Cooling tanks while filling...

[El Orans]

A shop I visit occasionally fills tanks standing in a water tub with a tap running cold water on the shoulder of the tank.

Another shop claimed that this is bad for the tank.

Is there any truth to that?

 

[Jim Ernst]

Great thread/question.

I must do some inquiring on that

 

[deepstops]

These two articles make a strong case for dry fills.

http://www.fillexpress.com/library/wetfills.pdf (Bill High, PSI President)
http://www.fillexpress.com/library/dryfills.pdf (Fred Calhoun, PE)

 

[fppf]

Oh boy, here we go again.

All I ask, have you ever filled a HP 120 steel cylinder at 500 PSI per minute, the standard fill rate?

And by the authors own math in the above links, he points out a hot fill on an AL80 will drop 200 PSI when it cools to room temperature. What diver out there would not b$tch up a storm if you gave them an AL80 with 2800 PSI in it?

I see 2 types of operations happen...
Some shops will fill a cylinder to its rated pressure and cool it to room temperature so the tank is properly filled. That cooling is by water, or a blower.
Some shops just purposely "over fill" a cylinder, and bank on the fact that the pressure will drop to the correct pressure when the cylinder is at room temperature. If they get it correct, there not over filling the cylinder, but if they get it wrong they are.

In the end, I feel it really does not matter how you fill a cylinder. As long as it ends up at its rated pressure at room temperature, and you fill it slow.

And its not just the dive industry that uses water to cool cylinders during fills.
If you get the chance, walk in the back of any industrial gas supplier. You will see them use water spray's and fans on any cylinders that have flamable gas in them during fill.

 

[spectrum]

I don't see where from my experience or from the references above that it need be bad for the tanks but there is some risk and reward.

The only risk I have a concern about is the introduction of water into the cylinder. If any water is splashed onto the whip or valve and not wiped and blown clear it will be pushed into the cylinder and cause obvious problems. If the fill person is reasonably competent this may not be any riskier than changing tanks on a 2 dive outing while gear is still wet.

I have not seen any danger of over filling when cooling is in the form of an ambient tub. That is because the process has limited effect. I have heard of shops running chilled or using outside water sources such as waterfront shops pulling from open water. I can't speak to those processes.

Splashing water over the crown sets up an evaporative cooling process. A flush extends the immersion as well as keeping the tank closer to tap temperature and the obvious overflow drain will limit the salinity build-up in salt water locations through a perpetual renewing of the water. Anything done to the crown will enhance the benefits of immersion. It probably also assures wet whips and the risk that brings.

What you need to keep an eye on is the fundamentals of a fill. Loading a scuba cylinder will result in heat as those molecules are forced to squeeze in together. The end result is a hot ball of gas sitting in the cylinder. That gas is essentially static when the fill ends moving only by virtue of convection. Since air is a great insulator it will take a while for that heat energy to be presented to the the cylinder wall to be conducted out of the cylinder by virtue of the water temperature and the combined conduction factors.

With the cylinder sitting in a water bath while filling the submerged cylinder surface will be cooled. The actual benefit to the fill process is a result of the conduction through the wall and the circulation in the cylinder. If you are getting a "while you wait" fill, especially on a steel cylinder you will walk out with a better fill. There will still be considerable cooling loss as that gas ball gives up it's heat energy for about 4 hours. If you did a side by side test I'd expect to see a 100 -150 PSI better fill on the quenched cylinder but will still loose 150-200 PSI on the way 70 F.

Again this is all based on ambient quenching. What happens in a mechanically chilled system is beyond my experience. I have heard of such installations but never seen one. A slow dry fill will be better fill than a fast wet fill.

Pete

 

[The Kraken]

Is it bad for your automobile to run coolant through the system while it's operating???

the K

 

[DA Aquamaster]

Running water over the tank after it is connected has about as much risk of introducing water into the tank as diving with it connected to your regulator.

The potential issue with water baths is the proximity of water to the open and exposed fill whips and tank valves. Getting water inside the valve or fill whip and then filling the tank is the only way to get water in the tank without fully draining it, or without having a very faulty compressor.

What is often ignored is that many, if not most operators fail to crack the valve and ensure there is no moisture in the valve, especially DIN valves, and/or blow any moisture out before connecting the fill whip. Water bath operators tend to be much more aware of the potential and I suspect introduce less water into tanks in a given year than operators who think water baths are bad but are located close to a body of water where recently dove and potentially wet inside the valve tanks are filled.

In short, it is not the water bath that matters, it is the extra step to ensure any tank that is ever filled anywhere with or without a water bath has no water whatsoever inside the valve.

The other issue has also been mentioned. Some operators refuse to ever exceed the service pressure on the tank - even though that is by definition the service pressure inside the tank after it cools to room temperature. In other words I can hot filla tank to 200-300 psi over its rated servcie pressure and as long as the pressure does not exceed the service pressure once it cools to room temp (70 degrees) it is in fact not over filled.

The same thing applies in reverse. If I perfectly fill a black colored tank to its service pressure at 70 degrees, and then store it outside on a 110 degree day in the sun where it reaches maybe 130 degrees and a pressure a few hundred psi over the stamped pressure, it is still perfectly filled. No more air snuck in there and when it cools back down to 70 degrees it will still be perfectly filled.

At the other extreme I have filled tanks outside on zero degree days and if you fill them to their rated pressure, they are in fact over filled as they will have more than their rated pressure if warmed to 70 degrees.

 

[300bar]

A shop I visit occasionally fills tanks standing in a water tub with a tap running cold water on the shoulder of the tank.

Another shop claimed that this is bad for the tank.

Is there any truth to that?

Any complaints about my (non cooled) fillings.

The only thing sofar,that realy helps is pre cooling(freezing) the air in the banks.
Go have a fill at "Waterworld"

 

[Slugrusher]

Alright, sounds good then.

 

[spectrum]

The only thing sofar,that realy helps is pre cooling(freezing) the air in the banks.
Go have a fill at "Waterworld"

Some of my best insta-fills have been first thing in the morning in the fall when the shop banks were full and cold and my tanks were chilly as well.