One of the things people have been telling me about my mCCR Dolphin is that the weakest part is the Draeger scrubber. Weakness has been described from a duration perspective for CCR use, and a scrubber design/construction perspective for deeper dives. Does anyone know how the ExtendAir system compares to the stock scrubber for this use? Will it perform longer/better for an mCCR? Is the dsign and build of the scrubber better suited for deeper dives (200-250').
ExtendAir vs Dolphin Scrubber on mCCR?
- Thread starter jkromelow
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caveseeker7
Contributor
The status quo is that the first cartridges/cannisters were designed for the Dolphin and the latter then adapted for the Azimuth. The cartridges were therefor rated originally to 5 bar (40 msw - same as the rebreathers they were made for). A while ago that was oncrease to 6 bar/50 msw. The current duration for the Dolphin is 210 minutes.
However, testing of the cartridge was performed at 40 RMV, 1.35 LPM CO2 injection, 13 degrees C/55.4 degrees F and 1 ata. The problem of course is the 1 ata, as ambient pressure plays a considerable role in duration (example Inspiration: 180 mins at 20 msw and 88 mins at 100 msw, both at 40 RMV, 1.6 lpm CO2 injection and 4 degrees C/39.2 degrees F)
As you may know, the new Dive Rite O2ptima uses the same cartridge in a Micropore cannister (the latter is different to contain the needed CCR electronic bits). Additional testing to 100 msw has been promised, and hopefully will be available publicly.
This should show the true potential of the cartridge system.
There is a bit of gas space around it, hence some insulation, the rolled grid is designed to always be 'perfectly packed'. So there is a fair chance that performance matches or surpasses the stock cannister even under same testing conditions. When Steam Machines tried a like system years ago they noted a better performance in axial scrubbers, but still less efficiency than radial or annular axial designs.
Two other big advantages are the extreme ease of use and almost no dust (reduced chance of caustic cocktail).
However, testing of the cartridge was performed at 40 RMV, 1.35 LPM CO2 injection, 13 degrees C/55.4 degrees F and 1 ata. The problem of course is the 1 ata, as ambient pressure plays a considerable role in duration (example Inspiration: 180 mins at 20 msw and 88 mins at 100 msw, both at 40 RMV, 1.6 lpm CO2 injection and 4 degrees C/39.2 degrees F)
As you may know, the new Dive Rite O2ptima uses the same cartridge in a Micropore cannister (the latter is different to contain the needed CCR electronic bits). Additional testing to 100 msw has been promised, and hopefully will be available publicly.
This should show the true potential of the cartridge system.
There is a bit of gas space around it, hence some insulation, the rolled grid is designed to always be 'perfectly packed'. So there is a fair chance that performance matches or surpasses the stock cannister even under same testing conditions. When Steam Machines tried a like system years ago they noted a better performance in axial scrubbers, but still less efficiency than radial or annular axial designs.
Two other big advantages are the extreme ease of use and almost no dust (reduced chance of caustic cocktail).
ZinnX
Registered
Also the ExtendAir cartridge has a lower breathing resistance, hence easier to breath through, hence the less you work to breath through the adsorbent. I've also heard the cartridges are able to be flood recoverable.
caveseeker7
Contributor
Having tried the cartridge in the Dolphin I didn't notice any difference in that respect,ZinnX:
then again, the Dolphin's WOB is pretty crappy to start with.
Meaning what? During the dive? How are you gonna get the water out of the loop?
My guess is that unless the cartridge is submerged for a prolonged period it may well be usable.
It may also well be that a flood reduces it's reactivity and capacity.
Even with the higher price of the cartridges I would rather err on the safe side and waste money rather than my life.
And money they waste: $130 per case of four, or $ 32.50 each.
Even a Sofnolime fill would cost me $10 less, and that's with a larger 6 lbs capacity.
As it is, the Sodasorb I use costs $16 per fill and gives at least 5 hrs duration.
That's about 50% more duration for about half the price.
ZinnX
Registered
What rebreather do you dive?
ZinnX
Registered
As in you get the water out and the cartridge still works (1-5 min flood time)
caveseeker7
Contributor
PRISM Topaz.
I can see how the cartridge can survive a brief flood, being that the absorbant is mounted onto the rolled grid. However, moisture content in diving grade absorbant is only around 15%, so any prolonged immersion will still translate into water being soaked up, especially at depth. So calling it flood recorable is simply not correct, as the cartridge can only be recovered to a very limited extend and the cannister likely not, certainly not in a Dolphin.
Aside from the problem you would still first have to get rid of the cause of the flood.
The only recoverable loop I'm aware of is the MK-5p's as the scrubber has hydrophobic membranes on both sides. You can actually open the loop briefly to fix a problem and pump the water out. If you manage to do that without damaging the sensors you can continue diving. But even in that unit, the scrubber is not recoverable. Soaked absorbant is soaked absorbant, no matter what rebreather it's in.
If you would add a hydrophobic membrane to the Dolphin, the absorbant wouldn't be damaged, but you're still missing the water drains in the loop and the means to purge it.
I can see how the cartridge can survive a brief flood, being that the absorbant is mounted onto the rolled grid. However, moisture content in diving grade absorbant is only around 15%, so any prolonged immersion will still translate into water being soaked up, especially at depth. So calling it flood recorable is simply not correct, as the cartridge can only be recovered to a very limited extend and the cannister likely not, certainly not in a Dolphin.
Aside from the problem you would still first have to get rid of the cause of the flood.
The only recoverable loop I'm aware of is the MK-5p's as the scrubber has hydrophobic membranes on both sides. You can actually open the loop briefly to fix a problem and pump the water out. If you manage to do that without damaging the sensors you can continue diving. But even in that unit, the scrubber is not recoverable. Soaked absorbant is soaked absorbant, no matter what rebreather it's in.
If you would add a hydrophobic membrane to the Dolphin, the absorbant wouldn't be damaged, but you're still missing the water drains in the loop and the means to purge it.
I recently flooded my Azimuth with an ExtendAir cartridge and managed to save it, though not underwater. It was (as is usually the case) operator error. I had done my predive checks but somehow my Oxy2 had "jiggled" loose and upon descent of the first dive of a two tank boat dive I began to flood my inhalation counterlung. I immediately bailed out to open circuit and got back on board. I emptied the counterlungs, emptied dried the scrubber and reinserted the ExtendAir cartridge as I didn't have an extra onboard the boat (I should have!). After repeating the pre dive checks I went back into the water. Anyway, I managed to make back to back one hour dives with no problems. I then changed ExtendAir cartridges before the afternoon trip.
Also, I personally like to use the ExtendAir cartridges when teaching students on the Dolphin or the Azimuth as you have a little more time after a flood before getting a caustic cocktail.
Caveseeker, you're the rebreather expert here. Do you think this sounds reasonable?
Also, I personally like to use the ExtendAir cartridges when teaching students on the Dolphin or the Azimuth as you have a little more time after a flood before getting a caustic cocktail.
Caveseeker, you're the rebreather expert here. Do you think this sounds reasonable?
caveseeker7
Contributor
I'm not half the expert I would like to be, much less on the subject of absorbants,
scrubbers and carbon-dioxide.
I've heard of similar experiences before, that's why I phrased my post above as I did.
The performance of the previously immersed cartridge probably would also depend on
the dive that follows. I certainly wouldn't want to push either depth or duration further
than I would on wet granules.
Again I'm not sure what exactly is being tested, and what results will be available, but
performance of the cartridge after submersion is supposedly part of it.
Regarding the caustic cocktail I agree, having the absorbant mounted to the grid very
much reduces the dust you have with granular absorbant. With the dust/water combo
making the initial caustic cocktail, chances of ingesting one are reduced and some
time to react added.
scrubbers and carbon-dioxide.
I've heard of similar experiences before, that's why I phrased my post above as I did.
The performance of the previously immersed cartridge probably would also depend on
the dive that follows. I certainly wouldn't want to push either depth or duration further
than I would on wet granules.
Again I'm not sure what exactly is being tested, and what results will be available, but
performance of the cartridge after submersion is supposedly part of it.
Regarding the caustic cocktail I agree, having the absorbant mounted to the grid very
much reduces the dust you have with granular absorbant. With the dust/water combo
making the initial caustic cocktail, chances of ingesting one are reduced and some
time to react added.
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