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larry

wrote:
On Mon, 7 Jul 2008 09:21:41 -0500, "S. Barker"
wrote:

Ya, and so if the tank is not empty when you take it to them, you are just
ripping your self off. Since they charge a flat fee for a #20, or a #30
etc. etc.

sold by the gallon here

Well, duh. Point is, they don't use "complicated instruments" as
claimed by someone else.

They actually sell a "gas gauge" for 20 pound BBQ tanks. It's a
foolish thing to buy for a few reasons. You can buy a second tank for
about the same cost as the gauge.

Actually, it's near a constant pressure until the last few
drops of liquid is used. The liquid "boils" off until the
vapor pressure reaches 51 to 172 psi in the tank, depending
on liquid temperature (32 to 100 degrees F range shown) See
"(S)tandard(T)emperature(P)ressure" in a chemistry book. A
pressure gauge would make a much better thermometer. ;-)
Weight or depth of liquid in tank is best way of determining
if you will make it thru that last steak.

wrote in message
...

they use a scale when filling propane tanks.
Set the tank on the scale, note it's weight and then fill it until it
reaches
it's "full" weight, which is stamped on the tank. Very complicated.

empty (tare) weight is stamped on the tank, add 80%(20%
vapor space) of 4.24 (lb/gal) times 5 (gal) to tare for a
full tank weight. The (O)verfill(P)rotection(D)evice valve
is a float in the tank that shuts off the valve when the
liquid reaches its maximum safe full level. Filling a tank
is easy, connect supply hose, and fill until the flow stops.
Charge for the gallons on the gauge (usually around 4.2
gal) or a flat 5 gal refill fee. ;-)

Sheesh.

Be safe, several years ago, two 20 gallon "stove" tanks
laying flat in the back of a pickup in the hot Texas sun
exploded like missiles. Appeared the tanks were improperly
filled, with no vapor space for expansion.

-- larry/dallas