Aqualung Legend LX First Stage Failure at depth

[Diving Dubai]

Good point, but I would guess that not torqued to spec is a problem because it could then loosen too easily, and that is when the problem would appear. Is that right, or is there some failure likely simply due to the inadequate torque, without actual "looseness?"

On the DIN version if its loose it leaks. Basically there is a shutter pushed closed against spring pressure. Mechanical force of you tightening the yoke onto the cylinder pushes the shutter open.

If the yoke nut is loose then it is possible for it not to open the shutter enough, but still possible for you to get an air seal.

For this to happen the A clamp will be loose on the first stage. If the first stage wobbles on the A clamp of any reg, get it seen too.

I dive 4 sets of the Din version no issues ever.

But like most equipment failures it comes down to basic preventative maintenance which some people choose not to do

 

[databob]

Fellow divers,
The ACD issue has nothing to do with the yoke being loose and the problem is not visible on an assembled regulator. It has nothing to do with the yoke nut being too loose to push the ACD in to allow air to flow and having air gush out of the tank because it is too loose. The ACD device threads into the first stage body and it is required to be torqued. You cannot see that when the regulator is assembled. If it comes loose it fails shut (safe?) exactly as described by the other person with the failure (Wynner) in this thread. That is a fact. I have hundreds of dives on a Titan LX with ACD and not a single issue and I had hundreds of dives on the Legend LX with ACD before the failure at 60 feet. Not having an issue yourself does not mean there is not an issue. I've never been killed in a car crash, but that does not mean you cannot be killed in a car crash.

Wynner had an issue described earlier and I had a nearly identical issue debated in a post a while back. The frequency of occurrence is probably minuscule, but the consequences are significant. People post to share issues and experiences and others read to learn from them. Because the issue has not happened to you, or because you can't mentally engineer the problem, does not make it a non issue. Aqualung thinks it is an issue. I think I'd go with them and the 2 people that were sucking a vacuum on their reg when it failed shut at depth (safe?)

If having an ACD prevents the mental anguish of remembering to put a dust cap on the reg after a dive, buy all means get one (I'll sell you my Titan LX cheap). Constantly rationalizing how it could not happen when it clearly does happen does no one a service on scubaboard. The reason you probably are not aware of other issues is no one wants to read the pages of nonsense that comes after a post about an issue

Risk can be thought of as probably of occurrence times consequence. In this case, P-occurrence is admittedly low. The real question is are you a good enough diver with a buddy close enough to deal with no air at 60 or 70 feet if that minuscule P-occurrence materializes? Allow people to read, learn and make an informed decision on whether they want to accept the risk. Muddying up the facts with endless speculation and pages of things that have nothing to do with the failure is not helpful to anyone.

With all due respect, happy diving.

 

[Freewillow]

Everything you say databob makes a lot of sense. Another alternative is to go DIN. Does not have that pitfall.

 

[Melanie White]

Do you still have it for sale? If so how much? We love ours and would use it as a backup.

 

[reefrat]

I have a Titan LX ACD first stage in DIN that I use frequently, sometimes with my DIN tank valve and sometimes using an adaptor on dive charters. I have never had an issue with it but still do not trust it completely- an unnecessary complication and potential failure point IMO.
Apparently (from previous posts I’ve found) there is no way to remove the ACD otherwise I certainly would! At this point I would happily swap my ACD version for a clean earlier non-ACD one or maybe just sell the reg and go with another brand.
For rental units or a casual and careless diver the ACD may be worthwhile but I am meticulous with my gear and the attributes I value for a reg are (in order) Reliability, performance, reliability, simplicity of design for servicing, reliability!
ACD’s and other related gadgets have no place on my regs, and especially on the first stage.

 

[admikar]

@reefrat ,with all due respect, why did you buy that reg in the first place?

 

[reefrat]

It was a clearance sale (prior to the Core release) and an impulse buy. The ACD. Is the only part of it I don’t like.

 

[Diving Dubai]

Since @databob has resurrected this thread, as a learning piece for all, I thought I'd summarise everything.

I do have a personal vested interest in any problems with the Legend ACD 1st stage, since I own 3 sets. All of them are regularly used (more than once a month) on dives beyond those considered recreational. Mine only differ from standard in that they have all been rebuilt as 100% O2 compatible

The OP originally had an OOA at 60' some 40 mins into the dive with 1500 psi still left in his tank. The Reg had been serviced some 25 dives before. He took the Reg to a different AL service centre who diagnosed that the Yoke nut and ACD shutter valve were loose and that was the problem. There has been some debate on this and a similar incident as to whether this was the correct diagnosis

In order to understand the issues, I've attached diagrams and pictures below.

AL in May 17 issued a technical bulletin recalling some regs because of a loose ACD

In Picture B you can see the gap in between what's called the shutter crown and the Nut. The Torque settings had been revised to help prevent this. The ACD beign loose isn't' as big an issue as one might think. (I'll come to that)

The Picture below identifies the major components so people can understand the terminology

Below is a cut through drawing

The Purple part in the centre is the shutter valve. It does not move. It's the Shutter crown which surrounds it, that is pushed back as you tighten the yoke or Din allowing air to pass through. The Shutter valve just screw in however retaining the whole assembly

Note the lower O ring. If the Shutter valve unscrews then this O ring will fail to seal allowing gas to come around the outside of the Shutter Crown. The user hears a gas leak as if there were no O ring. On Din Models, its not uncommon if the user removes the 1st with a bit of pressure remaining for the crown to turn loosening the shutter valve - the next time you put it on a tank you have a leak. Simple fix, tighten it with a hex keY

It does not need much to get this leak. If the Shutter valve unscrews 1 quarter of a turn you'll get a leak. This is the fail safe. If teh Shutter valve is not fully installed it give you a major leak when you pressurise the cylinder. The same can happen on Yoke if you over tighten and then twist the yoke to loosen the 1st stage

I know this because it's happen to me more than once when I've been careless (rushing) changing tanks I carry a Hex key to nip it back up. No problem.

This is why I reject the theory of the Loose ACD

What about the yoke nut?

This is a pic of my DIN ACD (which looks really grotty at this magnification - it's due a service in Dec after 200+ dives over 18 months)

The thing to notice here is the Gap between the end of my DIN threads and the back of the shutter valve. It's approx 1mm / 0.040" with the ACD obviously closed.

The Max movement of the ACD is this 1mm/0.040" That's all it need to move to fully open the airway.

Now look again at the first photo. There is a great deal of the shutter crown protruding past the yoke nut, at least 5mm/0.200"

Even if the O- ring is slightly recessed as long as around 2mm/0.080" of the shutter crown is exposed it will be enough to push back fully. If the Yoke nut was that loose, the User would have surely notice how loose the A clamp was.

So I also reject a loose yoke nut as the cause and even a combination of both.

Why did a Dive shop identify the loose ACD and yoke as the cause? It's not uncommon for people to see a fault and immediately label that as the problem. In this case I'm certain they were wrong.

I've also double check this with a very very well respected AL Service Eng who concurred with the above

So what was the cause?

Without the offending 1st stage it's impossible to say.

I presume and Correct me if I'm wrong being on a liveaboard the tank used on that dive had been used before and after the incident - generally in my experience they stay connected to your kit - ? We know they apparently checked the valve underwater. Otherwise the cylinder valve or debris tube inside could have been suspect/ partial blockage.

The OP might not have tighten the yoke properly thus not opening the ACD - although unlikely as you shoudl get a leak from a bad seal? Or the OP might have had a really loose yoke nut - but I'm discounting that because I'm sure the OP would have notice or their buddy would have seen bubbles

Because the reg had been used - a build service issue isn't obvious unless it took a few dives for the defect to appear

Or it could be a blocked/ partially blocked filter (in proper service).

So in summary, we'll never know the true cause. but it's safe to say the suggested cause was false. The ACD is designed to fail safe, in that if it comes loose you just don't' get any air at all on the surface, just a big leak

Whether you like the ACD or not (I do and I also have regs without ACD so I'm aware of the differences) is immaterial

The failure modes put forward initially by the dive shop just don't cut it.

I'm certainly happy to continue to use ACD I think others should be too

Safe diving

 

[Luis H]

??

 

[databob]

Since @databob has resurrected this thread, as a learning piece for all, I thought I'd summarise everything.

I do have a personal vested interest in any problems with the Legend ACD 1st stage, since I own 3 sets. All of them are regularly used (more than once a month) on dives beyond those considered recreational. Mine only differ from standard in that they have all been rebuilt as 100% O2 compatible

The OP originally had an OOA at 60' some 40 mins into the dive with 1500 psi still left in his tank. The Reg had been serviced some 25 dives before. He took the Reg to a different AL service centre who diagnosed that the Yoke nut and ACD shutter valve were loose and that was the problem. There has been some debate on this and a similar incident as to whether this was the correct diagnosis

In order to understand the issues, I've attached diagrams and pictures below.

AL in May 17 issued a technical bulletin recalling some regs because of a loose ACD

View attachment 482862

In Picture B you can see the gap in between what's called the shutter crown and the Nut. The Torque settings had been revised to help prevent this. The ACD beign loose isn't' as big an issue as one might think. (I'll come to that)

The Picture below identifies the major components so people can understand the terminology

View attachment 482863


Below is a cut through drawing

View attachment 482864

The Purple part in the centre is the shutter valve. It does not move. It's the Shutter crown which surrounds it, that is pushed back as you tighten the yoke or Din allowing air to pass through. The Shutter valve just screw in however retaining the whole assembly

Note the lower O ring. If the Shutter valve unscrews then this O ring will fail to seal allowing gas to come around the outside of the Shutter Crown. The user hears a gas leak as if there were no O ring. On Din Models, its not uncommon if the user removes the 1st with a bit of pressure remaining for the crown to turn loosening the shutter valve - the next time you put it on a tank you have a leak. Simple fix, tighten it with a hex keY

It does not need much to get this leak. If the Shutter valve unscrews 1 quarter of a turn you'll get a leak. This is the fail safe. If teh Shutter valve is not fully installed it give you a major leak when you pressurise the cylinder. The same can happen on Yoke if you over tighten and then twist the yoke to loosen the 1st stage

I know this because it's happen to me more than once when I've been careless (rushing) changing tanks I carry a Hex key to nip it back up. No problem.

This is why I reject the theory of the Loose ACD

What about the yoke nut?

View attachment 482865

This is a pic of my DIN ACD (which looks really grotty at this magnification - it's due a service in Dec after 200+ dives over 18 months)

The thing to notice here is the Gap between the end of my DIN threads and the back of the shutter valve. It's approx 1mm / 0.040" with the ACD obviously closed.

The Max movement of the ACD is this 1mm/0.040" That's all it need to move to fully open the airway.

Now look again at the first photo. There is a great deal of the shutter crown protruding past the yoke nut, at least 5mm/0.200"

Even if the O- ring is slightly recessed as long as around 2mm/0.080" of the shutter crown is exposed it will be enough to push back fully. If the Yoke nut was that loose, the User would have surely notice how loose the A clamp was.

So I also reject a loose yoke nut as the cause and even a combination of both.

Why did a Dive shop identify the loose ACD and yoke as the cause? It's not uncommon for people to see a fault and immediately label that as the problem. In this case I'm certain they were wrong.

I've also double check this with a very very well respected AL Service Eng who concurred with the above

So what was the cause?

Without the offending 1st stage it's impossible to say.

I presume and Correct me if I'm wrong being on a liveaboard the tank used on that dive had been used before and after the incident - generally in my experience they stay connected to your kit - ? We know they apparently checked the valve underwater. Otherwise the cylinder valve or debris tube inside could have been suspect/ partial blockage.

The OP might not have tighten the yoke properly thus not opening the ACD - although unlikely as you shoudl get a leak from a bad seal? Or the OP might have had a really loose yoke nut - but I'm discounting that because I'm sure the OP would have notice or their buddy would have seen bubbles

Because the reg had been used - a build service issue isn't obvious unless it took a few dives for the defect to appear

Or it could be a blocked/ partially blocked filter (in proper service).

So in summary, we'll never know the true cause. but it's safe to say the suggested cause was false. The ACD is designed to fail safe, in that if it comes loose you just don't' get any air at all on the surface, just a big leak

Whether you like the ACD or not (I do and I also have regs without ACD so I'm aware of the differences) is immaterial

The failure modes put forward initially by the dive shop just don't cut it.

I'm certainly happy to continue to use ACD I think others should be too

Safe diving

I just got back from a 10 day dive trip in Raja Ampat and had the same failure on my AL Legend ACD first state. When tank pressure got low (around 1000 psi) one breath on the second stage would reduce the pressure to zero. Over the next 10 seconds it would gradually build up to pressure again. I was at 70 feet when it first happened. I carefully tested to the problem on the next 4 dives and was able to repeat the problem on each dive. My reg is less than two years and only used for <100 dives. It is straight from the factory, not serviced anywhere. This is a dangerous problem.

Hello Wynner
Can I make a suggestion. I had the identical issue to you. Take your 70 feet and fill in 60 feet for me and the experience is identical. I also had the pressure return very slowly after the tank/reg got back to the boat (but not while in the water). I reported the issue to Aqua Lung and I am attaching their response. I'd recommend that you let him know the issue you had and the circumstances. Losing air at depth is not a satisfactory state for a regulator to fail in. I have no idea what the issue is - my mistake in the post was getting into the what caused it loop. ACD seems to fire up a lot of "no way" responses and that may be correct. I actually do not care what the issue is - I care that you suddenly lose air at depth. There was no crud in my reg from the tank - my reg was examined by every diver on board who could not believe it was possible to lose air from your first stage and it was serviced as soon as I got home. At least letting Aqua Lung know you had an issue would help them build a problem history. The service advisory came out shortly after I reported my issue, so they seem responsive to reports of issues. In their response - "eventually cause what you experienced" is no air at depth. That's not a good condition for any first stage for any reason and your post gives me confidence that the issue happened to more than me (which is why I resurrected this).
V/R Bob