Nitrox equipment

[roakey]

MikeFerrara once bubbled...
A mixture of gases will "mix" but it doesn't always happen immediatly.
...
Finally I dropped it on the flor and rolled it around. Yes, I felt silly. I then analyzed it again and measured 80% almost on the nose. I think adding that small amount of air that slow just didn't mix it up.

My theory on this is that the gas in the dip tube and valve body itself is stagnant enough that it doesn’t mix well, and that volume is significant when dropped to ambient pressure.

The first couple times you were getting poorly mixed gas from the dip tube/valve body and rolling it around and then checking a third time gave you a false coorelation with the rolling.

Note that with a doubles manifold you have even more restricted/dead air space.

As I said, this is just my current guess as to what’s happening with these anecdotail “gas layering” stories I hear.

Roak

 

[Genesis]

Blow off just a bit with the valve before you hook up the analyzer. I was shown that "trick" by a guy who's been doing it for a LONG time and he explained that when you top the tank the last bit of the last gas you use is in the valve and dip tube, and there's very little if any mixing that goes on there. The orifice flows so little that it'll take a LONG time before that is cleared out if you just hook it up.

 

[MikeFerrara]

That makes sense but thats the only time I ever had that happen so I never never got a chance to fool with it

 

[Uncle Pug]

And if this is stupid slap me....

Regarding gas mixing spontaneously and homogenously with in the tank:

Here is an experiment that will help you get a handle on how fast it does... even in the confines of the valve and dip tube.

Analyze some nitrox and then unhook the tube from the source but leave it connected to the sensor and watch the analyzer.

I am amazed at how fast it happens!

 

[Jarhead]

own an analyzer yet, but I use the shop's everytime I pickup a nitrox fill (rental).

Jarhead

 

[The Chairman]

Another experiment to demonstrate how temp effects readings...
Turn on your analyzer and set to 20% then hold the sensor in your hot little hand and watch the reading

 

[raviepoo]

 

[Atticus]

I purchased my analyzer for a bit under $200.

I use the shops analyzer when I pick up the tank, then my analyzer when I hook the tank up to my regulator. I have a couple of reasons for this -

a) I don't like carrying my analyzer around in the shop / setting it on the counter with everyone elses stuff / etc

b) I like seeing two different analyzers give me the same reading

c) I really like analyzing the tank just as I hook it up just in case I did something stupid or dyslexic when I picked the tanks up

My 2 cents...

--Atticus

 

[SLJ]

I do own my own but it's not really necessary. Almost any dive shop that does nitrox fills will let you use their analyzer. For calibration, just use air and a chart for humidity and temp.
SLJ