Bushwalk Australia

I have had a heap of old gas canisters hanging around, not quite enough gas in them for my trips and I can only use up so many when playing with my stoves. When I purchased my Kovea Spider I noticed on the same seller's site this little device for connecting 2 screw thread canisters so I added it to the order.



I have just tried out my new "Gas Saver" device and emptied 2 largely empty Elemental 230g canisters into another one and a 3rd into a small 110 gram canister.

While I do not recommend, or even suggest, anybody refill canisters themselves, I reserve my right to immolate myself at a time and in a manner of my own choosing.

To save issues with trying to decant part of canister, I weighed all my canisters and determined the weight of fuel in them. I assumed that a 230g canister weighs 135-140 grams. I then determined which canisters would allow me to refill while remaining within the stated weight of gas (230 grams) in the refilled canister at the end of the process.

I chilled the receiving canisters in the freezer for 15 minutes before starting. I screwed the canisters to the Gas Saver with the receiving canister at the bottom. Opened the valve and left them for 10 minutes. I then closed the valve, took off the now empty canister and weighed it and shook it to see if any gas was left - none was. The canisters all weighed in at 137 grams at this point. I connected each to a stove and burnt off the remaining gas. I was surprised to find that 6 grams of gas remained in each canister as the fully empty canisters all weighed 131 grams (Elemental brand).

The empty canisters were punctured with a hammer and screwdriver and recycled - have done this with a lot of empty canisters over the years and never had a problem - no need for a special gadget to do the job but I do make sure they are empty.

How do you know when the bottom one is full? Is there a pressure relief valve?

I assume it has a simple non-return/one-way valve built in.
It's nice to see a device that works to positively reduce waste and excess greenhouse gases.

There is no one way valve or pressure relief valve; just an on/off valve like all canister stoves. It is just a gravity feed system. By cooling the bottom canister ( the one being filled) there is a pressure differential which helps force the liquid gas from the top to the bottom. This shouldn't be absolutely necessary as gravity will do it but it should speed up the transfer.

As to not over filling the canister, I worked out the weight of the gas in each canister. To do this weigh the canister, subtract 140 and that is the weight of fuel remaining. I then only connected canisters that would make the total weight of gas in the bottom canister after the transfer less than 230 grams (the original fill weight). It would be nice to be able to pass only a limited amount of gas but to do this you really need a flexible tube connecting the canisters and having the lower canister sitting on a set of scales.

Mark F wrote: I reserve my right to immolate myself at a time and in a manner of my own choosing.

Which in turn will immortalise you on here.

I just remembered there is a solution to preventing a canister from over filling that was suggested on bpl. That is to tip the canister being filled at an angle to the vertical to maintain an air gap between the top of the container and the lindal valve in the canister. The suggestion was that a 20% volume air gap was required. It was also stated that calculating this would be a nightmare.

I have derived the angle by experiment rather than calculation for the elemental 230g canisters. They seem to be identical in profile to KMart's CampMaster 227g canisters and no doubt other brands as well. Please note that this angle is dependent on the profile of the canister. It is also dependent on the pressure in the two canisters being equal but this would normally be the case (unless you were filling with pure propane).

I knocked a second hole in an empty canister next to the valve. I filled the canister with water and weighed it - 633g. Subtract the canister 131g to get a volume of 502cc (1/2 a litre). We want an air gap of 20% or 100cc, so I poured out 100 grams of water. I then tipped the canister while aligning it with a protractor and read off 35 degrees just as water started to escape from the hole next to the valve.

I'm amazed at this over-engineered solution (IMO). Mind you, I do like Mark F’s methodology.

Assumptions : empty 230g net canister weighs approx 135g, you use 50g/day max.
If the canister weighs more than 250g, you can just take it on the next 2- or 3- day walk

Problem : gas canister with small amount of gas remaining – (ie less than 250g gross weight)
Solution : carry it and another (full) canister on the next short walk (use the lighter one first :)

You will be carrying up to 250g extra – big deal!

Good one Mark,
Where did you purchased the gas gizmo from please ? I also recycle my empty canisters but use a beer can opener on mine (are they still available ) .
corvus

I have this one, bought off e-bay
http://www.ebay.com.au/itm/130825485203 ... 1438.l2649

Same source as osm

http://stores.ebay.com.au/AUTTER-CHOVIN ... 34.c0.m322

It is worth having a look around the store - they have a Kovea section which is where I sourced my Spider stove.

Thanks for that both of you I think I need to get one as it is small enough to fit into my stove collection box
corvus

A 20% air gap sounds about right. That would allow you to warm the canister up several tens of degrees before the liquid expands enough to fill the volume and start pushing out the concave bottom of the canister.

Another approach is to control the receiving temperature. Put the lower canister in an ice bath, roughly 0°C. At that temperature 230g of n-butane would have a volume of on 383ml. So you would overfill n-butane if you loaded up 400ml. And, correct me if I'm wrong, but I believe Elemental fuel is primarily n-butane.

I'm not sure about your assertion that the (vapor) pressures would be the same. Why? The two canisters wouldn't generally start out at the same fill level, so they would have different fuel mixtures. And they would also not be at the same temperature. So it may not be the case that this tilt method achieves the 400ml fill you are after. I'd be interested in reading the bpl discussion. Do you have a link to it?

Ultimately you can be safe overfilling as long as you check afterwards with a scale. If it's overfilled you can easily dump it or drain it into another canister.

I personally use my odd canisters for car camping. Although sometimes I end up with a pretty large box of near-empties I do eventually use them. And on cold mornings in the bush I sometimes am quite happy to have that little extra ooomph of propane which the refilling/combining method can greatly reduce.

But it looks fun. I might spend the $20 just to have one.

excellent idea , and well done on the calc's...

One on order allready

Swampy

Slightly off topic but I just found packs of 12 220g tall, thin canisters for $8 - 67c per can - at Woolworths today. I shop at Woden in the ACT - they are tucked away between the sausage fridge and the chicken fridge. Best part is they are filled with an iso-butane mix rather than the normal n-butane so ideal refilling lindal thread canisters for cooler weather (perhaps not snow conditions)

There are various adaptors that allow you to use the tall thin (cheap) canisters with 'coventional' canister stoves
eg - there are many http://www.ebay.com.au/itm/200728470814 ... 1439.l2649
http://www.ebay.com.au/itm/221148148014 ... 1439.l2649
And here is one that turns a 'normal' gas canister into a remote one (you can then use it under a baking oven set up like a Bemco,or place a windscreen completely around it without overheating the canister, or it allow you to invert the canister for cold weather use) http://www.ebay.com.au/itm/121014837567 ... 1439.l2649
More stove heaven gadgets

Hi Mark
67c canisters...what brand ?

Franco wrote:Hi Mark
67c canisters...what brand ?

I'm guessing this is them..

http://www.ozbargain.com.au/node/96905

Anyone know what the difference is between the one posted earlier, and this one?

http://www.ebay.com.au/itm/G-WORKS-CART ... 7140wt_952

The canister in question is branded festiva - the importing company is AHM group code FT220C and marked made in Korea.

Franco - They are the same as the ones I have from a quick look and only $6. I didn't see any stoves or other devices.

Strider - I have also pondered this additional bit that is attached to the Gas Saver. It apparently allows vapour to be vented but for what purpose I have no idea.

Bernieq, a lovely response.

But how many partially empty canisters would you carry on a longer trip???

Like you, I'd plan to empty the partially emptied one first, and then move on to canister #2.

However, despite such plans, I have ended up with a few partially emptied canisters, so I see where Mark is coming from.....and I enjoyed the scientific discussion and thought process in his post.

Andrew A

Mark F wrote:It apparently allows vapour to be vented but for what purpose I have no idea.

Could it be a relief valve to let off pressure once the canister being filled becomes full?

Just had a look at my local Woolies and they have the Festiva canisters - but only a 4pack for $4.99. It would still work out cheaper to buy a pack and an adaptor from ebay than it would buying dedicated canisters, but my only concern is there is no way of knowing how much isobutane is in them (1%, 5%, 20%, ?).

Strider wrote:Could it be a relief valve to let off pressure once the canister being filled becomes full?

The description makes it sound like it is a way to vent air, as opposed to vaporized fuel, during the filling process.

They say to vent some gas, then close the vent valve and open the other valve to let fuel flow between the canisters. Then close that valve and repeat the process: vent, fuel; vent, fuel. On the manufacturer's website google translates the following line: "Accept the gas moving gas at atmospheric pressure...". You shouldn't have any air in a partially-used canister so I don't think you'd need this part.

They have quite an array of interesting parts: website

Thanks Strider
If those were regularly available it would make the adaptor to Lindal a viable proposition.
I once found Propane canisters of that type at Bunnings bau with the Lindal valve.
They had disappeared by the time I realised that they could have been a good buy for me.
They were meant for torches.

Strider wrote:Anyone know what the difference is between the one posted earlier, and this one?

http://www.ebay.com.au/itm/G-WORKS-CART ... 7140wt_952

I've wondered that myself. It's completely unclear from the description why one would need it. It seems like it's merely an extension although perhaps there's some pressure release valve in it.

Mark F wrote:Slightly off topic but I just found packs of 12 220g tall, thin canisters for $8 - 67c per can - at Woolworths today. I shop at Woden in the ACT - they are tucked away between the sausage fridge and the chicken fridge. Best part is they are filled with an iso-butane mix rather than the normal n-butane so ideal refilling lindal thread canisters for cooler weather (perhaps not snow conditions)

You're very lucky to have isobutane at those prices even if you have to fiddle with transferring the fuel to a bushwalking type canister. $0.67 for 220g is practically giving it away (where as $10 for 220g for a bushwalking type canister stops just short of robbery). And isobutane is a very good fuel. It's boiling point is about -12C, which means that you should have decent pressure down to about -5C (at sea level). As long as you can keep the canister temperature at -5C or above, you don't even need to take the risk of adding propane.

By contrast, regular butane is really only good to about +5C (canister temperature not air temperature), a difference of 10C. Being able to operate in conditions that are 10C colder is to me a distinct advantage. Add some propane, say 20%, and you've got a very nice cold weather fuel, particularly if you use an inverted canister stove.

HJ

Thanks for the link to this strider.

Love Mark's approach to the problem, but I think I will respect his intellectual property and simply check what's in there with scales as a lazy way to reduce the risk of overfilling. If I encounter bulging canisters I will break out the protractor.

I have ordered the canister to canister doo-hickey. It's well worthwhile for me to be able to carry only one full or nearly full canister instead the usual play safe system of one and a bit or two part full or whatever. I'm more than happy to save the weight of the second canister, no matter how much or how little is in it. That's a 250gm free kick !

Thought about using up the bits and pieces canisters when camping around the car, but much prefer to use a coleman stove and shellite when weight doesn't matter.

andrewa wrote:Bernieq, a lovely response.
But how many partially empty canisters would you carry on a longer trip???
Like you, I'd plan to empty the partially emptied one first, and then move on to canister #2.
However, despite such plans, I have ended up with a few partially emptied canisters, so I see where Mark is coming from.....and I enjoyed the scientific discussion and thought process in his post.

Sorry, andrewa, I haven't been back to this thread for a while.
(Note that, for me, 'partial' means a cannister with less than 2 days gas. If it has more than that, it goes on a weekend trip by itself !)

I've only ever carried one partial on a trip (but I've had 3 in the garage at one stage). The longer the trip (and so the greater the starting weight) the less likely I would be to carry a partial.

re the design of Mark F's experiment - yes, it is well thought out - all good fun.

Mark F wrote:Same source as osm

http://stores.ebay.com.au/AUTTER-CHOVIN ... 34.c0.m322

It is worth having a look around the store - they have a Kovea section which is where I sourced my Spider stove.

This seller does not appear to have an Add To Cart button for the Spider. How did you place an order for multiple items with this seller?

Gas Saver Field Kit
My two cents worth: To get some you gotta lose some.
In the field you won't have a fridge to cool the receptor canister and lower its vapor pressure. Gas exchange will be slow or won't happen.
Operating the field kit discharge device would result in a little cooling of the receptor canister and its contents, lowering the vapour pressure and enabling the gas exchange to happen.
The instructions say to repeat this process. Explanation: As gas is delivered to the receptor canister it will get warmer, thus requiring more cooling to keep the gas transfer going.

Avatar wrote:Gas Saver Field Kit
My two cents worth: To get some you gotta lose some.
In the field you won't have a fridge to cool the receptor canister and lower its vapor pressure. Gas exchange will be slow or won't happen.
Operating the field kit discharge device would result in a little cooling of the receptor canister and its contents, lowering the vapour pressure and enabling the gas exchange to happen.
The instructions say to repeat this process. Explanation: As gas is delivered to the receptor canister it will get warmer, thus requiring more cooling to keep the gas transfer going.

That's an interesting interpretation of the instructions for using the valve. I hadn't thought of that.

But wouldn't it be easier to simply warm the source canister?

Another $30 for the Field Kit sounded steep. Why would anyone care to spend a total of $60 to allow gas transfer b/n canisters in the field?