Water in tank – low pressure or air fill?

[captain]

If you rinse off your tank after a dive there is a very real possibility that water got into the valve. It only takes one time for the person filling the tank to forget to open the valve and blow it clear before connecting the whip and bingo, water in tank. That and bad compressor water removal is the only way to get water in a tank that has the least bit of pressure in it.
I fill my own tanks and I have not been immune from forgetting on ocassion to blow the valve clear. In my case sometimes I am filling tanks a couple of weeks later so any what that was in the valve has probably evaporated by then if I forget to blow it
Someone in shop in a hurry to turn around a large group of tanks for the next dive is even more likely to miss one.

As for cooling when blowing down a tank causing condensation inside there has to be wator vaopr in it in the first place. If the air fill was dry enough it would have a very very low dew point ( -65F for grade D and E air) and the tank would not get cold enough to cause condensation inside only on the outside.

 

[pescador775]

One comment about blow down; well; maybe a couple. Before use of chemical dessicants it was possible, even likely, for a small amount of moisture to enter as a gas via the compressor. So, a tank that was cooled to low temps such as might occur in weather or rapid decompression could develop some droplets of condensate on the interior walls. In today's world, this is much less likely and any minor moisture which would form would rapidly re-vaporize once the tank warmed. So, moisture forming inside a tank as a result of dumping air is unlikely. However, this is only true as long as the tank is sealed. I would suggest that a tank which has been cooled by some means in a warm, humid environment remain sealed (close valve) until the tank has warmed to ambient. This arises from the fact that a depressurized tank can become very cold and the exterior may actually become wet due to condensation. The same could happen to the interior if the valve is removed for a period of time while the tank is still cold. Condensation may also occur in the valve orifice or othe parts and this should be checked after removal and before installing. That is, the valve must be removed for inspection as a wet valve cannot be cleared once the tank is drained.

 

[Doc]

More from the :egypt: "old goats" !

Someone in shop in a hurry to turn around a large group of tanks for the next dive is even more likely to miss one..

Like at a dive resort.

When the tanks have internal or thread issues, who ya' gonna blame? Yourself?

No- the guests. They're just going to have to quit breathing the tanks down. Let's limit them to 500 psi.

Thus, the myth became rule.

Sometimes, old goats have some good historical recollections.

 

[drbill]

Several years ago my old 13 cu ft pony developed a leak. The air in it emptied, and it was 2/3rds full of water after my last dive with it. Good thing I didn't need it on that dive! I immediately got a 19 cu ft tank that has not had any problems.

Of course many say that air fills on California dive boats tend to be very wet... and ruin tanks. I blow the water out of my DIN valve and the whip as best I can before hooking it up for a fill on the boat.

 

[peterbj7]

I once had a steel 12 ltr tank (a bit bigger than an 80 cu.ft.) condemned on its first VIP, one year after I bought it. I had generally filled it at unimpeachable air sources, but there was one which I found out afterwards was notorious for wet fills. Never used that fill station again, but the damage was done. The rusting was so severe the tester thought that in another year or so the tank could have exploded.

I also had a 3 ltr aluminium pony condemned on its first test, which was actually a hydro because I hadn't had the visual done on time. I had been in the practice of fully draining it, and paid the price. The reg I used on it was also in poor condition from the salt water that was allowed to get into it.