Hybrid Rebreathers

johnv

it is possible to be too cautious.

adding redundancy almost always adds complexity. If you are not careful, you can find that your fully redundant system is much harder to manage, and therefore you are likely to cause an accident or make a simple problem worse.

For instance, with your double system, if your electronics give a high O2 alarm which system has malfunctioned? You might well tox whilst you turn off the wrong system - or maybe you turn off both - or maybe something else - see what I mean.

it's easy to forget why a KISS valve is so called - Keep it Simple!


John

Brainx3

Hi,


We all agree that there's no perfect unit. Trying to modify a unit to have more redundancy would require some design changes or ad-ons, and the diver will need good understanding and training in order to improve his/her ability to react according to the new design/mechanism.


Best Regards. Wael

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johnv

my point is that it is possible to introduce much greater risk in one area when slightly reducing the risk in another. In my view, a double system creates a load of new problems to solve ones that don't really exist in practice.

If the solenoid is crap use a good one, if the CMF orifice blocks use a filter. if the batteries fail use better ones. Those are examples of solving problems - adding a whole new O2 system doesn't add safety just complexity.

I've seen people with so much gear they can't achieve even a simple dive, this train of thought heads down that route - what if both your O2 systems fail - do you need a 3rd? what about a 4th - you can't be too careful.

I'd rely on O/C bailout or if necessary take a completely redundant CCR.

John

Brainx3

Hi,


John, I don't see your point really. If you are saying that everything can fail, then I agree with you, but if you are saying that since everything can fail then there's no point of having additional system or customize a design to be more redundant, then I definitely wouldn't agree. Eventually it is up to the diver whether he/she can dive the unit properly and is really prepared for emergencies or not. The same logic would apply for anything else. If you skydive then you definitely want to take extra parachute with you in case the first failed to open. Simplification is always the best, but development also makes things easier. As I said before, there's nothing perfect.


Best Regards. Wael

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johnv

My point is that unless adding extra components helps solve a real world problem, then added complexity makes your rig more unsafe.

paulraymaekers

hello Johnv, have you dive a hybrid unit already??

once you've done it, you'll understand, or better, 'feel' how it works.

paul

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Drmike

I looked into the idea of hybrid for a while but soon dismissed it.

I think your trying to add redundancy to solve one problem but by doing so increasing risk of bigger problem.


Hypoxia isnt a risk on a ccr at any place (other than the surface or shallows) so worst case even if your o2 feed system fails the most thats going to happen is your going to maybe effect your deco. The degree of effect will depend how frequently your checking your handsets or if your running near min loop. Either way your parachute isnt needed to stop you going hypoxic during the dive - thats almost impossible to do (other than in shallows when you will be running high ppo2s anyway for deco and not being distracted so much from checking.

Hyperoxia is a big risk (far easier to get than hypoxia) on ccr especiallly deep. PPO2 can increase rapidly at depth with little/no noticeable change in loop vol. Your degree again of risk depending on time between checking handsets.

Adding a 2nd O2 injection method effectively doubles your risk of a failure leading to hyperoxic loop. Stuck open solenoid, leaking,bypassing orifice manual inject oring bypass.

So yes solenoid parachute will reduce risk of hypoxia in shallows during ascents (but even then you really would have to work hard to do it and not be checking to go hypoxic) - but at the same time it does increase risk of loop going hyperoxic by leaking.

Afterall if your going to counter risk of hyperoxia (thru one of the o2 systems leaking) by relying on frequent monitoring - then you dont need the redundant o2 system in 1st place as your monitoring!


after considering the above I decided it was little advantage, some disadvantage, some extra complexity - so not worth it

I also found seldom used solenoids (when running eccr manually) stick more freq and are less reliable than ones used all the time)- so that may make an unwanted o2 leak even more likely

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Dave Sutton

Hi Mike, long time, no debate...

I'd have to toss this one up into the air and catch it with either one or the other hand: In the water? Dunno what advantage it really offers, and when I have an eCCR 'capable' rig on my back no matter hybrid or not, I always let the eCCR part do it's job and that's that. I'd never 'improve' an existing eCCR to add another system, just does not make sense. And at the same time, I'm equally delighted to dive a basic mCCR and find their simplicity to be a nice change of pace.

On the other hand, and this is unit specific: The thing I particularly like about the rEvo's hybrid design is the modular flexibility, which allows a 'trip saver' mode to be used in case the eCCR controller decides to go on walkies during the middle of a trip. No decision to be made... just jump in and dive it as an mCCR. Seems to hold value insofar as an expedition capable rig is concerned. Other rigs set up as hybrids? Dunno: The mechanation to me is just as important as anything else. Not many other rigs will offer dual PP02 monitors even after a total eCCR controller failure on site.


Dave

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Drmike

Hi Dave, long time,

Having done lots of trip rebuilds I like the idea of having a 'trip saver' in case one o2 inject system fails - but that is a different thing I think than the concept of a parachute system

Of course we could just all dive units with reliable controllers in the 1st place lol! [yeh I know and I aint even drunk!]

If I was diving a KISS unit and it failed on a trip - recon a few o-rings would sufice as a trip saver (pack smaller/lighter and cheaper) than a whole new electronic control system

Ive been forced to dive several of my eccr units with no electronic injection when they failed - I think its actually good practice to do it now and then anyway so wouldnt let no electronics spoil my trip. No need to add a KISS valve when I have a display and a manual inject button for those (hopefuly) very few times my electronics fail on a trip. If my electronics were so unreliable that I needed a back up Id be buying a different rebreather frankly

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paulraymaekers

Hi Mike, actually, on the hybrid rEvo, you don't have to take anything spare with you: in its basic configuration it already has 3 independent electronic systems: the controller, and 2 independant PO2 gauges with each their own HUD

if the controller fails, you just continue with the 2 gauges, like if you were diving the mCCR rEvo.

even more, without changing anything to the hose routing inside the unit, suppose you have a blocked/stuck open solenoid: you simply plug it with the plug you normally use to close off the orifice if you want to dive deeper then the max CMF depth: it's the same threath !

paul

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