Aqualung Legend LX First Stage Failure at depth

[reefrat]

Here is some actual new information to add!
Inspecting my store stock, I find that my most recently shipped Mikron with ACD has a small modification to the shutter valve. There is now a small raised ridge down the center on the top of the valve, not even 1mm high. My assumption is that this prevents the top of the valve from forming a metal to metal seal with the face of a tank valve, since there is no longer an unbroken, perfectly round edge on the top.
View attachment 486265
I also just received an order with that individual part, and the loose part is also the new version. So it looks like it is a running replacement using the same part number. (Can't guarantee the next parts order might not have the old version; depends on how diligent they are at rotating stock for first-in first-out.)
View attachment 486266
So at the very least, there is now an option to retrofit the ACD with an updated version of a $14 part, without completely removing the ACD and swapping it with a "standard" yoke retainer.

No, I have no idea if there are any manufacturer plans or discussions to make these a free replacement for a period of time or not.
I can say that I did my best this past week to make sure that Aqualung USA is aware of this thread - so time will tell.
Between all the resources that are probably currently focused on the DEMA show in two weeks, and the fact that Aqualung ultimate authority is in France and not the US, I would expect other updates (if any) to take some time. (Unless there is already something in the pipeline.)

But I will definitely post back if I hear anything new.

Thank you very much for your efforts in following this up and keeping us well informed.
Sounds like Aqualung is trying to keep a lid on this while finding and implementing a fix, the sort of thing you need to do when you rush an engineering change to market without due process. I hope they have applied appropriate analysis to this change to ensure it both fixes the original issue and does not create another.

 

[JackD342]

I think there are a lot more small running changes to these designs than most folk realize. And sometimes the minor addition (or subtraction) of material to the edge of a part is all it takes to keep it from an unexpected sticking or binding.

Back in 2001 they found that in very rare circumstances the Titan LX 2nd stage purge cover could "vacuum seal" to the circular depression in the diaphragm. Added a single small notch to the edge, problem solved. (Soon after added 4 raised ribs instead) This fix is kind of doing the same in reverse.

 

[Luis H]

I was wondering about just cutting a shallow groove on the face of the face of the existing shuttle valves. You would have to take ACD apart, but the groove could even be done with the corner of a file. It wouldn't require anything fancy.

 

[JackD342]

I was wondering about just cutting a shallow groove on the face of the face of the existing shuttle valves. You would have to take ACD apart, but the groove could even be done with the corner of a file. It wouldn't require anything fancy.

Purely speculation here, not advocating a physical modification beyond what the manufacturer has already begun to implement: I think it might be difficult (impossible?) to cut a groove that both allows the ACD to seal when it is supposed to, but also allows reasonable flow if planted against the face of a tank valve. I estimate this new version of the part leaves 80-85% of the valve edge free of contact if the shutter is loose enough to touch.

 

[walkonmars]

A possible easier solution is to modify the DIN/yoke adapter insert on the tank. Grind/cut a groove across the diameter inside of the O-ring ID. Then there is no way of the ACD shuttle valve face to seal up against the tank outlet. Also, the inserts are cheap and can be replaced easily if you make a mistake. The tank valve O-ring should still seal under positive pressure outward. This is a possible solution for yoke users only, correct?

 

[jd950]

I am just repeating something told for me and cannot vouch for its accuracy. I was in the LDS this weekend and was talking to the owner, who is also the main service guy and he said the ACD could be removed and replaced with non-acd parts if I wanted, and the cost would be about $50.00. He also said he was aware of the new grooved piece and that his understanding was that it had nothing to do with the ACD failure issue and had something to do with airflow. He also said this was not something that was being installed in older regs brought in for service, just a running change on new regs.

As I say, I am just repeating what was told to me and cannot really assess if it is accurate or makes sense.

 

[JackD342]

I am just repeating something told for me and cannot vouch for its accuracy. I was in the LDS this weekend and was talking to the owner, who is also the main service guy and he said the ACD could be removed and replaced with non-acd parts if I wanted, and the cost would be about $50.00. He also said he was aware of the new grooved piece and that his understanding was that it had nothing to do with the ACD failure issue and had something to do with airflow. He also said this was not something that was being installed in older regs brought in for service, just a running change on new regs.

As I say, I am just repeating what was told to me and cannot really assess if it is accurate or makes sense.

That is pretty much in line with what I have found, and I think previously included, except there has been no actual communication or documentation on the “why” of the running part change. I’m thinking there might be something mentioned after DEMA. I will also point out that the new part allows continued (although reduced) airflow even if the ACD valve is loose enough to contact the face valve, so we really might be saying the same thing in different ways.

I have been diligently researching the parts, and while I have found a clear path backwards for the Titan/Core ACD, the Legend ACD is less clear and involves a compromise or two. No current ACD model is offered with a non-ACD option, and Aqualung has not defined a non-ACD “kit.” So all is dependent on spare parts availability from previously produced models.
I think $50 is in the ball park for the parts.

 

[JackD342]

A possible easier solution is to modify the DIN/yoke adapter insert on the tank. Grind/cut a groove across the diameter inside of the O-ring ID. Then there is no way of the ACD shuttle valve face to seal up against the tank outlet. Also, the inserts are cheap and can be replaced easily if you make a mistake. The tank valve O-ring should still seal under positive pressure outward. This is a possible solution for yoke users only, correct?

I have no experience with cutting/grinding such parts, but do have a couple of thoughts.

1. That solution assumes you own or control the cylinder(s). Not suitable for rental, live aboard, etc.
2. How many cylinders do you own or use, and want to modify?
3. Isn’t the insert made of chrome over brass? Once cut, might you start some chrome flaking at the edges of your cut, possibly joining the air flow? Yes, there is a filter in the inlet, but stil...
4. Doesn’t a replacement insert cost more than replacing a $14 part with the new version?

 

[W W Meixner]

This issue goes back to my recent post along with a lot of others about the misnomer ''top tier'' regulator sets...regulator servicing...and certification to service regulators...

A few things to remember...

*Reg service certification certificates are handed out like Halloween candy after ''attending'' a six hour course...
*A regulator with less parts is always better than a regulator with more parts...
*Most ''better mouse traps'' aren't better...
*Spending $1500/$1800 for a set of regulators doesn't necessarily get you a better set of regulators...
*Take a few Service Tech courses...know the value of having a simple IP test gauge in your tool box...
* Not enough can be said about Care...Pre and Post Dive Inspection and Checking...Thorough Post Dive Cleaning and Drying...
* Learn the importance of Stand Alone Bailout...and not the ""Spare Air'' type...but a bottle large enough to get you safely to the surface from what ever depth you are diving...which may or may not include mandatory ''stops''

This is the exact set of circumstances where the desire to take that harmless ''solo'' dive without the required training and redundant back-up could have had disastrous consequences...

In this case the diver did the right thing...the manufacturer should be advised of the shop that serviced the reg set...were they factory authorized...was the service tech factory certified...

Dive Safe...
Warren

 

[rsingler]

his understanding was that it had nothing to do with the ACD failure issue and had something to do with airflow

While our dive shop guys may not be able to comment without placing their status at some risk with Aqualung, color me skeptical in the extreme if I'm supposed to believe that the ACD modification that Jack posted earlier

is not directly in response to this issue of the ACD shuttle valve loosening. Half of that statement above is definitely correct: it has everything to do with air flow.

I think we're getting closer, however, to a modification using Aqualung yoke retainers from other regulators that will allow owners to retrofit non-ACD capability to their Legends. It's not an authorized mod (yet), but initial indications are good. As noted above, $50 seems about right.

I'll be interested to hear what "official" suggestions come from Aqualung or their dealers, since we've still got only that one Service Bulletin that alludes to the problem, and now an assertion(?) that the shuttle valve mod above has nothing to do with keeping the hat of the shuttle away from the tank valve orifice in case of loosening. Cough, cough.

Pictures and part numbers to follow, if this mod pans out. Hey, @jd950 , maybe ask your shop guy exactly what parts he is going to use to change to non-ACD, and we'll see if it matches some other efforts underway. And how is he handling liability, since I've heard nothing from Aqualung about retrofitting a Legend to non-ACD?