UKC

I've recently become aware of these devices which allow you to either refill small empty cylinders from bigger ones or consolidate several nearly empty ones into one nearly full cylinder such as this https://tinyurl.com/p7dd3sv6 (others are available)

In pricipal this could be quite useful but wondered how well in practice they actually work.

From a physics perspective, if you connect two cylinders via an open two way valve the pressures will equalise which would allow you to largely fill a small cyinder from a big one but trying to drain the dregs from several nearly empties into a cylinder wouldn't work as soon as the pressure in the one you're filling exceeds the (already low) pressure in the nearly empties. Even with a one way valve the nearly empties couldn't force gas into the one you're filling.

The blurb suggests you need to cool the one you're filling and warm the other to overcome this. I can see that doing this at home with access to a freezer and a bowl of warm water you could create a big enough pressure difference to drive some of the gas from a nearly empty cylinder into the one you're filling but if you're already on a camping trip with no freezer how possible is this?

You could easily achieve a 50C temperature difference at home but otherwise you might only get 10 or 20C difference at best. Does it depend on simply draining the liquid fuel via gravity with the gas pressure having a lesser effect?

Has anyone used these and could comment on how effective they are both at home and in the field?

Thanks.

I have one. I think they are excellent. Only do re-filling at home, do freeze one canister but don't bother heating the other, never had issues but careful not to overfill the receiving canister. Basically use the near empty largest cylinders (450g) to refill the 113g and 227g smaller canisters I use for "proper camping" so I never have to take a half fill cylinder out with me.

Real money saver.

Remember that a lot of the fuel is in liquid form rather than gas, which benefits you here. The pressure in a nearly-full and nearly-empty cylinder is going to be similar if they're at similar temperature, with the difference being the amount of liquid remaining. Raising the temperature, and therefore the pressure, in the donor cylinder will help to transfer the liquid. If you were just equalising the pressure between two cylinders containing pure gas, it wouldn't make any real difference to put the donor on top. You'd also store hardly any gas that way.

Why would you want to do it when already on a camping trip? You'd just use the larger cylinder! 

Worth bearing in mind that the seals on the one use cartridges will have been designed for,  you guess it, one use only.

Would be worth date marking the cartridges and the number of refills so you can expire them as appropriate. Ie not use one to the point it starts leaking.

I use one I got cheap on Amazon and it works well. I put the receiving cylinder in the freezer for 5 mins first which reduces the pressure.

Thanks for the various replies. I can get one for £5 on ebay which is cheap enough but no point throwing a fiver away if they were useless.

Can anybody comment on how well it works if you can't freeze one of the cylinders and have to rely on just cooling it in cold water?

Yes, I realised that just by considering gas pressures it probably wasn't going to work so the presence of liquid must be a factor. I'm sure you could draw some interesting phase diagrams for how the freezing point of the gas changes as the relative volumes of gas/liquid change in the cylinder and the pressure of the gas changes if you really wanted to.

I think that's a good thing to remember, and date marking seems a sensible idea. They're not designed for one use are they, since you can screw/unscrew a stove multiple times over several trips. But the valves must still have a limited life.

I've been re-filling and re-using one old mini canister for over a year, so perhaps I ought to think about retiring it soon.

It's a brilliant way to save money and cut down on canister waste. 

My summer holidays generally consist of going away for a month or more. We'll be based on valley campsites for much of that time but interspersed with overnight or multi night trips into the mountains.

I take big 500g cylinders for use when car camping in the valley because they work out much cheaper but don't want to have to carry them up into the mountains so take smaller cylinders for that. After a few weeks you end up with several part full small cylinders, not full enough for an overnight trip but too much gas to waste. It would be useful to consolidate them into full small cylinders and cheaper than buying new small cylinders.

Fair does, understood.

I've got an adaptor so I can screw a Coleman type threaded stove onto a refillable 907 cylinder. Worth considering.

I read "one use" as "one emptying of the cylinder of its original quantity of fuel".

Though presumably it wouldn't make sense to develop different parts for the biggest and smallest canisters with the same valve, so it would seem safe to assume that the small canisters are good for as many cycles as the big ones could be expected to see. And you'd assume lots of margin built in on those estimates too.

They still work fine without a big temperature differential, though I've found it is harder to completely fill them up this way. Pop one down your jumper for 10 mins and the other in some cold water and you'll have a reasonable difference.

Thanks, useful to know.

Just a thought, how do you know not to overfill the recieving cylinder?

You can't do the process on scales because both cylinders are attached so there's no overall change in mass. Do you just guess, separate them and then weigh the refilled cylinder to check?

Sounds  like a plan.  Easy to vent or burn some off if overfilled.

The proprietory refillable cylinders and vehicle lpg tanks usually work on maximum fill of 80 % by volume , to allow for expansion presumably .

If you are valley camping in summer in warm conditions consider getting an adaptor so you can run cheaper butane cartridges that are common in Halfords ect. Rather than the 500gram butane/propane ones you get in the climbing shops. This reduces the cost further. Then just take a couple of the larger Butane Propane to refill your backpacking small canisters. Or if your away from base nights aren’t at colder elevation, you could just refill the 100gram with butane.

Ebay commonly has both the two way valve for refilling and the adaptor as a bundle for a quid or two more than just the valve.

You are transferring a liquid, not a gas as you have realised. The reason for not overfiĺling is as is common with say petrol the liquified gas has a relatively high coefficient of expansion, for lpg 1.5% per 5.5° C so leave a canister in the sun and the liquid will burst the can, most small canisters actually have a domed bottom which will pop out first, large cylinders have a blow-out plug

Large cylinders (Calor Gas etc) it is not unknown to actually remove the entire valve assemblies and just pour the liquid from one to the other, It just looks like pouring boiling water into something really. I've seen this done at gas filling stations and done it myself, you do this at your own risk!

I realise why it's not a good idea to overfill cylinders, I just wondered how you know when it's full and you need to stop!

Yes, I've got a couple of those I picked up years ago - cheap in a camping exhibition bargain bin. I've never actually used them, though - never got round to buying a 907 cylinder, as too bulky, both in the car and for the length of hose my stove has, therefore mainly used unleaded when it was just me.

I do use gas more now that I've got kids, though - saves the party-piece flare-ups.

Weight, presumably, though that'd probably involve a fair bit of trial and error.

These devices are an excellent idea - I’ve been using one to refill canisters for a while. There’re a number of YouTube videos videos which demonstrate how to do this, such as:  youtube.com/watch?v=V1XFDB05GSc&

This sounds wrong. What am I missing?
 

If I was going to try this (and I probably will eventually) I would start by looking at the weight on the canister as bought and then weighing it to check what the weight actually is.  That would give me a reference not to significantly exceed.

I think some form of weight assessment would be necessary in the outdoors to do this safely, unless you have a very precise personal judgement "muscle memory"!

Big spanners and bravery? One cools the cylinders as much as possible, the boiling point of butane is after all only -1°C (propane -42) so under that it's just like petrol or diesel and fairly cool it isn't particularly active either.

Exactly this.

I know the weight of a full cannister plus transfer valve. Whilst filling, I periodically remove the "big cylinder" and weigh the small cylinder with valve until I am happy I have managed to get it full enough for me. I keep the filling valve on the small receiving cylinder to minimize the amount of screwing/unscrewing on the canister I want to re-use the most.

In reality, I now have a good idea on how long it takes per however many grams of gas I need to I can pretty much do it with one weigh now.

So a bit of trial and error until you know through experience.

Thanks.

Exactly!

Something worth noting for demanding scenarios is that the different parts of the gas mix evaporate at different rates so be careful not to let the dregs of the less volatile gas build up in the smaller container.

For filling, i just leave it while i pack and judge by shaking then double check the fill by floating the canister in water.

That's a neat idea. I weigh refilled cylinders to be safe, but if you don't want to carry scales, just mark a line on a full cylinder where the waterline is when it's floating. After a refill, make sure it floats with the line on or above the water surface and you know it's not overfilled.

Not only that, but if you massively overfill a small camping cylinder as you very first use it, it can splutter a bit of liquid. Gas stoves without heating tubes might be a bit "exciting" as that happens 

I manage to overfill a small cylinder from a big one without any heating or cooling. It takes a little time for the liquid to drain through so I future I will disconnect and check the weight as I go.

Blog post on this subject by the ever-reliable Chris Townsend:

https://www.christownsendoutdoors.com/2023/07/refilling-recycling-backpacki...

Weighing both canisters together to prevent over-filling is a neat idea.

Hi, can you link the device for transferring from a 907? Thanks v much, S

It's not a transfer device, it allows screwing a Coleman type stove on top of a 907 cylinder. 

Peter.