Options for Keeping CELLS DRY

[v101]

Hello fellow RB divers.

Wanted to ask about any options that others have used to keep their cells dry during longer dives. I am diving a KISS Sidewinder rebreather. In the TOP of my CAN with my cells, i have that plugged. I am NOT using an OPV in that side. All normal pre-dive checks are done, Cell Linearity checks done pre-dive, 1.6 check is done at 20' and that checks out.

During the dive all is well, PP02 levels are normal, all appears good for majority of dive. However after a few hrs. on the unit. (3+) I will start to notice 1 cell start reading incorrectly, it will start reading much lower, then after a bit longer i will see it bounce back and read normal. then a bit longer, it will repeat and then stay low, then into hour 4 I will start to see multiple cells repeating this behavior. During deco stops I am not able to get the cells up past 1.15 - 1.17 even though 02 is flushed through through. Dill flush when the cells start reading wrong don't read the same PP02 level as my DIL is at...

I notice when I take the head off, I notice some moisture, but its not dripping out or pouring out. the sorb isn't soaked, normal amount of moisture in the loop/counter lung, but again not flooded.

Have anyone else had this issue I summarized above?
Is there any modifications that can be done to prevent water from getting to the cells that affect the PP02 levels?

Any ideas or options, Id appreciate hearing about it.

thanks

 

[RainPilot]

@cerich dives the Sidewinder, maybe he can shed some light.

 

[grantctobin]

How old are the cells? Have you noticed this behavior on a prior set of cells? How warm is the water you’re diving?

Downside with a dil flush on the SW compared to most CCR is that the dil doesn’t get blown over the face of the cells. I struggle to get to exactly 1.6 at the 20’ stop on a full O2 flush but haven’t noticed so strongly the behavior you note above. Grasping at straws, but maybe sucking the lungs flats, coming off loop once an hour for a few breaths on OC, add fresh loop of dil, and see if the decrease the magnitude of the behavior you’re having.

 

[cerich]

How old are the cells? Have you noticed this behavior on a prior set of cells? How warm is the water you’re diving?

Downside with a dil flush on the SW compared to most CCR is that the dil doesn’t get blown over the face of the cells. I struggle to get to exactly 1.6 at the 20’ stop on a full O2 flush but haven’t noticed so strongly the behavior you note above. Grasping at straws, but maybe sucking the lungs flats, coming off loop once an hour for a few breaths on OC, add fresh loop of dil, and see if the decrease the magnitude of the behavior you’re having.

Holding 1.6 at deco (20) is chasing your tail . I am happy as long as it stays over 1.4. It's CC and you are metabolizing and adding back lower PPO2 gas with every breath. You get it on the O2 check starting the dive because you're headed down and not staying at 20 long, then headed deeper and adding dil to lower the PPO2.. if you happen to be be doing something that takes a few mins like putting a reel in at 20 on the way in and doing your O2 check, you'll see holding 1.6 is just as annoying as trying to hold 1.6 on deco at 20.

The top of my sensor can is normally dry as a bone on a first dive and can get a bit moist on a second but still not seeing the cell issue described. If you are setting up outside in heat and humidity versus inside in AC, the cool water can create some condensation if the cans, loop, CL are full of atmospheric warm moist air. But... your pre dive should have replaced all that with gas from cylinders that is dry. If I leave the unit sit in the sun between dives and the unit heats up.. it will add moisture to the lids from whatever moisture is in the unit from expiration or any accidental small ingress.


Can the OP maybe do a cell linearity check and post it here with each step, the full worksheet. Maybe some mistakes there. I suspect the cells are the issue.

 

[cerich]

Hello felling RB divers.

Wanted to ask about any options that others have used to keep their cells dry during longer dives. I am diving a KISS Sidewinder rebreather. In the TOP of my CAN with my cells, i have that plugged. I am NOT using an ADV in that side. All normal pre-dive checks are done, Cell Linearity checks done pre-dive, 1.6 check is done at 20' and that checks out.

During the dive all is well, PP02 levels are normal, all appears good for majority of dive. However after a few hrs. on the unit. (3+) I will start to notice 1 cell start reading incorrectly, it will start reading much lower, then after a bit longer i will see it bounce back and read normal. then a bit longer, it will repeat and then stay low, then into hour 4 I will start to see multiple cells repeating this behavior. During deco stops I am not able to get the cells up past 1.15 - 1.17 even though 02 is flushed through through. Dill flush when the cells start reading wrong don't read the same PP02 level as my DIL is at...

I notice when I take the head off, I notice some moisture, but its not dripping out or pouring out. the sorb isn't soaked, normal amount of moisture in the loop/counter lung, but again not flooded.

Have anyone else had this issue I summarized above?
Is there any modifications that can be done to prevent water from getting to the cells that affect the PP02 levels?

Any ideas or options, Id appreciate hearing about it.

thanks

You may also be getting water on your molex connectors (Edd's first thought) he has a solution for that that involves using the little red caps that come with new hoses, slicing then up the side to the nipple and placing over.)

On another note.. I had to go look at mine to confirm my first thought when I read your post.., but the sensor side has a OPV not an ADV. I don't know now what you have blocked off, one or both but there is a chance it's leaking a bit. I have seen that on a friends unit when they blocked their ADV on the other can.

 

[JonG1]

I have had errant readings on 1 cell on a KISS Classic which turned out to be the molex not fully seated on the pins, I also had similar changeable readings when the Fischer was knackered.

 

[rddvet]

One other thought because you're saying you're not getting down to the dil p02 or up to 1.6. It may not be water on the cells at all, it may be your technique. The reason I say that is that I took the sidewinder crossover class this past weekend (I hated it btw, but that's a different story), and I found it difficult to get up to a 1.6 and down to dilp02 and it was my fault. I'm coming from a unit with bm cl's which have a dump. My standard dil/oxygen flush is to expel as much lung volume as possible through the nose, then lay on the mav and as the counterlung fills to a pressure that won't let water in the dump, I pull the dump and continue flushing. It's exceptionally easy to hit your number even with a little residual lung volume/gas from pre-flush. I've never had a single issue. The sidewinder cl does not have a dump, so as I'm sure you know you inhale cl volume, and expel via your nose until you have emptied the lung, then flush with your gas. I have horrible chronic allergies and half the time can barely breathe out of my nose. It's actually been my biggest annoyance since going to a CCR. But in class I expressed to Edd that I was having trouble getting the the right p02 of verification flushes. He said it's very common for people that exhale lung volume nasally to actually also simultaneously orally exhale a little bit back in the loop. Obviously with horrific allergies it's even worse for me. He suggested plugging the dsv with my tongue to see if that fixes it. That's something I never had discussed in 2 previous CCR classes since my CCR has a traditional lung dump making it a non-issue. After his suggestion I did exactly what he said, and miraculously I could get to dil p02 or 1.6 with ease.
So something to think about.

 

[cerich]

One other thought because you're saying you're not getting down to the dil p02 or up to 1.6. It may not be water on the cells at all, it may be your technique. The reason I say that is that I took the sidewinder crossover class this past weekend (I hated it btw, but that's a different story), and I found it difficult to get up to a 1.6 and down to dilp02 and it was my fault. I'm coming from a unit with bm cl's which have a dump. My standard dil/oxygen flush is to expel as much lung volume as possible through the nose, then lay on the mav and as the counterlung fills to a pressure that won't let water in the dump, I pull the dump and continue flushing. It's exceptionally easy to hit your number even with a little residual lung volume/gas from pre-flush. I've never had a single issue. The sidewinder cl does not have a dump, so as I'm sure you know you inhale cl volume, and expel via your nose until you have emptied the lung, then flush with your gas. I have horrible chronic allergies and half the time can barely breathe out of my nose. It's actually been my biggest annoyance since going to a CCR. But in class I expressed to Edd that I was having trouble getting the the right p02 of verification flushes. He said it's very common for people that exhale lung volume nasally to actually also simultaneously orally exhale a little bit back in the loop. Obviously with horrific allergies it's even worse for me. He suggested plugging the dsv with my tongue to see if that fixes it. That's something I never had discussed in 2 previous CCR classes since my CCR has a traditional lung dump making it a non-issue. After his suggestion I did exactly what he said, and miraculously I could get to dil p02 or 1.6 with ease.
So something to think about.

yeah, you can hit 1.6 at 20, but unless go deeper or just lay on the O2 and always breath out your nose into mask (essentially using your unit as OC), you CAN'T hold 1.6 at 20 on CCR. It's just how physics works.

 

[broncobowsher]

I'm more interested in knowing what cells are used (actual diving sells with the membrane or not)
How old they are?
Same batch for all of them?
Rule out some basic stuff before trying to engineer around possible bad cells.

My end of dive O2 spike I started doing at the end of my 30' stop. So much easier to get that spike and you have a nice rich mix on the way up to 20'. Time to leave 30', blow the O2, watch everything hit the red, yep all can still push over 1.6 PPO2. Now ascend to lower that number.

 

[cerich]

I'm more interested in knowing what cells are used (actual diving sells with the membrane or not)
How old they are?
Same batch for all of them?
Rule out some basic stuff before trying to engineer around possible bad cells.

My end of dive O2 spike I started doing at the end of my 30' stop. So much easier to get that spike and you have a nice rich mix on the way up to 20'. Time to leave 30', blow the O2, watch everything hit the red, yep all can still push over 1.6 PPO2. Now ascend to lower that number.

Just going to add that doing above you really need to be watching O2 units as well as PPO2 on CCR. I am sure you know, some reading may not and still be thinking more OC where it takes much more work to worry about units