Cells....

netmage

So .6 positive pressure = 8.82psi or 247lbs... hmm, still quite a bit...
Guess thats why the narked@90 pot is threaded and a much smaller surface area...

O.C.Diver

That's still 250 pounds of force trying to blow your lid latches.

Ted

oops, you got here before me.

__________________
Consider this my opinion.......sometimes I'm even right, but remember.........YMMV.

Ted Green
Charter Boat "OC Diver"
http://www.ocdiver.com

barney

Burning the cells in with O2 for 24 hours before installation is definitely a good idea and should be standard practice.

You also need to watch the cells during the dive, and not just on calibration. We recently went through a few cells that calibrated fine, but eventually (within 1 month) went a little squirelly. I had one that would continually and consistently climb (PO2) with no addition of ANY gas (everything shut down) and would be 1.8+ while the other cells were around 1.0. At one point I saw the mV of this cell at 88. After the dive and drying out, it would again calibrate fine, but then would consistently go AWOL during the course of the dive. Curiously enough, when put in a cell checker the tech could not get anything above 12 mV regardless of PO2. This cell was only about 6 weeks old.

Another cell started reading just a hair off, but checking the mV I saw it was reading less than 30 mV at 1.6 PO2. I kept watching it as an experiment and it steadily got worse and more unpredictable before I finally binned it. This cell had been sealed only 3 weeks earlier.

The point I am trying to make is that you should not just trust your calibration nor assume a new cell has ~12 months of service. During your dive, scroll through your menu to SYSTEM MONITOR and crosscheck your mV to your PO2.

The bottom line is never-ever-ever-ever blindly trust those fuqing O2 cells!

__________________
Michael C. Barnette
ASSOCIATION OF UNDERWATER EXPLORERS

Joe

The weak link in the Rebreather technology is the cells. IMHO, the most important thing for any Rebreather diver to understand is how the cells work and their failure points.

You need to check your cells during your dive and you need to check the cell linearity ideally before every dive but at least periodically. I'll not get into the debate over how to do it but on the Meg you can do it by pressurizing the inner chamber with 2 - 3 psig of pure O2 and reading your ppO2 on the handsets.
The down side to this is that you are putting pressure against the membrane face of the sensor and risk rupturing it since they were not designed to take pressure against the face. OTOH, 2 lbs. is not much pressure.....YMMV

As others have stated. 9 - 12 mv in air is normal and 40's to 50's in pure O2 is also normal. I recently had a cell that would calibrate fine and gave the correct mv's in air and in O2 and tested fine for linearity. It would go erratic mid dive and stay that way until it dried out the next day. Then it would test good again. Dive Rite Express replaced it *even though it tested good*, sent it back to the manufacturer and sure enough, per the manufacturer there was a problem with it. Kudos to Mark for that.

Mikes point is well taken here. Cell issues are the most dangerous aspect of Rebreather diving and the most likley thing to "get" you.