Friends don’t let friends dive with ACD
Aqualung Legend LX First Stage Failure at depth
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Using the least scientific method but what I have at my disposal (at 11pm at night)
It takes 16lbs of lead to compress the ACD. But it will close (in this case lift) with 14lbs of lead.
Here you can see how the ACD fits through the yoke. The "yoke nut" being loose will have no affect because as you tighten the yoke screw it'll remove the slack (As you pointed out)
Sorry about the poor picture, but here I've just turned the yoke screw enough for the shutter crown to make contact.
Here with the shutter fully opened so approx 1-2mm movement. I merely used my thumb and index finger to turn the yoke screw. It regd 1.25 turns - from first contact to the shutter fully opening (resistance)
I used a cylinder with an insert (pro valve?) The dark grey area is the shutter valve
The crown sits nicely in the recess for the O ring. Not too loose not too tight. I can move it from side to side, I guess by 0.5mm.
I cannot find a way (on this insert) to locate the crown in anyway that it does not fully contact the O ring without there being a gas leak when the tank is switched on.
In my opinion (from physically playing) I can't see that a foreign object could cause the shutter crown to get not fully contact the o-ring or that it would cause it to feel tight (when not fully open)
A mechanical "ding" is possible but it need to be a goldilocks size (not too big, not too small - just right and thus a fluke albeit a theoretical possibility)
If the gas pressure forces the shutter crown back and the yoke is loose you'll get a gas leak. So the valve whole have to only be open enough to deliver gas at with the tank above 1500 psi? And at the corresponding depth and would I believe cause a deflection on the spg when making test breaths (if done properly)
I'm open to suggestions of course, but I'm afraid I'm leaning toward either a filter being partially blocked or user error not fully tightening the yoke.
Your thoughts of course appreciated
One final thought..
My Yoke kit was brand new, the 1st stage was converted before it left the shop
If teh yoke screw had damage or corrosion then I guess that might cause it to offer some resistance which may lead to the user thinking its tight - but it's grasping at straws and the user would not have been paying attention in this case (opinion)
My Yoke kit was brand new, the 1st stage was converted before it left the shop
If teh yoke screw had damage or corrosion then I guess that might cause it to offer some resistance which may lead to the user thinking its tight - but it's grasping at straws and the user would not have been paying attention in this case (opinion)
Talk away but as a former accident investigator you seem to only be interested in ignoring the one constant in these “accidents” or mishaps if you prefer. I would not choose to dive anything designed like this and would strongly suggest anyone I dive with to avoid it if possible. I didn’t like the pneumatic MK5 either back in the day but I will defer to the adults.
Nice work, @Diving Dubai !
Gotta ponder your comments for awhile.
14-16# was far more than I expected from that spring. Very inventive technique, too!
With this extremely tight machining, coupled with poor maintenance (which you can't feel since you keep your gear so nice and shiny), I can indeed imagine a Crown/Retainer assembly that does not slide effortlessly. Add in a salt crystal from unsoaked gear, and I am positing a Crown that might have a very gritty feel. But with 14# of effort needed to test it, our hypothetical diver might never know.
So he attaches his tank and things feel "tight", but the Crown has hardly moved. This gives us a marginally open Shuttle Valve, and as you have just suggested, "user error [in] not fully tightening the yoke". If he's not used to the ACD, then he'd probably be very reluctant to keep turning the knob a full 1 1/4 turns (!!) after he started feeling resistance. From habit, most of us turn the knob no more than 1/12 turn after it meets the face of the reg. But of course, ours are not spring-loaded mechanisms.
I just have to figure out how we then get a little spring-induced rise in the Crown to the closed position, because tank pressure wants to push the Crown down further. It may be that simple debris provides the final closure, but that doesn't explain the DAN report with repeatable demonstrations of valve closure below 900 psi.
Gotta think about this...fourteen pounds of push-back is more than I expected.
Gotta ponder your comments for awhile.
14-16# was far more than I expected from that spring. Very inventive technique, too!
With this extremely tight machining, coupled with poor maintenance (which you can't feel since you keep your gear so nice and shiny), I can indeed imagine a Crown/Retainer assembly that does not slide effortlessly. Add in a salt crystal from unsoaked gear, and I am positing a Crown that might have a very gritty feel. But with 14# of effort needed to test it, our hypothetical diver might never know.
So he attaches his tank and things feel "tight", but the Crown has hardly moved. This gives us a marginally open Shuttle Valve, and as you have just suggested, "user error [in] not fully tightening the yoke". If he's not used to the ACD, then he'd probably be very reluctant to keep turning the knob a full 1 1/4 turns (!!) after he started feeling resistance. From habit, most of us turn the knob no more than 1/12 turn after it meets the face of the reg. But of course, ours are not spring-loaded mechanisms.
I just have to figure out how we then get a little spring-induced rise in the Crown to the closed position, because tank pressure wants to push the Crown down further. It may be that simple debris provides the final closure, but that doesn't explain the DAN report with repeatable demonstrations of valve closure below 900 psi.
Gotta think about this...fourteen pounds of push-back is more than I expected.
I think we all agree that the ACD is the common element, indeed the culprit in this issue. Diving Dubai is not defending it.
It's okay that we have a difference of opinion on this. Please, let's not get derailed into a fight over the utility of the toy. I tend to agree with you about a device inserted into my air path. But speaking for Diving Dubai, he finds a use for what is actually a very elegant piece of engineering, in his harsh environment. If he takes care of his gear, as he clearly does, then he accepts the risk (based on these few reports) in exchange for the benefit.
I think the more important issue in this thread is getting to the bottom of what might cause this rare occurrence. That investigation is pure fun, whether or not you'd dive with this toy. I'm sure we both would welcome your thoughts about the mechanism involved in this problem.
He was just teasing you back.
I accept there have been accidents/issues gas failures.
The issue is, that because these have been reported on an ACD unit, its been determined that it must be the ACD. Full stop
Now it may very well be that if you get the "perfect storm" of contributing factors that it can have a problem. One of those factors could be human error. I would rather there be a take away that if there is a human factor it be acknowledged and people be aware, rather than it being dismissed and people ignoring the fact.
It certainly appears that these failures are exceedingly rare, and that other failures are probably more common.
So rather that sweeping statement of the ACD must be bad let's try to find the probable cause
This gear is shiney as it's never seen water - The Reg was converted from Yoke to Din before it was ever used. My normal gear doesn't' look this pristine
While you ponder I took some more pics of that gap at higher mag with my phone (so I apologise for the quality)
There is a cunning bevel cut onto the side of the shutter and the outer case, presumably to alleviate to possibility of foreign object causing a jam. Maybe it's working as a scraper ring?
The more I examine this part the more admiration for the design I get. This isn't a cheap trinket - a lot of hard work and design has gone
into it especially with the fine engineering detail.
Don't forget the possibility of a filter blockage. I'd like your views on that
Agreed, just a quick poke back at the hush thing, I guess I should have included a smiley.
I see that you are headed toward the same point, a little build up or something along those lines stopping the device from proper function, doesn’t the device itself lead to the problem since it’s billed as something to allow or encourage the same behavior that could be the cause, namely not paying attention to proper maintenance?
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