Membrane use preventing Water?

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v101

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Just got done with a some diving in FL, while getting ready for a dive, I was Don'ing a stage bottle, and my loop was partially opened, (first time for me...) :-(.....

Anyway some water entered the loop, I am diving a KISS sidewinder, and enough water got into the can, to pass through to the counter lung. I went to 20' and did my 1.6 check, and my cells failed....

I had to end the dive, and re-pack the unit. I dried my cells off, and all was good for the dive later that day....

However this got me thinking about if anyone uses water resistant membrane filters in their rebreathers?

If a membrane was installed, it would prevent the majority of the water from entering. There are many companies that offer membrane filters, for various applications. I am curious if anyone has heard of these being used by other rebreather companies, or if anyone has researched this for practical use?
 
we are doing some testing and R&D on them now. The Cis-Lunar scrubbers had one that actually allowed them to change the scrubbers while underwater. The general problem is creating one that is sufficiently hydrophobic while minimizing the increase in WoB which is quite difficult. I have some more samples coming to test, but we'll see how well they do.
The specific problem with the Sidewinder is where you put that membrane. To prevent the first scrubber from getting wet, you would have to put it ahead of that scrubber and there is nowhere to add a water trap and OPV which is why the current device is in the counterlung. It's an inherent design flaw in the unit, albeit a minor one for most.
Are you using cells with membranes on them? The ones that Edd sells do not have membranes on them, so they are much more sensitive to water
 
The Cis-Lunar Mk5p had a hydrophobic membrane around the scrubber. It was designed to prevent water from contacting the scrubber material, and it was billed as being able to change the scrubber underwater. I don't know how likely that was to occur, but it has been done before.

You would have to fully seal the unit, in the case of the Mk5p it used a radial scrubber with the membrane attached to the screen. Because of the gas path around the radial scrubber, this is the easiest way to accomplish it. Doing so with an axial may be difficult to fully seal both ends. Doing so with a non-removable scrubber like the KISS presents the same problem as the axial, how do you seal the scrubber? I'm not sure it's really feasible in those type of scrubber canisters, and probably not so much with axial removable canisters either.
 
My older cells didn't have a membrane on them. I've replaced all my original cells a few times now, the new ones I use have membranes in them.

I am ignorant on the membrane placement here, but just thinking out loud here. What if a membrane was placed on the top and bottom where the screen's are at on the unit, could something be done to expel the water from the loop if the bulk of the water was being prevented from entering the can?
some water would most likely get through into the can but the water could then be expelled via the counter lung.

thoughts?
 
@v101 you can't prevent water from getting into the first can and get it out in the counterlung. You can do that with radial scrubbers, but not with axials where all of the gas has to flow straight thru. Right now the water can go through the first scrubber, but the caustic is cleaned out by the second one and you can ditch water in the lung. It's not ideal, but it's better than nothing. Unfortunately since they just took an existing unit and split it apart instead of redesigning the heads, there's nothing that you can really do.
If the membrane does it's job and it's on the inlet to the scrubber, then no water will get through and with no way to get rid of it, you'll cut the rebreather off.
 
I was under the impression that any cell designed for use in a rebreather had a membrane and the circuit board was also coated. Any thing else is intended for surface use only.
 
I was under the impression that any cell designed for use in a rebreather had a membrane and the circuit board was also coated. Any thing else is intended for surface use only.

I don't believe there are any officially endorsed for diving anymore and many retailers are selling surface use ones as referenced above. DGX still has ones with membranes, I buy direct from the factory and get them as well.
 
The sidewinder is especially sensitive to getting water in the loop. You have to be diligent on closing the DSV and keeping everything sealed tight. If you somehow put a membrane at the inlet side of the exhale canister, your exhale hose would be full of water and you wouldn't be able to breath anymore. The membrane would keep water from continuing to the counterlung and the flapper in the DSV would prevent it from draining back towards your mouth.

You have to be hyper diligent and keep the DSV closed when your lips aren't sealing it
 
Membrane = +WOB, no way around it. If you are using scooters and don’t anticipate any serious exertion maybe the peace of mind on a big dive is worth it?

However, I would be interested to know, how many people with OTS CLs have managed to get water past the exhale CL into the scrubber? I had a tear in my exhale OTS CL and found 10+ ounces of water in it after a 3hr dive, had no idea, not even any gurgling. Scrubber was untouched. Is flood tolerance more of an issue for BMCL designs than for OTS? I realize some of you feel the chest clutter is too much of a sacrifice particularly in caves, but isn’t flood tolerance more than just scrubber membranes and gas flow direction, and more a series of trade offs?
 
Membrane = +WOB, no way around it. If you are using scooters and don’t anticipate any serious exertion maybe the peace of mind on a big dive is worth it?

However, I would be interested to know, how many people with OTS CLs have managed to get water past the exhale CL into the scrubber? I had a tear in my exhale OTS CL and found 10+ ounces of water in it after a 3hr dive, had no idea, not even any gurgling. Scrubber was untouched. Is flood tolerance more of an issue for BMCL designs than for OTS? I realize some of you feel the chest clutter is too much of a sacrifice particularly in caves, but isn’t flood tolerance more than just scrubber membranes and gas flow direction, and more a series of trade offs?
With good design you can mitigate a lot of flooding issues.

On the other hand, the meg is not capable of going places the sidewinder can go. The sidewinder is ridiculously light (especially compared to a meg and I have both), can be packed in small dry containers and hauled through sumps, doesnt have a solenoid or even batteries to fail. Way smaller profile too. At a price of having terrible tolerance to flooding.
 
https://www.shearwater.com/products/teric/

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