Oxygen percent drop from 20.9 to 19.9 after I connect the stick to the compressors

[rjack321]

The compressor we use is a 10 cfm Max-Air and it has a pretty good O2 drop at the stick too. Taking an empty AL80 and filling it with the stick connected, then waiting a while and filling the empty tank again, this time with the stick disconnected, there was less than a 30 second difference. So in our case the stick is not effecting the compressors ability to pump air.

At some point I would like to see what the stick pulls on my magnehelic gauge.

I have no idea what a "pretty good" drop is. But there is a vacuum and its not a good thing. Expand the cross-sectional area of your stick and you will reduce the work your compressor has to do thereby extending its life and reducing heat which is not a good thing for oil and compressed gas. There is no good reason to make your compressor suck through a thin straw.

 

[Cave Bum]

Hi All
Yesterday after I connect the nitrox stick to my compressors I observed the Oxygen percent drop from 20.9 to 19.9 even before injecting the Oxygen to the stick and when I stop the compressors the percent go back to normal.

-The Stick location is between the stick and the compressors.
-the calibration don many time and look Ok.

Any one observed same problem or any one know what the problem is.

Thank you
Eisa

The issue here is the pressure. If you turn up the pressure that an O2 sensor sees, say open the valve on a tank pointing at an exposed O2 sensor, the reading is higher. Conversly, the vaccum the sensor sees in the inlet side of a compressor makes it read lower.

The way an O2 sensor works, is that the amount of O2, not the percentage, causes a galvanic reaction in the sensor and the meter, which is just a volt meter, measures resistance. The more the anode and cathode transfer the plating, the higher the resistance until the sensor eventually shorts out and has to be replaced. That's a rough, laymans explanation of the process.

There are a couple of ways to calabrate to accommodate this. I used to just calabrate to (in North Florida with 50% humitity) 20.5 on air then adjust my O2 input to 32% and my banked mix would come out correct. You might have to experiment within a decimal point of two. A more accurate way it to figure the correct offset. Calibrate with pure AIR directly out of the compressor, not out of the air bank, then 'read' the ambient air percent. Figure that offset and subtract it from 20.9 and set your calabration to that WITH THE COMPRESSOR RUNNING. Then adjust your O2 input to 32% (or whatever your mixing).

These procedures were developed whilst I was working in a fill station that mixed and sold 20,000 CF of Nitox a month (Incidently, it was also where the person who developed the Tri-Hunter Mixing stick was working at the time). Good luck! Let me know how it works out! Bruce