1st stage of regulator failed in close position - new diver freaking out a bit :)

[halocline]

Having looked fairly closely at the aqualung ACD drawings, it does look to be fail safe; i.e. it appears to be physically prevented from blocking the valve while the regulator is firmly and correctly attached to a tank. The oceanic version, which consists of a ball on a spring, is another story. You couldn't pay me to use one of those.

In this case the cause of the air loss was almost certainly either the valve not being opened enough or something clogging the dip tube which then fell off as the diver was ascending. The valve not being open enough is certainly more common.

 

[CuzzA]

If you can easily manipulate the valve in the water, a vindicator knob no longer solves any problem you actually have, and you can be all smiles and friendliness with the DM on the boat who fiddles with your cylinder valve, because you just don't care.

I can manipulate the valve. It's the extra layer of visual safeguarding where it has it's benefit and avoids the beginning of what could be the domino effect. Reminds me of an airplane crash story I saw on tv the other night about info simply not being intuitively displayed and resulted in a pilot error and crash. Consequently they changed the way that information was displayed after the investigation.

By the book, we've done all of our checks. In the real world, a series of events or distractions can lead to an error. I've geared up plenty of times and before splashing, stopped and questioned, "Is this thing on?" as we're plucking divers, fish and fins flying over the rail, 3-4 foot seas in a pitching boat, I'm thinking about all the things I need to do, checking if the camera's on, gun in one hand, stringer in the other, and then.... "Neutral... GO, GO, GO!" You start task loading and things can get overlooked.

Of course my tanks have always been on and a quick look in my mirror can confirm that. It's interesting earlier in this thread we had a debate on whether the "visual" bouncing SPG needle check was reliable or not, but some would question an $8 knob that leaves no doubt if the valve is ON or OFF or even partially closed.

Is it absolutely necessary? I don't think so. Should it be standard for any new valve? Probably. They're so cheap, manufacturers should just sell them with vindicators. In fact I believe a few are offered standard with the vindicator knob. It just makes sense, IMO. Like selling pro valves. Why make anything else?

Just my opinion though. I dive and configure my gear the way I want for my own reasons. I'm not looking to change the industry or the way anyone else dives. I thought it was prudent to share what I do given the topic.

It's a shame people have died from that though.

 

[Diving Dubai]

He did say it was an AquaLung. Some AL regs does have ACD, right? So, there is a reasonable chance that it did have ACD?

If so, it seems somewhat suspect for all the posts that offer speculation and don't include that possibility. Of course, I suppose it's all speculation and we'll never know for sure. But, given the other info about the dive op acting as if they weren't surprised and immediately telling him it was the reg, it sure makes me wonder if it wasn't an ACD reg and that's how the dive op people seemed to know right away that it was the reg.

If you had read the thread, you'd have seen that ACD was mentioned earlier and noted that it couldn't be the issue. Not because of speculation, but because of fact.

I have 3 regs with ACD, so participated in the last thread.

I'll explain it for you.

The ACD in simple terms is a sprung loaded protective sleeve. When you connect to the tank this sleeve is mechanically pushed back uncovering the airway. If teh sleeve was stuck closed you wouldn't get an air seal. There is a center bolt, if this bolt becomes loose - even by less than 1/4 turn you can't get an air seal either , so when you open the tank valve it's as though there is no O ring

The centre bolt can come loose on DIN if you loosen the reg a number of times with a little pressure in the system.

As an Engineer I thing the design is very good, by the fact that AL have gone to great lengths to ensure the ACD can't fail and disrupt airflow

Whether or not the ACD can fail shut during a dive is disputed.

It's not disputed at all. It can't fail shut period.

 

[stuartv]

If you had read the thread, you'd have seen that ACD was mentioned earlier and noted that it couldn't be the issue. Not because of speculation, but because of fact.

I have 3 regs with ACD, so participated in the last thread.

I'll explain it for you.

The ACD in simple terms is a sprung loaded protective sleeve. When you connect to the tank this sleeve is mechanically pushed back uncovering the airway. If teh sleeve was stuck closed you wouldn't get an air seal. There is a center bolt, if this bolt becomes loose - even by less than 1/4 turn you can't get an air seal either , so when you open the tank valve it's as though there is no O ring

The centre bolt can come loose on DIN if you loosen the reg a number of times with a little pressure in the system.

As an Engineer I thing the design is very good, by the fact that AL have gone to great lengths to ensure the ACD can't fail and disrupt airflow

It's not disputed at all. It can't fail shut period.

I did read the thread. Note the posts below. One that explains how an ACD reg supposedly failed shut by not being assembled correctly. And a following post that responds to me saying that information is not bogus. I interpret that as saying that an ACD reg could fail in the way described in david gutkin's post.

I also read earlier where someone said that an AL ACD reg cannot fail closed. But, there was no explanation given and it was unclear if that statement carried a presumption of the reg being assembled correctly. Okay, so it can't fail closed if assembled correctly. That does not address the question of whether it could fail closed if it was assembled incorrectly.

You said "it's not disputed at all." That means that there is nobody, anywhere, that disputes that. Are you sure that you made a true statement there?

BTW, I asked the question here, in this thread, because I was hoping someone could save me and anyone else that comes along and reads this thread, the trouble of reading that whole other thread and just give a synopsis here. E.g. that other thread concluded with "the shop that said the ACD failed closed was wrong. There is no way it could fail closed, even if it were assembled incorrectly." OR, "yep, that one in that thread did have an ACD that failed closed, because it was assembled wrong."

FYI, Came across this scenario described in the forums. Sounds like what happened to me...

I hope this information is useful to someone. 25 dives after a complete rebuild service for my Aqualung Legend LX I had my first stage fail shut at 60 feet 40 minutes into the dive. Fortunately my buddy recognized the international signal for out of air - eyes as wide as saucers - and he had his reg in my mouth ASAP. I had 1500 lbs left in the tank (although the gauge fell to zero until we got back to the boat). Took the regulator to a different Aqualung authorized service dive shop for analysis/repair and the issue was determined to be the ACD. From the dive shop - "We found that the ACD inner post valve and yoke nut had come loose." The regulator was rebuilt as listed on the intake documents and theses parts have been torqued to their proper specifications". So, holy cow - a bad service can result in a failed shut condition on the first stage with no prior indication that things are going south. Caveat Emptor.

So if not a quick kick to buddy: pull the weights and head up? Or is it just head up kicking and trying to exhale? Again, depth is at 25m starting in exhaled state? Are these viable options, or not? I seem to get conflicting answers from the dive guides.

No, it was not bogus. Perhaps you should read the other thread and examine the ACD design and see if you can figure out how an ACD could cause such a failure.

 

[redacted]

. I interpret that as saying that an ACD reg could fail in the way described in david gutkin's post.

.

IMO, you are interpreting it incorrectly. I suggest you examine the design yourself and see if you can devise such a failure mode.

A synopsis:. One group say the problem was the ACD but offer no explanation of the failure mode (how does an ACD cut off gas supply while the reg is attached, pressurized, and holding gas?). Another group that says the design can not fail in the mode of the reported failure. And a third group scratching their heads.

 

[stuartv]

A synopsis:. One group say the problem was the ACD but offer no explanation of the failure mode (how does an ACD cut off gas supply while the reg is attached, pressurized, and holding gas?). Another group that says the design can not fail in the mode of the reported failure. And a third group scratching their heads.

So, no conclusion with a general consensus. Thank you.

 

[cerich]

.

IMO, you are interpreting it incorrectly. I suggest you examine the design yourself and see if you can devise such a failure mode.

if the spring corrodes and breaks..

or is installed inproperly

 

[Diving Dubai]

if the spring corrodes and breaks..

or is installed inproperly

The design is quite clever. The shutter is pushed back by mechanical force as you fit the 1st stage to the cylinder. The spring is used to close the ACD when you remove the 1st stage

So if a spring breaks, the shutter could still move back but wouldn't re-close. No problem

If the spring caused the shutter to jam, you wouldn't get air in the first place. If the shutter doesn't' open fully, there is a bypass causing a tell tale leak as though there is no O ring.

So, no conclusion with a general consensus. Thank you.

What rubbish!!

One group has studied the drawings and understands first stages, and says through knowledge it can't fail in a way to cut off or limit gas supply.

The other side, has done nothing except claimed it could fail without being able to offer a failure mode

You don't have to like the ACD, some want to brand it as "an additional failure point" yet they can't give an actual reason why it would be.

Download the manual and look at the schematics. If you can present a reason how it might fail after doing that, then we could hold a reasoned discussion. Until then you're just spouting an ill informed opinion

 

[rhincodon]

Agree with above.

 

[archer1960]

The design is quite clever. The shutter is pushed back by mechanical force as you fit the 1st stage to the cylinder. The spring is used to close the ACD when you remove the 1st stage

So if a spring breaks, the shutter could still move back but wouldn't re-close. No problem

If the spring caused the shutter to jam, you wouldn't get air in the first place. If the shutter doesn't' open fully, there is a bypass causing a tell tale leak as though there is no O ring.



What rubbish!!

One group has studied the drawings and understands first stages, and says through knowledge it can't fail in a way to cut off or limit gas supply.

The other side, has done nothing except claimed it could fail without being able to offer a failure mode

You don't have to like the ACD, some want to brand it as "an additional failure point" yet they can't give an actual reason why it would be.

Download the manual and look at the schematics. If you can present a reason how it might fail after doing that, then we could hold a reasoned discussion. Until then you're just spouting an ill informed opinion

I haven't looked at the drawings, but would it be possible for a piece of a broken shutter or spring to block the path that the air needs to flow?