Is it safe to use a FlipFuel to keep refilling a 4oz fuel canister?

Hi Philip

You were (imho) just moments away from an exploding canister. When one blows, there is one hell of a bang. Plus consquences.
https://backpackinglight.com/exploding_gas_canisters_the_hazard_of_overheating/

You MUST keep weighing the recipient canister!
Cheers

Different canister brands may not have the same empty weight.  Weigh a new full canister and a completely empty canister for a more accurate filled weight.  Not overfilling is very important.  Different fuel blends will also have slightly different weights.

For sure they have different vapor pressures, so best to refill with the same fuel blend as the original canister fill (unless you have access to a chemical process simulator to calculate and compare the mixture vapor pressure, which I do).  Canisters are designed for the requirements of their specific blend, and are tested up to 130 F with the original fuel blend. If a blend with a significantly higher vapor pressure is used, the pressure will exceed the pressure of the tested blend when the canister gets hot.  Reducing the percent propane or increasing the percent n-butane should be safe, but the reverse might not be.

Well, I just consolidated the remains of three canisters into one, and I couldn’t be happier. It’s not full, just about 3 oz of fuel. I would add more if I had it, but I don’t feel the need to push the limits of capacity, I’m just happy to be able to make use of the remnants.

I am so pleased that I read this thread. The waste of fuel was one of the reasons I had switched to an alcohol stove in recent years, and TBH I’ve come to appreciate my caldera cone. But this little valve makes using a canister stove much more acceptable to me.

even better is to buy those 8 ounce cartridges of butane from an Asian grocer for $1.25 and put just what you need in the canister for each trip

below about 32F it requires technique so maybe use isobutane for that.  You can buy that in 16 ounce canisters a little cheaper

even better is to buy those 8 ounce cartridges of butane from an Asian grocer for $1.25 and put just what you need in the canister for each trip

I’ve noticed that all the usual suspects sell 16oz isobutane canisters for about $10, compared to $6 for a 4oz canister. So while not as cheap as those butane cartridges (which are also available at REI for $3), it would still represent a significant savings and more importantly reduce the waste of the metal cartridges themselves.

Dan,

Same.  From now on I plan to buy the XL canister (the 16oz one) and top off 4oz canisters as needed.

Weighing the receiving canister is the key. The MSR 3.9oz has a gross weight of 7.4oz. I put the receiving canister in my freezer for 20 minutes, then fill it from a room temperature donor canister until I hear the flow rate slow. I weigh it, rechill it, and then fill it to 7.1–7.3oz. All weights are without the canister cap or the transfer valve.

So I just bought one of these little gizmos – the FlipFuel brand – and I need to start dealing with all my partials. The instructions say to put the donor canister in hot sun for 5 minutes. I won’t have hot sun until next May, most likely! I suppose I could put it in my car in the sun for a bit. How important is that step?

I have to admit I’m a bit nervous about doing this! But I’ll weigh everything and err on the safe side.

A good question. If you want the fuel in the source can to go into the target can, there are two ways to move it.

The first is gravity, but that can be slow and it can be interfered with. It can be made to work, but is best used to support the next way.

The second is to have a temperature differential between source and target. You want the source to be warmer than the target, so the fuel is driven by the pressure differential. Gravity is certainly useful here as well, but this is all about the difference in temperatures.
If you start with the source canister at, say, +30 C (which is perfectly safe) and the target canister at -10 C, and the source above the target, then fuel will flow. You can use hot water from the kitchen to get the the source canister to +30 C, and you can put the target canister in your freezer to get the cold side.

Frequent checks of the weight of the target are essential: the target canister should never be filled beyond the original ex-shop weight. There must be some vapour space above the liquid fuel.

Cheers

I think putting one in the freezer and the other at room temperature would be enough. You will just need to do it a few more time.

In my experience it takes several “rounds” of cooling and heating to move much gas from one canister to another. The pressure seems to equilibrate pretty quickly.

@AK Granola, instead of the sun, put the donor can into a pot of warm water.

Yeah, freezer and bowl of warm water

When butane goes from the donor canister, it cools down from evaporative cooling

When butane goes into the donee canister it warms up, from condensing, the opposite of evaporative cooling.

Those two are why it takes several rounds of warming and cooling.

You have to position the donor canister so that liquid flows out of it.  If the donor canister is a canister, upside down.  If you use one of those cartridges from the Asian market, the notch has to go down and slightly angle it down.

You can hear whether gas or liquid is flowing

It is not considered safe and it’s illegal (USA DOT) to transport unapproved refilled containers. While government regulations may seem like overkill, it is usually only after a catastrophe that they’re put into place. After a failure, or several failures. Seeing how I’m not an expert on breaking the law, I prefer not to. I’ve been wrong before. Seeing how I’m not an expert on gas canisters, I can’t answer your question. It’s a little more weight, but spend the extra money and buy an approved container. Do it right.

is it illegal to transport them by car?

I assume you can’t take any canister on a plane.  Even checked baggage.  You have to buy it when you get somewhere

does anyone make an aluminum canister?

that could be good in cold weather.  The top would get hot from radiated heat from the burner, then conduct through the aluminum down to where the butane is.  Like a large mulder strip.

On the other hand, in hot weather it might burst.

It’s illegal to refill and transport a pressurized container on a public road that’s not Department of Transportation approved.

I am led to wonder why the DoT regs have been created.
Is it to stop one of us refilling a canister and taking it on a walk?
Or is it to stop dodgy commercial operators from refilling lots of empty canisters to unknown levels and selling them?

Btw – it has been known in Katmandu in Nepal for some backyard Thamel district ‘merchants’ to collect half-used canisters from departing expeditions and top them up to the correct weight with … water! And then sell them as new.

Cheers

It’s probably a quality/safety question.  It would be easy to round up a bunch of discarded propane canister, fill them from a bulk supply and resell them.  Without any sort of quality control, this could be dangerous.  It’s probably also a Sales/Marketing ploy to prevent cannibalization of their market.   Send a few lobbyist to Washington a “donate” to key members of congress to tweak the rules in the country.    Flame King has tried to enter the market with a refillable propane bottle, but I am not sure how successful they are.  My 2 cents.

Flame King has tried to enter the market with a refillable propane bottle,
Amusing in a way.
“Swap and Go” is a very widespread brand here in OZ: you bring your empty 5 kg propane bottle to a shop and swap it for a refilled one. I have to emphasise: REFILLED. But the refilling is done by the company, who (I assume) also QC the incoming empties first. Never been any problems, afaik.

Also, I believe one can take one’s empty to a different shop (here in Oz) and have a staff member refill it from a 50 kg or 100 kg tank, on the spot. I assume (!) that the staff member who does this has some sort of training.

Cheers

I would guess they would never prosecute an individual for refilling their own canister

They would just prosecute someone that sold refilled canisters.  And if there was an accident that injured or killed someone.

They sell the refill adapters on amazon.  No authorities tell them to cease and desist.

But it makes sense for someone to decide not to refill based on the risk of prosecution or overfilling and causing it to burst or just because it’s too fiddly.

Is there a good tutorial on how to do this safely? I have many huge cans I was gifted. Love to fill up my small cans.

Brad W: I made a presentation on this very topic to the Austin (TX) Backpackers MeetUp last year. Here is my handout. The prices listed on the last page may be a little dated.

I hope it proves useful.

It’s not illegal to sell the valves. The law doesn’t prohibit refilling, just transporting. I’ve personally decided that it wasn’t worth it. I use my leftovers anyway. I’ve refilled the 1 pound green bottles, but they really need to be bled. I bought the Mr. Heater ones instead. They take a proprietary valve. Same with the Flame Kings. Thicker bottles meant to transport. Much easier. They make approved smaller ones as well, but for packing, the disposables are lighter.

We don’t have “Swap and Go” though we have something similar. Here, they don’t fill them all the way. We get about 3.6 gallons in a 5 gallon tank.

in the USA, you can swap your empty tank for a fresh one.  The propane tanks are dated and cannot be used after they expire and they get recycled.  The tanks also have a shut off valve that prevents gas from flowing unless it is hooked up to a fuel line.

Refilling a canister stove’s canister from a green, one-pound, PROPANE canister is DANGEROUS. Propane’s boiling point is -44°F. Butane–and it’s various derivatives–boil at about 30°F (some a little less). The build quality of stove canisters is not robust enough to handle the higher pressures required  for propane.