RB80 course - Page 3

*JGrogan* · October 23rd, 2007, 03:31 PM

With the RB80 and its' clones, the volume of the counter-lungs is less than the volume of your own lungs. On the inhale cycle, the counter-lung compresses, the dump-lung dumps gas and when the counter-lung is empty, the regs fire to add more gas until you stop inhaling. The marginal increase of your stomach expanding outwards as you breathe in fully is less than the displacement of the counter-lung.

Quote: (Originally Posted by David Martin)

Really? The rest of the body is pretty incompressible and the gas in the lungs is pretty much at ambient pressure, so I would expect that the increase in lung volume and thus the increase in total body displacement to be virtually identical to the volume of gas breathed in at ambient from the counter lung. (With any variation being essentially unmeasureable.)

This would seem to reflect what you're saying, could this be the only reason?

David

tim · October 23rd, 2007, 04:24 PM

Thanks for the explanations. I'm still slightly baffled by the breathing-in side of things in terms of changing volume by moving gas - I don't get where the gas goes when you breathe in unless space in your body was at less than ambient pressure or you compress the gas as you breathe it. Both seem a bit improbable given body rigidity or lack of. I think I'm with David thus far in preferring to put the 'blame' on the gas dumped during the breath, which I didn't know about but makes a lot of sense in terms of becoming more negative.

Just curiosity, I have no aspirations to dive an RB but they look interesting in terms of mechanics

Tim

Retardboy · October 23rd, 2007, 10:27 PM

Quote: (Originally Posted by graham_hk)

But the gas is going into a space in your body and thus not causing any more displacement. I would agree but I have seen it in other RBs too where no gas is dumped on inhalation.

But the gas going into a space in your body needs space...In order to fill your lungs with gas without increasing the displacement of your torso, you would have to actually compress the gas in your lungs. I find it hard to see how that can be done.. If you are in a slightly head up position, and your lungs and the CL are at the same level (pressure), the total displacement should be the same...exept from the gas dumped by the inner CL.
For CCR, the only explanation I can see is that the CL is slightly above the divers lungs. That results in a very small difference in the pressure on CL`s and lungs, thus reducing the volume of the mass of gas transfered to the lungs.. Disagree?Shoot

*graham_hk* · October 24th, 2007, 01:52 AM

Quote: (Originally Posted by Retardboy)

But the gas going into a space in your body needs space...In order to fill your lungs with gas without increasing the displacement of your torso, you would have to actually compress the gas in your lungs. I find it hard to see how that can be done.. If you are in a slightly head up position, and your lungs and the CL are at the same level (pressure), the total displacement should be the same...exept from the gas dumped by the inner CL.
For CCR, the only explanation I can see is that the CL is slightly above the divers lungs. That results in a very small difference in the pressure on CL`s and lungs, thus reducing the volume of the mass of gas transfered to the lungs.. Disagree?Shoot

The only way to check this is to breath in in the bath and measure how much more you displace with inflated lungs. Then breath out into an RB and measure the displacement. My hypothesis is you displace more when you breath in since you are filling empty space in your chest. Any one bored enough to try it?

**GLOC** · October 24th, 2007, 07:46 AM

Quote: (Originally Posted by graham_hk)

....Any one bored enough to try it?

Joe or Igor?

*graham_hk* · October 24th, 2007, 10:47 AM

Quote: (Originally Posted by GLOC)

Joe or Igor?

ha ha

Incidently I can provide some photos if you wanna put this in the library

Joe Hesketh · October 24th, 2007, 11:02 AM

Quote: (Originally Posted by GLOC)

Joe or Igor?

OK, someone buy me an RB80 + training and I'll happily sit in the bath and try this for you.

Igor Beades · October 25th, 2007, 11:13 AM

Quote: (Originally Posted by graham_hk)

My hypothesis is you displace more when you breath in
since you are filling empty space in your chest. Any one bored enough to
try it?

I do not exactly understand the idea. The loop includes all the aerial zones and dead spaces. Apart from the buoyancy control, why should it be different than with OC? Breathing 3000lt per dive, the volume in my stomach is always the same... do you swallow gas while diving? Where does it go?

Why not testing it on a spirometer beter than a bath? What am I missing?

Quote: (Originally Posted by JGrogan)

the volume of the counter-lungs is less than the volume of your own lungs. On the inhale cycle, the counter-lung compresses, the dump-lung dumps gas and when the counter-lung is empty, the regs fire to add more gas until you stop inhaling. The marginal increase of your stomach expanding outwards as you breathe in fully is less than the displacement of the counter-lung.

From my point of view, the issue is not the relationship between your lungs and the outer/clean CL, because you can softly rebreath the loop without injection (the idea is that 1/8 to 1/13th of the exhaled gas is dumped and then it works like a big second stage).

- In this moment if your inhaled volume is less than the recicled volume (volume in the clean CL) there is no injection (and the recicled volume reduces 1/8)

- If inhaled volume is more than the volume in the clean CL, the injectors add the difference the same way than in OC there is an empty space of gas inside the regulator.

The stomach in SCR or in OC mode is always an empty space, so I can not realize how it affects to the buoyancy. Would you please elaborate a bit more on it

*graham_hk* · October 25th, 2007, 12:21 PM

Quote: (Originally Posted by Igor Beades)

I do not exactly understand the idea. The loop includes all the aerial zones and dead spaces. Apart from the buoyancy control, why should it be different than with OC? Breathing 3000lt per dive, the volume in my stomach is always the same... do you swallow gas while diving? Where does it go?

Why not testing it on a spirometer beter than a bath? What am I missing?

From my point of view, the issue is not the relationship between your lungs and the outer/clean CL, because you can softly rebreath the loop without injection (the idea is that 1/8 to 1/13th of the exhaled gas is dumped and then it works like a big second stage).

- In this moment if your inhaled volume is less than the recicled volume (volume in the clean CL) there is no injection (and the recicled volume reduces 1/8)

- If inhaled volume is more than the volume in the clean CL, the injectors add the difference the same way than in OC there is an empty space of gas inside the regulator.

The stomach in SCR or in OC mode is always an empty space, so I can not realize how it affects to the buoyancy. Would you please elaborate a bit more on it

Simply put - Breath out and you go up. Can any one offer an explanation? I can't but I have a hypothesis

Graham

MonkSeal · October 26th, 2007, 10:31 AM

Quote: (Originally Posted by graham_hk)

Simply put - Breath out and you go up. Can any one offer an explanation? I can't but I have a hypothesis

Graham

CL are higher then you lungs meaning at lower pressure. Exhaled gas in CL will be expanded more then in lungs. More displacement equals more bouyancy. Does this hold?

October 24th, 2007, 01:52 AM	#24 (permalink)
graham_hk(Offline) GUE instructor Join Date: Nov 2005 Location: Asia Posts: 1,112	Quote: (Originally Posted by Retardboy) But the gas going into a space in your body needs space...In order to fill your lungs with gas without increasing the displacement of your torso, you would have to actually compress the gas in your lungs. I find it hard to see how that can be done.. If you are in a slightly head up position, and your lungs and the CL are at the same level (pressure), the total displacement should be the same...exept from the gas dumped by the inner CL. For CCR, the only explanation I can see is that the CL is slightly above the divers lungs. That results in a very small difference in the pressure on CL`s and lungs, thus reducing the volume of the mass of gas transfered to the lungs.. Disagree?Shoot The only way to check this is to breath in in the bath and measure how much more you displace with inflated lungs. Then breath out into an RB and measure the displacement. My hypothesis is you displace more when you breath in since you are filling empty space in your chest. Any one bored enough to try it? __________________ ah herro

October 24th, 2007, 07:46 AM	#25 (permalink)
GLOC(Offline) Moderator and aka Mavis Join Date: Nov 2005 Location: Malmesbury, Wilts Posts: 2,772	Quote: (Originally Posted by graham_hk) ....Any one bored enough to try it? Joe or Igor? __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar “Set your expectations high; find men and women whose integrity and values you respect; get their agreement on a course of action; and give them your ultimate trust.” “It is far better to be trusted and respected that it is to be liked.”

October 24th, 2007, 10:47 AM	#26 (permalink)
graham_hk(Offline) GUE instructor Join Date: Nov 2005 Location: Asia Posts: 1,112	Quote: (Originally Posted by GLOC) Joe or Igor? ha ha Incidently I can provide some photos if you wanna put this in the library __________________ ah herro

October 25th, 2007, 11:13 AM	#28 (permalink)
Igor Beades(Offline) Growing up Join Date: Jun 2006 Location: Zanjalandia Posts: 173	Quote: (Originally Posted by graham_hk) My hypothesis is you displace more when you breath in since you are filling empty space in your chest. Any one bored enough to try it? I do not exactly understand the idea. The loop includes all the aerial zones and dead spaces. Apart from the buoyancy control, why should it be different than with OC? Breathing 3000lt per dive, the volume in my stomach is always the same... do you swallow gas while diving? Where does it go? Why not testing it on a spirometer beter than a bath? What am I missing? Quote: (Originally Posted by JGrogan) the volume of the counter-lungs is less than the volume of your own lungs. On the inhale cycle, the counter-lung compresses, the dump-lung dumps gas and when the counter-lung is empty, the regs fire to add more gas until you stop inhaling. The marginal increase of your stomach expanding outwards as you breathe in fully is less than the displacement of the counter-lung. From my point of view, the issue is not the relationship between your lungs and the outer/clean CL, because you can softly rebreath the loop without injection (the idea is that 1/8 to 1/13th of the exhaled gas is dumped and then it works like a big second stage). - In this moment if your inhaled volume is less than the recicled volume (volume in the clean CL) there is no injection (and the recicled volume reduces 1/8) - If inhaled volume is more than the volume in the clean CL, the injectors add the difference the same way than in OC there is an empty space of gas inside the regulator. The stomach in SCR or in OC mode is always an empty space, so I can not realize how it affects to the buoyancy. Would you please elaborate a bit more on it __________________ "Everything was going okay until we got into the water"

October 25th, 2007, 12:21 PM	#29 (permalink)
graham_hk(Offline) GUE instructor Join Date: Nov 2005 Location: Asia Posts: 1,112	Quote: (Originally Posted by Igor Beades) I do not exactly understand the idea. The loop includes all the aerial zones and dead spaces. Apart from the buoyancy control, why should it be different than with OC? Breathing 3000lt per dive, the volume in my stomach is always the same... do you swallow gas while diving? Where does it go? Why not testing it on a spirometer beter than a bath? What am I missing? From my point of view, the issue is not the relationship between your lungs and the outer/clean CL, because you can softly rebreath the loop without injection (the idea is that 1/8 to 1/13th of the exhaled gas is dumped and then it works like a big second stage). - In this moment if your inhaled volume is less than the recicled volume (volume in the clean CL) there is no injection (and the recicled volume reduces 1/8) - If inhaled volume is more than the volume in the clean CL, the injectors add the difference the same way than in OC there is an empty space of gas inside the regulator. The stomach in SCR or in OC mode is always an empty space, so I can not realize how it affects to the buoyancy. Would you please elaborate a bit more on it Simply put - Breath out and you go up. Can any one offer an explanation? I can't but I have a hypothesis Graham __________________ ah herro Last edited by graham_hk; October 25th, 2007 at 12:23 PM..

October 23rd, 2007, 03:31 PM	#21 (permalink)
JGrogan(Offline) GUE Join Date: May 2006 Location: London Posts: 858	With the RB80 and its' clones, the volume of the counter-lungs is less than the volume of your own lungs. On the inhale cycle, the counter-lung compresses, the dump-lung dumps gas and when the counter-lung is empty, the regs fire to add more gas until you stop inhaling. The marginal increase of your stomach expanding outwards as you breathe in fully is less than the displacement of the counter-lung. Quote: (Originally Posted by David Martin) Really? The rest of the body is pretty incompressible and the gas in the lungs is pretty much at ambient pressure, so I would expect that the increase in lung volume and thus the increase in total body displacement to be virtually identical to the volume of gas breathed in at ambient from the counter lung. (With any variation being essentially unmeasureable.) This would seem to reflect what you're saying, could this be the only reason? David

October 23rd, 2007, 04:24 PM	#22 (permalink)
tim(Offline) Big Grin Syndrome Join Date: Dec 2005 Location: Oxford Posts: 461	Thanks for the explanations. I'm still slightly baffled by the breathing-in side of things in terms of changing volume by moving gas - I don't get where the gas goes when you breathe in unless space in your body was at less than ambient pressure or you compress the gas as you breathe it. Both seem a bit improbable given body rigidity or lack of. I think I'm with David thus far in preferring to put the 'blame' on the gas dumped during the breath, which I didn't know about but makes a lot of sense in terms of becoming more negative. Just curiosity, I have no aspirations to dive an RB but they look interesting in terms of mechanics Tim

October 23rd, 2007, 10:27 PM	#23 (permalink)
Retardboy(Offline) New Member Join Date: Aug 2006 Location: Norway/Trondheim Posts: 48	Quote: (Originally Posted by graham_hk) But the gas is going into a space in your body and thus not causing any more displacement. I would agree but I have seen it in other RBs too where no gas is dumped on inhalation. But the gas going into a space in your body needs space...In order to fill your lungs with gas without increasing the displacement of your torso, you would have to actually compress the gas in your lungs. I find it hard to see how that can be done.. If you are in a slightly head up position, and your lungs and the CL are at the same level (pressure), the total displacement should be the same...exept from the gas dumped by the inner CL. For CCR, the only explanation I can see is that the CL is slightly above the divers lungs. That results in a very small difference in the pressure on CL`s and lungs, thus reducing the volume of the mass of gas transfered to the lungs.. Disagree?Shoot

October 24th, 2007, 11:02 AM	#27 (permalink)
Joe Hesketh(Offline) New Member Join Date: Nov 2005 Location: London, UK Posts: 705	Quote: (Originally Posted by GLOC) Joe or Igor? OK, someone buy me an RB80 + training and I'll happily sit in the bath and try this for you.

October 26th, 2007, 10:31 AM	#30 (permalink)
MonkSeal(Offline) New Member Join Date: Feb 2006 Location: Zagreb, Croatia Posts: 575	Quote: (Originally Posted by graham_hk) Simply put - Breath out and you go up. Can any one offer an explanation? I can't but I have a hypothesis Graham CL are higher then you lungs meaning at lower pressure. Exhaled gas in CL will be expanded more then in lungs. More displacement equals more bouyancy. Does this hold?