Adding the Dil MAV on a JJ

[darylm74]

Did anyone, outside of Europe, add the air MAV on the JJ? I was looking into moving into Trimix on the JJ, as I am Trimix certified OC. Hell the reason I got the JJ was to deep dive. I am just trying to determine if this is necessary or just an add on due to the European standards.

 

[michael-fisch]

Every RB I own, well with the exemption of my IDA 76, has a diluent MAV and an O2 MAV. Can't imagine diving without them.
Hope that when you write air MAV you mean diluent MAV.

Michael

 

[taimen]

The diluent MAV was not part of the original JJ configuration. I have been told it was added later when CE certification process required installing a flow stop to the adv hose.
Thus European standards didn't require the MAV itself, but with the flow stop closed there has to be another manual way to add diluent since pressing adv membrane doesn't give gas anymore.
I thought also international edition JJs ship with diluent MAV now.
Many JJ divers still remove the diluent MAV (and the flow-stop) for simplicity. Others keep the diluent MAV and connect ADV and diluent MAV to completely separate gas sources for redundacy. Both ways are well reasoned.

 

[darylm74]

Yes, when I said air, I meant diluent. Sorry, had been a long day. I have had my JJ for nearly 3 years and mine didn't come with one. I have never had a need for one thus far but I wanted to see if it might be something worth investing in.

 

[cathal]

The diluent MAV was not part of the original JJ configuration. I have been told it was added later when CE certification process required installing a flow stop to the adv hose.

Interesting, as a rEvo diver there is no shut off or flow stop on the adv and it passed CE? Not that I ever used it tbh.

 

[taimen]

Interesting, as a rEvo diver there is no shut off or flow stop on the adv and it passed CE? Not that I ever used it tbh.

That is related to a very specific test in the CE requirements. Obviously some other rebreathers have passed that test without shut offs, but this is how JJ solved the issue.
From the JJ-CCR manual:

3.2.1 Vertical head down position The JJ-CCR does not meet the requirements of EN 14143 section 5.6.1.4 (Hydrostatic imbalance test) with a pitch of -90 degrees (Vertical head down position). A vertical head down position during a dive is an extremely unusual position for a diver and normally never used when not absolutely necessary. Within a vertical head down position an unintentional activation or freeflow of the ADV can possibly occur. To avoid it when the diver is forced to a vertical head down position he can close the in line shut-off valve on the ADV and use the manual diluent adding valve to maintain an optimized loop.

 

[cathal]

That is related to a very specific test in the CE requirements. Obviously some other rebreathers have passed that test without shut offs, but this is how JJ solved the issue.
From the JJ-CCR manual:

3.2.1 Vertical head down position The JJ-CCR does not meet the requirements of EN 14143 section 5.6.1.4 (Hydrostatic imbalance test) with a pitch of -90 degrees (Vertical head down position). A vertical head down position during a dive is an extremely unusual position for a diver and normally never used when not absolutely necessary. Within a vertical head down position an unintentional activation or freeflow of the ADV can possibly occur. To avoid it when the diver is forced to a vertical head down position he can close the in line shut-off valve on the ADV and use the manual diluent adding valve to maintain an optimized loop.

Thanks for that clarification.

 

[Jack Hammer]

No real need for the dil mav, it's kinda redundant. You can just manually fire the adv. Additional offboard gas, if needed for some reason, can be piped in via the O2 mav.

 

[doctormike]

Seemed unnecessary to me, but maybe I'm missing something.

I haven't had an ADV free flow yet, but If you did, you could just shut down your dil and feather it if you needed a bit more, right? It's not like you are adding a lot of dil once you are at depth (I know, caves).

I guess the dil MAV also gives you a second way of plugging in offboard dil, so if you ran out of onboard dil you wouldn't have to sacrifice the ability to manually add O2 or keep switching lines. Also good for dilout.

 

[rjack321]

@darylm74
1) what does your instructor say? Some are pretty particular about configurations
2) are you using a BOV? In a pinch BO can be inhaled and then exhaled into the loop as dil