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On Thu, 2 May 1996, Gerrit Conradie wrote:
> Will somebody please amuse me by giving me some details on how the
> "continuous blending method" for filling a cylinder with nitrox works?
A low pressure O2 line is attached at the intake to your compressor.
Depending on the flow rate through this line you control the %O2 coming
out of the compressor. This is done using a flowmeter. >
I can have my cylinder cleaned, and then just fill it with my own >
compressor without anybody the wiser.
Sure...or you could unscrew the valve on your tank and put oil in it.
Hopefully you wouldn't choose to do either. If you go to the trouble to
get a tank cleaned for O2 you should only fill it from an oil free
compressor. Of course the only person who is really at danger is the one
filling your tank. If I analyze a tank prior to filling it and it doesn't
contain what the tag says it did I require it to be cleaned before I'll
fill it.
> > The way I see a "continuous blending method" is to make a "Y"
split > in the line coming from the air compressor and an O2 cylinder,
where > you can just control the flow of O2 to mix constantly with the air
> from the cylinder. With such a method you'll only need to ensure > that
a certain small part of your system is clean, not the customer's. > Right,
wrong?
Wrong. This method does not allow for the fact that the pressure in the
line changes. if you are filling a tank to 3000psi when the pressure in
the line reaches 2650 or whatever your low pressure O2 cylinder is at you
will begin overfilling and diluting the O2.
Concerning your question about O2 cleaning it isn't too difficult. The
cylinder is VIP'ed then it and the valve are cleaned with an
environmentally safe solvent. After cleaning the cylinder is checked
under a black light for signs of grease or other organic residue. It is
then dried and reassembled using O2 compatible lubricant and O-rings.
All of this is done using powderless latex gloves. This is not rocket
science. It also shouldn't be too expensive. You are essentially paying
for a VIP, cylinder cleaning (and tumble if needed), O2 compatible parts
and lube ( this is expensive stuff-about $40 for a little tube), and a
Nitrox fill when it is done.
Bob Favorite RVT
UC Davis VMTH UC Davis SCUBA The Octopus' Garden
VMD 490 Instructor safety diver safety diver
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