Refilling gas canisters. Small portable ones.

Yes - used it loads.  Great wee things.  Cool the receiving can and they just work.  Beware over filling

Personally, I think they are lethal. There is nothing to stop overfilling, whether that's through naivety/lack of awareness of the risks, a mistake (calculating the safe fill weight after checking the tare weight of the can) or 'it'll be ok, I'd rather have a full canister'.

Likely scenario is they leak into a hot car/van/tent and either create an unsafe atmosphere to breath, or create an explosive ignition when you unlock the vehicle

I have a refillable tank on my van, it's got both a safety pressure relief valve, and a float valve to cut off the filling valve when the level is at 80%.  Potential for human error is low and that's the way it should be!

Yep. I've used one.

spooky - its the same as fitting it to the stove and removing it

Have you ever used one?

I'm always tempted by these but I can't see how I would use it. So I've got an empty container, say a 300, and I'm gonna fill it, presumably from a 500. Then I end up with 200 left in a big cannister. Can I put that in a smaller cannister? Is there sufficient pressure? Or are you filling 100 cannisters from a big one, just for overnight trips? Most of my trips are multi day so I rarely use 100s. If I do an overnight trip I weigh my few used canisters so I know how much gas is in it and take one of them

Do you not still end up with almost empty cans?

I thought you could consolidate from a few near empties of any size to create one near full?

I've done it before but with a much less refined method using a push-on brass adapter and a couple of wee o-rings.
You can use it to amalgamate the dregs from a few near empties into one, fill a 100 from something bigger when you're only away for a short trip or maybe fill a screw-on from one of the much cheaper CP250 butane ones if you're summer camping.

I always do it by weight and don't fill butane/propane mix into a butane canister. And do it outdoors!

I've used one loads. Overfilling is possible but the main risk* of that is getting a really flare-y stove (I melted the insulation on my jetboil a bit when I got it wrong). As long as you start with an empty cannister and weigh it it's really easy to avoid.

Has saved a lot of canisters going to landfill for me.

*I haven't done the calcualtions but my hunch is that 100g** of propane in the volume of a car or tent is more of an annoyance than a real problem

**This is assuming the whole canister discharges, which it probably won't.

Nope, I'll leave that one to the Youtubers and dodgy Kathmandu gear stores. I only use gas for longer trips (meths for 1-3 days); bigger canisters, 250 or 500, taken down low with a stove that gives good output even on a depleted can. Use up the dregs at home for brews, etc, recycle the can (there are crusher/piercer tools you can get).
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You can check for overfilling with scales- not while you're doing it though because you have the weight of both cans and it doesn't change. But you can tiptoe up to it/release overpressure if you're worried.

I use one loads for our DofE stores. We will often have half empty cannisters after expeditions. Refilling them (freeze the recieving can and put a little bit of boiling water in the well of the donating can) means I can have only full cans in the stores and can recycle all the (now) emptys.

I always weigh new cans before they get used the first time and write the weight on the bottom with a paint pen. Avoids overfilling them when I come to it.

I also use one to refill my 100ml can for my Jetboil from a 500ml can and save myself some money.

Brilliantly useful bit of kit.

@tjagain

spooky – its the same as fitting it to the stove and removing it

No issues with the attachment method, it's the human error element.  You fill it full (of liquid) when the receiving can is cold/frozen, you then stick it in a car that could get left in the sun.  That liquid can't expand.  Does it leak out of the valve or does the canister split? Neither is a good thing.  Those that have had a flare and melted their stove have proved that it's a risk (and got away with it)

@schmiken

I can see the appeal here but can you imagine the fallout if a serious accident happened within a charity and it emerged that canisters covered in 'Do not refill' warnings were being refilled with a Chinese refill adaptor?  Has the refill process itself and the use of those cylinders by participants been risk assessed by DofE?  I can just imagine the media frenzy and witch-hunt that would follow an accident and the subsequent drains up of all those involved.

There is a reason these valves are all sold on eBay and Amazon, no responsible retailer would risk supplying them and as far as I'm aware they won't comply with any UK regs such as a CE mark.

There is no real risk here.  Loads of us use these frequently.  they are fine.

*I haven’t done the calcualtions but my hunch is that 100g** of propane in the volume of a car or tent is more of an annoyance than a real problem

I reckon you can form a flammable atmosphere of roughly 2.5m3 in a confined space from 100g of propane. I think people frequently underestimate how little gas you need to do yourself serious harm.
<p style="text-align: left;">100g is 0.0023kmol of propane. Molar volume is around 22m3/kmol so 100g is 0.05m3, but lower flammable limit is 2% so you could dilute that to 2.5m3 and still ignite it.</p>

I use one loads for our DofE stores. We will often have half empty cannisters after expeditions

I personally would use one.

Using one professionally and giving those cannisters to kids, no I wouldn't for the reasons another poster put up.

My physics is pretty rusty on this, but I’m curious to know how you can overfill when you’re effectively working within the constraints of Boyle’s Law - all you’re doing is pressure-equalisation, so unless the charging canister is infinitely large, it’ll never fully pressurise the receiving canister. Most pressure vessels have a test pressure of at least twice their working pressure so the risks of a pressure vessel rupture are probably quite small (but not accounting for damaged ones).
Clearly the biggest risk is a leak of flammable gas - anyone who does this in a confined space probably deserves their Darwin Award nomination.

its because the transfer is of liquid gas because the can you are filling from is upside down - so its liquid gas forced thru under pressure until the pressure equalises

all you’re doing is pressure-equalisation, so unless the charging canister is infinitely large, it’ll never fully pressurise the receiving canister

The top canister is 80% liquid and 20% vapour.  Many users of these adaptors will be using the most economical 500g cylinders to refill the smallest packable 100g cylinders.  You connect it to an empty cylinder and the liquid gas drains into the bottom cylinder.  (Heating/freezing respective cylinders makes it quicker/more efficient).  If you completely fill the bottom cylinder with liquid, you've reduced/removed the 20% vapour safety margin which allows the liquid to expand when it gets warm.

Propane expands 17 times more than water as it warms. A 33 degrees C increase in canister/propane temperature is 9% increase in volume.</p>

If you overfill a cylinder, how would someone fix it? Attempt to transfer it back by putting boiling water on the base of the overfilled cylinder?  Attach a stove and light it? Liquid propane jetting out of your stove will be quite dramatic and could easily flash and cause burns.

Many users of these adaptors will be using the most economical 500g cylinders to refill the smallest packable 100g cylinders

Yes, you can find instructions online to make sure you don't over fill. It solves a lot of problems! The only thing I'm not sure about is how many times you can refill a bottle- surely they will wewr out at some point? Maybe at the valve?

Nice explanation there @spooky_B329

If you overfill a cylinder, how would someone fix it?

I transfer very slowly, ensuring that the weight of the refilled cylinder is always lower than the weight it originally was at. As I am also only ever filling cannisters of the same size (both of which are around half empty), it is remarkably difficult to overfill them even if I wanted to. I've been doing this for a while now and never had any issues. There is more of a danger that the kids burn themselves boiling water for pasta.

Example: If I weight it at 355g when new, I will only ever refill it to a weight of 330g.

You fill it full (of liquid) when the receiving can is cold/frozen, you then stick it in a car that could get left in the sun.

If the weight is the same or less than the cannister when new, then using this logic a brand new cannister from the shop would be a dangerous thing surely?

If the weight is the same or less than the cannister when new, then using this logic a brand new cannister from the shop would be a dangerous thing surely?

<p style="text-align: left;">If it's the same or less weight, then it's not overfilled. However, that's reliant on people knowing and understanding why it's important to comply with that, forward planning to check and record the weight before using the cylinder, and having a reasonably accurate set of scales.</p>
Even if you are diligent and refill them safely, you could still end up in hot water if an accident happened.  It could be unrelated to the gas volume added, if the seal wore out or the cylinder became weakened due to repeated long term use it could still come back at you.

Having witnessed a canister (of unknown provenance) spew its entire contents in uncontrolled fashion when the stove was removed (fortunately without a naked flame nearby), I'd also want to know how many times you can pierce the valve before it fails.

(This has led to the loss of at least one bothy, btw. Wouldn't fancy it in a nylon tent).

I know we have done this before on here.

However, I don't see how the re-use of a pressure vessel that is designed for single use is sensible.

How many times do you consider to safe to re-use? Once? Twice? Ten times?

What inspection do you do before refilling?

As for refilling for other people to use, that's just crazy.

I have had valves fail in that they did not open when attached to the stove.  Never had one fail open.  Since then I have limited the number of times I refill.  those cans were a decade old.  there is no more reason for a valve to fail than it is screwing it on and off the stove.

Overfilled?  Just squirt a bit back into a empty can.  Its actually quite hard to overfill tho I have done it.  Its harder to get a full load.  NO need for boiling water or anything. The valves are nicely made and easy to use.

Its really not the drama some seem to think..  How many times do you refill a refillable lighter?  Very similar operation

Very interesting risk assessment going on in this thread, presumably to save a few pennies or out of a misguided sense of environmentalism. Rather than dodgy refills of small canisters for short trips - just get an alcohol stove. Fuel that's at least theoretically sustainable, which you can buy cheap in bulk from any hardware store in recyclable containers; decant what you need into a pop bottle that you can use safely many, many times, then chuck in the recycling when you're done.

Anyway, off to catch the train for a night on the hill - with my UK-made alcohol stove and old Lucozade bottle with a splash of meths in it...

I bought one last week and stupidly overfilled my 100g canister from a 500g. Was very impressed with myself for how much I’d managed to cram in there, about an extra 30g

Luckily I stopped for lunch on a beach and not some dry woods because it made quite the flame when I lit it. Released the overpressure and it was alright to cook dinner on later in the woods but I will be filling to just below capacity in future and only 3-5 times before getting a new canister. And of course pierced and binned the overfilled one

Yes I’m an idiot

If it’s the same or less weight, then it’s not overfilled. However, that’s reliant on people knowing and understanding why it’s important to comply with that, forward planning to check and record the weight before using the cylinder, and having a reasonably accurate set of scales.

Thanks, that's what I thought.

Even if you are diligent and refill them safely, you could still end up in hot water if an accident happened.  It could be unrelated to the gas volume added, if the seal wore out or the cylinder became weakened due to repeated long term use it could still come back at you.

I only refill a canister once. Lifespan tends to be new -> half used on exped -> refill from another can -> half use on exped -> use to refill another can -> recycle.
This saves a huge number of canisters that aren't quite full enough to take on expeditions into something that is actually useable. I'm very diligent in recording this and have trialled this on a number of personal canisters before I even considered doing this for others.

If you completely fill the bottom cylinder with liquid, you’ve reduced/removed the 20% vapour safety margin which allows the liquid to expand when it gets warm.

If is doing a lot of heavy lifting in your argument.

If I crash my bike I might break my neck, I still enjoy mountain biking though even with that random chance.

If I refill a 100g can from a 500g can then I can avoid any risk by just not overfilling it.

The only real risk (other than gross stupidity of a hypothetical other person that doesn't read instructions) is the valve wears out as it's screwed on/off the stove a lot more times in it's life. But then that number is the same whether it's a 100g can used 10x per refill and refilled 5x times from a big can. Or one big 500g can used 50x times. And I'd assume it's been tested to multiple times that anyway to remove the risk of it wearing out prematurely.

Its really not the drama some seem to think.. How many times do you refill a refillable lighter? Very similar operation

Arguably far safer, I've never managed to refill a lighter without getting butane all over my hands.

[edit - crossed posts with chrishc and apparently it's not just hypothetical idiots]

Very interesting risk assessment going on in this thread, presumably to save a few pennies or out of a misguided sense of environmentalism. Rather than dodgy refills of small canisters for short trips – just get an alcohol stove. Fuel that’s at least theoretically sustainable, which you can buy cheap in bulk from any hardware store in recyclable containers; decant what you need into a pop bottle that you can use safely many, many times, then chuck in the recycling when you’re done.

A good point.

I rarely use my gas stove now. Stopping for a brew is a chill-out moment. Cooking tea on camp I am in no rush. I am therefore happy to not have a Jet-Boil (clones are available) heat in 0.03 seconds quicker. I am happy to chill with the meths stove and take in the surroundings.

Plus sooooo much cheaper and better for the environment.

If I refill a 100g can from a 500g can then I can avoid any risk by just not overfilling it.

The challenge is knowing how much is enough. Obviously you can't weigh as you will. Maybe someone needs to invent a reusable transparent canister or maybe a connector hose type refill tool where you can place the receiving canister on scales.

The challenge is knowing how much is enough. Obviously you can’t weigh as you will. Maybe someone needs to invent a reusable transparent canister or maybe a connector hose type refill tool where you can place the receiving canister on scales.

It's not that accurate.

If the can weighs 95g, then anything above 160-170ish is enough for a few days. It's not like you need to sit there pouring the last few decimal points of a gram in. If I needed 100g of gas, I'd take a 200g can, nothing worse than running out of gas and not having a brew!

And if it is slightly overfilled, just vent it. It's unlikely to be more volume than you spill filling the car or lawnmower, degreasing a chain, etc. 100g of propane is about half a pint as a liquid, yes it's a highly flammable vapor once it's (quickly) boiled off, but so it petrol. In a well ventilated area away from ignition sources, I'd be more worried about the risk of freezer burns.

There is no real risk here. Loads of us use these frequently. they are fine.

That's an incredibly naive statement. There is always, without exception, someone out there who either thinks they know better or is the victim of a garden variety screw up of human error or mechanical failure.

I have had valves fail in that they did not open when attached to the stove. Never had one fail open.

I have, on DoE funnily enough. We assumed the liquid froze the valve and when we removed the cylinder from the stove it came pissing out and ignited. Again, likely a lot of human error going on there but that's exactly my point!

Its really not the drama some seem to think.. How many times do you refill a refillable lighter? Very similar operation

Funny story, at my wedding my best man told the tale of the time I was helping a pal by filling lighters, there was a small puddle on my trousers which someone ignited to great amusement. I continued on my merry way and the same happened, looked exactly the same so I lit it and was engulfed in a fireball that singed the hair up my back, my nose hair, eyelashes and eyebrows. I was lucky, that could have gone far worse.

Was it stupid? Yes.
Would you do that? No.
Can you rely on someone with less sense not to?

And FWIW refillable lighters have failed on me more than a few times with gas pissing out a frozen valve.

If the weight is the same or less than the cannister when new, then using this logic

If. That's a big if. If it's not you reduce the safe operating margin. And I'm pretty sure they already warn you against keeping cylinders in hot cars or direct sunlight for exactly this reason.

Clearly the biggest risk is a leak of flammable gas – anyone who does this in a confined space probably deserves their Darwin Award nomination.

That's not really a good justification.

Most pressure vessels have a test pressure of at least twice their working pressure so the risks of a pressure vessel rupture are probably quite small (but not accounting for damaged ones).

Again, probably? You mean you don't know? FWIW single use pressure vessels are tested assuming optimal storage through their life. Leave a cylinder in a damp shed for a season between uses and all bets are off. The thermal cycling will be doing nothing for the structural integrity either, especially if filling from empty.

One final note, for anyone doing this outside of a personal capacity you're in breach of the PSSR regs. My work recently banned B2C coffee machines from site and bought in their own with service schedules as someone realised that was also in contravention. Seemed daft at the time but if one of those popped and injured someone then they'd have been hung out to dry.

presumably to save a few pennies or out of a misguided sense of environmentalism

I've toyed with the idea of getting one for wild camping. I'm not going to lug half a kilo of gas up a hill for an overnight stay, and continually buying tiny gas canisters is inefficient and expensive.