Passive Scr Superiority?

silent running · 20th October 2006, 07:32

Quote: (Originally Posted by silent running)

And what about at high RMVs on the XCR? Does the bellows have more resistance the harder you breathe?

Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy

robertfondren · 20th October 2006, 09:28

The dc55 seems to be a beautiful design. I would love to get my hands on one or 3 of those. If it comes down to mechanical vs. electronics under pressure... callibrate your gut feeling with your brain.

Marc T · 20th October 2006, 12:25

Quote: (Originally Posted by silent running)

Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy

Yes I think so and its perhaps a reason why the DC55 is more confortable ( ratio 1/12 ), the less you eject gaz through the exhaust valve the lower the WOB is, all other thing being equal.
When you turn the pSCR into mCCR the WOB is instantly far better because no more gas exhaust during each inhale and the small CL is "open" so exhale resistance when gas enter in it.
Hope Im clear enough regarding to my english

**trob09** · 20th October 2006, 12:41

Quote: (Originally Posted by O.C.Diver)

You certainly have a valid point regarding the difference in average dive risk when comparing different types of units.

My point was to say that if a manufacturer produces 50 rebreathers and 1 user dies on his unit, the fatality rate is 2%. This wouldn't be considered a very safe unit. If we then learn that each unit has an average of 2,000 dives on it (1 death per 100,000 dives), the unit starts to look safer. Finally, we learn that the one death was the result of the user being attacked by a shark, the death becomes pretty meaningless as it relates to the rebreather. My point was that units that have 1 or 2 deaths associated with them probably can not accurately be judged due to such a small sample.

Ted

Thanks for the clarification Ted. I agree 100% that the available data is meaningless in terms of determining if one unit is safer than another. Statistical modeling is part of what I do for a living so I get a little jumpy when people start making claims on insufficient data. Sorry if I jumped down your throat.

Aircraft has been mentioned previously as a model for how we approach understanding diving accidents. I suggest automobiles may be more appropriate. We know that the driver is the primary cause of auto accidents and that equipment is rarely to blame. The only recent case I can think of is the Ford/Firestone fiasco of a few years ago. Much has been done to make auto accidents more survivable for the driver without taking away the freedom and decision processes of the driver. This is a result of careful study of the causes of accidents.

This is a model I would hope we pursue - how to make accidents more survivable - rather than pursuing a sense of smug, self-satisfaction that "mine is better than yours" (note that I am not suggesting that you are saying this).

anyway, I'll shut up now.

Tim

silent running · 20th October 2006, 18:21

Quote: (Originally Posted by Marc T)

Yes I think so and its perhaps a reason why the DC55 is more confortable ( ratio 1/12 ), the less you eject gaz through the exhaust valve the lower the WOB is, all other thing being equal.
When you turn the pSCR into mCCR the WOB is instantly far better because no more gas exhaust during each inhale and the small CL is "open" so exhale resistance when gas enter in it.
Hope Im clear enough regarding to my english

Thanks for the info and CCR conversion comparison Marc, I undertsand now. -Andy

gtzavelas · 20th October 2006, 18:25

Quote: (Originally Posted by wookey)

not forget to mention, that it is with a twin pscr using the same inner construction than the dc55 that Sylvain Redoutey did his amazing exploration of the Goul de la Tannerie (1200m penetration -209m deep and 21hours long dive) !

very interesting
any info in engish available on the net? all i can find is in french....

wookey · 20th October 2006, 20:36

perhaps on the cdg (cave diving group) newsletter issue of april 2004?

db8us · 24th October 2006, 15:56

Quote: (Originally Posted by silent running)

Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy

You need exactly 10mbar to open the OP on the bellow on high workloads if you "overbreathe" the unit. Then you use more gas, but this is not an error it is intended to work that way, because you then also produce lots of CO2.

In general high RMV are easy to manage, but we avoid them for deco reasons etc.
And: Why work hard, if you just can cruise along with your scooter :-)
Swimming past 100m is stupid anyay.

Michael

20th October 2006, 07:32	#101 (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: 1,813	Re: Passive Scr Superiority? Quote: (Originally Posted by silent running) And what about at high RMVs on the XCR? Does the bellows have more resistance the harder you breathe? Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy
(Online)

20th October 2006, 09:28	#102 (permalink)
robertfondren New Member Current Rebreather/s: Ray Other Rebreather/s: Not Bought Yet Ray Join Date: Mar 2006 Location: u.s.a. Posts: 74	Re: Passive Scr Superiority? The dc55 seems to be a beautiful design. I would love to get my hands on one or 3 of those. If it comes down to mechanical vs. electronics under pressure... callibrate your gut feeling with your brain.
(Offline)

20th October 2006, 12:25	#103 (permalink)
Marc T hell is in the details Current Rebreather/s: RB80 / Clone Home Build Other Rebreather/s: Not Bought Yet RB80 / Clone Home Build Join Date: Sep 2005 Location: FRANCE Carcassonne Posts: 470	Re: Passive Scr Superiority? Quote: (Originally Posted by silent running) Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy Yes I think so and its perhaps a reason why the DC55 is more confortable ( ratio 1/12 ), the less you eject gaz through the exhaust valve the lower the WOB is, all other thing being equal. When you turn the pSCR into mCCR the WOB is instantly far better because no more gas exhaust during each inhale and the small CL is "open" so exhale resistance when gas enter in it. Hope Im clear enough regarding to my english
(Online)

20th October 2006, 12:41	#104 (permalink)
trob09 . Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Posts: 698	Re: Passive Scr Superiority? Quote: (Originally Posted by O.C.Diver) You certainly have a valid point regarding the difference in average dive risk when comparing different types of units. My point was to say that if a manufacturer produces 50 rebreathers and 1 user dies on his unit, the fatality rate is 2%. This wouldn't be considered a very safe unit. If we then learn that each unit has an average of 2,000 dives on it (1 death per 100,000 dives), the unit starts to look safer. Finally, we learn that the one death was the result of the user being attacked by a shark, the death becomes pretty meaningless as it relates to the rebreather. My point was that units that have 1 or 2 deaths associated with them probably can not accurately be judged due to such a small sample. Ted Thanks for the clarification Ted. I agree 100% that the available data is meaningless in terms of determining if one unit is safer than another. Statistical modeling is part of what I do for a living so I get a little jumpy when people start making claims on insufficient data. Sorry if I jumped down your throat. Aircraft has been mentioned previously as a model for how we approach understanding diving accidents. I suggest automobiles may be more appropriate. We know that the driver is the primary cause of auto accidents and that equipment is rarely to blame. The only recent case I can think of is the Ford/Firestone fiasco of a few years ago. Much has been done to make auto accidents more survivable for the driver without taking away the freedom and decision processes of the driver. This is a result of careful study of the causes of accidents. This is a model I would hope we pursue - how to make accidents more survivable - rather than pursuing a sense of smug, self-satisfaction that "mine is better than yours" (note that I am not suggesting that you are saying this). anyway, I'll shut up now. Tim Last edited by trob09 : 20th October 2006 at 12:56. Reason: I still can't spell
(Offline)

20th October 2006, 18:21	#105 (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: 1,813	Re: Passive Scr Superiority? Quote: (Originally Posted by Marc T) Yes I think so and its perhaps a reason why the DC55 is more confortable ( ratio 1/12 ), the less you eject gaz through the exhaust valve the lower the WOB is, all other thing being equal. When you turn the pSCR into mCCR the WOB is instantly far better because no more gas exhaust during each inhale and the small CL is "open" so exhale resistance when gas enter in it. Hope Im clear enough regarding to my english Thanks for the info and CCR conversion comparison Marc, I undertsand now. -Andy
(Online)

20th October 2006, 18:25	#106 (permalink)
gtzavelas Rebreather World Writer Current Rebreather/s: Megalodon RB80 / Clone Other Rebreather/s: RB80 / Clone Join Date: Jan 2006 Location: Athens,Greece Posts: 247	Re: Passive Scr Superiority? Quote: (Originally Posted by wookey) not forget to mention, that it is with a twin pscr using the same inner construction than the dc55 that Sylvain Redoutey did his amazing exploration of the Goul de la Tannerie (1200m penetration -209m deep and 21hours long dive) ! very interesting any info in engish available on the net? all i can find is in french....
(Offline)

20th October 2006, 20:36	#107 (permalink)
wookey New Member Current Rebreather/s: Sport Kiss Other CCR Other SCR Home Build Other Rebreather/s: Other CCR Other SCR Home Build Join Date: Nov 2005 Location: switzerland Posts: 65	Re: Passive Scr Superiority? perhaps on the cdg (cave diving group) newsletter issue of april 2004?
(Offline)

24th October 2006, 15:56	#108 (permalink)
db8us Custom Title Allowed! Current Rebreather/s: Other SCR Other Rebreather/s: Other SCR Join Date: Sep 2005 Location: Germany Posts: 225	Re: Passive Scr Superiority? Quote: (Originally Posted by silent running) Still wondering about this. Do higher RMVs on a RMVK SCR have a big increase in WOB due to the bellows resistance? Anybody? Thanks, -Andy You need exactly 10mbar to open the OP on the bellow on high workloads if you "overbreathe" the unit. Then you use more gas, but this is not an error it is intended to work that way, because you then also produce lots of CO2. In general high RMV are easy to manage, but we avoid them for deco reasons etc. And: Why work hard, if you just can cruise along with your scooter :-) Swimming past 100m is stupid anyay. Michael
(Offline)

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