DIR- Generic ADV question - converting JJ-CCR to GUE JJ-CCR

[Rich1280]

Afternoon,

For our CCR2 class we were taught plan a hypoxic zone and manage the loop through it, making sure you knew what was in the loop, descending quickly past it, etc. We weren't taught to switch off hypoxic bailout for the BOV, it was part of the planned hypoxic zone briefing so knowing and having a plan to bail to a stage not BOV if needed.

Was just reading the cons above and having a think. I'd never considered adjusting the loop volume without moving my arm, if I want to and I'm at min loop, I'd just take a big breath and trigger the ADV, no movement at all. Plugging hoses across didn't feel cluttered, I'd thought it might, but wasn't really a problem. If I want to add dil from off board, I'd have had both cylinders off, right post on the ADV, left post on the BOV where I can inhale and exhale into the loop, or finally I can add off board. This is a multi step failure to get to that point, and manual adding dil and doing a manual O2 flush at 6m is way down the cascade.

I've not dived a standard JJ set up, so can't say when and how much I'd use the Dil MAV, but intuitively it seems infrequent as I think about my diving. It mainly seems like an entry port to the loop for dil issues? Similarly the shut off reduces my options for adding dil from the ADV, which seems to be then why I need the dil MAV, and one is the fix for the other?

Rich

 

[justinthedeeps]

I was wondering about BOVs and hypoxic bailout as well. At one point even tested a shutoff slider on the feed right next to the BOV, but this actually can result on a collapsed second stage diaphragm--leaks or damage possible, on a Divesoft BOV at least. Also another confusion point on an already complex system.

On the onboard hypoxic dilout rig, the 'post' valve feeding the BOV (and/or ADV) could be temporarily closed to avoid unwanted shallow hypoxic gas delivery?

Unlikely though. Either the conditions are easy, so shutting is unnecessary. Or conditions are rough, and nobody will waste time prophylactically operating more post valves in those conditions.

I have witnessed the ADV blowing off vigorously and over-filling the loop on a head-down diver who was near the surface, trying to descend, exacerbated in that case by the rig being head-heavy. I am not sure how much the 'valves up' configuration contributed. Fortunately the diluent was air, in that case.

The ADV is not always effortless to engage by breathing, though it depends a lot on positioning.

The diluent MAV does a different job than the ADV, and does not replace it. It does provide an effortless gas addition in all orientations, but does not automatically engage in head-down positions. These are small but noticeable luxuries, even if not strictly necessary. You'll never need it on a formally executed DIR team dive, but it can come in handy on a more freeform dive exploring around a reef doing photography or something.

 

[flymolo]

I don't have an ADV on my unit so I'm interested in hearing how people manage to avoid accidental addition of hypoxic dil on those that have them. Is the answer just being mindful to not bottom out on your CLs while descending through the hypoxic zone?

 

[rjack321]

I don't have an ADV on my unit so I'm interested in hearing how people manage to avoid accidental addition of hypoxic dil on those that have them. Is the answer just being mindful to not bottom out on your CLs while descending through the hypoxic zone?

I think the first question we should be asking is how many people are actually using hypoxic dil?

And on a CCR that wouldn't be mass dumping O2 into the loop if the ADV fired.

I haven't tried but I suspect it'd be super hard to even get a hypoxic breath on the surface on my eCCR Meg. The dil is on the exhale CL and the O2 add will be copious and long before your lips. This is/was all by design. Obviously a mCCR is going to struggle to keep up the ppO2 if the ADV fires.

 

[Rich1280]

I just spent 2 weeks with hypoxic dil, 10/70. No issues identified really, the pre check before sticking it in your mouth so it's PO2 0.7 on the surface, then sensibly descending flat or slightly head up stops the ADV. Not sure if mine is set tight, but to trigger my ADV I need to really get left shoulder down, and even then it's not like a purged reg. If I slightly roll, I'll hear it gently adding and can reorient before big volumes are injected.
If I want to collapse the lungs to do it, it's then hypoxic gas on top of the lung full of known gas, so to my mind it's the last bit of the ventilation, so a small fraction of the gas exchange volume and then dead space. I then blow it first back through the canister to mix. The next breath is the short section of hose full of hypoxic gas from ADV to valve, then the rest of the volume is premixed and oxygenated.
I'm sure it will be possible to ventilate with hypoxic gas with multiple lung collapsing breaths to inject on every cycle, but practically how often are we doing that? I know there's been multiple deaths on hypoxic gases, I've read a number of the reports, but I think good awareness and volume management mitigate them if you're not on single digit oxygen percentages.
Rich

 

[flymolo]

And on a CCR that wouldn't be mass dumping O2 into the loop if the ADV fired.

Good point I keep forgetting about solenoids

 

[rjack321]

I'm sure it will be possible to ventilate with hypoxic gas with multiple lung collapsing breaths to inject on every cycle, but practically how often are we doing that? I know there's been multiple deaths on hypoxic gases, I've read a number of the reports, but I think good awareness and volume management mitigate them if you're not on single digit oxygen percentages.
Rich

Ending up on a hypoxic loop at or near the surface following an ascent and being on the surface starting a dive and going hypoxic are from a "realism" perspective pretty different.

 

[GF99/99]

I think the JJ configuration and to have or not to have the flow stop and dil MAV really just depends on what you require out of your unit and what kind of diving your doing. I don't think there really is no right or wrong answer. The best answer is what setup works for you and your dive team is the correct setup.

I know me personally like having a flow stop and second MAV on the dil side. But I have them for odd reasons that most probably don't need them for so there is very good argument that they are not required for a standard GUE dive.

Flow stop is great for dil switches (not trying to start a conversation about the pros and cons just stating what I use the flow stop for) prevents you from accidently sucking in your onboard dil. Also when I dil switch I passive flush as I think it is alot more efficient so having a flow stop helps to vent out the current gas and fully pull your unit into a negative. The flow stop I have also found on occasion comes in really handy when cave diving and you get into a weird tilted down position, its nice to be able to shut your ADV off so its not just firing away.

The other odd ball is the flow stop is kind of a must if your diving trimix offboard and your onboard 3l dil tank is air used only for inflation.

For the dil MAV once again I like this for convenience for dil switches. It is also nice just for standardization (and of all things GUE I can't believe they don't do this) of Lean Left and Rich Right (once again not trying to start another discussion just stating what I do) so I try and carry deco o2 rich gas on my right and if I plug any of those into my unit ill plug them into the O2 MAV and my trimix I carry on my right so if I plug any of those in they go into my dil side.

Now the other odd ball that I'm sure does not apply to most is for dual CCR/BOCCR diving. I mostly dive JJ and Triton as a B/O unit and I have started to dive with a splitter/manifold that connects my JJ MAV and the Tirton together and an offboard that can be plugged into one LPI nipple that feeds both. For hose routing and not to get confused having a Dil side MAV is kind of key for this. (once again not trying to start another discussion and have people tell me this stupid just stating what I do because it works for me)

Now yeah you can dive with out this stuff. Heck like @flymolo said I have another unit that also that does not even have an ADV and only has an O2 MAV and I can dive it no issues but at the same time for me having a flow stop and dil MAV on the JJ is just easier. Its that whole works smarter not harder thing.

 

[Matan]

The shutoff valve+ dil MAV are the children of CE testing nothing more.

1. Either configs (I dive both factory and GUE one) it's nice having a spare MAV as I don't need a dil MAV.
2. The shutoff is nice to add to a switchblock just like a lot of GUE CCR divers do for other reasons.

The above are just to avoid throwing away good parts that aren't really necessary in the unit


You can dilute the loop with a BOV (factory config) or backup regulator/ BOV (GUE config) - The only usage here IMHO is when I'm trying to flush and the ADV doesn't work for some reason.


*for clarification BOV should be fed from backgas (GUE) or bailout bottom gas (factory) - never from a 3L cylinder ^^

 

[rjack321]

The other odd ball is the flow stop is kind of a must if your diving trimix offboard and your onboard 3l dil tank is air used only for inflation.

why? When I was backmounting CCR in caves I offboarded dil and wing gas (QC6->>Yblock-->>BC whip for wing / LP hose for dil). The left side onboard tank was suit gas with only a BC whip on it. Not sure how/why that would require a flow stop? I had one but was perfectly capable of removing it too.

I have a Meg with TOS CLs though, not a JJ