hmm, interesting. well, I can tell you that on a Wing Lynch machine, the nitrogen does two things. Primarily the pressure in the tanks works to pump the solutions out and into the processing trough located above. The tanks are sealed up, and a nitrogen blanket is laid down on top of the remaining chemsitry this way. It's really a simple processor in a way, and very trouble-free, because there's no pumps to worry about it--the only moving part is a drive bar--that rotates the tube sets you load your film onto. At any rate, even with a setup like this, using the best nitrogen grade, you get about 2-3 weeks tops for E6 chemistry. One thing they'll recommend, even while using the nitrogen blanket as a selling point--is to "top off" the chemistry weekly with fresh mix. So you pretty much try to turn it over ASAP. My experience has been that after a week, you can start to see things like the color dev starting to darken a bit, and maybe the first dev. turning slightly as well--the sorts of visual indicators of oxidation...we usually try to use it every day, and top it off at least once a week. btw--the way they recommend topping off, is to purge the nitrogen actually as you reseal the tanks--they have these rubber gaskets for a seal. You pump out a bit of chemistry and screw the cap on & seal it up. When the seal is made, the chem runs down the drain...the nitrogen runs into another part of the tank though, along with the heaters & temp probes etc. The whole beast sits there at processing temp round the clock, ready to go.....

KT