Tank filling question

[BuoyantC]

I have a question concerning tank filling, more specifically steel HP tank filling. Is there a sequence of opening valves that can help reduce the amount of heat build up during a fill?
I know about filling slowly, but I interested in reducing the heat build up from from the actual movement of the air. I've heard a term for it... something like "adiabatic compression" (please forgive my aging memory!)
Just curious if I can do a better job filling tanks.

Thanks,
Dennis

 

[Snowbear]

I have a question concerning tank filling, more specifically steel HP tank filling. Is there a sequence of opening valves that can help reduce the amount of heat build up during a fill?
I know about filling slowly, but I interested in reducing the heat build up from from the actual movement of the air. I've heard a term for it... something like "adiabatic compression" (please forgive my aging memory!)
Just curious if I can do a better job filling tanks.

Thanks,
Dennis

I too use HP tanks. The heat buildup in the tank is from the compression of the gas, so you are right - the slower the tank is filled, the less it will heat up. The sequence of valve opening really shouldn't make much difference. That said - I like to have my tank valve all the way open and control the flow of gas via the in-line needle valve or source tank. 1-2psi per second (60-120psi/min) minimizes heat buildup, but that last 500psi still gets 'em pretty warm...

 

[Drew Sailbum]

Usually flow control is not accomplished by the tank valve.

The act of compressing gas into the cylinder generates the same amount of heat, regardless of speed of fill. Filling the cylinder slower simply allows some of that heat to dissapate into the surrounding air.

Some places do fill cylinders in a water bath to better allow the heat of compression to dissapate. The increased chance of unintentional introduction of water into the cylinder's interior makes this a less than desirable option.

It is possible that manipulation of various valves on the control panel would alter the rate of fill, but that would be specific to the particular fill station.

 

[WarmWaterDiver]

Drew's science is correct - cooling baths etc. are one example of an attempt to make the process more closely isothermal than adiabatic. The water bath is used here as a "heat sink" - just like the scuba regulator first stage uses the water you're diving in as a "heat sink" for the cooling effect of dropping gas from tank pressure to intermediate pressure (and second stages with heat exchangers use the same principle for the cooling resulting in pressure reduction from intermediate pressure to ambient pressure).

 

[Ontario Diver]

I have a question concerning tank filling, more specifically steel HP tank filling. Is there a sequence of opening valves that can help reduce the amount of heat build up during a fill?
I know about filling slowly, but I interested in reducing the heat build up from from the actual movement of the air. I've heard a term for it... something like "adiabatic compression" (please forgive my aging memory!)
Just curious if I can do a better job filling tanks.

Thanks,
Dennis

This is more of an issue when you fill with pure O2 (for partial pressure blending). In that case, you would start from the tank and work your way back to the O2 control valve so that there are no places for heat to build up.

Within the tank, the heat will build up as the gas compresses. It is simply the physics of the situation and there ain't much to do about it. Water baths don't do too much because of the thickness of the metal. Since the walls of the tank are so thick, rapid cooling on the outside from the water bath combined with heating on the inside from the compression of the gas can actually be worse for the steel tank. There is a paper on it at http://www.psicylinders.com/library/wetfills.htm and Bill says it better than I.

Filling slowly so that the metal walls do not encounter big swings of temperature is best. 300 PSI per min is best.

 

[pescador775]

I've written on this subject extensively. Yet, because I don't have a forum outside of this board my job will never be done. That is, to debunk the industry fluff pieces. Yes, it still annoys me when I see bull printed by industry flacks and later have it turn up here again and again. For example, aluminum tanks ARE thicker (duh). They got that right. What PSI fails to mention is that the heat conductivity of aluminum is twice that of steel. That is the real reason that aluminum absorbs heat and dissipates heat with a relatively lower rate of temperature increase than steel. The rest of that so called paper is just so much bilge water. No truth in it whatsoever; just a few half truths spun to push some agenda. For the life of me I can't figure why they would push such unscientific nonsense. Normally, I would look for a profit motive. I can only guess that the PSI people are jumping on a request made informally by their boss after a converstion that he had at a local bar, with a dive shop owner who wanted to avoid the inconvenience of a water bath and needed cover for his actions.

 

[quimby]

I never figured out what got Fred Calhoun so wrapped up, but everything said negative about water tanks all refers back to him. If your sloppy you can put moisture in a tank etc etc but I would be more concerned with the dew point and quality of what was pumped and have a real problem with shops and their understanding of compressor maint let alone their tank monkey.
the rest as pecador said is leaning on a agenda

 

[teknitroxdiver]

I'm not for sure, but if you're filling doubles, it would seem like you would get a slower fill rate with the crossover open, and thus less heat. Right?

 

[ScubaDadMiami]

This is more of an issue when you fill with pure O2 (for partial pressure blending). In that case, you would start from the tank and work your way back to the O2 control valve so that there are no places for heat to build up. . . . 300 PSI per min is best.

Just to make sure there is no misinterpretation by anyone reading your comments, oxygen fills should be no more than about 60 psi per minute. I am guessing you were talking about air fill rates after your oxygen reference. Some may have confused this to mean O2 at 300 psi per minute.

 

[Ontario Diver]

Just to make sure there is no misinterpretation by anyone reading your comments, oxygen fills should be no more than about 60 psi per minute. I am guessing you were talking about air fill rates after your oxygen reference. Some may have confused this to mean O2 at 300 psi per minute.

You are in deed, correct sir! I thank you for catching that small yet soooooo important detail.