Nitrox stick

[tony13]

Hi all,
I'm in the planning process of building my nitrox stick and have a question on the location of the 02 sensor. I have a trimix analyzer. I was thinking of installing a 1/4" hose barb into the stick (where the o2 sensor would normally go) and plugging in my analyzer thru the tubing. I was told that some have installed a small aquarium air pump between the stick and analyzer to eliminate the negative vacuum pressure so the analyzer gets proper flow and I can get a good reading. Is anyone doing this or tried it? I'm trying not to buy another analyzer, so any suggestion are welcome.
Thanks,
Tony

 

[clownfishsydney]

I tried this but it never worked accurately (it would read say 30% but I ended up with 35%). I decided to forgo the in-line sensor. I worked out what percentage I get from each 50 kPa on the oxygen regulator and then dial this up. I get to within 0.5% each time.

 

[Peter_C]

Are you familiar with the Airspeed Press book Oxyhackers Guide? There is some excellent information to be learned from it.

No comment on using the wrong meter for the job, unless you plan to blend trimix? Trying to use an aquarium pump might work though, and I can't think of any reason it wouldn't.

I tried this but it never worked accurately (it would read say 30% but I ended up with 35%). I decided to forgo the in-line sensor. I worked out what percentage I get from each 50 kPa on the oxygen regulator and then dial this up. I get to within 0.5% each time.

There shouldn't be much vacuum at the O2 sensor. For the minor amount of vacuum correction necessary you can start the compressor, and zero the O2 meter. Then if you put 32% in you should get 32% out. I can consistently hit 32% +- .5%.

 

[rjack321]

I tried this but it never worked accurately (it would read say 30% but I ended up with 35%). I decided to forgo the in-line sensor. I worked out what percentage I get from each 50 kPa on the oxygen regulator and then dial this up. I get to within 0.5% each time.

You have way too much vacuum on your stick. Which makes your compressor work much harder and hotter. Too many baffles, too many restrictions or the inlet filter is clogged. To verify, you can "zero" your analyzer to 20.9% in ambient air. Then start the compressor just pumping air, no O2 flow at all. The analyzer should not drop below 20.8%. As is yours would read about 15% pumping ambient air - indicating too much vacuum.

The OP should just get an el cheapo analyzer for $99 and use the right tool for the job. You need 2 analyzers anyway cause sooner or later the sensor will die and then you are stuck until you can get a replacement.

 

[divingtactics]

You have way too much vacuum on your stick. Which makes your compressor work much harder and hotter. Too many baffles, too many restrictions or the inlet filter is clogged. To verify, you can "zero" your analyzer to 20.9% in ambient air. Then start the compressor just pumping air, no O2 flow at all. The analyzer should not drop below 20.8%. As is yours would read about 15% pumping ambient air - indicating too much vacuum.

The OP should just get an el cheapo analyzer for $99 and use the right tool for the job. You need 2 analyzers anyway cause sooner or later the sensor will die and then you are stuck until you can get a replacement.

Spot on with both suggestions, I read this a couple of days ago and thought exactly the same thing on both counts.

@clownfishsydney: Michael, when I first built my two sticks there was too much restriction and I got similar results to yourself, after hooking up the manometer to it, I discovered where the issue was and fixed it. No more problems and accurate on both helium and oxygen now.