Water Bath Fills

Brian: When we were "wet" filling the old steel tanks in the FD, our fill station was specifically designed to hold the tank vertical, with the shoulder just barely submerged, and the bottom of the tank resting on the bottom of the water tank, with the bottom of the water tank over 1' off the floor with an air space below it. PVC pipe was used as holders to keep the tanks upright.The tanks had over 1 foot of water surrounding them to the sides, and less than 2" of water above and below them.

The theory was that in case of a catastrophic failure, the water would hopefully "shape" the blast. Same way sandbags shape a dynamite charge. And channel as much of the blast energy as possible up and down. In most steel tank failures, the sidewall fails, and the blast energy tends to go to the side of the tank. Where the fill operator is standing, at the control station, several feet to the side of the fill chamber.

Our current fill station is "dry", and the tanks are contained inside a 1/2" thick vertical tube of stainless steel, with the tops and bottom open, inside a larger chamber. Same idea, channel the blast energy vertically, with the operator standing to the side of the fill chamber.

I do agree with the theory that if a tank is just laid down in a tub of water, the water and tub material could increase the amount of kinetic energy directed at nearby humans.

How about.. If you lay a tank down in a tub of water, put the tub up on some cinder blocks around the tub's edges? Create an airspace below the water tub. That would create a "weak spot" to blast energy, and channel more of the energy down into the ground. The theory being that a blast takes the path of least resistance, and will direct the shock wave in a direction away from any mass that blocks it's free travel.

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Originally Posted by Greenwood_60

This is EXACTLY what I was talking about earlier. I am under the impression that under ideal circumstances that (other than friction, which I can not quantify) the equation is balanced. As in the only heat the cylinder will gain is the heat the bank lost. Based on that I was trying to get a feel for where this extra heat came from. The gas in the bank (that ends up in the cylinders) is at a higher pressure than in the cylinders, thus the cylinders SHOULD end up cooler than the banked gas. Of course it doesn't, and I would like to know why.

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All that matters is the ideal gas law (conceptually anyway, actual numbers are significantly off at the high pressures we're talking about). You are correct that the equation is balanced, but that's for the entire system. You have to look at the bank and the cylinder separately. The bank's pressure drops and therefore its temperature drops. The cylinder's pressure rises and therefore its temperature rises. The system as a whole undergoes zero change in average pressure and average temperature. If the whole system were completely isolated from the environment, once pressure had equilibrated, the cylinder would be hotter and the bank would be cooler, but the temperature too would also eventually reach equilibrium (and the average temperature would have a zero net change the entire time).

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Originally Posted by Brian Kakuk

Bill High... did not recommend it as it promoted over-filling.

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This is the most illogical argument I have ever heard. One PSI-trained store owner I know refuses to use a water bath, then fills AL80s to 3400psi so they'll cool down to 3000.:roll:

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Originally Posted by Slüdge

This is the most illogical argument I have ever heard. One PSI-trained store owner I know refuses to use a water bath, then fills AL80s to 3400psi so they'll cool down to 3000.:roll:

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Even when hot filled to 3400 psi, the tanks in question are by definition not overfilled if they are at the 3000 psi service pressure when they cool to room temp.

On the other hand, heating them to the point you have to go to 3400 psi to get a full 3000 psi fill is bad form and a water bath may help reduce the temperature increase if higher fill rates are desired.

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Originally Posted by Greenwood_60

My statement was based on friction being of any significance. Even "uncontrolled" fills will have some sort of a restriction somewhere... just not a valve in that case. If friction is not an issue, than my statement is pointless.



This is EXACTLY what I was talking about earlier. I am under the impression that under ideal circumstances that (other than friction, which I can not quantify) the equation is balanced. As in the only heat the cylinder will gain is the heat the bank lost. Based on that I was trying to get a feel for where this extra heat came from. The gas in the bank (that ends up in the cylinders) is at a higher pressure than in the cylinders, thus the cylinders SHOULD end up cooler than the banked gas. Of course it doesn't, and I would like to know why.

My theory was that you could stop a lot of the heating by not losing the cool. Ever had a paintball CO2 cylinder filled? Mine typically come back icy. Why?

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You don't "lose" cold. Cold is not a thing, or substance. It is the absence of heat(energy). If you want to facilitate the cooling efficiency of the bath, you could circulate the water. If you want to go all out, you could install a fountain to increase evaporation.
In some systems, say a busy one, The mechanical heat caused by the compressor can be transmitted to the tank being filled. If the banks are big enough, some of this heat would dissipate from the banks themselves as long as the ambient temp was lower than the banks. As Boru said, it's the heat of actual compression that is the biggest factor. Creating a change of state to remove large amounts of latent heat will produce the most efficient transfer of energy.
I agree with Tegg:smt102, If you get enough fills, in more than one season, you already know the effects of a bath on fill pressures.

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Originally Posted by Gene Powell

I agree with Tegg:smt102, If you get enough fills, in more than one season, you already know the effects of a bath on fill pressures.

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In an ideal world, when mixing gas for customers, you have the luxury of letting the tanks cool several hours or overnight between O2, helium and the top off gas - but in the real world you need a reasonably accurate mix in a short period of time - an hour or so. I agree that anyone who does any amount of that type of filling and does it well probably understands the effects of a water bath as well as the differences between AL and steel tanks.

But that type of experiential knowledge still does not answer the OP's original request for some hard data on the issue.

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Originally Posted by Gene Powell

You don't "lose" cold. Cold is not a thing, or substance. It is the absence of heat(energy).

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Oh man, the one time in this thread I didn't refer to losing cold with lose (losing, lost) in quotes, someone busts me on it.

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Originally Posted by DA Aquamaster

In an ideal world, when mixing gas for customers, you have the luxury of letting the tanks cool several hours or overnight between O2, helium and the top off gas - but in the real world you need a reasonably accurate mix in a short period of time - an hour or so. I agree that anyone who does any amount of that type of filling and does it well probably understands the effects of a water bath as well as the differences between AL and steel tanks.

But that type of experiential knowledge still does not answer the OP's original request for some hard data on the issue.

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True! But I wanted to agree with Tegg while I had the chance.:yawinkle:

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Originally Posted by Gene Powell

True! But I wanted to agree with Tegg while I had the chance.:yawinkle:

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Doesn't happen often for most people... ;)

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Originally Posted by Greenwood_60

Oh man, the one time in this thread I didn't refer to losing cold with lose (losing, lost) in quotes, someone busts me on it.

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Sorry. I didn't mean to "bust" you. It's just that it's an important concept
What it all comes down to, is that as long as you fill slow enough that the heat in the tank dissipates at least as fast as it is being produced, There probably won't be a difference. The water bath dissipates heat faster, therefore you can get away with a faster fill. At least that's how I understand it.

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