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Good info. Wish I would have checked into the existence of this pump before Dec. Would have saved me a lot of work on my LPG snow plow. Oh well it's almost done.

As for tbone95's concerns the pressure in the bottle would not increase unless it is overfilled. The vapor pressure of propane is a function of temperature. As you add liquid to the tank the vapor will condense back to liquid, that's why the chilled bottle will accept more liquid before the tanks equalize without a pump. (The opposite for draining fluid from a tank, the LPG must evaporate to maintain the vapor pressure. That's why they get cold. You can also heat the supply bottle to fill the smaller one but this is dangerous.)

The overfill device is for thermal expansion of the liquid, LPG at -40 takes up less volume that LPG at +40 C (Canada).
 

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Read what I said. . .use it up, if you fill one in ice fishing temperatures, then set it on your shelf in the garage until July, the pressure will go up, no?

Also, when you use up the little bottle, it doesn't empty to "vacuum". There is vapor left equal to atmosphere. You put liquid in, some of that vapor may condense, but so what? It's not just temperature, there is also a change in volume of the vapor. P1*V1/T1 = P2*V2/T2 of any vapor, temps and pressures in absolute scales. Yes, there's phase changes and such, but it will pretty quickly equalize to a steady state.
 

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I know what you were saying in the first post. But the way it reads to someone who may not understand vapor pressures is "that the pressure will increase as they fill the bottle." Just wanted to ease fears, you can fill them but research and do it safely.

The vapor pressure in the tank is directly proportional to the LPG temperature in the tank. Regardless of volume -> UNTILL the bottle is 100% filled with liquid. At that point if the temperature goes up the thermal expansion of the fluid will burst the tank -> Liquid cannot be compressed. If the temp went down the liquid volume would shrink and the LPG would vaporize to occupy the space.

And yes I should have re-stated the fact that ~80% is full in most bottles. 80 to 100% is overfull. To many accidents have lead to the overfill shutoff devices and propane filling courses. I'm not sure what the safety factor is but I'm with you and would not want to be there in the summer with a bottle filled to 90 or more in the winter.

As per the last post the formula stated is for the gas state only (Ideal gas law does not deal with liquid). As you add gas to a fixed volume the pressure will increase. But once you hit the vapor pressure of that gas the it will condense into liquid, the pressure will not go any higher until the container is full of liquid. *Keep in mind that the vapor pressure is temperature based and as you add or remove gas or liquid from the container the temp will change causing the pressure to change with it.*

This post is getting long.

I fill in stages with a electric pump and use a IR temp gun to find the liquid level. This would be harder with the hand pump to get the volume amount transferred that causes a noticeable temp drop in the liquid from the vapor condensing. Solution -> the new fiberglass tanks that are see through. They have 10 lbs but I don't know if they have smaller ones.
 

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Put lil tanks in freezer the colder the one is ur filling the better n the tank ur tank it from should be warmer than the one ur filling...
I fill lots of tanks ,,use a regular 1/2 T valve with supply line and valve on one side. then the T valve that acts as a bleeder , then the fitting going into the tank ,,it s easy to shut off supply open bleeder and bleed excess vapour out and then refill again ,for one lb bottle rigid up a valve from a small propane torch to fill them with 20 pounders upside down
 
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