how do you get hot fills from air bank?

[Atticus]

My experience is the same as the other responders (and the rules of physics, go figure). The tank gets hot if it's filled too quickly, whether that be from a compressor or a bank. It should take 5-10 minutes to fill an alu80. I overfill by a 200 psi or so to account for the heating even at those fill rates.

You might suggest that your dive op either fill your tank more slowly or that they top it after a delay.

 

[spectrum]

As H2Andy said the movement of those molecules under pressure will do it.

Remember that you are talking about a mass of air in that cylinder. When you are feeling the cylinder you are touching the radiator that is releasing the heat. Meanwhile the air is moving in slow motion to the cylinder walls where it releases heat energy. In other words the air within the cylinder can be warmer than the cylinder wall you feel. It takes a bout 4 hours for the whole thing to equilibrate.

Putting the cylinder in a water bath will accelerate the removal of heat by keeping the cylinder wall cooler and allow you to leave the LDS with more molecules of air.

Slow fills that let the molecules enter gracefully are your friend.

If the timing works out I will bring them in and make sure the fills start and then leave for lunch. When I return we do a top off. It's not 4 hours but it helps a lot. Idealy I leave them overnight but that's not always practical.

FWIW I dive all HP steel. A little patience, tecnique and a slight initial overfill can do a good job in one shot.

Pete

 

[Dive-aholic]

When im filling my tanks i throw them in a barrel of cold water, helps alot.

How long do you leave the tanks in the water? Unless you're leaving them in there until they're back at room temperature, they water bath isn't doing a thing for them. The tanks will still get hot during the fill, which BTW is because the air is being compressed into the tank even though it's coming from a bank, but that's already been addressed here. The water may or may not help pull some heat off the tank while the tank is in there, but it isn't that fast. You would have to leave the tanks in the water until they completely cool, and you're still going to have pressure loss.

Try an experiment - fill a tank in your water bath from 1000psi to 3000psi. Check the pressure 2 hours later. Then fill the same size and composition tank from 1000psi to 3000psi dry. Check the pressure 2 hours later. You won't have much difference.

 

[herman]

Here is something else to consider, how are you actually measuring the fill? It's not uncommon for SPG's to be off a couple of hundred pounds. If the shop is using one gauge and your using another, that alone could be some or all of the problem.

 

[cummings66]

I thought JeffG's answer was right on target. He asked who was right and indeed the LDS is right and this guy owes that person an apology for being rude.

As others have said after the fact getting a full fill should not be an issue and the guy doing the fills has some problem or limitation placed on him. For example, are you waiting on the tank wanting to take it from there and immediately go diving? In those cases you'll end up with a hot fill and be short more often than not. If you tell him to fill it and give him the time he needs you should get a full fill.

I take my tanks by and pick them up the next day and I'll get a full fill nearly every single time.

For what it's worth, I have had dive shops fill mine quickly and the steel sure got hot when they did it. So, yes you can get hot fills from a bank. Some of them hot enough to burn you if they wished to do so.

 

[jrockosaurus]

I thought JeffG's answer was right on target. He asked who was right and indeed the LDS is right and this guy owes that person an apology for being rude.

As others have said after the fact getting a full fill should not be an issue and the guy doing the fills has some problem or limitation placed on him. For example, are you waiting on the tank wanting to take it from there and immediately go diving? In those cases you'll end up with a hot fill and be short more often than not. If you tell him to fill it and give him the time he needs you should get a full fill.

I take my tanks by and pick them up the next day and I'll get a full fill nearly every single time.

For what it's worth, I have had dive shops fill mine quickly and the steel sure got hot when they did it. So, yes you can get hot fills from a bank. Some of them hot enough to burn you if they wished to do so.

who said anything about being rude? my complaint was that i wasn't getting the fill that i paid for. i guess it's not ok to ask for the last 10-20% of my tank to be topped off? i admit that i was wrong in arguing that you can't get hot fills from a bank but regardless, i still shouldn't be getting underfilled tanks. the tank is life support, 2100 psi in my lp108 is like 23 cu ft less than what the tank is rated at and ultimately less time on the bottom. my error in thinking was picturing the tank added to the bank as an increase in total volume of the system. but, as someone pointed out, the higher pressure banks act as the compressor and while they will experience cooling, the tank being filled will warm up. he couldn't give me any reasons why what i was arguing was wrong so thats why i posted here

 

[Dive-aholic]

You should be getting your tank + rated. You're actually getting shorted 22cf by not having it + rated, if you go by the rating. If you go by what the tank can actually handle, you're getting shorted a lot more. Find another shop.

 

[redacted]

I thought JeffG's answer was right on target. He asked who was right and indeed the LDS is right and this guy owes that person an apology for being rude.
.

Seems to me they are both right. LDS got the physics correct and the OP seems to understand that now.

But there is absolutely no reason a customer should not be able to get a 3000 psi fill in his AL80. (For my local diving, I usually don't care about a few 100 PSI but if I tell my LDS I'd like a good fill, I always get it.)

Apologies from both seem to be in order.

 

[CompuDude]

Unless you overfill your tank, there is no way to get a quick, fill-while-you-wait full fill. Unless perhaps someone has a cryogenic fill station.

Leave your tanks overnight. From my discussions with multiple LDSs, the general consensus seems to be it takes a good 6 hours for the heated gas to cool in a freshly-filled cylinder. If they top it off in the morning (or perhaps that evening, if you started in the morning?), you should have your full fill. The only other way is an overfill that cools to the proper full pressure.

Packing gas into a tank generates heat, as others have pointed out, no matter where that gas comes from (bank or compressor). Pulling it out does the opposite. Easy way to demonstrate. Crack the valve open a smidge on a full tank. As the air rushes out and expands, it absorbs energy, and feels cool. Crack it wide open, and the air rushes out a LOT faster. Not only will it feel really cold, the massive heat absorption will cause condensation to start forming on the valve and eventually ice, all from the gas' ability to pull heat from the surrounding area as it expands from the compressed state. Going back into that compressed state, the opposite happens, and it dumps heat into the surrounding area (the tank). Slow the fill rate, you slow the heat generation, just like the valve went from merely cool to cold when you opened the valve to demonstrate the other side of the principal.

Pretty simple process, no physics needed when you lay it out in easy terms.

 

[SparticleBrane]

http://thedecostop.com/forums/showthread.php?t=19687

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