Genesis HP Steel hot fills?

[tbone1004]

So I had drained a HP120 to about 1000 psi last week and had stuck it on the compressor. Had it just barely open and it took about 20 minutes to fill to 3500. It was hotter than the AL80's that I was having to fill as fast as possible from 1000 ish to 3200, with valves wide open, filled in about a minute each.
Just wondering if this is common with these tanks, if I should be worried about it, and if there is any other ways to fill them to keep them cool. We fill wet, so they were in about 70 degree water, but it doesn't seem to help much.

thanks
Tom

 

[Indian Valley Scuba]

It is basic thermal dynamics. You took long enough (20 minutes) for the heat of the re-compressed gas to finally soak thru the steel cylinder walls.

When you rapidly fill the aluminums, you won't see the temp rise in one minute through 1/2" aluminum walls. But wait 20 minutes and it will be there too.

There is no denying the heat that is generated when gasses are compressed, and the amount is predictible and consistent.

It is only the time factor that is fooling you here.

And, wet filling does nothing except cause puddles around the fill station, as you can see by your own experiment, you would have to leave the tanks in there a long time to allow the heat to transfer from gas to cylinder and then finally to water. By then the gas is essentially already cooled.

Hope that helps explain things a bit!

 

[Jim Baldwin]

So I had drained a HP120 to about 1000 psi last week and had stuck it on the compressor. Had it just barely open and it took about 20 minutes to fill to 3500. It was hotter than the AL80's that I was having to fill as fast as possible from 1000 ish to 3200, with valves wide open, filled in about a minute each.
Just wondering if this is common with these tanks, if I should be worried about it, and if there is any other ways to fill them to keep them cool. We fill wet, so they were in about 70 degree water, but it doesn't seem to help much.

thanks
Tom

I dive PST HP steel tanks, 100 and 120. When I had the tanks filled they would come out hot. And when I started filling them myself the same thing. Realize that the steel tanks are thinner than the AL so they are going to heat up faster.

I rountinely fill my tanks to 4000 to ensure that I actually get all the gas I need for a full fill. When cool and checked the next day they read 3500 to 3700.

 

[coldwaterlloyd]

The trick is to fill them as slow as possible , allow to cool and top up if possible .
I rarely hit the water with more than 3300 unless the shop allows to cool and top up .
Jim is 100 per cent on this one , If you run up to 4000 you will get 3500 when cool , some shops just will not oblige .

 

[dannobee]

The trick is to put them in the deep freeze for a few hours before you fill them to 3500psi.

 

[Scared Silly]

The geek answer:

The heat transfer is based on several factors as noted above the thickness of the material is one factor but the type of material is also a factor. Now interestingly enough Aluminum conducts heat better than steel. So if you take a billet of steel and aluminum of the same dimensions heat will be conducted faster in the aluminum than the steel. On average the difference is around 4x faster (modulo the exact alloy type).

So even though the aluminum cylinder is thicker it will conduct the heat faster than a steel cylinder that is half as thick.

So if you had started the fill for both cylinders at the same time the aluminum cylinder would have been hotter than than the steel initially. At some point, aka equilibrium or steady state both would be the same temp.

 

[tbone1004]

I've got a firm grasp of thermo *mechanical engineer...*, which is why this didn't really make sense. 2500 psi in less than 2 minutes on an AL80 vs 2000psi over 20 on a HP120. The steel was hotter than the aluminum the whole time which didn't really make sense. Even a 200psi change in a couple of minutes got the steel hotter than the AL80 was after the quick hot fills.