Optima ADV Adjustment

n2diving

I don't recall the state of the ADV. Many experienced O2ptima divers don't jump with the ADV enabled, especially when performing a free descent, preferring to use the manual addition valve. The Dil valve was well enough open to deliver reasonable performance with the on-board bailout, certainly at just 50 fsw. I don't routinely open my diluent valve as much as was observed in this case. I open both my O2 and Diluent valves only slightly more than one turn and we both had exactly the same brand/model of valve. If the diluent valve was open enough to provide enough gas via ADV or manual addition for descent, then the on-board bailout would have delivered enough gas that it's highly unlikely he would have spit out the on-board bailout before having another regulator in hand. However, almost anything is possible.

As I mentioned, we can speculate endlessly on what happened in the moment between the time he gave the buddy an "OK" and the buddy looked up to find the victim swimming toward him. But most of these scenarios require more time than the very brief time between the two events. The simplest and most straight forward scenario is the most likely.

Tony_Q

Hi Mark,

Perhaps there is an additional lesson hidden in this incident.

Jumping in with the ADV disabled may not be a particularly safe method of diving.

Once at depth and system is working okay disabling the ADV would be a different proposition to having the ADV disabled at point of entry and during initial descent when problems may manifest.

There may be sound reasons why experienced divers dive this way, but it is one less safety device automatically available in an emergency.

Tony

RichClark

Hi Mark

Thanks for posting your original report, anything that causes to stop and think about our own procedures is worthwhile.

Without detracting from the original thread too much, could you expand on your comment above? It seems to me that the descent is the ideal time to be using the ADV.

I dive a KISS so don't have the ability to disable the ADV, but was under the impression that in general divers with units that allow you to shut the ADV only do so once at depth and PPO2 stabilised.

Cheers

Rich

__________________
The more I learn about women, the more I want to go diving... just don't tell my wife I said that

To taste something a little different, try http://www.thechillikitchen.co.uk

n2diving

We do not know if the ADV was open or closed at entry, but the ADV does not appear to be a factor involved in this accident. It's possible for the victim to have gone open loop via the ADV rather than manual addition, but there is very little reason to think that he would have attempted it.

Some experienced divers prefer finer control of the counter lung volume than an ADV can provide, which is why they prefer manual addition and leave the ADV off. Even having an ADV is not an absolute requirement and they are optional on some rebreathers.

Drmike

I close my adv on ascent and can see logic in that, but whats the logic in closing adv on descent?

__________________
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

Drmike

what fine control is needed during descent? indeed what level of 'fine' control is really needed at anypoint in the dive?


I jump in, breathe in, breathe out -and let the expensive machine do what I paid all that money for it to do.

__________________
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

Ben Field

I couldn't agree more- you have a complex electronic CCR controlling your PPO2 and you don't trust a simple ADV? Doesn't make sense.

__________________
www.hugsac.org.uk

MarcLaukien

I dove the Optima and now the HH, and in both cases, the ADV doesn't work for me. With each inhale, the ADV kicks in, with each exhale, the OPV releases (or I have to release gas around my mouthpiece). I was told many times that I would be doing something wrong, but so far nobody has been able to tell me what exactly. My counter lungs have been adjusted numerous times in all possible directions, and my breathing pattern is normal. I have large lungs, but not as large as the volume of the CLs. Therefore, I switch the ADV off in all but the most rapid descents. The only way the ADV works for me is if I do very shallow breathing, which is something I want to avoid for obvious reasons.

Drmike

so your cls are way too small?

i still dont get it though. if your adv fires everytime you breathe in that suggests the cl volume is way too small for you -so how does turning the adv off help with descents???

__________________
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

mempilot

That was my question as well.

Having conversed at length with some local Optima divers, I understand the Optima ADV is not very proactive or aggressive as other ADVs. This may or may not be a design objective, but I guess many of them don't even use it to do DIL flushes. That being the case, it seems it may have gone the way of the appendix as a useful tool on the Optima, and many of the Optima divers are either being taught to use the MGB for flushes, fine tuning loop volume, and adding volume on descent. If that were the case for me, I'd remove the thing from the rig as an unused pieced of kit.

__________________
Eric Stadtmueller, otherwise known as, MEM "Da Pilot"