Ean 18 ???

[rjack321]

I'm not really familiar with how these analyzers work, but could it be that they detect an offset in the oxygen %, and then add that to the calibrated 0 ( In this case 21%) ? If so it could be that the tank contains 24% and not 18%. Try it with a different analyzer and see what yo get.

Also try a tank known to be 36, and see if it winds up being 6%. (21%-15%) If so the logic in your analyzer is reversed?

They are basically voltmeters on a reconfigured scale. The sensor is a weak battery which puts out more voltage at higher ppO2. You can get them to read high by shifting either the O2 content with nitrox or the pressure by running too high a flow past it.

When they go bad the battery is basically too weak to calibrate and they will read <20.9% at their max adjustment. Since this sensor will read 21% in ambient air, the sensor is fine. There's some fraction of "other" in that tank. He, Ar, its hard to know.

You could try a helium analyzer, but they don't actually read helium. They sense differences in thermal conductivity which are presumed to be due to helium since you know that it was put in there. However, since you have no idea what was pumped, you cannot presume anything here. For all you know there's % quantities of CO2 or argon, God knows what in there.

Since the shop obviously did something weird have them drain it and VIP it (for free IMO).

 

[Thalassamania]

Sounds like some oxidation has happened. Viz time.

Viz is a good idea, but I don’t think so, do the Stoichiometry

 

[DandyDon]

Viz is a good idea, but I don’t think so, do the Stoichiometry

Approx 21% O2 went in, now he has about 18%. Approx 14% of the 21% is not O2 anymore...??

 

[Thalassamania]

Approx 21% O2 went in, now he has about 18%. Approx 14% of the 21% is not O2 anymore...??

That’s a start, now how much aluminum oxide would have to be produced to drop the O₂ from 21% to 18%?

 

[DandyDon]

That’s a start, now how much aluminum oxide would have to be produced to drop the O₂ from 21% to 18%?

Yak, was it a steel or aluminum tank?

And you said "from a shop that only fills air" - did you have scuba air not cleaned to Nitrox standards added to a O2 cleaned tank...?

 

[Rick Murchison]

... face it most tri-mix is hypoxic ...

There ye go showin' your age again! These days there's a whole crowd burnin' 30/30 all day every day
Rick

 

[Rick Murchison]

That’s a start, now how much aluminum oxide would have to be produced to drop the O₂ from 21% to 18%?

Too much.
Something's not right.
Drain the tank and inspect it.
Rick

 

[DandyDon]

Even if the actual content was 19%, that's still a 10% change in O2 - or more since he had some Nitrox in there and topped it off. Drain & Viz.

 

[Thalassamania]

There ye go showin' your age again! These days there's a whole crowd burnin' 30/30 all day every day
Rick

Divin' it? Really? I thought they said theY were filling [SIZE=-1]DIRigiables[/SIZE].

 

[yak]

It's a steel tank. I'm going to visit the nitrox shop today to first see what their analyzer reads, then drain & viz (unless theirs reads fine, which would indicate a problem with my analyzer).