the MH permissible range is 1 – 1.7 bars, so we set it to 1.4.
It works fine on the ground, we are test flying it on Monday.
I believe that we paid around £150 for the cylinder. I don’t think it is an annual rental as such, I think we keep it as long as we like. We can then take it back to the welding shop and exchange it for a small amount of money (I can’t remember how much, but too little to lose sleep over, maybe £30-40). My guess is that we’ll need to do that less than once a year.
We are very lucky that the fit is perfect, within the depth of the carpet pile, so it is easy to remove and replace, but is not going to slide around.
It is a bit of a faff to get in and out of the aircraft. It weighs 30Kg and therefore needs a strong lift, but it’s not too bad. I wouldn’t want to do it every flight, but once a year should be doable. I have an estate car anyway.
I cannot say that it’s ideal for everyone, but it works very well for us. I am happy to meet anyone who is interested at Biggin to show them, or I can post some photos, if people want to see how it’s done.
I am sure pics would be of much interest to many.
I vaguely recall this Q of buying the cylinder outright i.e. no annual rental, came up before, and it would be an ideal deal for pilots, because the annual rental dominates in most GA scenarios. I can’t remember why I am not doing that too… maybe it was because nobody near here was offering it. There is some firm near Brighton which does it with various gases e.g. argon but not oxygen.
A 30kg cylinder is one of the smaller ones. From this table I have the W size which is 85kg. It looks like you have the S or T, at 34kg.
I was out test flying today, but only remembered my promise to post pics just after I had removed the cylinder from the aircraft. Apologies.
But I think you can make sense of it all from the photos I did take.
This is the cylinder. You can see a regulator tap to the right and and you can just see the pressure gauge to the left. Behind it (sorry I didn’t take better photos) is another hole in the green plastic with an on/off valve:
Here are identification plates, including the 31Kg weight.
This is the space it goes into, across the aircraft, just behind the spar. You can see the indent in the carpet where it fits precisely:
In the picture above you can see the three way splitter on the floor, but this is a close-up:
The three pipes go to three O2D2s, all velcroed to the aircraft:
I am happy to take other photos or provide specs if anyone needs them.
Just an update… I used the firm mentioned here for one of my MH 48 cu ft cylinders. They did it for £60 all included. A really good contact for cylinder testing.
TPF Parachute Services