Filter blockage could be an issue but wouldn’t that be spread over other designs as well? Does the ACD use a cone or a disc filter?
Aqualung Legend LX First Stage Failure at depth
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It's a good point. with contamination/debris.
I use DIN which I accept does have some differences. That said I use my regs quite hard. 100-150 dives a year. Here in the Middle East we get high salinity content in the summer (evaporation) It's significant. The weighting change from winter to summer near teh coast can be the same as fresh water to salt in normal climates
Also we have lost of fine sand particles near the coast in the water, and it's ever present in the air (wash your car and you'll have a fine flour like dust covering it the same day - worse in a sandstorm.
My regs don't get washed after ever day's diving if I'm doing consecutive days, The most they see is a over night dunk in warm water. no brushing etc. They get serviced every 18 months - 2 years depending on how they breath.
My point here is that I find them quite robust
Now the OP had oly 25 dives since his last service (and from his accounts his shops don't' seem to be that switched on). The recent service might have played a part - we can't' know
They Filter BTW is cone
I use DIN which I accept does have some differences. That said I use my regs quite hard. 100-150 dives a year. Here in the Middle East we get high salinity content in the summer (evaporation) It's significant. The weighting change from winter to summer near teh coast can be the same as fresh water to salt in normal climates
Also we have lost of fine sand particles near the coast in the water, and it's ever present in the air (wash your car and you'll have a fine flour like dust covering it the same day - worse in a sandstorm.
My regs don't get washed after ever day's diving if I'm doing consecutive days, The most they see is a over night dunk in warm water. no brushing etc. They get serviced every 18 months - 2 years depending on how they breath.
My point here is that I find them quite robust
Now the OP had oly 25 dives since his last service (and from his accounts his shops don't' seem to be that switched on). The recent service might have played a part - we can't' know
They Filter BTW is cone
That seems to be the way it's turning out, though I'll bet Aqualung would say differently. Their position is probably that "routine maintenance is now easier" because you don't need that "pesky cap", lol! The Law of Unintended Consequences. But for harsh, sandy, salty environments, it might be nice to just pull the reg off the tank and not worry about stuff getting in the inlet. I can see some potential benefit.
Like some other Aqualung designs, the tolerances are too fine. Similar problem with the second stage. Those two plastic sleeves that form the dive/predive venturi lever seem to suck up grit. No matter how you try to keep your reg clean, after one beach dive the lever operates like sandpaper until you take it apart. Not my favorite.
But I can see that Diving Dubai's DIN version is a different animal, and as he says, "quite robust."
Call me chopped liver. My theory in post 139 ignored.....off to get a beer and cry in the corner.
Lol, I love ya, @couv!
I read your comments but didn't want to say I didn't agree with my friend.
The above is what I struggled with. It's a good theory! It's the missing piece I am searching for. But...
if tank pressure gets by one of the two o-rings around the Shutter Valve, it looks to me like it would percolate right out the seam between the Crown and the yoke retainer, which has no oring.
I wanted your explanation to be the one. I should have been honest enough to say that it requires both an oring leak, and enough crud around the Crown to trap air. That would do it, I admit!
But Occam's Razor made me say no. I apologize for not replying, amigo.
Here's where I sit right now.
I think it's likely that a minimally opened Shutter Valve is where we start. Maybe the mechanism doesn't matter. It could be the Crown hanging up early in the process of screwing the knob in? It could be an ACD neophyte just barely making contact with the reg, screwing things together the way he would with no spring: touch, then 1/12 turn more? Either way, it leaves the Crown high on the shutter, just barely open.
At this point you might be able to invoke ACD spring pressure. 15 pounds constantly squashing the tank valve oring for an hour's dive, until it compresses enough to raise the Crown just a hair more and close the shutter. And maybe invoke decreasing tank counterpressure pushing out on the Crown.
But it still doesn't sit well with me yet. I have to try an experiment at home.
I'm trying to balance in my mind the 15# of upward pressure on the Crown with the tank pressure's downward force on the same part. For the shutter to close, the Crown has to rise on the shutter valve.
If you do the math, the area of the face of the Crown inside where the oring sits is maybe 0.25 sq in. At an almost-empty tank's 200 psi, that still makes 50 lb force coming out of the tank on that area. That's more than enough to overcome the ACD spring, keep the Crown depressed and keep the Shutter Valve open.
But here's my dilemma. I was recently draining tanks in preparation for hydro and had one down to around 200 psi. Just because I'm an idiot, I put my thumb over the hole, and was easily able to stop the leak from the open valve. I didn't think about it at the time, but it occurred to me today that there's no way that was 50 lb of force.
So I'm computing something incorrectly.
Maybe the governing area is the diameter of the little hole coming out of the tank valve. I don't know. But what occurred to me after @Diving Dubai 's closure force experiment is that @couv has a point. If there's really 15# from that spring, when it was so easy for me to keep my thumb on that open valve, then just maybe there's less of an imbalance of force on that Crown than I thought. Maybe as the tank gets really low (like @databob 's chart), if there's insufficient pressure on the Crown from a loose attachment, the ACD spring might have enough force to push on the Crown, compress the tank valve oring a hair, and bingo. A barely open Shutter Valve now closes.
Like I said, I need to experiment...
I think it's likely that a minimally opened Shutter Valve is where we start. Maybe the mechanism doesn't matter. It could be the Crown hanging up early in the process of screwing the knob in? It could be an ACD neophyte just barely making contact with the reg, screwing things together the way he would with no spring: touch, then 1/12 turn more? Either way, it leaves the Crown high on the shutter, just barely open.
At this point you might be able to invoke ACD spring pressure. 15 pounds constantly squashing the tank valve oring for an hour's dive, until it compresses enough to raise the Crown just a hair more and close the shutter. And maybe invoke decreasing tank counterpressure pushing out on the Crown.
But it still doesn't sit well with me yet. I have to try an experiment at home.
I'm trying to balance in my mind the 15# of upward pressure on the Crown with the tank pressure's downward force on the same part. For the shutter to close, the Crown has to rise on the shutter valve.
If you do the math, the area of the face of the Crown inside where the oring sits is maybe 0.25 sq in. At an almost-empty tank's 200 psi, that still makes 50 lb force coming out of the tank on that area. That's more than enough to overcome the ACD spring, keep the Crown depressed and keep the Shutter Valve open.
But here's my dilemma. I was recently draining tanks in preparation for hydro and had one down to around 200 psi. Just because I'm an idiot, I put my thumb over the hole, and was easily able to stop the leak from the open valve. I didn't think about it at the time, but it occurred to me today that there's no way that was 50 lb of force.
So I'm computing something incorrectly.
Maybe the governing area is the diameter of the little hole coming out of the tank valve. I don't know. But what occurred to me after @Diving Dubai 's closure force experiment is that @couv has a point. If there's really 15# from that spring, when it was so easy for me to keep my thumb on that open valve, then just maybe there's less of an imbalance of force on that Crown than I thought. Maybe as the tank gets really low (like @databob 's chart), if there's insufficient pressure on the Crown from a loose attachment, the ACD spring might have enough force to push on the Crown, compress the tank valve oring a hair, and bingo. A barely open Shutter Valve now closes.
Like I said, I need to experiment...
Lol, I love ya, @couv!
I read your comments but didn't want to say I didn't agree with my friend.
The above is what I struggled with. It's a good theory! It's the missing piece I am searching for. But...
View attachment 483764
if tank pressure gets by one of the two o-rings around the Shutter Valve, it looks to me like it would percolate right out the seam between the Crown and the yoke retainer, which has no oring.
I wanted your explanation to be the one. I should have been honest enough to say that it requires both an oring leak, and enough crud around the Crown to trap air. That would do it, I admit!
But Occam's Razor made me say no. I apologize for not replying, amigo.
I prefer being correct more than I dislike being corrected, so feel free to correct me.
You are right-I mean, that was a test and you passed! A closer look at the drawings shows an escape path (also a saltwater intrusion path) past the springs and between the moving parts.
Back to the corner and another beer for me.
As I was mentioning on the phone: I think you are in the right track, but to calculate your pneumatic area, you need to subtract the area of the shuttle valve. The shuttle valve (that center piece) is thread into the body and therefore it is fixed and not affected (actuated) by the pneumatic pressure force. The pneumatic pressure area is only a ring.
I don't have any dimensions for the ACD, but I was trying to estimate some of the areas using the dimensions from the CGA 850 yoke valve interface drawing.
At this point I am still puzzled.
Luis,
Great to talk to you! You make an excellent point. After subtracting out the shutter valve area, the outward tank pressure forces on the crown are substantially less. And as we discussed, at depth at least, there is also the contribution of seawater pressure on the back of the floating crown pushing it up toward a closed position. At low tank pressures, at depth, the floating nature of the shuttle crown is far less in favor of the open position than it initially appeared.
Add in a little corrosion induced friction, plus looser attachment of the yoke due to binding, or the operator not knowing that the crown must be fully compressed, and we are edging closer to a possible explanation.
Gotta give this some more thought.
Great to talk to you! You make an excellent point. After subtracting out the shutter valve area, the outward tank pressure forces on the crown are substantially less. And as we discussed, at depth at least, there is also the contribution of seawater pressure on the back of the floating crown pushing it up toward a closed position. At low tank pressures, at depth, the floating nature of the shuttle crown is far less in favor of the open position than it initially appeared.
Add in a little corrosion induced friction, plus looser attachment of the yoke due to binding, or the operator not knowing that the crown must be fully compressed, and we are edging closer to a possible explanation.
Gotta give this some more thought.
johndiver999
Contributor
Makes me a little nervous about my yoke legend regulator with the ACD. I got it used this year and it has performed with no issues. Makes me want to list it for sale, but it breathes very smooth.
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