Equipment Exploding tank shrapnel injures boy - Ploče beach, Montenegro

[TooCold]

Yes, that's exactly what I mean.

i.e. water in the donor (pressurised) tank.

I tried exactly what they suggested and,

i.e. water in the receiving (empty) tank.
So you did both sets of tests? I'm just trying to understand.

The flow of gas is from high pressure to low pressure. How would water from inside the lower-pressure cylinder enter the higher-pressure cylinder?

Clearly I have a blind spot here, as that is exactly what confused me in their statement. Would you mind explaining how that would happen?

I have no idea. In fact it seems really very implausible to me. But testing assumptions is the point of empirical investigation, which is why I'm interested in your results (and cudos to you for actually testing).

 

[iain/hsm]

Not sure if we should move this away from the accident aspects of this post and into another separate post on the technical side. But water into a scuba cylinder is a finite application. Sub divided from the 3 general headings of compressor, sea water ingress or fresh water.
1. Compressor: Lack of mechanical draining of the water condensate or failure of auto drains.
Both causation factors are lack of compressor operators vigilance.
I also know of a operation that dropped the air intake hose over the side into the water but that just hydraulic locked the compressor and smashed the conrod, guide pistons and cylinder liner.
Biggest cause of water by volume but it's distilled water with oil and hopefully the taste is the give away.

2. Sea Water. Best ever cause and worse internal corrosion in the quickest time possible is using the cylinder to fill lifting bags until empty at depth. Then leaving them empty for a couple of months before taking a peek inside. Technically re filling them could be worse as the damage is quicker. Hence why IMHO commercial diving suffer more failures than recreational.

3. Next is using the cylinder until empty (we all have done this) but not then going snorkelling for the next two hours while still wearing it with it turned on and open and doing 20 meter duck dives on a snorkel.

4. Not that important normally just a slight staining inside the cylinder is just fitting the regulator without first blasting the pillar valve clear of salt water spray off the deck or when fitting a rubber cap or a wrap of duct tape is too much trouble to protect from deck spray.

5. Variation on above is in the fresh water category is when dunking the regulator in a water rinse bath or hose pipe without sticking your thumb over the sintered filter hole or using a cracked plastic cap. Next pressing the 2nd stage purge valve in fully while jetting or dunking in a bath when water so the hose pipe or bath water gets fully inside. Water gets in at both ends including the hose. Next you attach the regulator and turn on pressure and fully unscrew the valve knob now the 2nd stage is full of water the intermediate hose is also full and the 1st stage is gain full of water and with water being pretty much incompressible water from the 1st stage HP upstream of the HP seat drains water back by gravity into the cylinder at equalisation while at a later time the water downstream of the HP seat safely purges out at the first push of the purge button. Again not much damage only slight staining the water drys out after a couple of fills.

6. I guess the other contender would be the stunt diver variations messing about again ending up with an empty cylinder at even a shallow water column as you keep pushing the purge the other option is during training I guess heck knows what they get up to.

7. Breathing from a cylinder without a demand valve fitted directly off the HP cylinder again until empty or you half drown and drop the cylinder in your repeating said stunt to achieve utmost perfection and the subsequent pulling power with the girls on deck.

And Hands up if you have not done all 7 repeatedly.

 

[Tanks A Lot]

[...]
So you did both sets of tests? I'm just trying to understand.
[...]

Yes, I did both. Back then I assumed they made a typo and started with the reverse of their statement. I only managed to transfer a tiny amount of water when the donor cylinder contained a ridiculous amount of water.
I thought that I must be obviously missing something, so I tested with water in the receiving cylinder. Even with a nearly full receiving cylinder, no water transferred at all.

I’m sure there are variables such as dip tube geometry that influence this to some degree (for example, sideways holes). Still, I don’t understand how a water-filled receiving cylinder could transfer water into a donor cylinder. I have not managed to replicate this, but that doesn’t mean it isn’t possible.

The times I have seen water ingress, other than from a compressor, always came down to neglect outside normal operation:

• Muffling the sound of emptying cylinders by throwing them into the ocean.
• Transferring partially opened and empty cylinders in a flooded boat bilge.
• I’ve also heard stories from colleagues about dive instructors who let students completely empty cylinders to simulate out-of-air scenarios, then left the empty cylinders at the shallow end of the pool after changing them.