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Old 01-07-2014, 09:01 PM   #1
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4 1/2 lb propane tank refill

Is there a way to refill the 4 1/2 LB propane tanks from a 20 LB tank? Like one can refill the 1lb disposable bottles.
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Old 01-08-2014, 07:00 AM   #2
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Yes, but just as with the 1 pound units you will only get about 60 or 70% of the rated capacity at best.

A traditional filling station pumps the LP in, with a tank to tank transfer you're only using the pressure difference between the two tanks to transfer the LP.
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Old 01-09-2014, 07:12 AM   #3
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Would I use the same refill adapter I use to refill the 1lb bottled?
Thanks!
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Old 01-09-2014, 11:45 AM   #4
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Purchased a 1 lb. propane tank filler from Harbor Freight. Works like a charm! I put the empty 1 lb. cylinder in the Refrigerator or better yet the freezer and set the 5 gallon tank in full sun for some time. Doing this creates a BIG pressure difference and you will get a FULL 1 lb. cylinder. -Tom-
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Old 01-09-2014, 11:51 AM   #5
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I was not clear, sorry! Can the 41/2lb tank be refilled from my 20lb tank?
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Old 01-09-2014, 12:25 PM   #6
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I think you would have to buy a special hose to connect the two just like the to fill the 1 lb bottles you need that special adapter.
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Old 01-09-2014, 12:31 PM   #7
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Thanks .... However it only cost me $3.50 to fill it at U/Haul!!! Cheap
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Old 01-09-2014, 08:05 PM   #8
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Quote:
Originally Posted by TomJames View Post
Purchased a 1 lb. propane tank filler from Harbor Freight. Works like a charm! I put the empty 1 lb. cylinder in the Refrigerator or better yet the freezer and set the 5 gallon tank in full sun for some time. Doing this creates a BIG pressure difference and you will get a FULL 1 lb. cylinder. -Tom-
I suspect that's a bit of optimistic thinking.

Propane boils at around -44 degrees F. so at any temperature warmer than that the propane is under about the same pressure.
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Old 01-09-2014, 08:13 PM   #9
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Quote:
Originally Posted by Murf2u View Post
I suspect that's a bit of optimistic thinking.

Propane boils at around -44 degrees F. so at any temperature warmer than that the propane is under about the same pressure.
IMposed on the tank or cylinder a higher temp will raise pressure and lower temp will reduce pressure of propane or any other compressed gas. It's physics.
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Old 01-10-2014, 07:00 AM   #10
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The pressure on a propane system is caused by the boiling propane, not because the cylinder is pressurized. If you allow a full cylinder of propane to reach a temperature lower than it's boiling point and open the valve, nothing will come out.

That's why propane vehicles and appliances don't work in low temperatures, there isn't enough vapour to provide sufficient fuel. It's also why larger appliances need pot-belly or horizontal tanks, more surface area equals more vapour boiling off.

Once the propane reaches it's boiling point there's very little difference in the static pressure on a vessel contains it.

That's physics.
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Old 01-10-2014, 07:56 AM   #11
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Originally Posted by Murf2u View Post
The pressure on a propane system is caused by the boiling propane, not because the cylinder is pressurized.
And that pressure can be raised by a temperature increase. Ever heard of a BLEVE?
If you allow a full cylinder of propane to reach a temperature lower than it's boiling point and open the valve, nothing will come out. Of course that's true of any liquid. But, where is it practical to do that with propane?

That's why propane vehicles and appliances don't work in low temperatures, there isn't enough vapour to provide sufficient fuel. That's not true either. Most vehicle engines use a vaporizer to turn liquid propane into vapor. The vaporizer uses engine heat to provide the latent heat of vaporization.
It's also why larger appliances need pot-belly or horizontal tanks, more surface area equals more vapour boiling off.

Once the propane reaches it's boiling point there's very little difference in the static pressure on a vessel contains it. There can be a tremendous difference in static pressure of the propane vapor in a container. That pressure is raised by the application of heat. That is why propane containers are required to have pressure relief valves.

That's physics.
Back to where you took exception (post #8) to refilling a cylinder by temperature difference.........that process is an efficient way to get an empty cylinder at least partially filled. A greater temp. difference between the two containers will make the process more efficient as described in post #4.
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Old 01-10-2014, 08:00 AM   #12
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Originally Posted by larrydp View Post
I was not clear, sorry! Can the 41/2lb tank be refilled from my 20lb tank?


Yes.......see post #4
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Old 01-10-2014, 08:09 PM   #13
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Even if you had the correct hose and full supply tank, you would be wasting your time. The vapor pressure in the supply tank will feed into the empty, but only up to equalized pressure. Unless you can transfer the LIQUID, you gain nothing, The vapor pressure in the tank is maintained by the boiling of the liquid propane in the tank as the the vapor pressure drops from discharge.The POL valve is designed to prevent liquid from escaping the cylinder. Remember, propane is measured in Gallons. You might be able to put propane in a tank by using a tank off of a forklift, they have a liquid port as well as a vapor port. Handling Liquid Propane is not for the normal consumer.
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Old 01-10-2014, 08:14 PM   #14
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Turn your 20# cylinder upside down.
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