MCCR two or three oxygen cells ?

Joseph Grech

Would you feel safe to dive Manual Closed Circuit with just two oxygen cells ?

Joseph

GKAM

I see no real reason not to.

You can check the 2 displays side by side during the dive. If they do not agree, do a loop flush with diluent. Check the reading against the expected ppO2. It is always a good idea to have such a table handy (in addition to bailout tables ) to avoid doing calculations under stress.

If one cell is still off, you then run the loop as SCR or bail out. This is how I dive my unit. I think that Kerry once wrote a very good article on why 3 sensors are overkill in mCCR. Look around his site for it.


GKAM

Ken

What's the URL for Kerry's site? Thanks.

Crazyduck

http://www.vk4tub.org/tubby/pagedex.html


Here you go Ken.

Regards, Andrew

Ken

Thank you Andrew. Ken

dave t

The idea of three cells in a ECCR is voting logic, I dont see any difference in a manual CCR just the computer between your ears does the voting logic!

AD_ward9

FYI: the probability of two galvanic cells going down with a ceiling fault during a single dive is 85K hours. Replace them at the same time from the same batch, then 5.6K hours. With a ceiling fault, your ears are going to have to be pretty good at integration if you are going to come out alive.

Why are people using galvanic sensors anyway? Because they exist, are easy, do not involve change. Sol-gel and opto sensors are available and are the future. They are already in use in medical O2 and CO2 applications.

In a few years time, the O2 and CO2 sensor will be printed onto the scrubber cartridge. Throw away. Just like on food packaging. I have put a post on this onto the Open Revolution area, with links showing the technologies working.

Alex

decoweenie

I agree!

With 3 cells, you do voting logic with your head. And you have redundancy. If one fails, you still have 2 and could continue the dive with confidence (if you had/wish to).

With 2 cells, you could do diluent flush to figure which one is good, but would you continue the dive or stay on the loop with 1 cell ? If yes, then how would you then know the single remaining cell will still be good in the next 5 minutes since you now have no frame-of-reference ? Or will you continuously do diluent flushes to check ?

Just IMHO...

__________________
"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM

dave t

I have had two cells fail at the same time and they were only one week old. I have also had two cells fail by fairly small amounts, enough to make me wonder which one is right, they were a month old. I have also had three cells run in perfect harmony and perfect acuaracy (as well as can be measured) for over two years.

bottom Line, who knows what they are gonna do )

GKAM

Yeah guys, I think we all agree that 3 is better than 2.

However, I feel that all Rebreather dives should be run in such way that one is able to bail out at any point during the dive and make it safe back to the surface. Even with total loop failure. So, I do not dive alpinist.

OK, 3 cells give you redundancy, and you can still complete the dive if one fails. I give you that. But I see no harm in just going to SCR mode or bailing to OC if one of the two fails, or even if both cells fail.

Then again, it depends on the type of diving one does. I do not dive overhead environment nor do I do extreme depth/time exposures (yet ) It is all about personal choice (unless you guys are all DIR fanatics and want to assimilate us all )


GKAM