Aqualung’s ACD - safe or not?

[Lopez116]

I have a Legend with the ACD in the first stage. I read some reports about the ACD closing during dives, which has now led me to consider dumping the Legend and picking up a new reg. In the research I’ve done, I don’t know if it’s entirely clear that the ACD failed or there was servicer error in play. In any event, re-thinking things now, the ACD seems like a dumb idea.

Thoughts?

 

[WillHartNZ]

I’ve been using mine for a few years now and haven’t had any issues.

I also sold quite a few sets for the shop I used to work at. We never were made aware of any customers having issues nor did we hear anything from the manufacturer about any potential issues.

If your legends are still working like they should I wouldn’t think there would be any need to get rid of them.

 

[rsingler]

It is a question of proper torque for the ACD valve and the yoke fittings. There is a Consumer Safety Notice out which you can find at www.aqualung.com. It applies to Titan LX ACD Yoke SNs beginning with E, F;
to Core ACD Yoke regs with SN's beginning with E, F, G and H prior to H043301;
to Legend ACD Yoke regs with SN's beginning with E, F, G and H lower than H043301.

It should be a ten-minute disassembly/reassembly of the ACD & yoke fittings.

DIN is not affected.

There was apparently one gas shutoff incident related to rocking of the yoke under pressure, where the ACD valve unscrewed.

With only one incident that I'm aware of (third-hand), and Aqualung's retorque request, you should be fine. BUT! Make sure your shop is aware of the Bulletin and is completely conversant with the reassembly and torque settings. The service is no charge. If they don't know about it, change shops!

But IMHO, the whole ACD concept is a solution looking for a problem. What diver needs a valve to keep water out of his first stage? And it won't help the diver who has a wet yoke and reconnects it to his second tank on the boat. As soon as he tightens the yoke and pressurizes, the droplets of salt water are blown past the now open ACD, and get inside the reg anyway.
Old fashioned is better: dry your yoke with a bit of towel before you fit the cap between tanks. It's why I don't let the boat crew ever switch my tank between dives. They're just moving too fast.

Retrofitting to pre-ACD yoke is only possible for a few early ACD legends.

Just go get it checked, if your serial numbers are in the range above.

Here's a reported incident:
Aqualung Legend LX First Stage Failure at depth

 

[Lopez116]

Right. I remember checking my serial when the bulletin came out and it not being of the affected units.

I guess the crux of my question is - if it’s not an affected reg but still has the ACD “feature,” any reason to worry?

 

[rsingler]

I guess the crux of my question is - if it’s not an affected reg but still has the ACD “feature,” any reason to worry?

I wish I could tell you. My Aqualung certification is a couple years old now. I don't know if they've changed the parts since the Consumer Bulletin, or whether they're just more careful about torque. I won't have access to the latest specs for another few months.

My gut says have the assembly checked anyway. The design of that assembly is interesting (and good) engineering. But putting it together is NOT intuitive, and unless a shop does Aqualung 90% of the time, there is ample opportunity for a mistake.

Better yet, switch it to DIN.

 

[Diving Dubai]

I can't reliably comment on the yoke because my 3 ACD regs are DIN.

However the bases for the ACD operation is that the mechanical force clamping the Yoke of Din to the cylinder will open the shutter (valve).

On a DIN if the centre post becomes loose (can happen on all DIN) then it will leak on the surface in a similar way to not having an O ring

On a yoke, if the yoke nut is loose then yes its possible to get a gas seal between the O ring but not open the shutter enough.

The clue here is the loose yoke. If your yoke wobbles on the first stage, it needs tightening.

While I appreciate @rsingler opinion on the need for ACD - and I agree you don't need it. I prefer it on my regs. I have another couple of Apex sets without ACD. The nice thing for me, is its worry free when packing or washing kit. I have no dust cap to loose and I can fully immerse my regs (or they can be knocked into the wash tank) without worry.

After a hard day's diving or teaching under the hot middle East Sun, I appreciate this little advantage

I can and do live without the ACD, but I prefer not to.

 

[halocline]

I suspect that Aqualung has researched the function of this feature pretty well, and looking at the schematics, it's very tough to see a way in which it could actually cut off air without simply falling apart.

But, I personally would never buy a regulator with one of these. There is simply no justifiable reason to put any possible obstruction in the air path. The oceanic system, which involves a plastic ball on a spring that opens and closes with each breath, is far worse, but why bother at all?

I'll tell you why, because it gives the salesmen something to talk about that can sell new regulators. That is the sole motivation behind a design like this. It will never make the reg breathe better or be more reliable. Dust caps have shown that they work perfectly in keeping water out of the HP section of the first stage. And the consequences of a small amount of fresh water getting into the first stage are minimal anyhow, easily fixed with a cleaning.

Plus, these things don't address other real causes of water in the first stage anyhow, which are wet fills and water on the fill whip (notorious in boat fills) or on the regulator and/or tank valve (when switching tanks). What they DO accomplish is hiding the filter from plain sight, which makes inspection for water intrusion much more difficult.

 

[decompression]

We’ve been using the ACD Titans on our rental fleet for many years now.......zero incidents......if they are trusted with students that might say something about them.

 

[Lopez116]

Thanks everyone for your replies.

 

[reefrat]

Keep in mind also that if you are using a yoke adaptor it is important to ensure that the adaptor is screwed fully in and tight to open the ACD and seal the yoke/adaptor connection before fitting the first stage to a tank. However this is all basic stuff and applies whether the first stage has an ACD or not.
The Aqualung ACD works as far as keeping moisture out of the first stage when it is removed from a tank but it is another attempt to engineer out the consequences of substandard diver knowledge and technique, it is therefore an unnecessary complication if the diver knows their gear and is correctly trained.