On 12/18/2015 7:05 PM, Mark Lloyd wrote:
On 12/17/2015 08:09 PM, Stormin Mormon wrote:

[snip]

When I worked for one place, they told us the 80%
capacity was already figured in, and we put 20
pounds in the 20 pounders. I thought it was 16,
but the boss said 20, and also the guy who taught
the certification course so I could pump propane.

Also read on line, Blue Rhino was at one point
put 15 pounds instead of 16. Maybe still do.


I just got a 20 pound propane tank filled. It weighted 20 pounds more
than the empty tank.



http://www.orangecoat.com/the-truth-...-propane-tanks

These "20 lb" tanks are designed to take up to 20 pounds of propane. You
may get a pound or 2 less, depending on the temperature of the tank and
surrounding air when the tank was filled. Cooler = more propane in,
hotter = less in. Tanks can actually fit another 20% in the tank, but
that extra space is designed for expansion as the temperature rises.

In very cold winter climates, like Canada, there may be more
concern/rules about filling a tank to a complete 20 lbs. This is because
if you leave a tank outside in very cold temps, filled the tank when the
tank is cold, and then bring it into a hot basement/garage for a space
heater, the gas will expand as the tank warms. With enough of a
temperature increase, the tank's pressure relief value will release a
bit of gas. This would be less of an issue if the relief value were
bleeding to outside air.

Propane Tank Tare Weight on Collar

All propane tanks have a "tare weight" or "T.W." stamped on the collar
of the tank. For a grill sized tank you simply calculate the tare weight
+ 20 lbs, and that's how much the tank should weigh when it's full. Most
20 lb tanks have a tare weight of +/- 17 pounds when completely empty.
This means a "full" propane tank should weigh about 37 pounds.

There is also a month and year on the collar indicating the date the
tank was made. For 20 lb propane tanks, you have 12 years from the
manufacture date before the tank must be re-certified with a new date
stamped on it. The re-certification only adds 5 years before having to
re-certify again. The cost and inconvenience of re-certifying almost
always outweighs the price of a new tank.

Brand new propane tanks may come with air inside and need to be "purged"
before the first fill. Some newer tanks, like Bernzomatic, will have a
sticker on them saying they don't need to be purged within 6 months of
the manufacture date.

Purging requires a special adapter to allow a small amount of propane
in. The pressure then pushes air out of a one-way bleeder valve. Purging
may add another $3-4 dollars to a new tank, though some places don't
charge, especially if you buy the tank from them.

Internet searches suggest the following:

1 gallon of propane weighs 4.2 pounds
A "full" 20 lb cylinder should have 4.7 gallons or propane in it