Water Bath Fills
Anyone have any real data on the effects of filling tanks in a water bath versus not in the water bath? Something more than opinion and hearsay? Something with graphs, charts, tables? Empirical, not theoretical or mathematical (but that too is ok, just not sufficient on its own).
skip
"Learning the techniques of others does not interfere with the discovery of techniques of one's own." B.F. Skinner, 1970.
The best fill is a slow fill. I'll still see a pressure drop of a couple hundred psi after a wet fill if it is filled too fast. I've also seen a drop of only 50psi after a dry fill if it was filled very slowly. I haven't noticed much of a difference wet or dry with the same time to fill. I use the water bath to prevent the tank from heating up on the outside. Our station is sometimes in direct sunlight and with outside temps in the high 90's just sitting in the sun can heat the tanks up so hot they are hard to pick up.
Mark Schroder
The way of a fool seems right to him, but a wise man listens to advice. (PV12:15)
Boru, I can't believe you deleted those posts. You were right. That link is a bunch of hogwash. His arguments fail the logic test on many layers. Your scientific points carry a lot more weight than his nonsense.
Whoever said money can't buy love never bought a puppy.
Unfortunately the link does not address Skip's question.
That article has some serious BS in it. For example:
"an informed and responsible dive store operator slowly fills the aluminum 80 to 3,000 psig (maximum, because tanks must not be over-filled). The tank experiences a rise in temperature to 95 degrees...it’s warm and that’s fine. The dive is in water at a temperature of 60 degrees will produce a pressure drop of about 190 psig...a change of only 6% (you can still trust my mathematics). If water baths “worked” (they don’t, by the way – and the whole purpose of this treatise is to point that out to you) so that the aluminum 80 at a pressure of 3,000 psig could leave the dive store “cool” it would then have to be protected from any subsequent temperature rise because such a temperature rise would cause the pressure to go over 3,000 psig and that would be irresponsible and against regulations."
The author, despite implying he knows the regs and represents "an informed and responsible dive store operator" clearly does not. The regs require that the tank not exceeed the service pressure when the tank and the gas in it are at room temperature (70 degrees). His math is pretty good as his fill example does indeed result in the infamous 2800 psi dive shop fill in an AL80 - the end result of a "responsible" shop thinking it is illegal to exceed 3000 psi in an 3000 psi service pressure tank during the fill. That is not the case, and using his same math, you can demonstrate that exceeding the fill pressure on a warm tank at the same temperature by 190 psi woudl then result in a propelry filled tank with a 3000 psi pressure, but to get it you have to "fill" it to 3200 psi so that it will in fact be full when it cools to room temp.
His suggestion that if the tank is "cool" and at 3000 psi means it would have to be "protected" to ensure it did not increase in temp and as such increase it's pressure above the service pressure. That ignores the regulatory reality that the service pressure is tied to the temperature and it is both understood and expected by the DOT that a properly filled 3000 psi tank will have a higher pressure if left in your trunk or sitting out in the sun on a 105 degree day. That won't cause it to be "overfilled" just becasue it is warmer than 70 degrees.
Which is to say, the author has a serious credibility problem given that he fails to understand either the DOT regulations or the reasons why the service pressure has a significant safety factor (5/3rds or 3/2s depending on the engineering/certification standard used) between the service, and burst disc/test pressures.
The article is just a big educated sounding excuse for shitty fills:
"We must not feel that we have been cheated when a 3,000 psig tank cools to 2,700 psig. That’s life!"
No...its just a shitty fill by a poorly informed dive store operator.
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I do agree that a wet fill is perhaps the best way to get water into a tank. If a tank monkey is doing that, they need to ensure they blow any water out of the whip as well as out of the tank valve, and this is particularly true with DIN valves where the female threads in the valve can hold a great deal of water that can take a few seconds of air being released from the valve to totally remove.
I do VIPs for a couple of dive shops and worked for a hydro test facility prior to that. From time to time I see evidence of an improper wet fill. This usually manifests itself as streaks of flash rust or discoloration down the inside of the tank where water was deposited at the start of a fill. The pattern is pretty evident - but it is fresh water and non problematic on an isolated basis as it results in flash rust on a steel tank and discoloration in a AL tank - not major rust or corrosion issues (unless its a regular occurrence).
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I've noted that steel tanks and aluminum tanks dissapate heat differently, and I'd argue a steel tank benefits from a water bath more than an aluminum tank, and that comes into play when using fudge factors on trimix fills on dry filled tanks where you need to fill the tank fairly quickly yet with reasonable accuracy.
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If someone has an accurate pressure gauge, a four whip manifold, a water bath and a room at 70 degrees where the tanks could cool, it would be fairly easy to do side by side comparisons of 2 AL and 2 steel tanks of comparable internal capacity (since all tanks need to have the same volume of gas pumped into them for the experiment to be meaningful) filled to the same fill pressure (2400 psi if that's the lowest service pressure or 3000 psi out of respect for the AL80 if you are in north Florida and fill steel tanks to 3600 psi anyway). The protocol would be for all tanks to start empty and at room temp (70 degrees) with one steel and one AL tank filled in the water bath and the others filled dry with all tanks filled at the standard fill rate of 600 psi per minute, then allowed to cool to room temp before measuring the final pressure.
How much of an effect you'd find would depend to some extent on the temperature of the water bath as a greater temperature differential between water and the tank would promote greater heat transfer, but again to make the experiment meaningful the air and water bath temps need to be the same (no cheating with chlled water on a 95 degree day). In addition to the over all effect, you'd be able to measure the difference between steel and aluminum tanks that are filled with the same volume of gas.
So, my 3500 psi stage bottles are frowned upon?
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Reconsidered how I had worded it lol.Originally Posted by Slüdge
Well reword it, and put it back
Gschaut, your reply was good as well, don't be intimidated by the "PE" in that link.
Ok, brief, revised PC edition.
In order to address wet fill/dry fill issue we need to accept some constants.
water weighs approx, 8.37 lbs/gal. Heat is not temp. Heat is energy. Steel and aluminum are somewhat elastic materials. Steel has a higher tensile strenght than Al.
Charles law states that pressure and temp are directly proportional.
Thermal conductivity of material indicates the number of Joules (a measurement of energy) which will be transferred in 1 second through 1 square metre of the material being 1 metre thick given that the opposing faces have a delta t of 1 degree celcius. Thermal conductivity of steel is 45, Al is 140-160 (SAIT thermodynamics 3)
It requires 12000 btus to raise 1 lb of water 1 degree. 12 000 Btu = 12 660 670.8 joule which shows that water has immense cooling properties. in fact at the points of latent heat, (Changing from a solid to a liquid, and changing from a liquid to a gas) we need to add tremendously more heat/energy before we see a temp rise.
Steel is porous on a molecular level, however we maintain a positive pressure on the inner walls of our tanks, this means that water can only be introduced to our tanks by injection ie. poor fill practices.
Immersion reduces stress on the tanks by removing excess heat in the filling procedure and also acts as a buffer/dampner in the case of catastrophic failure of the tank. (This will not necessarily save anyone in the immediate vicinity)
The most likely method to introduce moisture to your tank is to store it dry or at extremely low pressure.
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