Why would a reg become difficult to breathe from?
- Thread starter MrChen
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ok this is defo above my paygrade, y'all need the tinkerer in brass
OP
OP
Lol, it would have been the only snack on the boat.
Impossible to make a good guess with so little info. Did it have the ACD by chance?
OP
Here's how much I know, what's an ACD? 
That was my thought exactly - the rare but deadly ACD shutter valve torque problem. That's the only thing I can think of that would be a sudden loss of ability to suck air, with an onset at depth.
As others have pointed out, too little data to judge.
What do we know?
- Aqualung
- Rental Reg
- Dive/Predive - knob? or lever? fixed the problem
- Onset at depth
If it was an Aqualung Venturi adjust, that is a mechanical "roof" that rotates over the outflow, about 1/8" away. That "spider" suggestion is a great one, as whatever was living in the barrel and was blown to where it plugged up the outflow hole in the barrel subsequently was dislodged by the movement of the roof sliding across the outflow track. That actually seems most likely, as it accounts for four out of the five pieces of data: sudden onset, Aqualung Venturi design rather than Scubapro vane, rental reg stored for how long?, and a cure with moving the Dive Predive lever. Depth of onset remains unexplained, however.
If it were an actual knob, rather than a Venturi lever, then it was a cracking effort adjuster, and cranking that in shouldn't produce a sudden fix.
If it were the ACD, all three of the known cases were at depth, and sudden, though depth's contribution to the original problem was never clear. But then the rest of the occurrence in this case doesn't fit: curative effect of the Venturi knob. But it does account for the sudden onset at depth, although a spider may have the same association due to the passage of time, rather than depth in the water.
I think @Mobulai wins conceptually, and @rhwestfall wins for plausibility. Plugging up that hole would have required something bigger than "tiny", and much as I'd like to, I can't really blame Aqualung.
Great story!
But yuck!
As others have pointed out, too little data to judge.
What do we know?
- Aqualung
- Rental Reg
- Dive/Predive - knob? or lever? fixed the problem
- Onset at depth
If it was an Aqualung Venturi adjust, that is a mechanical "roof" that rotates over the outflow, about 1/8" away. That "spider" suggestion is a great one, as whatever was living in the barrel and was blown to where it plugged up the outflow hole in the barrel subsequently was dislodged by the movement of the roof sliding across the outflow track. That actually seems most likely, as it accounts for four out of the five pieces of data: sudden onset, Aqualung Venturi design rather than Scubapro vane, rental reg stored for how long?, and a cure with moving the Dive Predive lever. Depth of onset remains unexplained, however.
If it were an actual knob, rather than a Venturi lever, then it was a cracking effort adjuster, and cranking that in shouldn't produce a sudden fix.
If it were the ACD, all three of the known cases were at depth, and sudden, though depth's contribution to the original problem was never clear. But then the rest of the occurrence in this case doesn't fit: curative effect of the Venturi knob. But it does account for the sudden onset at depth, although a spider may have the same association due to the passage of time, rather than depth in the water.
I think @Mobulai wins conceptually, and @rhwestfall wins for plausibility. Plugging up that hole would have required something bigger than "tiny", and much as I'd like to, I can't really blame Aqualung.
Great story!
But yuck!
And here's another thought, should you find yourself in the situation that began the experience. If you have a good working regular set with a blown high pressure hose, take the high pressure hose from the rental set and put it on your set.
Tanks A Lot
Contributor
Another possibility, which I have seen in the past. It has nothing to to with the the regulator itself:
Debris from the cylinder can partially block the dip tube of the valve. On aluminium cylinders a big ball of aluminium-oxide greater than 3cm in diameter can easily develop. On steel cylinders like ECS, the base metal does not form a powder, but big flakes of rust, very thin and a good 3cm long.
If a diver goes down head first or does a overambitious back roll, this debris can fall on to the dip tube, partially blocking it. As there is no imbalance between the cylinder and the inside of the valve until a diver inhales, the debris can just sit loosely lodged in the tube. Breathing becomes harder as the diver empties the air from inside the regulator and hoses, while some air may bleed past the partially blocked tube. If the pressure imbalance gets high enough, the debris may get dislodged and usually broken up into smaller pieces, allowing more or less normal breathing.
Chances of this are very low. I thought the first time I have seen it happen it's a one in a billion chance, but it did happen again at a later stage. It of course has nothing to do with you using the pre-dive switch. In a situation like this, the person usually abruptly moves his body, which may also help to dislodge whatever is in there.
As I could not believe it after I have seen it for the first time, I experimented with an old ECS cylinder in the workshop and sure enough, if the bottle is flipped as in a fast back-roll, this can happen.
Without the cylinder turning upside down at some stage, this is impossible to happen, as the air would not suck the debris up the cylinder.
Debris from the cylinder can partially block the dip tube of the valve. On aluminium cylinders a big ball of aluminium-oxide greater than 3cm in diameter can easily develop. On steel cylinders like ECS, the base metal does not form a powder, but big flakes of rust, very thin and a good 3cm long.
If a diver goes down head first or does a overambitious back roll, this debris can fall on to the dip tube, partially blocking it. As there is no imbalance between the cylinder and the inside of the valve until a diver inhales, the debris can just sit loosely lodged in the tube. Breathing becomes harder as the diver empties the air from inside the regulator and hoses, while some air may bleed past the partially blocked tube. If the pressure imbalance gets high enough, the debris may get dislodged and usually broken up into smaller pieces, allowing more or less normal breathing.
Chances of this are very low. I thought the first time I have seen it happen it's a one in a billion chance, but it did happen again at a later stage. It of course has nothing to do with you using the pre-dive switch. In a situation like this, the person usually abruptly moves his body, which may also help to dislodge whatever is in there.
As I could not believe it after I have seen it for the first time, I experimented with an old ECS cylinder in the workshop and sure enough, if the bottle is flipped as in a fast back-roll, this can happen.
Without the cylinder turning upside down at some stage, this is impossible to happen, as the air would not suck the debris up the cylinder.
This is what I was going to suggest, but you did it much more articulately!
Was this your own cylinder or the dive operators? If yours, I'd get it VIP'ed right away if so. If there is any corrosion that may be your issue. Get the valve serviced at the same time as well and pay close attention to the dip tube.
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