I just made a remark on Tony Beasley's SUUL stove thread and thought I would put this idea into play.
It is not enough to make a very light gas stove you need a light system. That means minimizing the weight of the canister and being able to only carry the amount of gas you need.
1)We could do a survey of different sizes and makes of empty valved gas canisters to find the lightest of each of a range of sizes.
2)buy a large canister or cylinder of the best gas for heat per gram and season of use. The "mother" canister
3) get 2 remote canister valves one for the mother and one for the lightest canister found for the weight of gas you need, the "baby"
4) join the valves with a flexible hose and connect the canisters, the mother upside down.
5) put the mother in warm water, put the baby in iced water on a scale.
6) open the valves. I think that quickly or slowly the baby will fill with gas until you have the gas you estimate you need for your trip. Close both valves. Disconnect the baby.

Will that work? If it does we have control and we have also brought the price of camping gas down to bulk prices.

I don't know about the UK, but this isn't legal in the US or really safe. The disposable tanks are not designed to be used more than once and you do run the risk of explosion if your cannister has been fatigued and you over fill it or fill it past its happy point.

If weight is your issue and you consistently find you are bringing a lot of gas back home with you you can approach this a different way. I have a small BBQ at home that takes camping gas canisters. If I wanted to lighten the canister and only take half a can I can use half of it in my BBQ first. If you don't have a BBQ that can take the canisters maybe just use the stove at home for normal cooking until you get the weight you want. Easy to find out the right weight by trial and error. Weigh when you buy it and weigh when you get home.

Try rigging a disposable butane lighter.

I'm not sure of the legal restrictions, but I've seen this with propane tanks. There is an adapter available that allows one to refill the smaller 1 pound propane canisters from their big 20 or 50 pound tanks.

The 'adapter' that is sold has a disclaimer that states it is not legal to transport refilled disposable canisters.

The risk is that if you overfill the cannister and it warms up it can explode on you (BLEVE: boiling liquid expanding vapour explosion). You don't want this happening if the cannister is on your back in a lightweight backpack.

If this were economically feasible, someone would offer the service.

Here in the USA, it's illegal and in the opinion of many.....both dangerous and foolhardy.

Canisters come in two sizes now; 100 grams (3.5 oz) and 227 grams (8.0 oz) net.

The 8 oz canister weighs 12 ounces gross, meaning the canister and valve assembly together weigh 4 ounces. The remaining 8 ounces is the gas, which should be sufficient to boil 11 liters of water at sea level. Doing the math, the smaller canister should boil about 5 liters.

Be smart. Be safe. Otherwise, switch to Esbit tablets and save a whole lot of weight, especially over a long hike.

Bob,
I was referring to LPG, not the isobutane mixtures you cite. I agree it is dangerous and foolhardy, as with any gas under pressure.
Esbit works well, and I can use it interchangeably with the FireLite tabs, but I noticed a big difference in the MPI fuel tabs. I've only used it twice, and never with a timer, but they don't seem to burn as hot as the others. With Esbit/Firelite, I can boil two cups of water twice (or almost twice, depending on conditions). The MPI uses over 3/4 of a cube to get the same result. I bought the MPI for less soot, but I don't see me buying it again if I can get more umph out of another cube the same size. For this, I really like my Ti-Tri. Flexibility with alcohol and wood fuel options are nice to have for the occasional unplanned usage.

>The 8 oz canister weighs 12 ounces gross, meaning the canister and valve assembly together weigh 4 ounces. The remaining 8 ounces is the gas, which should be sufficient to boil 11 liters of water at sea level. Doing the math, the smaller canister should boil about 5 liters.

My tests show if the flame is adjusted properly I use about 12 grams to boil 1l so an 8 oz (228g) canister should boil approx 19 liters so a 4 oz (113.6g)should do boil around 9.5l. even with the most efficient Alcohol stoves on Ethanol to boil 9.5l you would need at least 228g of fuel(methanol would use about 280g), canister stoves start to become economical for long trips and they have the added advantage of no wasted fuel.

Tony

I accept it is illegal and dangerous and I do not advise anyone to do it.
It is illegal to transport any gas cylinders, on many forms of transport. It is dangerous to use a windshield round an upright gas stove. It is dangerous to cook with gas stoves inside a tent. You can find warning signs nowadays warning you not to carry hot drinks.
Putting all that aside if you fill a 100gram reusable cylinder with no more than 100 gram of the same gas it will be hardly more likely to explode than a new one. There must be an expectation that the lindal valve will be opened and closed many times more than they usually are. It is a controlled risk to reuse a disposeable cylinder a few times. Even new ones have been known to leak. At that point it is the same danger as the non resealable canisters, you cannot take the stove off the cylinder until it is empty.
I am not suggesting that this is a commercial opportunity.