Scuba Duck
Contributor
It's a good idea to completely bleed down the system from the compressor to the fill whips. This way there is no air in the filters and lines to dilute your nitrox mix. This will reduce your purge time and the amount of oxygen that is unusable.
It also helps to fill multiple Nitrox tanks at one time, that way you waste less bottled oxygen associated with purging the system, or left over in your filter towers and lines when you are done.
200+ cuft of air in your filter towers seems excessive. Remember that there is filter medium in those towers that takes up space too, its not all void space. Its hard to believe that your filter towers have more volume that two 80 cuft tanks.
Also keep in mind that moisture in the air throws off the process a little. Moisture in the air displaces nitrogen and oxygen, meaning that you have less than 20.9% oxygen in humid air. This matters because you are analyzing wet air at the inlet to the compressor but have dry air at the outlet. The more humid the air, the greater the error will be at the outlet of the compressor. The root of this error is the fact that you are mixing dry oxygen with moist air.
Check out this spreadsheet. If you can determine the relative humidity and temperature, you can calibrate your oxygen sensor at the inlet side of your mixing stick so that you will get a closer mix at the outlet of the compressor. In all likelyhood, you'll want to calibrate your inlet oxygen analyzer to indicate 20.7% to 20.8% depending on the amount of humidity. You can purchase cheap clock/temp/humidity meters from fisher scientific.
http://www.rubberduckiedesigns.com/Documents/Nitrox%20Controller%20Downloads/Humidity%20Spreadsheet.xls
Good luck with the home built stick.
It also helps to fill multiple Nitrox tanks at one time, that way you waste less bottled oxygen associated with purging the system, or left over in your filter towers and lines when you are done.
200+ cuft of air in your filter towers seems excessive. Remember that there is filter medium in those towers that takes up space too, its not all void space. Its hard to believe that your filter towers have more volume that two 80 cuft tanks.
Also keep in mind that moisture in the air throws off the process a little. Moisture in the air displaces nitrogen and oxygen, meaning that you have less than 20.9% oxygen in humid air. This matters because you are analyzing wet air at the inlet to the compressor but have dry air at the outlet. The more humid the air, the greater the error will be at the outlet of the compressor. The root of this error is the fact that you are mixing dry oxygen with moist air.
Check out this spreadsheet. If you can determine the relative humidity and temperature, you can calibrate your oxygen sensor at the inlet side of your mixing stick so that you will get a closer mix at the outlet of the compressor. In all likelyhood, you'll want to calibrate your inlet oxygen analyzer to indicate 20.7% to 20.8% depending on the amount of humidity. You can purchase cheap clock/temp/humidity meters from fisher scientific.
http://www.rubberduckiedesigns.com/Documents/Nitrox%20Controller%20Downloads/Humidity%20Spreadsheet.xls
Good luck with the home built stick.
