I used to carry a medical O2 cylinder on my boat but after its contents got used up I found it was a long term lease cylinder of BOCs and they wanted it back.
Anyway the problem with it was it only had a continuous flow output from the pin index reg to feed a face mask.
Since then I have been using a scuba deco cylinder. Problem with that is that I could use only a demand valve 2nd stage off the standard O2 clean DIN reg.
What I needed was a solution that could do both.

I didnt cant to get another medical cylinder as I alread have 2 dedicated O2 scuba cylinders. So what I have done is get a BC inflater hose, a male quick disconnect toi fit it and a barbed fitting to go to a medical O2 mask hose.
1st problem is flow rate. Adjustable would be great but would require a metered needle valve which are quite expensive.
What I needed was a CMF (Constant Mass Flow) orifice also known as a Sonic orifice, leaky valve or in layman's terms a very small hole.

I solder up the inside of the barb fitting and using the smallest drill I had (0.5mm) and even this was too big. But after fiddling around with the soldering iron and a pin I managed to create a very small hole in the solder, which I should point out is lead free solder.

To calculate the flow rate I filled up a bottle with water and inverted it in a bowl of monohydrogen dioxide ( you need to be very careful with this stuff as It kills thousands of people every year). Then feed the hose into it and turned on the tank. It took 10 seconds to blow all the water out of the 1.75L bottle in to the bowl of monohydrogen dioxide. this equates to a flow rate of 10.5 LPM which is what I was after.


So now I can add a LP inflater hose to my deco reg and if I ever need to use a constant flow of O2 I simply plug in the fitting and away it flows!!

That seems a workable solution.. any idea if the solder being soft will result in an increased flow rate anytime soon? Though I guess as you won't be subjecting it to a heavy work cycle (I hope) it will prob be fine.

If you find it doesn't last long then a method I've been recommended would be to drill a hole (say .5mm as you have it) then draw a slightly smaller diameter wire through it and bend it in a loop on both sides to hold it in place. It will result in a possibly more durable alternative.

Ah yeah and when the O2 flows thru the hole it will jiggle the wire around and help dislodge any obstructions that may build up!! ( I read Oxyhackers guide too )


I did think about that but the orifice is right at the end of the barb and the wire would get knocked around a bit when the hose is put on or off.

I dont think the solder will wear down too quick.As I said its lead free solder and its quite a bit harder than standard solder