Aqualung Legend LX First Stage Failure at depth

[redacted]

Take a look at the tech manual and see if you can figure out how that makes any sense. Perhaps your shop can explain that in the context of a cutaway of those devices.

 

[Nemrod]

The OP needs to find a different shop. The AL ACD is fail proof. If the yoke retention nut is not torqued, wow, sloppy work.

I just serviced my wife's Legend with ACD for a trip next weekend. All of these canuder valves and post valves and such that are being talked about inside the Legend ACD first stage do not exist.

N

 

[redacted]

I took a trip to the dive shop that serviced my regulator post failure this afternoon. The service manager was there and he took the time to explain to me why he believes what we have been discussing in this thread could cause the out of air situation. There were 2 things loose on my regulator when I took it to them. The yoke nut and the ACD inner post valve. This caused both the outer cylinder (the part you can push in with your finger) and the fixed inner cylinder have play relative to each other. The combination of looseness of both parts of the ACD were sufficient to allow it to go shut. As he was demonstrating (on a fully assembled regulator) it sure sounded believable to me. Please also understand - this is my translation of the conversation so I may not use terms as accurately as he did. He did stress to me that both pieces have torque specifications and that both need to be torqued to the proper specification.

Your dive shop is a bit scary. A shop tech can perform a routine service on regs without understanding how they work if they follow the instructions. But, when a problem occurrs, it really is quite an advantage to have an understandinf of how the devices function and how they may fail. A loose yoke retainner will eventually leak gas between the body and the retainer.

A loose shutter valve will increase the clearance between that valve and the shutter crown, not cause that valve to close and block air supply.

Now, if you told me they found a misplaced o-ring between the yoke retainer and the shutter valve, I could see the reported failure mode. But would have to wonder how it worked without problem for so many dves. Probably not a bad idea to check the movement of that shutter valve crown often.

 

[Luis H]

Your dive shop is a bit scary. A shop tech can perform a routine service on regs without understanding how they work if they follow the instructions. But, when a problem occurrs, it really is quite an advantage to have an understandinf of how the devices function and how they may fail. A loose yoke retainner will eventually leak gas between the body and the retainer.

A loose shutter valve will increase the clearance between that valve and the shutter crown, not cause that valve to close and block air supply.

Now, if you told me they found a misplaced o-ring between the yoke retainer and the shutter valve, I could see the reported failure mode. But would have to wonder how it worked without problem for so many dves. Probably not a bad idea to check the movement of that shutter valve crown often.

I have been reading some of this thread and I agree with you.


The only thing that I am wondering is if the Shutter Valve (Item 32) is loose, could it loosen up enough to partially block the tank valve outlet, but otherwise go unnoticed? Not likely, but looking at the manual, I can’t see a failure mode that explains the description of the events. I don’t think the part is long enough to come in contact with the tank valve face, but I am not coming up with another good failure mode.

If the “Shutter valve” is not tight, I can see it loosening further with any twisting of the regulator on the valve.


A clogged filter… yes.


A loose Yoke retainer (Item 35), just causes a big leak (and it is independent of the ACD mechanism). I have helped several dive friends fix that on the field. The Yoke retainer on their Legend loosen up, most likely from the dive help lifting the gear out of the water by pulling from the wrong place.

Big WARNING. If the yoke retainer loosens up and air leaks out, don’t just tighten it!! When the air leaked out, it will dislodge the O-Ring (item 28) from its groove and if you just try to tighten it, you will cut the O-ring. I have seen it happen.

You need to take the Yoke retainer assembly completely off and place the O-ring back in its groove and then carefully reassemble it and tighten it.

And don’t let anyone rotate the first stage when it is installed on the tank valve.

 

[Diving Dubai]

I have been reading some of this thread and I agree with you.


The only thing that I am wondering is if the Shutter Valve (Item 32) is loose, could it loosen up enough to partially block the tank valve outlet, but otherwise go unnoticed? Not likely, but looking at the manual, I can’t see a failure mode that explains the description of the events.

From my experience with the DIN ACD. If the shutter valve is loose. then you get a leak similar to a missing O ring when you pressurise the system. It only needs to be 1/4 turn. I presume (looking at the drawings) that when correctly tightened the base of the shutter valve provides a seal.

If loose, then the gas escapes around this, past the O ring and out past the shutter.

I'm not certain of the exact process only the fact you get a leak. This 1/4 isn't enough to cause a restriction on the back of the valve, so I presume the fact that it will leak is that it's a designed fail safe.

My point here is that if the Shutter valve were even slightly loose you'd know about it pre dive.

I think it's fair to say that the ACD isn't at fault and that the LDS was wrong with their diagnosis. My guess is that they jumped on two loose items and have decided that was the cause.

NB the shutter valve can become loose over time, caused by the shutter rotating around the valve if there is the slightest pressure in the system. Happens on all 4 on my 1st stages and they've all been correctly torqued by me and the local shop. It's a known if not slightly annoying issue

 

[Freewillow]

I agree to with Diving Dubai. Same thing happened to me with Din. Since then I am taking the first stage away MYSELF in order to make the refill on LOB.

 

[Luis H]

From my experience with the DIN ACD. If the shutter valve is loose. then you get a leak similar to a missing O ring when you pressurise the system. It only needs to be 1/4 turn. I presume (looking at the drawings) that when correctly tightened the base of the shutter valve provides a seal.

If loose, then the gas escapes around this, past the O ring and out past the shutter.

I'm not certain of the exact process only the fact you get a leak. This 1/4 isn't enough to cause a restriction on the back of the valve, so I presume the fact that it will leak is that it's a designed fail safe.

My point here is that if the Shutter valve were even slightly loose you'd know about it pre dive.

I think it's fair to say that the ACD isn't at fault and that the LDS was wrong with their diagnosis. My guess is that they jumped on two loose items and have decided that was the cause.

NB the shutter valve can become loose over time, caused by the shutter rotating around the valve if there is the slightest pressure in the system. Happens on all 4 on my 1st stages and they've all been correctly torqued by me and the local shop. It's a known if not slightly annoying issue


View attachment 384626

I am not surprised that it would leak, with very little unscrewing of the “Shuttle valve” from the yoke retainer body. The Shuttle valve does not have to be tight to seal (because that is a gland seal), but since it is only designed to seal in one spot, if it starts to unscrew too much the O-ring will run out of sealing surface very quickly (from your description).

Both of the O-rings shown in the picture you posted are radial sealing O-rings, also known as gland seals (as opposed to a face sealing O-ring).

Examples of face sealing O-rings are the tank valve to regulator face O-rings, also the O-ring between the “yoke retainer” and the regulator body. With a face seal O-ring, the joint has to be properly tightened to get a good seal and to avoid gaps that will allow O-ring extrusion.

With a gland seal (or radial sealing surfaces) the sealing is normally accomplished on the outer and inner circumference of the O-ring and a good seal depends on properly designed and manufactured mating parts.

Gland seals do not required that the parts are tight and they can often be used for dynamic seals (or moving parts). Example of dynamic gland seals is most swivels including the hose to second stage joint.

Another example of a dynamic gland seal is the O-ring between the Shutter crown (item 31) and the Shutter valve (item 32). The Shutter Crown is designed to slide up and down while maintaining a seal and not leaking. Therefore it has a sealing surface long enough for the design travel of the part.

The other gland sealing O-ring (between the Shuttle valve and Yoke retainer) is a static seal and it is only designed to seal in one spot, when the part is bottomed out. Any torque requirements for this part are to keep it from backing out, not for sealing purposes.



Note: I have minimal experience with this regulator, so I am mostly going by the diagrams and pictures in the manual.

At this point, I don’t have an explanation for the failure mode, except for again a clogged filter or similar obstruction.

I should add that this first stage is mostly based on the design of the Conshelf regulator and before that the Royal Aqua Master double hose regulator first stage. I am talking about designs that date back to around 1965. They are extremely reliable. I started servicing them about 45 years ago and in my experience, I have not seen another first stage design that comes close to them in long term reliability.

The ACD addition is a new addition, and I personally have not serviced one so I have no direct experience with them.

 

[admikar]

Actually with AL, it's done online. All you need is a credit card to become a authorized technician....

Since AL owns Apeks, can it be done for them too? I would love to get my tech spec, so I can legally service my DST/XTX50 regs.
If positive, would you, please,provide link or instructions how to do that?

 

[Freewillow]

Since AL owns Apeks, can it be done for them too? I would love to get my tech spec, so I can legally service my DST/XTX50 regs.
If positive, would you, please,provide link or instructions how to do that?

Just curious, what kind of law would impeech you from servicing your OWN regulators?

 

[admikar]

None at all, but no LDS that I know off will sell me Apeks service kits, unless I'm a certified tech.