manual addition...old school?

silent running · 17th January 2008, 08:06

Quote: (Originally Posted by Abbo)

The 1st, 2nd and 3rd Golden Rules in rebreathers are 'always know your PO2'. The body can only survive in a narrow PO2 range of 0.16-1.6ATA. Every CCR bar none measures this with a notoriously unreliable piece of ELECTRONICS called a galvanic cell. It doesn't matter whether you use an mCCR or an eCCR, it is the ELECTRONICS that brings you home alive, if at all. Therefore the 'electronics and water don't mix' argument shouldn't on its own cause you to choose mCCRs over eCCRs.

There are 2 main differences between m- and e-CCRs. The first is oxygen injection: with mCCRs, if you forget, you die. Without warning. With e-CCRs, if you forget to keep your PO2 in the safety zone the electronics will attempt to do it for you. I am of the school that thinks an unreliable parachute is better than none at all. Rule 0 says 'trust nothing'. I have a head up display, or HUD, on the bottom right corner of my mask. In your driving test, if you fail to check your rear-view mirror every 8-10 seconds you fail. The same should be true of HUDs and diving tests, because in real life you either do ..or die. Electronics sometimes fail; God knows, so do humans! The price of life is eternal vigilance.

The other difference between e- and m- is the constant flow orifice, which adds O2 at a rate slightly below the rate you metabolise oxygen. This slows the fall in PO2 in the loop. Most e-CCRs don't have these, but they are an important safety feature, and there is no reason you couldn't add one. I've played with the idea of a needle valve like in the Pelagian: this would make sense especially for shallower dives.

Thanks for all the good points Abbo. Yes, a galvanic O2 sensor is indeed a pc of electronics, albiet a very simple one, never thought about it that way. But like the galvanic sensor, I prefer my electronics simple-SP only, less to go wrong, less to worry about.

I too have wondered about putting a needle valve O2 add as backup on my unit. Turns out SMI tried this on an early prototype and nixed it-too many extra variables. Keep it simple, stupid, whether it's E or M, keep it simple. We are not gueniuses and never less so than in a crisis...

Icarusflies · 17th January 2008, 09:02

I ll have to pass in installing an orifice in a eccr....it would be suicidal and I have plans for next year...

decoweenie · 17th January 2008, 09:24

Quote: (Originally Posted by silent running)

...We are not gueniuses...

Or even good spellers...

silent running · 17th January 2008, 16:28

Quote: (Originally Posted by decoweenie)

Or even good spellers...

Argh! I usually don't miss that one, but it was late...

17th January 2008, 08:06	#21 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,832	Re: manual addition...old school? Quote: (Originally Posted by Abbo) The 1st, 2nd and 3rd Golden Rules in rebreathers are 'always know your PO2'. The body can only survive in a narrow PO2 range of 0.16-1.6ATA. Every CCR bar none measures this with a notoriously unreliable piece of ELECTRONICS called a galvanic cell. It doesn't matter whether you use an mCCR or an eCCR, it is the ELECTRONICS that brings you home alive, if at all. Therefore the 'electronics and water don't mix' argument shouldn't on its own cause you to choose mCCRs over eCCRs. There are 2 main differences between m- and e-CCRs. The first is oxygen injection: with mCCRs, if you forget, you die. Without warning. With e-CCRs, if you forget to keep your PO2 in the safety zone the electronics will attempt to do it for you. I am of the school that thinks an unreliable parachute is better than none at all. Rule 0 says 'trust nothing'. I have a head up display, or HUD, on the bottom right corner of my mask. In your driving test, if you fail to check your rear-view mirror every 8-10 seconds you fail. The same should be true of HUDs and diving tests, because in real life you either do ..or die. Electronics sometimes fail; God knows, so do humans! The price of life is eternal vigilance. The other difference between e- and m- is the constant flow orifice, which adds O2 at a rate slightly below the rate you metabolise oxygen. This slows the fall in PO2 in the loop. Most e-CCRs don't have these, but they are an important safety feature, and there is no reason you couldn't add one. I've played with the idea of a needle valve like in the Pelagian: this would make sense especially for shallower dives. Thanks for all the good points Abbo. Yes, a galvanic O2 sensor is indeed a pc of electronics, albiet a very simple one, never thought about it that way. But like the galvanic sensor, I prefer my electronics simple-SP only, less to go wrong, less to worry about. I too have wondered about putting a needle valve O2 add as backup on my unit. Turns out SMI tried this on an early prototype and nixed it-too many extra variables. Keep it simple, stupid, whether it's E or M, keep it simple. We are not gueniuses and never less so than in a crisis...
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17th January 2008, 09:02	#22 (permalink)
Icarusflies New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Feb 2007 Location: Miami Posts: 52	Re: manual addition...old school? I ll have to pass in installing an orifice in a eccr....it would be suicidal and I have plans for next year...
(Online)

17th January 2008, 09:24	#23 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: manual addition...old school? Quote: (Originally Posted by silent running) ...We are not gueniuses... Or even good spellers...
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17th January 2008, 16:28	#24 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,832	Re: manual addition...old school? Quote: (Originally Posted by decoweenie) Or even good spellers... Argh! I usually don't miss that one, but it was late...
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