Why does depth matter for scrubber lifetime

Shawn · 31st October 2007, 03:18

So if there were a radial scrubber with a hydrophobic membrane, and you could keep yourself from becoming hypoxic...that would be the way to go???

So that I'm not misinterperting information ( again my spelling sucks ) would you plase explain break through.

Thank you

silent running · 31st October 2007, 06:22

Quote: (Originally Posted by Shawn)

All good information...the Lithium Hydroxide question came from the Extend air link on the ISC web page under options. So I started reading everything I could about Extend air.

Back to the radial scrubber thing for a minute....

I have seen a lot of talk about a radial scrubber especially the CIS lunar. If break through is easier (??) with a radial scrubber then why all of the hub bub? or is it more that the Cis Lunar had a water resistant scrubber canister?

thanks

Hello Shawn, the main hubub about the Cis scrubber is the hydrophobic membrane AND the fact that it's a radial, which gives it the capacity to use LiHO, thus greatly increasing it's duration over say, a same sized axial with regular CalHO sorb. That being said, some people have said the additional WOB on the hydrophobic membrane is not worth the benefits-flood recovery and LiHO capacity.

IMHO, the biggest benefit of the a good radial is the easier WOB and the added efficiency is secondary as reducing the likelyhood of a CO2 hit from overbreathing is more important than mere duration-we are all more likely to have a CO2 hit from retaining CO2 from a high work rate and high WOB than we are from forgeting to change our sorb.

Because I fly to all my dive destinations, I have never given LiHO much thought as an alternative to CaHO as you can't fly with it because it's so caustic... -Andy

Abbo · 31st October 2007, 06:23

Quote: (Originally Posted by Shawn)

So if there were a radial scrubber with a hydrophobic membrane, and you could keep yourself from becoming hypoxic...that would be the way to go???

So that I'm not misinterperting information ( again my spelling sucks ) would you plase explain break through.

Breakthrough:
You can see it quite clearly if you buy the kind of scrubbber with a dye, but obviously the scrubber at the bottom gets used up first and above that there is a cone of used up scrubber material. With time the cone gets bigger and gets closer to the top until the tip of the cone finally breaks through the top of the canister. Like electricity taking the easiest route in lightning, the CO2 takes the easiest route through the scrubber canister: up the cone and through its tip. There is now a route through the canister through which CO2 can bypass the scrubber material. The diver's inhaled FCO2 starts to rise as the breakthrough hole gets larger and larger.

A radial scrubber is effectively a very short fat scrubber canister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond.

silent running · 31st October 2007, 06:38

Quote: (Originally Posted by Abbo)

A radial scrubber is effectively a very short fat scrubber cannister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond.

Hi Abbo, while I don't doubt this description of a CO2 hit, I'd point out that Richard Pyle uses his Cis radial to 8 hrs in warm water and depths in excess of 400ft. He also said that at 11 hrs of diving the Cis radial he begins to "feel it" meaning elevated CO2 levels. It's only anecdotal, but it suggests that radial breakthrough at normal RMVs may not be so drastic, which is inline with my own experience on a radial...

Abbo · 31st October 2007, 08:12

Quote: (Originally Posted by silent running)

Hi Abbo, while I don't doubt this description of a CO2 hit, I'd point out that Richard Pyle uses his Cis radial to 8 hrs in warm water and depths in excess of 400ft. He also said that at 11 hrs of diving the Cis radial he begins to "feel it" meaning elevated CO2 levels. It's only anecdotal, but it suggests that radial breakthrough at normal RMVs may not be so drastic, which is inline with my own experience on a radial...

I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial.

I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it.

Nad · 31st October 2007, 08:13

Quote: (Originally Posted by Abbo)

Breakthrough:
You can see it quite clearly if you buy the kind of scrubbber with a dye, but obviously the scrubber at the bottom gets used up first and above that there is a cone of used up scrubber material. With time the cone gets bigger and gets closer to the top until the tip of the cone finally breaks through the top of the cannister. Like electricity taking the easiest route in lightning, the CO2 takes the easiest route through the scrubber cannister: up the cone and through its tip. There is now a route through the cannister through which CO2 can bypass the scrubber material. The diver's inhaled FCO2 starts to rise as the breakthrough hole gets larger and larger.

A radial scrubber is effectively a very short fat scrubber cannister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond.

Never had breakthrough problems, at list I never felt them!
The canister of the Ouroboros has some wings mounted inside, to reduce channeling and, eventually, breakthrough.

I think the possibility to have a solid and great breakthrough depend on us: I never do speculation on the scrubber. Not more than 4 hours in 8°C water.

Nad

Shawn · 1st November 2007, 23:17

Gentlemen...this has been very good information...

So in the end it sounds like the Extendair would be a good alternative if it were not for the cost. All this talk makes me want to get on with my class and find out what it's really all about.

Thanks

silent running · 1st November 2007, 23:38

Quote: (Originally Posted by Shawn)

So in the end it sounds like the Extendair would be a good alternative if it were not for the cost. Thanks

The Extendair has it's benefits, but if you're traveling with them and intend to stay near the manufacturers recomendations for duration, you won't have enough room in your luggage for a weeks worth of diving. For traveling, sorb is much more economical and space efficient...

silent running · 2nd November 2007, 05:32

Quote: (Originally Posted by Abbo)

I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial.

I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it.

Hi Abbo, the NEDU tests of the Prism scrubber list the average breakthrough to .5% surface equivalent value as 255 minutes at 1.35 slpm of CO2 with a 40 lpm RMV, continuos. Then 283 min to 1.0% SEV and 306 min to 2.0% SEV. So it takes 28 then 25 minutes respectively, at a reasonably high RMV and CO2 flow to double the CO2% in the loop.

While I wouldn't call this average of 26.5 minutes at a high flow to reach double the CO2 a really slow breakthrough, it certainly doesn't seem so fast to either.

I think I understand the idea behind the different breakthrough characteristics of axials and radials, but in an in-out flow radial the gas flow slows as it reaches the outside and the dwell time increases and so does the chance that the CO2 will react with whatever unused sorb is left. There should always a greater portion of unused sorb on the outside of an in-out flow radial and a slower gas velocity, thus the not so drastic breakthrough.

I tried to imagine what the opposite flow out-in radial breakthrough characteristics would be given the opposite effect-faster gas flow as the surface area narrows and finally reaches the narrow, inner tube-yikes...

31st October 2007, 03:18	#31 (permalink)
Shawn Custom Title Allowed! Current Rebreather/s: Megalodon Other CCR RB80 / Clone Other Rebreather/s: Other CCR RB80 / Clone Join Date: Oct 2007 Location: Kansas City Kansas Posts: 142	Re: Why does depth matter for scrubber lifetime So if there were a radial scrubber with a hydrophobic membrane, and you could keep yourself from becoming hypoxic...that would be the way to go??? So that I'm not misinterperting information ( again my spelling sucks ) would you plase explain break through. Thank you __________________ WWW.DiveOne.net
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31st October 2007, 06:22	#32 (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: 1,836	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Shawn) All good information...the Lithium Hydroxide question came from the Extend air link on the ISC web page under options. So I started reading everything I could about Extend air. Back to the radial scrubber thing for a minute.... I have seen a lot of talk about a radial scrubber especially the CIS lunar. If break through is easier (??) with a radial scrubber then why all of the hub bub? or is it more that the Cis Lunar had a water resistant scrubber canister? thanks Hello Shawn, the main hubub about the Cis scrubber is the hydrophobic membrane AND the fact that it's a radial, which gives it the capacity to use LiHO, thus greatly increasing it's duration over say, a same sized axial with regular CalHO sorb. That being said, some people have said the additional WOB on the hydrophobic membrane is not worth the benefits-flood recovery and LiHO capacity. IMHO, the biggest benefit of the a good radial is the easier WOB and the added efficiency is secondary as reducing the likelyhood of a CO2 hit from overbreathing is more important than mere duration-we are all more likely to have a CO2 hit from retaining CO2 from a high work rate and high WOB than we are from forgeting to change our sorb. Because I fly to all my dive destinations, I have never given LiHO much thought as an alternative to CaHO as you can't fly with it because it's so caustic... -Andy
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31st October 2007, 06:23	#33 (permalink)
Abbo Nicholas Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 449	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Shawn) So if there were a radial scrubber with a hydrophobic membrane, and you could keep yourself from becoming hypoxic...that would be the way to go??? So that I'm not misinterperting information ( again my spelling sucks ) would you plase explain break through. Breakthrough: You can see it quite clearly if you buy the kind of scrubbber with a dye, but obviously the scrubber at the bottom gets used up first and above that there is a cone of used up scrubber material. With time the cone gets bigger and gets closer to the top until the tip of the cone finally breaks through the top of the canister. Like electricity taking the easiest route in lightning, the CO2 takes the easiest route through the scrubber canister: up the cone and through its tip. There is now a route through the canister through which CO2 can bypass the scrubber material. The diver's inhaled FCO2 starts to rise as the breakthrough hole gets larger and larger. A radial scrubber is effectively a very short fat scrubber canister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond. Last edited by Abbo : 1st November 2007 at 07:58.
(Online)

31st October 2007, 06:38	#34 (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: 1,836	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Abbo) A radial scrubber is effectively a very short fat scrubber cannister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond. Hi Abbo, while I don't doubt this description of a CO2 hit, I'd point out that Richard Pyle uses his Cis radial to 8 hrs in warm water and depths in excess of 400ft. He also said that at 11 hrs of diving the Cis radial he begins to "feel it" meaning elevated CO2 levels. It's only anecdotal, but it suggests that radial breakthrough at normal RMVs may not be so drastic, which is inline with my own experience on a radial...
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31st October 2007, 08:12	#35 (permalink)
Abbo Nicholas Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 449	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by silent running) Hi Abbo, while I don't doubt this description of a CO2 hit, I'd point out that Richard Pyle uses his Cis radial to 8 hrs in warm water and depths in excess of 400ft. He also said that at 11 hrs of diving the Cis radial he begins to "feel it" meaning elevated CO2 levels. It's only anecdotal, but it suggests that radial breakthrough at normal RMVs may not be so drastic, which is inline with my own experience on a radial... I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial. I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it.
(Online)

31st October 2007, 08:13	#36 (permalink)
Nad Rebel to the Bone Current Rebreather/s: Ouroboros Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Join Date: Mar 2005 Location: Europe Posts: 980	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Abbo) Breakthrough: You can see it quite clearly if you buy the kind of scrubbber with a dye, but obviously the scrubber at the bottom gets used up first and above that there is a cone of used up scrubber material. With time the cone gets bigger and gets closer to the top until the tip of the cone finally breaks through the top of the cannister. Like electricity taking the easiest route in lightning, the CO2 takes the easiest route through the scrubber cannister: up the cone and through its tip. There is now a route through the cannister through which CO2 can bypass the scrubber material. The diver's inhaled FCO2 starts to rise as the breakthrough hole gets larger and larger. A radial scrubber is effectively a very short fat scrubber cannister. The incoming gas works on a much larger surface area of scrubber material, which means the work of breathing is much lower, but when it breaks through it breaks through in style. The diver's FCO2 then rises very sharply. The narcotic effect and panic response take out the diver's reasoned thinking, increasing his response time, and a number of other effects effectively pull out his power cord, reducing his ability to respond. Never had breakthrough problems, at list I never felt them! The canister of the Ouroboros has some wings mounted inside, to reduce channeling and, eventually, breakthrough. I think the possibility to have a solid and great breakthrough depend on us: I never do speculation on the scrubber. Not more than 4 hours in 8°C water. Nad __________________ The Impossible is often the Untried
(Offline)

1st November 2007, 23:17	#37 (permalink)
Shawn Custom Title Allowed! Current Rebreather/s: Megalodon Other CCR RB80 / Clone Other Rebreather/s: Other CCR RB80 / Clone Join Date: Oct 2007 Location: Kansas City Kansas Posts: 142	Re: Why does depth matter for scrubber lifetime Gentlemen...this has been very good information... So in the end it sounds like the Extendair would be a good alternative if it were not for the cost. All this talk makes me want to get on with my class and find out what it's really all about. Thanks __________________ WWW.DiveOne.net
(Offline)

1st November 2007, 23:38	#38 (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: 1,836	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Shawn) So in the end it sounds like the Extendair would be a good alternative if it were not for the cost. Thanks The Extendair has it's benefits, but if you're traveling with them and intend to stay near the manufacturers recomendations for duration, you won't have enough room in your luggage for a weeks worth of diving. For traveling, sorb is much more economical and space efficient...
(Offline)

2nd November 2007, 05:32	#39 (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: 1,836	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Abbo) I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial. I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it. Hi Abbo, the NEDU tests of the Prism scrubber list the average breakthrough to .5% surface equivalent value as 255 minutes at 1.35 slpm of CO2 with a 40 lpm RMV, continuos. Then 283 min to 1.0% SEV and 306 min to 2.0% SEV. So it takes 28 then 25 minutes respectively, at a reasonably high RMV and CO2 flow to double the CO2% in the loop. While I wouldn't call this average of 26.5 minutes at a high flow to reach double the CO2 a really slow breakthrough, it certainly doesn't seem so fast to either. I think I understand the idea behind the different breakthrough characteristics of axials and radials, but in an in-out flow radial the gas flow slows as it reaches the outside and the dwell time increases and so does the chance that the CO2 will react with whatever unused sorb is left. There should always a greater portion of unused sorb on the outside of an in-out flow radial and a slower gas velocity, thus the not so drastic breakthrough. I tried to imagine what the opposite flow out-in radial breakthrough characteristics would be given the opposite effect-faster gas flow as the surface area narrows and finally reaches the narrow, inner tube-yikes...
(Offline)

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