Gas Stove Configurations
Gas stoves come in various forms, so the subject is not that simple. The gases used for bushwalking stoves are mainly a blend of propane and butane, although some cheap warm-weather stoves use straight butane. In general, straight propane is not used for
Gas Stove Configurations
Gas stoves come in various forms, so the subject is not that simple. The gases used for bushwalking stoves are mainly a blend of propane and butane, although some cheap warm-weather stoves use straight butane. In general, straight propane is not used for bushwalking as the propane cylinders are too heavy, although it is used for car camping. Straight butane has very poor performance in cold weather, and old experiences with it may be responsible for many myths about how gas doesn't work. Hopefully, this page will shed much light on modern gas stoves.
Early Bleuet Stoves
Straight butane has problems when it gets cold: below 0 C it ceases to boil off vapour, so the old Bleuet puncture canisters simply didn't work in the snow. Even if the butane is above 0 C and starts to vaporise, it will cool down (like hot water does as steam comes off) and go below 0 C, and effectively cease to evaporate out of the canister. In fact, it is possible for a butane-powered stove to sit there at -10C with the valve wide open and just not burn: the fuel isn't vaporising enough to make enough pressure for anything to come out the jet.
Early 'Bleuet' puncture-style gas canisters sold in Australia contained pure butane, and they didn't work in the snow. I was trying to make a cup of tea in the Blue Mts once in mid-winter with one of these Bleuet stoves when it went out. There was still fuel in the canister (I could hear it sloshing around), but the base was covered in ice! I think 'they' thought Australia was too hot for the propane to be included here. I was lucky enough to get some of the first Bleuet butane/propane canisters brought into Australia: they were wonderful in comparison. They were however a short-lived thing, and have since been replaced now by the far safer resealable canisters.
The puncture-type canisters were cheap but carried a significant safety risk. If the seal between the stove and the canister was at all disrupted you could get the gas leaking out. You could also get a leak if the valve was not done up properly, and I have had that happen to me inside my pack. This design has been superceded by the resealable canister: these allow you to remove the stove and pack the sealedcanister away separately.
Modern Gas Stoves
These days we use a resealable gas canister. I have found the seals on these canisters to be extremely reliable. Most of them contain a mix of n-butane and/or iso-butane and propane, with somewhere between 10% and 30% propane. By blending propane with n-butane (or 'butane') and/or iso-butane we get something which will work at lower temperatures while still being safely enclosed in a light steel or aluminium canister. The more propane present, the harsher the sound of the flame, and the lower the temperature it will take. You will find that the 'tourist' brands of canisters have less propane than the bushwalker ones: this is because 'tourists' do not normally like cold weather. If propane is so good for cold weather, why don't the manufacturers offer canisters with 100% propane in them? Well, in fact some of them (eg Coleman) do offer 100% propane, but the propane makes a much higher pressure in the canister in warm weather so the canister itself has to be much stronger. You end up with something like a small LPG bottle - which is quite logical because LPG is largely propane. I guess if you were equipping an expedition to the South Pole (with sleds) you could easily make the case for taking straight LPG - it would work wonderfully. But for lightweight bushwalking, those LPG bottles are a bit too heavy.
As an aside, I should mention that arguments have raged over whether the contents of the canister are a 'mixture' or a 'solution', and what happens to the boiling points. The subject is rather complex, so if you want to pursue the matter I will refer you to the FAQ page solely dedicated to the subject of mixtures. Suffice to say here that adding propane to the butane (or isobutane) does let the canister work at lower temperatures, but they do not boil off separately.
We can divide bushwalking gas stoves into two main sorts: the 'upright' and the 'liquid feed', and their differences are important. However, there is a third category which can best be described as 'uncertain'; these use canisters which look identical to paint spray cans. We will start with the more common upright version.
Upright Gas Stoves
A typical 'upright' stove is shown here: a small stove (Snow Peak GST-100) on top of a resealable gas canister. Successful operation of such a gas stove requires that the liquid gas in the canister be able to boil when you open the valve. For this to happen the liquid must be warm enough. So you have to keep the canister warm - but not hot! Being warm lets the liquid gas boil and the vapour goes 'up the spout' to the burner. You start the stove using whatever gas pressure there is, let the general cooking heat warm the canister a little bit so the contents stay above boiling point, then you cook away happily on the mix. This works very well in warmer conditions - anything more than a good few degrees above freezing.
However, failure to keep the canister warm in cold weather and in the snow can result in great disappointment. The stove may run for a while with a new canister, but eventually it won't work any more. The canister will still have liquid gas in it but will refuse to do anything. What has happened is that the mixture has cooled down by evaporation, so that the gas coming off towards the end was mainly propane, and the butane has been left behind. Being as how the canister has frost around it, we can safely say the remaining butane is well below its boiling point, and is now too cold to give off enough gas. If this happens you will have to warm it up gently: put it inside your clothing or dunk it in luke-warm water for a while. Then keep it gently warm. If the canister is getting too cold and the stove is dying, try pouring a few spoonfuls of hot water (out of the pot of course) gently over the canister. It usually works wonders. You might also want to partly remove the radiation shield to let the canister absorb a little warmth but use care.
The root cause of the problem is that the liquid inside the canister has cooled down because the evaporation is happening inside the canister. If we could prevent the evaporation from happening inside the canister, we would have a much better result. This means we need to feed a liquid out of the canister - just like the liquid petrol coming out of a tank on a petrol stove. This is covered in the next section.
I suggested that you should allow the canister to get warm. This, surely, is directly the opposite of what all the stove companies say? One or two of them go almost hysterical about not using a windshield or anything near your stove which might make the canister 'warm', for fear of explosion. Well, in America the Tort Lawyers rule the roost, and they dictate the warnings printed on the consumer labels. The instructions on some stoves seem to be more than 50% hazard warnings - which few people ever read anyhow!
But the reality is different. Every canister sold in America has to pass Dept of Transportation (DOT) regulations (because the canisters get transported ...), and a key requirement for approval is that the canisters must be able to be stored at 50 C, and must safely pass tests at a higher temperature as well. Now 50 C is quite hot - too hot to keep your fingers on it for very long. In fact, your fingers make an extremely good thermometer for this temperature - we call it the 'touch test'. If touching the canister does not produce an immediate 'ouch' reaction, it is below 50 C and probably below 40 C (I assume normal fingers here!). So just by monitoring the temperature of the canister while you cook you can ensure it stays within all the safety limits. It's as simple as that.
Remote Canister Gas Stoves
Not all canister stoves have the burner sitting on top of the canister: some have the burner separate and at the end of a hose. In this they are very much like many pumped-tank petrol stoves. The advantages are - I suppose, that the burner is lower to the ground and the canister can be shielded from the heat of the stove. Yes, well, but this design has a serious disadvantage in cool to mild weather. As the stove runs and the gas evaporates, the canister cools down - and does not get warmed up by the stove. So it gets colder and colder. If the canister is nearly empty, the amount of thermal mass in the remaining liquid gas will be rather small, so it will cool down rather fast. In fact, it can easily drop below 0 C and then you can be in the same spot of bother when the butane stops boiling. The stove can die, just like an upright canister stove. It is in fact easier for this to happen with a remote canister stove than with an upright, simply because of the lack of thermal feedback.
However, not all remote canister stoves have to suffer this fate. Some of them have a 'preheat tube', even though the stove is sold for use with an upright canister. One must ask why? Well, because while the stove is sold for one manner of operation, the manufacturer has chosen to make it possible for you, the user, to use it in another manner. To be sure, in general the manufacturer does not mention this alternative, but that is usually because the manufacturer has not obtained type-approval in countries around the world for the stove to be used in the alternate manner. Yes, I have actually been told this by managers from two large and very well-known stove companies. So we will discuss this 'alternate manner' in the next section. In the meantime, please note that the Optimus Stella + shown here does not have the preheat tube and cannot do this.
Liquid Feed Gas Stoves
A variation on the conventional gas stove treats the liquefied gas as a liquid fuel - like petrol or kero. The gas canister is arranged so the gas pressure from the propane forces the liquid fuel into the stove, where it is heated in a preheat tube and burns normally. This is identical to a petrol or kero stove, except that most of those rely on pumped pressure to drive fuel to the stove. Since propane boils (and pressurises) at -42.1 C, this sort of stove can be run down to below -20 C (the limit is about -26 C). This is colder than most anywhere in Australia. Why can't it work down to -40 C?
This design has the advantage that the propane/butane mix in the canister is fed to the stove without any separation into its components. The Coleman Xtreme stove shown to the right is a classic example of this - and is regarded by some as the finest winter/snow canister stove on the market - the Gold Standard. It's only problem is that it is a little heavier than we would like - but the special Powermax canisters are lighter than the normal screw-thread ones. It has a preheat tube, shown with a red line pointing to it. There is also an Xpert stove with four legs rather than three which is very similar. (Updated in 2008: the Xtreme is no longer produced, but the Powermax canisters and the other stoves in this series are still produced. Meanwhile, the second hand prices on eBay for the Xtreme are rising ...)
The special Powermax canisters contain an excellent 60% butane / 40% propane mix. Now, how do these stoves get a liquid feed when they are lying on their sides? There is an internal pickup tube which collects the liquid from the bottom of the bottle, just as with the fuel tank for a petrol stove. However, Coleman do also sell an adapter which converts a standard screw-thread canister to a liquid feed for the Xtreme (and Xpert) stoves. This may not be available in Australia, but try the web for sure. However, it does make for a heavy combination.
A recent release is the new Coleman Fyrestorm Ti (or SS) which includes a stand for holding a conventional screw-thread canister upside down! This stove is almost as good as the Coleman Xtreme for serious winter use. It is wierd that it is Coleman, who many think of as a 'family camping' company, which produces the two best winter stoves for snow conditions. Other well-known stove manufacturers (we name no names) get very hysterical about the idea of inverting canisters, not to mention cooking inside a tent in a snow storm. Equally, it is interesting that the Coleman winter stoves both have very low carbon monoxide emissions - which is just what you want when cooking in the vestibule of your tent in a howling snow storm. Coleman seems to have worked out how to manage a liquid feed and a clean flame, while most of the other companies are still trying. (Personal note: having actually built many small canister stoves from scratch, I can say that their construction is a damn sight more complex than you might think!)