why NOT using OC/DSV?

jradomski

The NEMO DSV miGht not do great on pos or negative test thats Because there are no orings to shut off the hoses, just machined surfaces.. while the diver is on the loop this isnt an issue since the breathing ckt is gas tight.. if you bail to oc, it doesn;t matter that there is no perfect seal because the gas is going to come prom the path of least resistance which is the OC reg.. It just makes loop integrity checks a bit harder.. What you can do is just plug up the mouthpiece and chech the rest of the loop integrety..


The original Nemo DSV did not have any orings on the barrel and some gas was able to escape from around the barrel..

The 'wetness" will vary based on position, this is due to the oc second stage "exhaust" valve..

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Joe Radomski
CCR Trimix Instructor Trainer
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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

ScubaDadMiami

After hearing of so many episodes where carrying a second stage is not adequate, I am convinced. It doesn't matter what would seem logical; it only matters what actually happens in real life.

I am okay about spending the money. Now, I just need to start looking into which I should choose. I do really like the fact that the Dive Rite Optima DSV has no o-rings. I wish that they would come out with it before my search is over. That would make things very easy for me.

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ROB DAVIE

Try the Divematics USA unit. You will like it!

Rob

Simon Mitchell

Mike and Keith,

Thanks for so eloquently putting some real-world context on the nature of CO2 hits. It may have sounded a bit supersilious when I advised Pelagian to talk to someone who really had suffered a bad CO2 event, but anyone reading your accounts should immediately appreciate why I suggested it.

Simon M

iain-hsm

Hoffi.

Could you give more information about your C02 trial? From your post I read you’re using a LARV oxygen set a 1 MSW? Did you get to measure the C02 content or was it just a subjective test. I know it’s a lot to ask but I would love to have a reference to a trial along these lines. If not then a fully detailed description of the dive, date etc and your account of your cognitive ability together with an account from the person/people who supervised you to give there account of what your capability was after the dive.


Also although stretching the thread again to clear up any misunderstandings between military designers and the general public I would like to submit in our defense the following:

1. There are no military designs of rebreathers in any form of trial or beta trial in use with the general public nor have there ever been.

2. Your comment that the soldier’s life is secondary? I think your wrong on this. Military designs require that said soldier to be delivered in one piece, alive and on time!!


While you may be aware that under our present state of readiness current military diving operations are allowing combat mission dive profiles and this has increased the level of risk (and deaths) The only mil spec equipment in question is LARV, Mk16, Stealth, and CDBA Mk3 and for the US and Canada CUMA and SIVA. I suppose I should also include the FROGS and CRABS.


3. BOV or OC/DSV call it what you will. I would give this priority at the moment it a no brainer, use it.

nskdrs

Hi Ian,

sorry, either me or my Mac-browser is struggling a bit with Rebreather World quoting-options.


It was a subjective Test to gain firsthand experience on CO2 tox with high and low PO2.

Did two tests on different weekends.
Modified LAR (not sure III or V) owned by a friend ( needle-valve, 1-2lpm ) with 100%O2,
no scrubber. No exercise inwater, just breathing.
Heavy symptoms of ensoufflement, fear of drowning, lack of focus after approx. 5min minutes, hard to manage swap to OC-regulator right in front of me.
Aborted test while swapping to reg.

Left me with dizziness, headache, feeling weak for the rest of the day, did not breathe any O2 after test on surface, just air.

on another occasion:
Dolphin active SCR with 6lpm orifice ( or close ) 50% Nitrox ( or less )
Full scrubber with approx. cold 3-4 hours on it.
Took out flappervalve on exhaleside.
Swimming towards tree in a lake.
Swimming stronger after 3-5min.

Swap to OC-reg on the first symptoms which show up softer, recover, going back to loop,
abort test approx. after 10-12 min.

Same symptoms as above but more mild.

Surveilled by a friend who was into homebuilds at that time, no certified instructor present.
Did this summer 2002 when I started to do deeper dives with Rebreather's and mixed gases.


On the other topics:

I'll stand corrected on my speculation mode, was too fast with typing.


cheers,
Hoffi

silent running

Hello all. I don't like BOVs for the lack of comfort, lack of simplicity(I have seen people with plenty of problems with orings/leaking) and poor WOB at depth. That being said, they are obviously useful in some designs where a manual dil addition is not possible or easy. But in those units with OTS CLs with manual dil add on the inhale lung, like a properly set up Meg and Prism where fresh dil involves raising your hand to your chest and pushing the dil add button, why would it be needed? Other than redundancy, what is the major difference in the moment of crisis btw doing this then going open loop and a BOV? -Andy

Drmike

Manual flushing can add another task right when you dont need any more tasks - controlling your bouyancy. It may not sound like much of a big deal now but when your really panting for breath, stressed and have no coordination going to the BOV or OC and to a lesser extent Open loop doesnt need much degree of control or thought, and doesnt cause much if any change in bouyancy. Manual injections/blow offs are a little harder to pull off whilst not effecting bouyancy especially when you are a panting disorienated bag of sh1t



FWIW my BOV is comfortable and only has two more o-rings in it than my DSV does.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

silent running

Hi Mike, I'm a tad confused. If I'm injecting fresh dil into my inhale lung, which is right next to my inhale hose and then venting through my nose, why would there be any change in bouyancy? Glad to hear your BOV is not a drag, but I imagine the lack of discomfort in your case might have something to do with your FFM taking the load of the BOV off your jaw, no?

Drmike

LOL Im sure the FFM has a lot to do with it.



With open loop it takes no effort to ensure what you suck in = what you blow out as you control both actions with your lung capacity so gas volumes are kept constant

With the BOV your loop is closed and your lung volume in/out is fixed and equal so the overall average gas volume at any one time is constant.


With manual inject in and blow out your finger controls how much gas goes in the loop and your lung/nose controls how much you vent. The gas volumes need to be balanced between how long you press the button and how often against how much you breathe out and how often.

It just takes more effort and thought to balance thats all. I dont want to have to think or balance anything when taking a hit.

Obviously its easier at depth but try it worse case during deco at 6m (assuming a scrubber breakthrough) and see how easy it is

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment