"Drew_Y" wrote in message
oups.com...
I think recommended refilling levels of co2 cyclinders is to 50 barrs.

No. If people would refill to 50 bar, the tank would be almost empty.

I do not think going to 80 barr on a refill is a good idea, atleast
with std pressurized equipment. If you had it refilled in the US this
is probably the case.

It's not possible to fill a CO2 tank to 80 bar, at least not at room
temperature. At room temperature, CO2 stays at 60 bar. Some
of that is in liquid form, and some of that in gaseous form. As the
tank empties, the pressure gauge continues to read 60 bar until
the tank is almost empty -- the pressure reading drops only once
all of the liquid CO2 is gone. Conversely, if you try to raise
the pressure of CO2 above 60 bar (at room temperature), you
will find that this is impossble -- any additional gas you pump
in immediately liquifies, and the pressure will remain constant
at 60 bar.

If you read 80 bar on a CO2 tank, you have a serious problem
because by then, CO2 will have gone beyond its critical point.
The critical point is the point at which it becomes impossible to
keep the gas in liquid form, no matter how high you raise the pressure,
and the gas is present as a superfluid, with some of the properties
of both a liquid and a gas. Above the critical point,
pressure rises rapidly with temperature and, eventually, you'll
have the burst disk on your tank rupture. The critical point
for CO2 is at 73 bar and 31C. You shouldn't allow your
CO2 tank to get warmer than that. Leaving it in a car in the sun
is definitely a bad idea...

Cheers,

Michi.

--
Michi Henning Ph: +61 4 1118-2700
ZeroC, Inc. http://www.zeroc.com