transfer whip usage

[captain]

I have a steel 72 I bought new in 1957. The shop had a fill whip right at the front door where you walked in. They would connect the whip and fill it in about 45 to 60 seconds. It got hot as hell and I got a short fill, I really couldn't tell as there were no SPG's at that time. Moral is I still use that tank and it passes hydro every time.

 

[duckbill]

I believe your air would have to be "super wet" to condensate inside a tank.

"Super wet"? Why? At the very cold temperatures one would be inducing by a quick release of air it wouldn't take much moisture to precipitate out at a low dew point. That's the main reason to bleed tanks slowly, instead of all at once.

 

[deepstops]

"Super wet"? Why? At the very cold temperatures one would be inducing by a quick release of air it wouldn't take much moisture to precipitate out at a low dew point. That's the main reason to bleed tanks slowly, instead of all at once.

Grade E scuba gas (which isn't nitrox compatible) has a water vapor content of 24 ppm and a dew point of -65F. Your gas would be seriously "substandard" if it was able to condense inside a tank because you drained it too quickly.

You can't have condensation taking place if there's no water vapor in the gas to begin with. The rust you hear about inside steel tanks happens during the fill process.

 

[Luis H]

Grade E scuba gas (which isn't nitrox compatible) has a water vapor content of 24 ppm and a dew point of -65F. Your gas would be seriously "substandard" if it was able to condense inside a tank because you drained it too quickly.

You can't have condensation taking place if there's no water vapor in the gas to begin with. The rust you hear about inside steel tanks happens during the fill process.

That is the dew point of that air at standard pressure (one atmosphere). The dew point goes up in the compressed air.

I do not have the tables handy, but if I recall correctly that same air at 2500 will condense at about 5 F and at 3500 psi it will condense about 15 F (don’t quote me on this numbers, as I said, I am going by memory and I am partially guessing, my memory is just not that good).

The point is that compressed air will allow condensation (of that very small amount of moisture) at much higher temperatures.

During the winter time I store my full tanks in my warm basement to avoid condensation. When I go ice diving I suspect there may be a little condensation if the outside air temperature is very cold, but it will be for a short time. After the pressure goes down the dew point drops down dramatically (approaching -65 for a completely empty tank).


As it may be noticed the problem of condensation is worst with higher pressure tanks.
The higher pressure 3442 psi tanks really need dryer air if they are going to be used in cold environment.

While ice diving, the water temperature rarely gets that cold (normally above 32F), but the air temperature can be colder and the expanding air will cause the compressed air to get much colder.


Captain
Your experience with quick fills is with steel tanks. I would avoid that practice with aluminum tanks.

 

[deepstops]

Agreed.

The question was - can you form condensation inside a tank from a fast draining and I stand by my answer that it simply won't occur unless the gas inside is really wet to begin with.

 

[duckbill]

At least we're down from "super wet" to just "really wet". That still makes it sound like it must be so dripping wet that a sponge would be an efficient means of removing the water For my tanks, I'm inclined to assume everyone's air is just "really dry", not "super dry". (It's all relative)

You can't have condensation taking place if there's no water vapor in the gas to begin with. The rust you hear about inside steel tanks happens during the fill process.

True, but we aren't talking about "no" water vapor. I doubt anyone offers air with absolutely no moisture in it at all. Some just have less moisture than others, and that is the rub. If you concede that water could have entered a cylinder during filling regardless of how dry it was to begin with, then you could also concede it may not be a good idea to promote conditions that may cause that water to condense on the interior walls of the cylinder.

I stand by my answer that it is not a recommended practice to quickly drain a cylinder, whether during an air transfer to another cylinder, or into the atmosphere for removing the valve. In fact, quickly draining the cylinder then immediately removing the valve is about the worst thing one could do to cause condensation and flash rust inside a cylinder.

 

[deepstops]

I doubt anyone offers air with absolutely no moisture in it at all. Some just have less moisture than others, and that is the rub.

My LDS is is always under 7ppm water vapor (exceeding the ABO standards).
http://fillexpress.com/library/testresults.pdf

If you concede that water could have entered a cylinder during filling regardless of how dry it was to begin with, then you could also concede it may not be a good idea to promote conditions that may cause that water to condense on the interior walls of the cylinder.

Water can enter your tank during the fill process if you've got "tank monkeys" doing the job. That's all I'll concede in that regard. Crack open the whip and the valve before you begin filling the tanks and you've eliminated that from being a possibility.

I stand by my answer that it is not a recommended practice to quickly drain a cylinder, whether during an air transfer to another cylinder, or into the atmosphere for removing the valve. In fact, quickly draining the cylinder then immediately removing the valve is about the worst thing one could do to cause condensation and flash rust inside a cylinder.

Again, seriously, only a "tank monkey" would do that and that's the only way you're going to cause flash rust when draining a tank if the fill gas was decent that was in the tank to begin with.

 

[Troutmaster]

Filling a tank slowly is better for the tank long term, more so with aluminum than steel. If you are not in a big hurry, do the transfer slowly so the tank won't get hot and you will be fine. But as long as you are not filling oxygen rich mixes you are not going to blow yourself up with a "hot fill"

 

[duckbill]

Deepstops, my mistake was that I just assumed not everyone got their fills at your shop. Sorry about the misunderstanding.
The duckbill- out.

 

[IDS3]

Luxfer recommends between 300 and 600 psi. Take your time, fill slow, enjoy your surface interval pland next dive.