Importance of being able to dewater?

[Akimbo]

If a unit floods that completely, how likely is it that will be able to de-water it and it not just flood again immediately?

Depends on how it floods and if it can be corrected. A relatively slow leak on a rig you can't easily dewatered is a real problem when facing a hour of decompression without a downline. Meaning it just keeps getting heavier. I was trying to make the point that being able to dewater it, even if it is unusable, has value. You can get a lot of water in the loop by getting the mouthpiece knocked out during a rescue or entanglement problem. Stuff happens.

 

[Tassi Devil Diver]

It can get REALLY heavy and jettisoning it is a pretty expensive option. Allowing it to flood enough to soak sensors isn't cheap either.

I filled my CCR to the brim one (practicing bailout in shallow left the BOV open a smidgen) did not notice until cells started to go crazy, did not notice any increase in weight, the cells were fine flushed them in fresh water and cycled them through the unit as normal.

The thing about the whole flood tolerance debate is people will justify their unit in what ever way they can and their views will shift depending on what the latest unit is they are besotted with. For example there is a unit at the moment that is very popular in the cave diving fraternity (keeping unit brand out of this as the OP wished but I am sure most will know the unit I am referring to) now this unit has a very poor flood tolerance and no flood recovery from what I understand. I have watched as divers totally changed their tune in regards to flood tolerance in order to justify this newest and greatest rebreather. It is just remarkable that people are able to over look an issues that once was so important, such as flood tolerance and recovery, then clearly dismiss it as an issue when they get another unit that allows them to do dives they may not have done on another, after having dissed other units for many years because of poor flood tolerance, those concerns are forgotten in a flash as they trundle off down 1000's of ft of cave passage.

 

[Akimbo]

I filled my CCR to the brim one (practicing bailout in shallow left the BOV open a smidgen) did not notice until cells started to go crazy, did not notice any increase in weight, the cells were fine flushed them in fresh water and cycled them through the unit as normal.

How can you not notice several KG of lost buoyancy???

The thing about the whole flood tolerance debate is people will justify their unit in what ever way they can and their views will shift depending on what the latest unit is they are besotted with.

I don't have a dog in that fight. I am only talking about desirable features that apply to any rig.

 

[Tracy]

Dewatering is a primary for me. I do stupid things and my loop often gets knocked out of my mouth. On my particular unit, it is very flood tolerant and easy to de-water. I have had my exhale lung OPV come off during a dive, I was able to reinstall it without issue and continue the dive. I know a guy who may have done a rather deep dive on a virgin wreck with an inhale lung flange attached entirely with flex seal tape. Dewatering ability was paramount in deciding if that dive should be conducted.

 

[rddvet]

First, I'm glad to hear that y'all got out safely!

Second, I'm unclear on when she bailed to BOV and what prompted her to do so.

Third, she did not get a caustic. But, if she had not bailed, is there some way that she COULD have? I.e. if she had still been on the loop after getting all that water in there, is there some maneuver she might have done underwater that would/could have resulted in getting a caustic? Some series of head up/down, roll to one side or the other, etc, that would/could have channeled some caustic through the system and into her mouth?

Fourth, I think this example is one that is not example of what I'm looking for. I.e. it's not an example where an ability to de-water was particularly important. Her flood was the result of something that meant the dive was over, regardless, right?

she bailed out but not immediately. She started noting a higher wob and a gurgle that kept getting worse. She tried problem solving, and when she realized that would take too long she bailed out. Basically the wob started getting worse fast enough that she knew bailing out was the only option and to stop problem solving. She didn’t get a caustic, but at the end of the dive there was caustic when we opened the loop, but not a ton. The going head down for a bit is likely what allowed the caustic to make it into the inhale side. It may not be an example of exactly what you had in mind, but my thoughts are just like Jon’s: flood tolerance is just as important as dewatering. If she had a tear in her mouthpiece or something she could have dewatered through the counter lung. But since the tear in the adv allowed so much water in, it was impossible to effectively dewater. But the units flood tolerance allowed her time to to recognize, think, then act. So to me flood tolerance and dewatering really go hand in hand.

 

[rjack321]

On units that you can't dewater at all (revo and most kiss units come to mind but I'm sure there are others) you have the least time to evaluate the problem and react to water ingress since none is leaving passively or actively.

Units with OTSCLs, baffled T pieces, and OPVs that function as drains have the most warning of full or partial floods. Included in this are units with rear mounted CL and the butt mounted OPV although they arent usually self draining (eg RB80, SF2)

I am baffled why the need to dewater is a question coming on the heels of your near catastrophic flood. The thought of ripping or loosening a hose tower in a cave, due to a restriction is terrifying to me. Where I don't have a huge pressure clock on CCR I can suddenly have a dire emergency to extricate myself if I am forced to bail. Worst case, I have to go deeper into the cave just to turn around, and rack up OC deco like crazy.

 

[broncobowsher]

If you are planning on a 300' dive for 3 hours that could turn into 6 hours and plan for a flood, that is when the bail out plan starts turning into a bail out breather. In which case you still have a rebreather.

I think we are also missing another key part of the question, how are you diving? Solo back in a cave is a lot different than a group in open water. 300' with 2+ hours of planned deco is a lot different than 150' with 20 minutes of deco.

I have one of the non-flood tolerant rebreathers. I only have my 200' ticket and rarely down that far, but 150+ is usually the preferred range. I don't do caves. I am completely happy with my choice. But if I were to go for my 100m ticket (maybe caves) I would likely consider a different rebreather even though my current one could do it. There are better tools for certain jobs. Which way do you want to shift priorities?

If my planned diving was more severe I can see the greater desire to dewater and keep on the loop. But my profile, it really isn't a priority. The ability to travel with it is much greater.

 

[PfcAJ]

On units that you can't dewater at all (revo and most kiss units come to mind but I'm sure there are others) you have the least time to evaluate the problem and react to water ingress since none is leaving passively or actively.

Units with OTSCLs, baffled T pieces, and OPVs that function as drains have the most warning of full or partial floods. Included in this are units with rear mounted CL and the butt mounted OPV although they arent usually self draining (eg RB80, SF2)

I am baffled why the need to dewater is a question coming on the heels of your near catastrophic flood. The thought of ripping or loosening a hose tower in a cave, due to a restriction is terrifying to me. Where I don't have a huge pressure clock on CCR I can suddenly have a dire emergency to extricate myself if I am forced to bail. Worst case, I have to go deeper into the cave just to turn around, and rack up OC deco like crazy.

RB80 will self drain. Flow path is exhale loop, down a tube to the plenum between the scrubber and the injectors, counterlung. Any water that comes in is trapped in that plenum and hits the inner bellows one way valve, and out it goes. The air path for the outer bellows is two ports at the top of the injector plate, which prevents water from getting in there. Also, the plenum space is separated from the scrubber by a water draining center plate and a spacer.

If you fill that space up and invert I suppose some water will hit the scrubber, but its quite the maneuver.

 

[kensuf]

I once knocked my loop out briefly while rooting around in some stuff I shouldn't have, about 2 miles from home in 160' of water. It was on my KISS Classic, which doesn't have a way to de-water. I poured about a cup or two of water out of the unit when I surfaced 4 hours later.

I bought my SF2 shortly after that incident. The SF2 dewaters in a similar way as an RB80.

I'm now on a Fathom, which has pretty incredible flood tolerance and can be easily de-watered too.