Re: [a/s] Propane tanks

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Charlie,
 The "air space" does serve to allow the liquid to gasify, but it also
allows the liquid to expand w/o pushing out the pressure relief valve.

Propane is a liquid when it's under pressure; the actual pressure will
vary with the ambient temperature. You could attach a calibrated
pressure guage to your tank and use it as a thermometer. As you know,
liquid expands when heated, and as you also know, liquid cannot be
compressed. So, what happens inside your propane tank as temperatures
rise is that the liquid level rises, adding a bit of pressure to the
tank. However, the gas in the "air space" will re-liquify, preventing
the pressure from rising above the normal vapor pressure. If there's no
"air space" due to overfilling, the liquid has no place to go but out
the pressure relief valve. The pressure in the tank will never rise
above the 'normal' amount FOR THAT AMBIENT TEMPERATURE, no matter how
full or empty the tank is. That's why a pressure guage is useless as a
"fuel guage", the pressure won't start to drop until ALL the liquid is
gone, leaving only a bit of vapor that will be used up quite rapidly.

                                           <<Jim>>