Is a BOW fast enough to save a life?

Ben Field

I've never fully understood closing ADV's once at depth, I suppose that they (ADV's) must be really easy to trigger on some rebreathers? On my KISS you have to suck like a backalley ho before the ADV kicks, certainly keeps you aware of loop volume and is maybe too much effort for "open loop"? Will have to give it a try and see.

BEN

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Dave Sutton

Why in the *world* would anyone do that? Having an active ADV (connected to a sensible diluent) is a *huge* advantage for the thinking diver with absolutely no downside.


Dave

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Dave Sutton

Hi Ben,

Makes no difference how well or poorly an ADV breathes.... I can see no reason to shut one down. Ranging from the Mark-15 (makes the KISS ADV seem like a high performance regulator) to the 'Boris and rEvo ADV's (which *are* high performance regulators), they all ought to be left on. The better they breathe, the more usable they are for an open-loop flush. I'd be damned if I'd loose that hands-free flush capability. Just seems silly. My rEvo ADV breathes as well as any BOV regulator (probably better) when being used as an open-loop supply regulator, and save for caustic cocktail or a ripped hose can do all of the work that a BOV does. Why would anyone turn it off?


Dave

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"Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com

PCDiver

Let me explain how I use my ADV (no rocket science here ).

Before I switch on my rebreather I make sure my ADV is closed. This ensures that only O2 gets added to the loop. I do not inject diluent manually. The ADV remains closed until my 6 meter cell check (if circumstances allow such a check in the water). This way I know that my cells are not limited.
I can easily reach my ADV shutoff valve, even in a dry suit.

For the descend part of the dive I open the ADV. Since I shoot video on the way down, I cannot inject dilent manually. I need both hands on the camera.

When I reach the bottom part I close the ADV. Why?? A couple of reasons:
1. It allows me to detect loop volume loss.
2. A closed ADV cannot leak diluent in the loop.
3. If it is closed when I reach the bottom, it will be closed when I start the ascend :-) One less thing to do before starting the ascend.
4. It gives me a better feel for my loop volume. I manage my diluent consumption better with the ADV closed.

I'm not saying that this is the best way, but it works for me.

Peter

PCDiver

If my memory serves me correctly there is no way to isolate the ADV on a rEvo since it sits on your back inside the case.

Dave Sutton

And why would *anyone* want to isolate it? ....

If an ADV fires due to positional changes of the diver, the system is poorly designed. Let's isolate "desired mode of use" from "a suboptimal method of use used to compensate for poor design".

No well designed system should fire an ADV without demand. All else follows good design. The Mark-15's cracking pressure is at one end of the extreme (IE: "barely usable for open loop") and the rEvo at the other end of "good" (IE: "Breathes like a good regulator but never flows due to divers position"). If we're worried about freeflowing, we're either not using a good design or we're not maintaining it.


Dave

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PCDiver

Dave,

any ADV is a combination of springs, valves, levers, membranes ... These are all moving parts that can get stuck in open or closed position. Closed is not an issue, you just add diluent manually. Open means either partially, a trickle of diluent in the loop, or fully open, a freeflow. Both are dangerous, especially at or near the surface.

Not having the possiblity to isolate the ADV is in my book a negative point.

Peter

Dave Sutton

Not if they are (1): Well designed and (2): Correctly maintained.

I'll re-recite my mantra:

Dive well designed and correctly maintained gear and it'll be trouble free.
Dive poorly designed or poorly maintained gear and it'll be troublesome.
Dive the former and you'll be confident.
Dive the latter and you'll be skitterish and will be adding more and more crap and will be performing more and more in-water routines to support your unreliable rebreather.

It's a case of the tail chasing the dog.


There's a huge difference between the *ability* to shut off an ADV and the *routine procedure* of shutting one off. We all have a diluent valve we can use to deal with an unexpected problem, and many have the ability to add an isolator. I just am troubled by the routine use of same. But, hey: Knock yourself out and use what works for you. As long as all goes well it makes little difference.


Best,

Dave

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"Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com

PCDiver

Come on Dave, you cannot guarantee that an ADV will never fail. Think about a week long dive trip with limited cleaning possibilities. Salt can easily prevent a valve from fully closing.

I like the APD solution. The ADV is sensitive, hence breathes easily. I use it when I need it (during descend) and it shut it off when I don't need it (bottom part, during ascend). Easy.

I know that on the standard rEvo, the only way to isolate the ADV is closing the diluent tank. But that also means that you need to operate your diluent manually by opening and closing the tank. I personally find the ADV + shutt-off valve a more elegant solution. And certainly not, like you implied, a flawed design.

PC

schford

.... but who decides on what is well designed - some might argue that units with rear mounted counter lungs like the Sport Kiss and rEvo give much higher WOB than other units like the Insp or Evo or Meg so could be a pretty poor design - but it gives them the advantage of a clutter free chest area (amoungst others) and it also means that the ADV location is not in the OTS lungs and does not cause it to fire when you collapse one of the lungs due to rolling etc.

You could move the ADV location to stop this happening with OTS designs but then it might mean it was not so easily accessable to assist with a fast dil flush of the loop.

I believe that all design are a compromise with trade offs depending on what the designer believes is the most important.

To say that no well designed system should fire off the ADV is a simplistic view point and does not, I believe take into account the trade off decisions that designers have made.

If it really was a bad design then I am sure that the hundreds / thousands of people who have bought those Rebreathers would not have bought them.

Is it perfect - no. But then I dont know of a Rebreather that is! They all have design trade offs, that us as users may or may not agree with, be it:

Higher WOB on some units to have a clutter free chest area.
Electronics in or out of the loop
Proper breakthrough testing done on a scrubber
CE marking
mCCR or eCCR

etc etc oh and not to mention a decent price!

I think the basis of our unit seleciton is how much we agree with the designers or not!

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