Paul C’s Inspo with back-mounted lungs.

Mikel-Deko · 8th May 2007, 18:53

Hum, Hum, interesting modification...

Do you know how much weight have you put away?

Sorry about my English but i don't undestand very well way affects so much to the WOB? And why change so much with this modification?

Thanks

Mikel

PD: waiting for my kit

AD_ward9 · 8th May 2007, 19:47

Quote: (Originally Posted by Mikel-Deko)

Do you know how much weight have you put away?

Sorry about my English but i don't undestand very well way affects so much to the WOB? And why change so much with this modification?
Thanks
Mikel
PD: waiting for my kit

It certainly got lighter!

It affects the WOB because the breathing bags have to expand and contract. If the counterlungs are in a tube, it has to push the water out of the tube. That means as well as pumping gas around the loop, your lungs have to pump water up and down. Bottom line is the effect of pumping water up and down is the same as having a very big hydrostatic imbalance.
In the original version, a large part of the CL is equivalent to being in the tube.

There is also an effect that the counterlungs are not completely smooth in the folded SS tube, but that is another story.

Alex

colinicky · 8th May 2007, 21:02

But if you only ever use minimum loop volume then the cl bags in the frame do not need to expand anyway

the wob will come from having to suck the air from the "bottom " of the cl's when in a slightly head down position ,but then that's easily cured as well ,as you say though " thats another story "

AD_ward9 · 9th May 2007, 05:51

Quote: (Originally Posted by colinicky)

But if you only ever use minimum loop volume then the cl bags in the frame do not need to expand anyway

the wob will come from having to suck the air from the "bottom " of the cl's when in a slightly head down position ,but then that's easily cured as well ,as you say though " thats another story "

Sorry, please excuse me if I am getting slow, but is it possible to fill me in on the trick of how to breathe without the CLs expanding and contracting?

Alex

decoweenie · 9th May 2007, 06:43

Quote: (Originally Posted by AD_ward9)

...is it possible to fill me in on the trick of how to breathe without the CLs expanding and contracting?

If you read Colin's post again, he did say how (partially)...

AD_ward9 · 9th May 2007, 09:46

Quote: (Originally Posted by decoweenie)

If you read Colin's post again, he did say how (partially)...

Unless I missed a trick or two, they still need to expand and contract. If the tidal volume is very low, the outer bag may not appear to move, but the inner bag is moving and forcing water through the holes in the outer bag and then sucking it back in again. The water then has to displace water up and down the water column in the SS "tubes".

There is a WOB in Colin's post due to the hydrostatic pressure, but the amount is not substantial. I attach a diagram below showing the numbers and also a table showing the comparable ideal numbers for the other common CLs configurations with respect to the lung centroid as per NORSOK U-101.

Alex

NB: Ignore the canister shape below - I took the table from some of the O.R. compliance documents. The canister is rigid so does not affect the hydrostatic imbalance. Paul's BCMLs are not curved as shown here, but their centroid is in about the same place.

decoweenie · 9th May 2007, 10:26

Quote: (Originally Posted by AD_ward9)

...they still need to expand and contract...

Without the fancy illustrations, all I could say is the bottom section of the unmodified DT BMCL doesn't expand and contract with each breath.

And was the point that Colin was making, I believe.

AD_ward9 · 9th May 2007, 11:23

Quote: (Originally Posted by decoweenie)

Without the fancy illustrations, all I could say is the bottom section of the unmodified DT BMCL doesn't expand and contract with each breath.

And was the point that Colin was making, I believe.

Thanks for clarifying. Colin is correct. The resistance is high so on small tidal volumes the top of the CL that is not in the tube moves in and out but the bottom does not. On larger tidal volumes, the whole counterlung has to move in and out.

Colin's point would mean that with a very low tidal volume, no-one would notice the increase in WOB with the BMCL, but when a large tidal volume was needed then the increase in WOB would be considerable.

Cheers,

Alex

decoweenie · 9th May 2007, 11:42

If you are talking about the increase from forcing water out of the tube, then you need to qualify your statement so since there is, at least, one other BMCL system doesn't have that issue.

If you are talking about hydrostatic pressure, then I am still not convinced since I have dived a lot of different BMCL systems and don't notice that issue qualitatively.

.

colinicky · 9th May 2007, 12:28

Basically Phi has covered it ,Alex all I can say is that with the bmcl as I have them set up I do not have extra metal work & I can draw 1 full breath at the surface with the wing & drysuit fully inflated ,with everything deflated I get about 1 1/2 full breaths .

8th May 2007, 18:53	#181 (permalink)
Mikel-Deko RBW Member Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Other CCR Join Date: Jul 2005 Location: Basque Country -Sp- Posts: 470	Re: Paul C’s Inspo with back-mounted lungs. Hum, Hum, interesting modification... Do you know how much weight have you put away? Sorry about my English but i don't undestand very well way affects so much to the WOB? And why change so much with this modification? Thanks Mikel PD: waiting for my kit __________________ Mikel-Deko Basque Country www.olatu.net "DIR is the nanny state for divers who cannot think on their own" Ron Micjan
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8th May 2007, 19:47	#182 (permalink)
AD_ward9 - Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,004	Re: Paul C’s Inspo with back-mounted lungs. Quote: (Originally Posted by Mikel-Deko) Do you know how much weight have you put away? Sorry about my English but i don't undestand very well way affects so much to the WOB? And why change so much with this modification? Thanks Mikel PD: waiting for my kit It certainly got lighter! It affects the WOB because the breathing bags have to expand and contract. If the counterlungs are in a tube, it has to push the water out of the tube. That means as well as pumping gas around the loop, your lungs have to pump water up and down. Bottom line is the effect of pumping water up and down is the same as having a very big hydrostatic imbalance. In the original version, a large part of the CL is equivalent to being in the tube. There is also an effect that the counterlungs are not completely smooth in the folded SS tube, but that is another story. Alex
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8th May 2007, 21:02	#183 (permalink)
colinicky RBW Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Join Date: Mar 2005 Location: uk Posts: 678	Re: Paul C’s Inspo with back-mounted lungs. But if you only ever use minimum loop volume then the cl bags in the frame do not need to expand anyway the wob will come from having to suck the air from the "bottom " of the cl's when in a slightly head down position ,but then that's easily cured as well ,as you say though " thats another story " __________________ Colin I trust my rebreather completely , I just don't trust the user onwards & downwards
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9th May 2007, 05:51	#184 (permalink)
AD_ward9 - Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,004	Re: Paul C’s Inspo with back-mounted lungs. Quote: (Originally Posted by colinicky) But if you only ever use minimum loop volume then the cl bags in the frame do not need to expand anyway the wob will come from having to suck the air from the "bottom " of the cl's when in a slightly head down position ,but then that's easily cured as well ,as you say though " thats another story " Sorry, please excuse me if I am getting slow, but is it possible to fill me in on the trick of how to breathe without the CLs expanding and contracting? Alex Last edited by AD_ward9 : 9th May 2007 at 06:05. Reason: The hydrostatic issues can keep for another time.
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9th May 2007, 06:43	#185 (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: Paul C’s Inspo with back-mounted lungs. Quote: (Originally Posted by AD_ward9) ...is it possible to fill me in on the trick of how to breathe without the CLs expanding and contracting? If you read Colin's post again, he did say how (partially)... __________________ "...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
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9th May 2007, 10:26	#187 (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: Paul C’s Inspo with back-mounted lungs. Quote: (Originally Posted by AD_ward9) ...they still need to expand and contract... Without the fancy illustrations, all I could say is the bottom section of the unmodified DT BMCL doesn't expand and contract with each breath. And was the point that Colin was making, I believe. __________________ "...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
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9th May 2007, 11:23	#188 (permalink)
AD_ward9 - Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,004	Re: Paul C’s Inspo with back-mounted lungs. Quote: (Originally Posted by decoweenie) Without the fancy illustrations, all I could say is the bottom section of the unmodified DT BMCL doesn't expand and contract with each breath. And was the point that Colin was making, I believe. Thanks for clarifying. Colin is correct. The resistance is high so on small tidal volumes the top of the CL that is not in the tube moves in and out but the bottom does not. On larger tidal volumes, the whole counterlung has to move in and out. Colin's point would mean that with a very low tidal volume, no-one would notice the increase in WOB with the BMCL, but when a large tidal volume was needed then the increase in WOB would be considerable. Cheers, Alex
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9th May 2007, 11:42	#189 (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: Paul C’s Inspo with back-mounted lungs. If you are talking about the increase from forcing water out of the tube, then you need to qualify your statement so since there is, at least, one other BMCL system doesn't have that issue. If you are talking about hydrostatic pressure, then I am still not convinced since I have dived a lot of different BMCL systems and don't notice that issue qualitatively. . __________________ "...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 Last edited by decoweenie : 9th May 2007 at 12:37.
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9th May 2007, 12:28	#190 (permalink)
colinicky RBW Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Join Date: Mar 2005 Location: uk Posts: 678	Re: Paul C’s Inspo with back-mounted lungs. Basically Phi has covered it ,Alex all I can say is that with the bmcl as I have them set up I do not have extra metal work & I can draw 1 full breath at the surface with the wing & drysuit fully inflated ,with everything deflated I get about 1 1/2 full breaths . __________________ Colin I trust my rebreather completely , I just don't trust the user onwards & downwards
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