In article ,
Richard J Kinch wrote:

Bob Engelhardt writes:

You have to waste (by venting) a lot of flammable gas to overcome the
thermodynamic work needed to move the stuff from one place to another.

I never do. It's not necessary if the small tank is cooler, as gas
there will condense if the pressure exceeds the vapor pressure for that
temperature.

This requires additional apparatus which one assumes the OP is not using.
You might as well assume he has a pump in the transfer line. Something has
to perform the work, and venting is the simplest method, although not most
materially efficient.

I have one of those 'refillable' tanks and I consider it too dangerous
to use. It's quite easy to arrange a temperature differential to do the
work without wasting gas and creating an explosive environment. Putting
the big tank in sunlight and a wet rag on the small tank works well.
Also, if you don't object to the stink of unburned propane you are
probably a smoker who can smell little if anything.

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