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"George P. Wentland" wrote:
> This is not a quote from me. ("I can understand that someone doesnt want to
> do the more dangerous Nitrox fills, but with Trimix..."). I never so much as
> mentioned nitrox in my post. However, from a filling point of view, this
> statement is correct. When filling nitrox, by partial pressure blending, you
> are generally dealing with higher O2 pressures than with trimix. Higher O2
> pressures equate to more dangerous.
To clear things up, this statement is from me. It refers to the fact that you
CAN mix trimix without having to worry about oyxgen hazards at all.
The drawback to this was that you can start mixing your own trimix without
first buying expensive equipment. What you need is:
* An analyzer (any nitrox/trimix should have one)
* A precicion gauge
* A transfilling whip (if you want to do "real" trimix rather than heli-air)
* Access to a compressor
* And of course a helium cylinder :-)
Filling goes like that:
* Transill EAN32 or any low fO2 Nitrox to the trimix cylinder
* Blow helium on top of it
* Top with air as required
* Analyze
You can buy the requried nitrox in a shop and use your stages to carry it
home. Connect the helium cylinder with an apropirate hose to a plastic
bag and the bag with the air intake hose of the compressor. Seal all with
tape. While filling you will have to regulate the helium flow with the cylinder
valve to match the demand of the compressor. The bag will serve as buffer.
Of course having a modified regulator would be a nicer solution. We fill the
helium to a preassure that is 10% higher as calculated. This compensates
the different helium compressibility. Eg. for 3000psi of 16/46 this would
mean transfill 1260 psi EAN32, add 1390 + 0.1*(1260+1390) psi of
helium (= 2915psi fill pressure) and than top with air to ~3300psi. The end
pressure is compressor dependent due to the generated heat. I might note
that one might want to account for the air in the compressor and filtering
system (ie. it takes some time for the helium to get thru the compressor).
If you want to do heli-air just skip the first step.
Doing it that way you dont need to have an expensive hyper filter,
check valves at the filling whips, any exotic high preassure connection
(ie. from the helium cylinder). Not to mention that you dont have to worry
about oxygen service.
Nevertheless sooner or later you will end up with a full blown home
mixing station anyway :-)
Regards,
Frank
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