Aqualung Legend LX First Stage Failure at depth

[Freewillow]

I concur with what Diving Dubaï has said. I have a titan from Aqualung with an ACD . My system has a DIN connection. If one tries to dismount the forst stage by pulling on the first stage as opposed to the plastic ring thats screws on the bottle , the ACD becomes loose AND a huge leak happens when you have a new tank. It happens to me and has NOTHING to do with the maintenace/revision team. It is due to LOB help that are not careful when they unscrew the forst stage for a tank refill.

I suspect that the same thing can happen on the Yoke version but that the leak does not happen. Creating a risl at depth.

Would this be the answer?

 

[databob]

The short answer is I have no idea. I have attached a file with a side-by-side drawing of yoke style ACD closed and ACD open. Looks like the tank mating o-ring and surface pushes the ACD back against spring pressure so you get air. I see what looks like 2 o-rings in the ACD device and nothing else that looks serviceable. It is hard for me to imagine what could possibly happen to allow the spring to force the ACD back out toward the tank mating surface ( or the other piece to move back into the reg) a sufficient distance to close the port. I offered the answer the dive shop gave, but as I read the replies and look at this attachment it makes no sense to me. I was on a live aboard. I removed the first stage between dives for tank refill and replaced the first stage before diving. No one touched the regulator other than me. I snugged the yoke tightening screw myself when putting the first stage on the tank. I don't understand how the yoke can come sufficiently loose to cause this without a host of other issues first (like a big leak from tank to first stage and a ton of bubbles flowing). This also happened well into the dive and I was essentially still and clear of everyone/everything. Not sure how the yoke could move at all at that point in the dive. I also looked at the rebuild parts from before failure and after failure services and they all look brand new to me. Hard to imagine any of those were the issue.

 

[Ongrade]

My comment on shifting the yoke wasn't really well written, hurrying out the door at the time. What I was thinking is that if you had the yoke screw slightly out of the dimple on the tank, or the screw walked out as it was tightened you could have the ACD open and not have a leak. Then a slight tug on a hose or a bump on the 1st stage like your head bumping as you looked up could slip the screw back into the dimple and allow the ACD to close. Too late to look now but maybe the tank valve had a groove or gouge at the yoke dimple.

 

[databob]

I believe I do see what the dive shop is referring to and why it would cause the issue. In the attached picture of my reg you can see the ACD and the yoke nut. With my fingers I can push the ACD in about 1/2 of what you see and this allows the air to flow. That is a very small distance. If the yoke nut is loose and backed off a little I am compressing the tank valve to the regulator, but not close enough to the first stage body to push the ACD in all the way. The ACD is anchored in the first stage body. If it was close enough at the start of the dive to allow air flow but backed out just a little at some point in the dive it would allow the ACD to move out and abruptly block air flow. This could happen as my second stage hose tugs on and rotates the first stage a little. You can see my prior post attachment to see a cut away of the ACD closed and open and visualize the importance of the yoke nut being tightened in all of the way. This would then agree with both Diving Dubaï and my dive shop. This shows what can happen in a design where the ACD spring is trying to close off your air and a nut comes loose allowing the spring to win. If this is indeed correct I am really not a fan of this setup and you can bet I'll pay attention to the yoke nut.

 

[databob]

My comment on shifting the yoke wasn't really well written, hurrying out the door at the time. What I was thinking is that if you had the yoke screw slightly out of the dimple on the tank, or the screw walked out as it was tightened you could have the ACD open and not have a leak. Then a slight tug on a hose or a bump on the 1st stage like your head bumping as you looked up could slip the screw back into the dimple and allow the ACD to close. Too late to look now but maybe the tank valve had a groove or gouge at the yoke dimple.

I think you are right but I think the issue is that the yoke nut was loose and backed out enough to not push the ACD in sufficiently. That is in keeping with what the dive shop said. I think I posted my conclusion as you were posting this.

 

[halocline]

Just looking at the drawing, it does look like if the yoke was not tightened enough to compress the ACD spring completely, air pressure from a full tank could compress it enough to open the ACD. However, as the tank emptied, the spring would start to decompress, and I suppose eventually it could do so enough to close the ACD. I would think that initially the pressure from a full tank would push the thing off the tank valve o-ring, causing a leak. This is all a guess on my part.

I'd never buy one, that's for sure. I'll stick with the old simple regs that have been working for decades.

 

[Ongrade]

I think you are right but I think the issue is that the yoke nut was loose and backed out enough to not push the ACD in sufficiently. That is in keeping with what the dive shop said. I think I posted my conclusion as you were posting this.

What your post above hypothesizes sounds likely. I still like the ACD, for the same reason Diving Dubai stated, it allows me to quickly and thoroughly clean the reg without worrying about water intrusion. Lots of hand wringing about it being a dangerous complication but yours is the first problem with it I've heard of and it took an incompetent tech to cause it. This could happen with any reg if it's serviced improperly.

 

[redacted]

This could happen with any reg if it's serviced improperly.

not that easily done. Most service errors leave you with a reg that is leaking or obviously not working properly. The excption is torqueing errors, which this may have been.

 

[Ongrade]

I didn't mean that specific problem, just that ANY reg can fail in some form or fashion if it's serviced by an incompetent tech.

 

[Diving Dubai]

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