Gadget to stop wasting camping gas near empty cans

Made this quick video to show you a gadget a friend recommended to me

Refilling disposable gas canisters. Very sensible.

I’ve got a similar adaptor, works a treat. I can buy cheap 500ml canisters and use them to refill eye-wateringly expensive 100ml. Also I can ensure I start every trip with a full C100.

Fantastic tool – without it gas wouldn’t be viable for me, I’d have to use meths.

Cool gadget, will have to get one of those. I don’t understand the need to weigh the canisters though – surely both the big and the small ones are rated to the same pressure so you could just open the valve till they equalise?

why weigh it?

im looking to do this with helium. i cant see much difference tbh

It has been recommended to me to be safe not to over fill the canisters so I weigh them

Running dofe expeds I always weigh the canisters before and after each trip. It’s a faff but means I can give near empty ones to bronze groups or use them in training whereas anything half full and above goes on exped.

Clever. That suggests you might already have a database of canister weights you might be willing to share (or do you assume all canisters are equal?)

FWIW I’ve recently started using meths in order to get around the partial canister/canister disposal problem but it doesn’t really work well at low temps.

Perfectly safe. I have been using this for years. Beware overfilling. Liquid gas comes out of the burner. I don’t weigh them, just shake it.

I don’t understand the need to weigh the canisters though – surely both the big and the small ones are rated to the same pressure so you could just open the valve till they equalise?

As TJ says the contents of a full canister are mainly liquid (you can hear it slosh around) which is why you can overfill.

C100 canisters (the small ones) vary a bit but they’re all around 200g – Colemans are 190g full, the red MSR ones 210g.

And (because I’m lazy) are “winter” gas mixes available in the larger sizes?

im looking to do this with helium. i cant see much difference tbh

Yeah, it’s light but takes ages to boil a kettle 🙂

And (because I’m lazy) are “winter” gas mixes available in the larger sizes?

Yes but harder to find and a lot pricier, £8-£10 for MSR red isopro versus £3.50 for standard Coleman C500s if you buy them in bulk.

The trouble with winter gas mixes is the propane boils off first, the colder it is the more propane it uses relative to butane. So unless you run the cans until empty then refill from a full can you’ll tend to end up with less propane with each partial fill.

Best bet is to just use butane (it’s got a higher calorific value so works out lighter anyway) and save the expensive winter gas for those days when it’s sub zero.

You can get propane only cylinders for proper cold weather but they’re much tougher and heavier (more like a miniaturised version of the one you connect to a BBQ).

Keep meaming to do something similar for mrsmidlife’s girl guide camp gear. They use a bunch of 907s (2.75kg) which are a rip off to refill, and a couple of 13 or 15kg for the burco and main stove. I’m sure I’ve seen adapters on sale before now, or they should be simple DIY.

Perfectly safe. I have been using this for years. Beware overfilling. Liquid gas comes out of the burner. I don’t weigh them, just shake it.

There is so much wrong with that sentence!

So this place, who wants to string up people for driving at 35 in a 30 or drinking 1 pint of beer before driving, think it’s perfectly safe to decant flammable gas from a larger cylinder, at a higher pressure into an untested, disposable cylinder?

I work with compressed gases a lot and always treat them with respect.

There are good reason for the rules regarding hydro static testing and visual inspections of cylinders.

Keep meaming to do something similar for mrsmidlife’s girl guide camp gear.

Doing this for yourself is one thing, deciding it’s a safe thing to do for a bunch of kids is quite another.

I use one, handy wee gadget, but I only refill a canister twice then dispose. Haven’t died yet but wouldn’t do it for anyone elses kids.

Gobuchal.
Sorry dude you have completely missed the point

The valves are not single use as you attach and detach them to the stove

You are refilling with the same mix from a big can to a small one. It’s a similar process to the initial fill. Of course the cans are tested! And finally you show your lack of understanding as the pressures are the same.

I use the Coleman c500 (approx 440g of gas) and the performance c300 (approx 240g of gas). Sharpie the starting mass and then after each exped. It’s a pain but otherwise I was ending up with dozens of partially used cans.

Silver and gold got a 300 each (cooking in 3s but under strict instructions to only open the next when the empty one was warm (in sleeping bag/up jumper) and empty.

Of course the cans are tested!

When do you test them?

the pressures are the same.

Not in that video, the bloke freezes the cans to reduce their pressure before refilling.

the pressures are the same.

Also, you talk about over filling, how is that possible if they work at the same pressure? I don’t how LNG behaves but that would seem very strange to me. When you connect the 2 cylinders, the pressure would equalise across both of them.

Doing this for yourself is one thing, deciding it’s a safe thing to do for a bunch of kids is quite another.

You’re right, they should incorporate it into some badge work and do it for themselves.

Also, you talk about over filling, how is that possible if they work at the same pressure?

Because the contents are mostly liquid not gas. What you’re actually doing is draining the liquid from the larger can into the smaller one and it’ll quite happily carry on past the nominal fill level.

The freezing thing isn’t essential but it does speed it up especially when the larger can is getting low.

And finally you show your lack of understanding as the pressures are the same.

^Real lack of understanding right there!

What you’re actually doing is draining the liquid from the larger can into the smaller one and it’ll quite happily carry on past the nominal fill level.

^This, and to continue:

If you over fill the container, there isn’t enough expansion room for the liquid part of the fill when the container get warm. This means that the container gets over pressurised AND WILL BURST if/when it gets hot. (If the container isn’t fitted to a stove, etc. it *may* vent through the take-off instead when it gets hot – e.g. in a parked car…)

If you’re going to do this, make sure that you actually understand what you’re doing.

think it’s perfectly safe to decant flammable gas from a larger cylinder, at a higher pressure into an untested, disposable cylinder?

There are good reason for the rules regarding hydro static testing and visual inspections of cylinders.

What circumstances should trigger the testing you’re suggesting? If you need to test every time you screw something onto the cannister then you need to test every time you connect a burner. If you need to test every time the pressure changes you need to test all your cannisters every time the temperature changes.

This means that the container gets over pressurised AND WILL BURST if/when it gets hot. [snip] If you over fill the container

Nobody is advocating overfilling the container. The reason people weigh/shake the cannister is to ensure about 20pc space is left for expansion. If you filled a rigid Meths bottle brim full thermal expansion could rupture the container. If you filled a rigid bottle of milk brim full thermal expansion could rupture the container. We don’t all stink of rotten milk from ruptured containers so most of us have managed to master the art of leaving a gap for thermal expansion.

If you’re going to do this, make sure that you actually understand what you’re doing.

Agree, but it’s pretty basic stuff. My Chemistry/Physics stopped at GCSE and I understand. to be honest, on this topic I think the people who don’t understand are the ones who are needlessly fearful. They just hear gas and get scared without thinking it through.

Having said all that I have never considered your point that the valve won’t safely vent if a stove is attached. Not an issue for me because I don’t leave the stove attached but it’s worth remembering so thanks.

The lack of knowledge being shown here (with the exception of tillydog and elliptic) is a bit scary if I’m honest.

TINAS

The trouble with winter gas mixes is the propane boils off first, the colder it is the more propane it uses relative to butane.

Aren’t the mixtures Azeotropes?

Aren’t the mixtures Azeotropes?

I dunno, but I *have* noticed that emptier cannisters have lower pressure and since pressure is relative only to temperature I can’t explain that unless the remains at the end of the can have a higher butane ratio and lower propane.

Maybe a forum chemist/physicist can explain what’s actually happening.

butane (it’s got a higher calorific value so works out lighter anyway)

Only it doesn’t.

Butane has a higher cal:mol than propane
Butane also has a higher g:mol than propane.

The ratio is actually very very simlar to the point at which the cal:g rate is almost the same, (iirc propane is marginally lighter per cal, but not so as you’d notice).

A lighter can of butane produces less heat than a can of propane of even marginally more weight.

Edit values here https://www.google.com/amp/s/www.engineeringtoolbox.com/amp/gross-net-heating-values-d_420.html

oob it’s entirely possible that you are right and that there isn’t an azeotrope of propane and butane, I just assumed that there would be.

If you filled a rigid Meths bottle brim full thermal expansion could rupture the container. If you filled a rigid bottle of milk brim full thermal expansion could rupture the container. We don’t all stink of rotten milk from ruptured containers so most of us have managed to master the art of leaving a gap for thermal expansion.

For many reasons your analogy is significantly flawed not least because all the liquids you have mentioned are subcooled and have an atmosphere above them that is full on non condensables; an LPG mixture of C3 & C4 as contained in these cans is saturated so is a very different situation.

For many reasons your analogy is significantly flawed

It’s not really. If you have a fluid in a container with no gap to expand into it can split the container. The consequences might be different but even so, we don’t typically worry too much about thermal expansion when we fill bottles and very few of us have had a bottle of anything split due to thermal expansion.

I’d also imagine that those metal cannisters have a fair bit of give in them so if you did overfill one with a stove attached it will bend a bit before a seam split. In fact if I had be asked to design one I’d have made the tolerances enough to survive being filled brim full in frozen Alaska and moved to direct sunlight in Death Valley without rupturing.

I feel an experiment coming on… 😀

Anyway, two specific questions above. Can one/all of the experts answer:

I *have* noticed that emptier cannisters have lower pressure and since pressure is relative only to temperature I can’t explain that unless the remains at the end of the can have a higher butane ratio and lower propane.
Maybe a forum chemist/physicist can explain what’s actually happening.

What circumstances should trigger the testing you’re suggesting? If you need to test every time you screw something onto the cannister then you need to test every time you connect a burner. If you need to test every time the pressure changes you need to test all your cannisters every time the temperature changes.

I feel an experiment coming on… 😀

I was joking, but seriously, can someone suggest an inert fluid with the same coefficient of expansion as Propane/Butane mix? I wanna try this and I’d rather not do it with gas. (Although at the bottom of my garden I reckon it could be done with gas.)

It’s not really. If you have a fluid in a container with no gap to expand into it can split the container

The limits that are in place for a saturated liquid are there not just because of thermal expansion they also have to consider the rise in pressure caused by the increased mass of gas in the head spaced. The fact that this liquid is saturated is the fundamental flaw in your analogy. I am the “chemist/physicist” that you are asking for. (Well strictly I’m a chemical engineer with about 25 years working with hydrocarbons but let’s not split hairs here).

My earlier post should have read “same pressures as in normal use” sorry for that

Its clear those of you who are saying this is unsafe have really not thought it through at all

1) the cans valve is designed to be fitted and removed multiple times. There is no limit to the amount of refitting possible marked on them

2) the design of the cans makes it impossible not to leave an expansion gap as the filled protrudes into the can below the top. there will always be a expansion space even if overfilled. Its actually very difficult to overfill to the point you get liquid gas out of the burner

3) I guess none of you have ever refilled a refillable lighter. Much more dangerous mashing two ill fitting valves together with no safety valve between them and no screw threads. do you pressure test a lighter before every fill? Do you refuse to refill refillable lighters? Please tell me how this is differnt

4) I do understand how gases work, how these gas cans work, how this gadget works and thus am able to say with certainty its perfectly safe assuming some level; of mechanical sympathy. The only possible issue is that if you overfill it you get a small amount of liquid gas thru the burner. simple to deal with – don’t light it until this small amount of liquid gas has evaporated away.

Jeepers guys. This has been done by many many people over many many years and I have never heard of a single adverse incident.

Scotroutes – if you want to weigh cans for an extra safety check simply weih the empty one. When I do refills I make sure the receiving can is totally empty before refilling so you could weigh that then refil then weigh to see if its the empty weight plus the weight of gas the can is supposed to take

I *have* noticed that emptier cannisters have lower pressure and since pressure is relative only to temperature

Less stuff = less pressure?

I am not a chemist and this is a wild guess but,

If you put a gas in a container and compress it, it will start to condense, to turn into a liquid. The greater the pressure, the more liquid is formed.

Ergo, the butane / propane mix is only liquid because it’s under pressure, if you were to open the can it’d turn to gas (after all, the stoves don’t burn liquid). As you use the stove, more liquid turns to gas inside the canister, less liquid trying to turn to gas => lower pressure?

Tj I have no doubt that refilling cans can be fine safely, provided appropriate equipment is used. “Some gadget off the internet” would not qualify to in my mind. But yeah you’re right, it’s not as if the behaviour of hydrocarbons is part of my day to day job…

Less stuff = less pressure

I’m afraid not in this situation. If you considered a butane tank the pressure is the same no matter what the liquid level is as it is only a function of temperature as the liquid is always at its boiling point (it’s a saturated liquid)

gonefishin – so go on. Explain what is unsafe about this please. always willing to be educated

The valve I uses is a wee bit differnt to the one in the vid but the same principle

What about refilling refillable lighters?

the cans valve is designed to be fitted and removed multiple times

I guess none of you have ever refilled a refillable lighter

I’ve not watched the video so forgive me if this is covered there in but…

The valve in a gas canister is designed to let gas out. In a lighter, the valve in the base is designed to let gas in.

They’re not intend to be bidirectional valves are they?