what exactly constitutes a troll?

The gas coming in isn't cold. The gas left in the filling tank is cold. The
gas coming into the scuba tank isn't expanding all that much...a little
through the lines, and a little as it comes into the lower pressure scuba
tank, but no that much.

mike

"Jose" wrote in message
et...
My point was that I don't understand where the confusion is as to where
the heat comes from in filling a scuba tank. You are cramming a whole
crapload of molecules into a confined space and it makes heat.

Yes, but you are cramming a whole crapload of =cold= molecules into that
space. The heat generated seems like it wouldn't be enough to compensate
for the cold of the inflowing gas.

That gas is cold because it expanded from the other tank, which was under
even higher pressure.

Jose
--
"Never trust anything that can think for itself, if you can't see where it
keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

"mike regish" wrote in message
...
(they're filled in a water tank, no?),

That practice tends to be discouraged these days... It has been determined
that a slow fill is better... There are some that say that especially with
aluminum tanks, the water tank method is especially bad since the
temperature of the surface of the metal might be radically different than
the temperature of the inner metal thus increasing the chance of fractures
in the metal...

That makes sense. It's been a while since I got mine filled, but they did it
in a water tank.

In researching this, I found scuba divers complaining about "hot fills"
where the tank is filled too rapidly and when it cools down they are left
with a less-than-full tank.

mike

"Grumman-581"
"mike regish" wrote in message

(they're filled in a water tank, no?),

That practice tends to be discouraged these days... It has been determined
that a slow fill is better... There are some that say that especially with
aluminum tanks, the water tank method is especially bad since the
temperature of the surface of the metal might be radically different than
the temperature of the inner metal thus increasing the chance of fractures
in the metal...

"mike regish" wrote in message
. ..
In researching this, I found scuba divers complaining about "hot fills"
where the tank is filled too rapidly and when it cools down they are left
with a less-than-full tank.

I suspect that the water bath approach just results in the skin temperature
of the tank being cooler whereas the gas hasn't really decreased that much
in temperature... Thus, they're still getting "hot fills", they just don't
notice it... The easiest solution to hot fills is to just fill it higher
than normal and when it cools, it's at the target pressure... Or you could
just do it right and slowly fill the tank...

Well, the water bath does keep the skin cooler, but that is because the
water increases the tanks ability to shed the heat produced in the gas. The
heat goes from the gas to the tank to the water. Over filling the tank and
letting it cool could over stress the tank. Not a good idea, IMO. Like you
say, much better to fill it slowly enough for the heat to dissipate to the
surroundings, be it air or water, and you get a full tank. Those tanks are
already under tremendous stresses without not only going over pressure, but
doing it when the tank is hot and the tanks strength could be weakened with
enough heat.

mike

"Grumman-581" wrote in message
...
"mike regish" wrote in message
. ..
In researching this, I found scuba divers complaining about "hot fills"
where the tank is filled too rapidly and when it cools down they are left
with a less-than-full tank.

I suspect that the water bath approach just results in the skin
temperature
of the tank being cooler whereas the gas hasn't really decreased that much
in temperature... Thus, they're still getting "hot fills", they just don't
notice it... The easiest solution to hot fills is to just fill it higher
than normal and when it cools, it's at the target pressure... Or you could
just do it right and slowly fill the tank...

"mike regish" wrote in message
. ..
Well, the water bath does keep the skin cooler, but that is because the
water increases the tanks ability to shed the heat produced in the gas.
The
heat goes from the gas to the tank to the water. Over filling the tank and
letting it cool could over stress the tank. Not a good idea, IMO. Like you
say, much better to fill it slowly enough for the heat to dissipate to the
surroundings, be it air or water, and you get a full tank. Those tanks are
already under tremendous stresses without not only going over pressure,
but
doing it when the tank is hot and the tanks strength could be weakened
with
enough heat.

More of a concern for the aluminum tanks than the steel ones... I've had
fills that were hot enough to the touch that I wouldn't keep my hands on
them... Probably not as hot as a black car left out in the sun during a
Houston summer though... grin

When they overfill them, they'll prehaps put 3300-3500 psi into a 3000 psi
tank... Considering what the hydro test pressure is for the tank, that's not
that big of a deal... One concern with a fast fill on aluminum tanks is that
since the tank is about 1/2 inch thick, there's a difference between the
surface temperature of the tank and the inner wall temperature which could
result in a greater chance of cracking... It is believed that having the
entire wall thickness the same temperature is less likely to produce a
problem... Well, at least that is what I've read on the issues over the
years... There's still come companies that fill with water baths and even
some who refrigerate the water in the bath, which probably further compounds
any potential problem that there might be... Personally, I prefer not having
my tanks filled in a water bath... If nothing else, it means that any
contaminates on the tank are at least my own doing, not what might have been
in the water bath tank...