While we’ve heard of do-it-yourself methods of transferring fuel from one isobutane canister (those typically used in backpacks) to another, we’ve yet to see a dedicated valve designed for the purpose marketed to the outdoor world. Well, until recently.
Eric Flottman, an Arizona-based backpacker, was tired of the partially filled cans piling up in his garage, so he set out to design a simple, inexpensive device to fix it. It relies on simple physics to work.
When the fuel is cold, it condenses. When it gets hot, it expands. To use Flipfuel, you put the canister you want to fill (intake) in the freezer to cool the fuel, and the one you want to empty (output) sits directly in the sunlight to heat the fuel.
You wait a few minutes for the temperature difference to rise, after which you slide the intake can out of the freezer, screw FlipFuel on, put on the outlet container and open the valve. The hot fuel expands into the colder container and voila, you now have an empty can and one that is not empty.
The latter can be a problem as you really don’t want to overfill a fuel tank. Unfortunately, there is no easy way to tell how full a container is. One method we like is to float the containers in water. Some brands (MSR is one) print a small label on the cans that shows the approximate level of fuel that will be in the can when it is flowing at a certain level. As long as you do something like the float test and make sure the cans you fill are less than half full, you should be good to go.
Then of course you still have to dispose of the used can and here is a good primer on it.
Would be cooler if there was a way to refill the cans somehow, instead of having to buy new ones all the time, but this is a step towards far less waste.
The device costs $35and weighs a comfortable 35 grams, although it’s hard to imagine carrying one with you in the backcountry.