Originally Posted by
kaos joe
I've got lots of experience using my friends canister stove backpacking out west, as flying with a liquid fuel stove or tank, even an empty one, is problematic. We usually sleep with the canisters (and cameras) in the sleeping bags to keep them warm.
Said friend just bought a (one-way?) valve which allows you to suck some of the last fuel from a low-pressure tank into a fuller one. This of course defies the laws of physics except the trick is to submerge the recipient tank in a pan of ice water, which condenses the fuel and drastically lowers the pressure. The 2 tanks are linked by the valve and resemble an hourglass, with the recipient on the bottom. I suggested pouring some hot water into the concavity on the bottom (now top) of the donor tank to cause an even greater pressure differential.
I haven't seen it but he says it works.
I have one of those couplers too. Works best when the canisters are both pretty low. And you don't want to put more in a tank than it originally could hold. Some are just a coupler, you thread the two tanks together, some also include a manual shutoff valve which is the better option.
When new, the gas in the canister is a mixture of gases in liquid form. The most volatile of those gasses is mostly burned first, the less volatile later and that is why a canister that has mostly been used does not burn as hot, even if you are comparing two canisters that are the same temperature. It gets complicated to explain, so i won't try, if you are curious look at Raoult's law.
I agree about the sleeping bag thing, but when a canister is 80 percent gone, the remaining fuel in the canister will get cold pretty fast, possibly before your coffee water is hot. Thus the pan of lukewarm water can work well on such chilly mornings to keep the canister warm.