how do you get hot fills from air bank?

[jrockosaurus]

"well... as far as i know (and i know very little), it's the friction of putting all that
air into the cylinder"

that was one of the things i said to him, the only temperature increase would come from heating at the valve where the air is compressed again before it enters the tank but I didn't think that this would be enough to throw off the tank as much as he's claiming or even heat the entire tank for that matter. my last lds used a bank and always gave quick fills (like less than 5 minutes and without a water tub) and my tanks never got hot. thanks for the replies

 

[Debraw]

It does not necessarily have to get hot when they fill them. It is from the filler opening up the valve to much and filling at a faster rate than the recommended 600PSI rate. I typically fill at 300-400 PSI a minute. Takes a bit longer out of the bank but you will get a full fill. We can also let it sit, "cool down" and then top off for what some will call a "cold fill" . Some shops will use a cold water bath, we don't, and do not need to.

Check out this site for a lot more information on cylinders and fills. http://www.psicylinders.com/ and click Library. Great resource!

http://www.psicylinders.com/library/Current/library.htm

 

[1_T_Submariner]

This happens because your tank starts at 500 PSIG and they are compressing air into it using stored pressure. If they where to just release the air into the atomosphere it would be cold due to the pressure drop (Like if your tank had a hole in it) but since the Volume of your tank isn't changing and the pressure is going up just like when the compressor piston moves up in the cylinder. Type "Ideal Gas Law" into google and you will find a more techincal explanation.

 

[jrockosaurus]

This happens because your tank starts at 500 PSIG and they are compressing air into it using stored pressure. If they where to just release the air into the atomosphere it would be cold due to the pressure drop (Like if your tank had a hole in it) but since the Volume of your tank isn't changing and the pressure is going up just like when the compressor piston moves up in the cylinder. Type "Ideal Gas Law" into google and you will find a more techincal explanation.

ok, i got it, i didn't think about it like that. nice analogy with the piston.

 

[MichaelBaranows]

That is the reason I try to not get fast fills. I normally drop my tanks off and pick them up a few days later.

 

[SteveAD]

"
. my last lds used a bank and always gave quick fills (like less than 5 minutes and without a water tub) and my tanks never got hot. thanks for the replies

I'd love to get my hands on some of the magical fairy dust they used.

1 t submariner hit it right on the head. Any fill will result in heating, mitigated or aggravated by the fill rate. filling direct from a compressor is worse than from a bank, because the air is being compressed (and heated) in the compressor, and then compressed (and heated) into the tank.

I feel some people get too fixated on what a "good fill" is. When an al80 has a working pressure of 3000 psi, per DOT regs it should have NO MORE than 3000 psi at 72 degrees F. Meaning that if it was filled to 3000 at room temp and then left in a hot car (95 degrees F), the increase in temp would bring the pressure to about 3130 psi however that same tank upon hitting 45 degree water would drop to about 2850.

this is a neat little application to play with what happens when you change any variable in the pressure volume temp triangle:


http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegasc.html


I think it's funny that some people get so uptight about short fills and hot fills yet the same people are bringing their tanks in to be filled with 800 to 1200 psi left

 

[mike_s]

Hate to tell you this... but you can get warm fills from a bank fill. So your dive shop is right. However, him giving you short fills is a different argument.

The warmth is from the pressure induced into the tank.
If you empty your tank very quickly, guess what, it'll get much cooler. you might even get condensation on it if it cools quick enough.

Pressure, volume, and temp are all directly releated to each other.

Check out the Ideal Gas Law PV = nRT (feel free to google it).


Also check out the Combined Gas Law

PV
---- = k
T

Also
P1V1....P2V2
----- = -----
T1........T2


If you get bored from there, check out Boyles Law.

You can reduce the 'warm fill' effect some by simply slowing down the fill process. that will allow the heat to dissipate over more time and will be less noticable.

have fun.

-mike

 

[Brand0n]

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

 

[mike_s]

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

Actually they suggest not to 'wet fill' tanks anymore.

see http://www.psicylinders.com/library/Current/wetfills.htm

 

[Debraw]

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

When you say "helps alot" , what do you mean?