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#1
02/05/09, 08:44 AM
 Join Date: Jun 2008 Posts: 711
how much does a 20 pound propane tank hold?

I assumed 20. One place told I get 20 pounds while another place will only fill it to 80 percent, to which I don't have a clue how much that is.
#2
02/05/09, 08:45 AM
 More dharma, less drama. Join Date: May 2002 Location: Texas Coastal Bend/S. Missouri Posts: 30,594
Most only fill to 80% due to dangers of overfilling.

Multiply 20 times .8

Eighty percent is like 80 cents of a dollar. Or 8 dollars out of ten. Or sixteen dollars out of twenty.
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#3
02/05/09, 09:02 AM
 Join Date: Aug 2007 Location: Northeastern Oklahoma Posts: 5,039
When I moved here last January, it was my first experience using propane, and several different companies told me they will only fill to 80% capacity, because they have to leave room for the gases to expand and contract. So Rose is correct, and your 20-pound tank will hold 16 pounds maximum.

They also told me to never let my tank (320 gallons) get below 20%, so that's another fraction to throw into the equation. Who knew I'd actually have to use that math from school. But I guess that part doesn't matter with the small tanks, as people run them completely out all the time. So I don't know, maybe they do fill the smaller ones all the way up. Sorry, I know I've been absolutely no help at all, lol!
#4
02/05/09, 09:05 AM
 Join Date: Jun 2007 Posts: 1,064
A gallon of propane weights 4lbs, so assume that 80% of 20 lbs is 4 gallons. Weight is a good way to check on the amount of propane you just payed for. One time I had my tank filled by someone who didn't know what they were doing and they wasted about half of the propane out to the air. After weighing the tank I saw they had only managed to get 10lbs into the empty tank.
Michael

P.S. For reference, a gallon of gasoline weighs 5lbs, and a gallon of diesel weighs 6lbs. That's one of the reasons why a diesel engine is more efficient than a gasoline one, and a gasoline engine is more efficient than a propane one.
#5
02/05/09, 09:33 AM
 Join Date: May 2003 Location: Zone 7 Posts: 10,837
The tank referenced is designed to safely transport 20 lbs of propane. The actual capacity of the tank is approximately 4.7 gallons.
Look on the side of the tank and somewhere you should see a marking TW. The TW is the tare weight which is the empty weight of the tank. When full the tank should weigh the TW plus 20 pounds, hence the referred to 20 # tank. You are aware that on a 20# tank that nothing will come out when the valve is opened if there is no connector on the big threaded part of the valve? Do not guess if there is propane in the tank, just weigh the tank and subtract the TW stamped on the side of the small tank to get the weight of propane in the tank.

Michael, where did you get those numbers above? Those are some rough estimates or bad rounding off results.
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Last edited by agmantoo; 02/05/09 at 09:49 AM.
#6
02/05/09, 10:14 AM
 Join Date: Oct 2008 Posts: 32
Quote:
 Originally Posted by calliemoonbeam They also told me to never let my tank (320 gallons) get below 20%, so that's another fraction to throw into the equation. Who knew I'd actually have to use that math from school. But I guess that part doesn't matter with the small tanks, as people run them completely out all the time. So I don't know, maybe they do fill the smaller ones all the way up. Sorry, I know I've been absolutely no help at all, lol!
That tank direct piped? They told you not to let it run below 20 % because if you run it empty, by law they have to pressure test the system before the fill it again. They are trying to save you money on the pressure test
#7
02/05/09, 10:17 AM
 Join Date: Sep 2007 Location: Ohio Posts: 755
The place where we get our tank filled, they put it on a scale and fill it while on the scale. That is how they know when it is full, when it weighs what it should, and that is how they charge us.
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#8
02/05/09, 10:49 AM
 Join Date: Feb 2007 Location: Wisconsin Posts: 964
A 20lb propane tank holds... 20lbs. Most places that refill tanks do it by weight. Some now cheat and use the overfill protective device, which is a bad idea, but some do it. A properly filled 20lb tank with 20lbs of propane will only be 80% full. Large tanks are listed as total volume, of which only 80% is usable.

From this site it gives the following densities:

# 1 Oil (Kerosene) gallon 6.81 lbs/gal 135,000 BTU/gal
# 2 Oil (Diesel) gallon 7.13 lbs/gal 139,400 BTU/gal
Biodiesel (Methyl Soyate) gallon 7.38 lbs/gal 121,770 BTU/gal
Gasoline gallon 6.13 lbs/gal 125,420 BTU/gal
Ethanol gallon 6.55 lbs/gal 83,640 BTU/gal
Methanol gallon 6.60 lbs/gal 64,510 BTU/gal
Propane gallon 4.24 lbs/gal 91,600 BTU/gal

I routinely weigh my tanks to see how much they have left. Typical full weight is 35lbs, empty is 15lbs. 20lbs of propane. I'm decent with grab the handle to get the amount left, except for the last couple of pounds.

Michael
#9
02/05/09, 11:56 AM
 Join Date: Aug 2007 Location: Northeastern Oklahoma Posts: 5,039
Quote:
 Originally Posted by cantcutter That tank direct piped? They told you not to let it run below 20 % because if you run it empty, by law they have to pressure test the system before the fill it again. They are trying to save you money on the pressure test
Thanks! I figured it was to keep air from getting in the lines, sort of like brake lines on your car, so that makes sense. This is my first time living in the country, I'm learning new stuff every day!
#10
02/05/09, 01:44 PM
 Join Date: Jun 2008 Posts: 711
okay.....- weighed my full tank and it

Weighed almost 36 pounds. - guess I'll have to wait till its empty to weigh again.
#11
02/05/09, 01:51 PM
 aka avdpas77 Join Date: Dec 2008 Location: central Missouri Posts: 3,432
I think maybe the regulations are different for "portable" tanks and tanks that are permanently installed. Permanent tanks are usually feeding appliances witth pilot lights, and the company does not want to be responsible for fillinng them if the tank pressure has dropped so low inside a dwelling that the pilot may have gone out.
#12
02/05/09, 02:02 PM
 Voice of Reason Join Date: Sep 2004 Location: Las Vegas, NV Posts: 39,323
Quote:
 Originally Posted by mldollins I assumed 20. One place told I get 20 pounds while another place will only fill it to 80 percent, to which I don't have a clue how much that is.
The 20# tank will nominally hold 5 gallons. The required void space in the tank is not counted in nominal tank volume. In other words, the tank will actually take about 5 gallons and still leave the necessary void space.

The void space allows for expansion of the propane. The void space level is indicated with the bleed valve. As your tank is being filled you will notice the operator opening the bleed valve a little. That valve has a dip tube that goes into the tank a few inches. When the tank reaches the maximum safe level the bleeding gas will start to sputter liquid propane, indicating that the tank is full.

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