Airstream - Other
2016 Interstate Grand Tour Ext
Bosque Farms
, New Mexico
Join Date: Jan 2004
Posts: 7,026
The notion of gallon when dealing with propane is a tricky one because a gallon of propane at, say, 50 degrees is not a gallon of propane at 100 degrees. That's why fillers rely either on pounds or volume (removable cylinders) or on only volume (non-removable cylinders as on motorhomes). Volume is determined by a spew valve that is mounted at exactly the 80% level.
2012 Interstate Coach
From All Over
, More Than Anywhere Else
Join Date: Dec 2011
Posts: 10,868
The ASME tank on my Interstate holds 14 gallons by volume. That's actual volume, or 80% of total capacity. Exactly how many pounds you get for those 14 gallons depends on the ambient temperature when you fill it.
Since you can't take the ASME tank off to weigh it, unlike the removable DoT cylinders, the propane is usually dispensed by the gallon because flow meters do a good job of measuring volume but not of measuring weight.
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2010 30' Classic
Vintage Kin Owner
South of the river
, Minnesota
Join Date: Dec 2009
Posts: 4,169
Well, technically, the meters are temperature compensated so they're effectively measuring mass.
Larger (125 gallon and up) propane tanks are filled by volume using a temperature-compensation curve printed on the gauge placard, which shows the maximum fill volumes based on temperature. The curve is designed to provide 80% fill at, iirc, 60 degrees.
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2014 Interstate Ext. Coach
Poconos of Pa
, Pennsylvania
Join Date: Sep 2013
Posts: 239
In a big installation the meters are SUPPOSED to be temperature compensated to I believe 60 degrees F. But in the real world many small installations DO NOT HAVE temperature compensated meters. I have filled many small tanks at local places, especially gas stations that have the scale to fill the 20 # tanks and also a meter for larger tanks, and there is no compensation meters on them. The truck that comes to my house to fill the 500 & 1000 gal tanks with propane DO HAVE temp compensating meters though.
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