FAQ - Gas Stoves

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Gas Stoves

Here we concentrate solely on gas stoves. We cover the fuels and containers used, the different sorts of stoves available, and various technical details. As to why you should use a gas stove in preference to all others: that will emerge pretty quickly.

Gas Properties - Summary

We summarise here the key points from the Fuel Efficiencies page.

• Propane: boils at -42.1C,
  So it is suitable as a fuel under most conditions, including very colds snow conditions around the world.
  Cylinders for straight propane (think LPG) have to withstand high pressures and have therefore to be made of quite heavy steel. They are too heavy for most bushwalking.
• Butane: boils at -0.5C,
  So it requires much lighter cartridge construction. However, the 'high' boiling point means it will have problems in the snow. It is also known as n-butane, where 'n' sort-of stands for 'normal'.
• Iso-butane: boils at -12 C,
  So works better in snow conditions than n-butane.

In practice, the 70% n-butane / 30% propane cartridges are fine for warm weather with an 'upright' stove, while the 70% isobutane / 30% propane cartridges (eg Kovea) are good for cold weather, but not very far below freezing. The 80% butane / 20% propane cartridges and ones with even less propane (including the Bleuet 100% butane ones) are really only suitable for tourist activities in warm weather. For snow conditions you will a different sort of stove: one with a liquid feed. All this is explained in much detail below.

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 cartridges 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 cartridge. 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 just isn't vaporising enough to make enough pressure for anything to come out the jet.

Early 'Bleuet' puncture-style gas cartridges 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 cartridge (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 cartridges 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 cartridges.

The puncture-type cartridges were cheap but carried a significant safety risk. If the seal between the stove and the cartridge 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 cartridge: these allow you to remove the stove and pack the sealed cartridge away separately.

Modern Gas Stoves

These days we use a resealable gas cartridge. I have found the seals on these cartridges to be extremely reliable. Most of them contain a mix of butane or isobutane 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 cartridge. 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 cartridges have less propane than the bushwalker ones: this is because 'tourists' do not normally like cold weather. There are more details in the Fuel efficiency page.

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 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 bushwealking, those LPG bottles arte a bit too heavy.

As an aside, I should mention that arguments have raged over whether the contents of the cartridge 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 and Solutions. Suffice to say here that adding propane to the butane (or isobutane) does let the cartridge work at lower temperatures.

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 cartridges 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 cartridge. Successful operation of such a gas stove requires that the liquid gas in the cartridge 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 cartridge warm - but not hot! For further details on this, see the pages on Technical Details and Gas Mixtures. 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 cartridge 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 cartridge warm in cold weather and in the snow can result in great disappointment. The stove may run for a while with a new cartridge, but eventually it won't work any more. The cartridge 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 cartridge 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 hot water for a while. Then keep it gently warm. If the cartridge 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 cartridge. It usually works wonders. You might also want to partly remove the radiation shield to let the cartridge absorb a little warmth (see below under Smart Tricks), but use care.

The root cause of the problem is that the liquid inside the cartridge has cooled down because the evaporation is happening inside the cartridge. If we could prevent the evaporation from happening inside the cartridge, we would have a much better result. This means we need to feed a liquid out of the cartridge - 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. But the reality is different. Every canister sold in America has to pass Dept of Transportation (DOT) regulations (becasue 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 (I assume normal fingers here!). So just by monitoring the temperature of the canister while you cook you can ensure it stays within the safety limits.

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 a 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. Ahem - yes, I was told this by the R&D manager of one large and well-known stove company. 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 cartridge 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 is discussed in the page on Gas Mixtures.

This design has the advantage that the propane/butane mix in the cartridge 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. 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. The special Powermax cartridges contain an excellent 60% butane / 40% propane mix. Now, how do these stoves get a liquid feed? 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. There is a picture of the insides of a Powermax cartridge showing the pickup tube below. For availability of the stove and canister (not easy), see below under Cartridge Formats. 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, this is not the end of the story. You can turn many other remote cartridge stoves into liquid feed stoves. The Snow Peak GS-200D (at one stage selling for a horrendous AU$320) has a preheat tube and is shown on the cover of its box with a standard screw-thread or "Epigas" cartridges placed upright. The manufacturer does not go so far as to recommend you tip the cartridge upside down to get a liquid feed, but it has been shown to work quite well. The MSR WindPro stove is similar but lighter, and also works reasonably well in the snow with the canister inverted, although the valve did get a little clogged up on one trip and needed continuous clearing while I was cooking. A photo of the gunged up valve is shown to the left. Part A is the lock on the valve, while thread B is what drives the needle valve. The two O-rings at C are what keep the gas in: these should be kept in perfect condition, and a little silicone grease once every year or two is a good thing. The tip D is the actual needle valve, while the shoulder E serves as a definite shut-off seal onto the valve seat. Exactly what the white gunge F is remains a bit of a mystery at present - possibly the odorant added to the gas so you can smell any leaks? I cleaned it off when I got home. Some of the Primus stoves (eg Omnifuel, GRavity MF and EtaPower) also have a preheat tube, and could do the same. In fact, the new Primus Gravity MF handles gas, petrol and kero, and works fine with the gas cartridge upside down. I gather that Primus does (or did) actually mention this possibility somewhere, although they advise great care in tipping the cartridge upside down. It doesn't work quite so well with Shellite, and works poorly with kero in my opinion. Making genuine multi-fuel stoves is hard.

A recent release is the new Coleman Fyrestorm Ti (or SS) which includes a stand for holding a conventional screw-thread cartridge 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 stove manufacturers (8we name on names) get very hysterical about 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!)

Note added in mid-2007: the Primus Etapower stove features an effective heat-exchanger pot, an integrated windshield, very low carbon monoxide emission (unlike some of its competitors) and the valve on the canister swivels so you can easily invert the canister. This stove should be another excellent winter stove, although one could wish it was a little lighter. But a lighter version is coming as well, some time in 2008 I believe.

How do you tip a cartridge upside down in a stable manner is of course a good question. One method which the author has used is to fit the cartridge with some Lexan legs, as shown to the left. The weight of the three legs plus the rubber bands is about 20 grams: hardly significant. The configuration is quite stable, by the way. The stove is an MSR WindPro, and I have used this combination in the snow. Another way is to make a little three-legged stand to clip onto the neck of the cartridge, as shown to the right. While the aluminium legs may not be a strong as the black painted magnesium legs on the Fyrestorm canister stand shown above, they are quite adequate and much lighter. They are shown with a Kovea Moonwalker; on this stove the hose swivels at the canister connector. It's only slightly heavier than the Xtreme or Fyrestorm too.

Why does the liquid feed idea work so well? There are two reasons. The mix forced up the tube is just that: the full mixture of butane and propane. And there is no variation in the mix because there is no evaporation inside the tank - for details see the page on gas Mixtures and Solutions. It's a liquid hydrocarbon fuel just like petrol or kero, and it behaves just like kero or petrol. The only real difference is that it boils at a somewhat lower temperature than petrol or kero. The curious thing is that, while valving liquid kero or petrol can be tricky, the liquid feed gas stoves seem to manage to valve the liquid gas fairly well. Anyhow, all the liquid feed stoves mentioned simmer very nicely, although any adjustment has a small delay time.

Is there any danger in using a liquid feed on a gas stove? It is hard to see why there should be if the stove has a preheat tube. The liquid fuel will reach the preheat section and vaporise with the heat from the flame (if it hasn't vaporised earlier). The jet hole, which is typically of the order of 0.3 mm diameter, will only let a certain amount of gas through at a time. The back pressure will simply limit the amount of fuel reaching the preheat section. This is exactly the same as for petrol and kero stoves: exactly the same. Just make sure you have a flame at the burner before you turn on the valve, and do that gently at the start. However, do not try this if the stove does not have a preheat tube, and the author accepts NO responsibilty for what you do!

There is one exception to this rule about preheat tubes, and that is the Optimus Nova + stoove. It hasa very clever design - but Optimus are a very old stove company! Like the MSR XGK, it uses a vortex burner (which just like the XGK makes quite a lot of noise), and the heat from the vortex cone is coupled back to the jet to vaporise the fuel. No preheat tube is needed here. This stove works with gas, Shellite and kero.

Spray Can Cartridges

No-one is ever satisfied with convention, are they? So there are also cartridges on the market which look exactly like a paint spray can, but they contain either straight butane or a butane/propane mix. Part of the reason for this may be that you can buy spray cans extremely cheaply, and they are already rated for use with these gases. The gases are sometimes used as the propellant for the 'real' contents. But note that the connection you get on these spray cans looks exactly like what you get when you pull the spray attachment off a paint can. It's a short straight bit of tube, with no screw thread!

One application I have seen for these is in little flat desk-top stoves: you stick the can into the base of the stove where it is somewhat shielded from the radiation. The can is locked in place by the body of the stove. These stoves usually take the straight butane cartridges as they are designed for the average family picnic use. They are also used, I gather, in some Asian restaurants for cooking on the customer's table.

The other use appears to be for use with remote-cartridge stoves as described above. Kovea make such cans with a 30% propane mix, and supply an adapter with some stoves to take these spray cans. But the question is then whether you should run the spray can upright or on its side? If you run it upright, the hose may be a bit short so the can is a bit close to the stove. If you lay the can on its side you may not know whether you will get a gas or liquid feed! This could be a bit exciting if the stove you are using does not have a pre-heat tube - rather deadly, actually. More details of this oddity are given below.

Cartridge formats

The gas cartridges available come in several physical formats, and you have to get the right one for your stove. The different physical formats (below) cannot be swapped between stove types (with one exception), although the different brands of butane/propane mix can be swapped around with (almost) no problem. This is despite bleatings by some manufacturers that you must 'only use our cartridge on our stoves'. It is interesting to note that the Kovea screw-thread cartridges actually have a notice on the side saying 'This cartrdige is compatible with any good quality and approved threaded appliance'. Kovea make both stoves and cartridges for a number of very well-known brands (like MSR), so this seems fairly authoritive. However, there is a small safety problem putting a pure isobutane cartridge onto a stove not designed for it. This is discussed under Isobutane. In Australia all stoves and cartridges are subject to the Australian Gas Authority (AGA) for licensing.

• The (French) Gaz Bleuet puncture-type cartridge is the oldest common one. This is cheap and still widely available, but has a narrow base which can be easy to tip over. The cartridge cannot be removed from the burner, which is a real disadvantage. It is not recommended any more. I have had one leak inside my pack when the valve handle was knocked: after a while I got worried about the hissing noise I was hearing behind my head. My pack smelt a bit for the rest of the day.
   

• The screw-thread or "Epigas" cartridge was pioneered by the UK firm Epigas, and is now probably the most common type around most of the world. Epigas themselves were subsequently bought out by Coleman of America. The cartridge comes in a miniature 100g size, a squat 220 g size, and a tall 450 g size, and it can be removed from the stove for packing (or weighing or shaking to see how much is left). The squat middle size is definitely the most convenient one to go for in most cases: it has a wide base for stability and is available with a variety of gas mixes. You can easily identify it by the threaded fitting shown here, known as a Lindal valve. Actually, the valve is inside the threaded bit shown here, and is discussed below. You may see references to "compatible with EN417" in catalogues, but as explained below that Standard does not cover the screw thread: it's a European Safety Standard governing pressurised cartridges. The thread is explained below as well. Cartridges and burners are sold by Epigas, Primus, Coleman, MSR, Snow Peak, Kovea, Caribee, Trekka and a whole range of others. The 220 g cartridge, at 30 g/day, lasts us about 7 days reliably in summer. The taller 450 g cartridge lasted us about 2 weeks in poor weather in the Pyrenees (measured over two trips of 6 and 8 weeks). While the 450 g is taller than the 220 g one and might be considered less stable, we never had any problems with it as long as we placed it on a small base of 3-ply.
   
  I have also seen either butane or the common butane/propane mixes in screw-thread spray-can cartridges at some hardware stores, at exaggerated prices, and I believe such cartridges may be available in some supermarkets at much lower prices. Placed upright they would be rather unstable, but a few suppliers do make adapters for these cartridges. These are mentioned again below (3 points down, under 'Gasmate'). Other brands exist I believe, such as Markill.
   
• The clip-on CampingGaz cartridge looks almost identical to the above but has no thread. It fits only the French CampingGaz range of stoves. CampingGaz were also bought out by Coleman. The plastic parts of the stoves do look good (with neat piezo-electric igniters too) and the cartridges have reasonable availability in Australia, but they are most widely available in France. Why did the French have to be different? (Otherwise they are pretty much the same as the screw-thread cartridges.) Unfortunately the Campingaz stoves have a relatively clumsy mechanical design and are rather heavy.
   

• The Coleman liquid gas PowerMax cartridges (60% butane / 40% propane) look like small Sigg bottles, with a Lindal valve which is similar to the CampingGaz one. They are designed to feed the liquid gas mix to a Coleman Xtreme stove, thereby eliminating the problem of different evaporation temperatures. They are available in some walking shops in Australia as a specialist item. Sadly, it seems their availability in Europe and the UK is now rather limited as they proved to be poor sellers there - but the cartridges are still available there in principle. The stoves are widely available in America where they are a very popular winter stove, and Coleman USA has confirmed that they will remain available there.
   
  Sadly, few shops now stock the Coleman Powermax canister. Coleman Australia do still import the cartridges (but not I think the stoves any more) from America, and shops can still get them in for you if you hassle them - if they can be bothered. After some discussion about this difficulty with Carla Cincotta, who looks after 'Customer Service' for Coleman Brands Pty Ltd in Sydney (Ph: (02) 8762 5000), we have come to an agreement that you can now (2006) buy them from Coleman themselves, through their Service Centre in Minchinbury. Their address is: Shop 43/44 Minchinbury Hometown, Gt Western Hwy, Minchinbury, NSW 2770, phone 02 9675 0800. You could ask for a staff member by the name Nassar. This is REAL customer service, and I applaud the lady. (Checked Oct-2007: the Powermax canisters are still being imported from USA into Australia.)
   
  Their chief use is in the snow, where they are excellent performers. How do they do it? They have the same valve mechanism but with a little spigot inside. Onto this spigot goes a little bit of flexible tubing, and onto that goes a long length of plain steel tubing, with another bit of plastic tubing for padding over the end. The weight of the steel tube makes the end sink to the bottom of the PowerMax bottle, where it always gets the liquid rather than the gas. So if you shake the PowerMax bottle you will hear a clank-clank: that's the steel tube hitting the side of the bottle. A very small amount of the liquid gas is used to pressurise the rest of the liquid gas, so there is no cooling down by evaporation. The stoves are not cheap, but they do work very well. (I have two of them, and I am keeping both!)
   

• As mentioned above, here are also cartridges which look like a standard pressure pack paint spray can. They have a 'bayonet' connection which looks identical to the top of a spray can without the nozzle. They seem to be popular for some car-camping stoves where the cartridge clips inside the stove body. The cartridges are quite cheap ($2 each?), but most brands seem to contain just 'butane'. I am not sure what this means, since one vendor website defined 'butane' as 'A mixture of hydrocarbons which is predominately butane'. Mind you, the same website claimed that '1 Candlepower = 0.625 W' and '1KW = 3.6MJ'. The Candlepower is a unit of light intensity, not power as in Watts. And kW is a measure of power, while MJ is a measure of energy. Oh Dear. Straight butane without some propane is not recommended for cold weather: it freezes up.
   
  What is interesting is that you can buy an adapter which converts the Gasmate pressure pack can into one leg of a low stove support: you put your favorite screw-thread stove on top of it. I am told by Leigh Smith that the cartridges and the adapter can be obtained from Gasmate, with the adapter costing about $25.
   
  And, as mentioned above, you can buy Kovea 'spray cans' of 70% butane 30% propane with the same bayonet fitting, and get an adapter with some of their stoves. Frankly, this one worries me slightly, and I wouldn't do it. However, information from a reader has brought to light the fascinating information that the spray cans with a spigot fitting PLUS a notch in the rim around the neck have a dip tube inside them, very much like the Powermax canisters! I think the story goes thus. They are designed for use in flat table-top stoves for woks etc. The can will only clip in place with the the dip tube UPwards, due to the notch in the ring. This prevents the flat-top stoves from getting a liquid feed. But ... you could try using them with the notch downwards (still on their side). All you needs is an adapter to go from the spray can fitting to your remote-canister stove - but make damn sure your stove has a preheat tube! I have to say, it seems a little more risky as there are no guarantees of correct connection this way. Not for me, thank you.
   
• I have seen another miniature cartridge format, something like a miniature Max cartridge or miniature spray can. It is a Coleman CV 360. I have yet to see the stove, although I believe it is called a Rando 360, and it weighs about 300 g. It may once have been known as the Epigas Micro and may now be known as the Coleman Peak 1 Micro. It may be obsolete, or restricted to France. I have seen the cartridges on sale in France and in Australia: apparently the cartridge is also used by a small flame thrower used for browning the top of merangues and such: a 'bruleur'. Fascinating - but rare.

Interchangeability of cartridges between brands

You may find that the instructions with your gas stove warn you to use only cartridges made by the stove manufacturer. "Horrible things will happen if you use another brand rather than giving us your money." Phooey. They all have to meet official safety standards (mainly EN417 in Europe and DOT regulations in America), and all good screw thread cartridges are interchangeable. For that matter, I understand that all the cartridges are made by just a few 'third party' companies who have the necessary gear. For instance, Dae Ryuk Can Co in Korea makes cartridges for Kovea, MSR and many others. All these good canisters seem to use the Lindal valve made by the Lindal company. More details are given below. I have to confess some admiration for the Kovea cartridges which bear a label saying "This cartridge is compatible with any good quality and approved threaded appliance". That's honesty. The Kovea cartridges contain an excellent cold-weather mix and appear to be cheaper than the others (in Australia).

However, do make sure the gas stove itself carries an approval swing tag from the Australian Gas Association (or your local equivalent). According to Sean Hill all cartridges sold in Australia have to meet the requirements of Australian Standard 2030, which I think just refers across to the European Standard EN417. Some Asian or Chinese ones found in Australia around 2000 did not have the tags, did not seal properly, and sometimes jammed on the thread too. I gather they are still around in Asia. I assume they were using a clone of the Lindal valve. Hazardous stuff: check what you buy carefully. Better to buy a slightly dearer known brand than risk a fireball.

The one multi-format stove the author knows of is the MSR SuperFly. This has a cunning socket and clip on its base which can mate with both the screw-thread and the French CampingGaz or KwikClic connection. There is a technical reason for this: the connections are physically extremely similar in almost all aspects. Put an O-ring seal in the right place and away you go. I would add that when I tested a pre-production SuperFly stove I did have some reservations about the strength of the design, but I gather the production versions were stronger. However, I don't think it stayed on the market for very long.

It is in fact possible to make an adapter to allow a screw-thread stove to go on a CampingGaz cartridge, but it is tricky getting the O-ring seals just right and it would require expensive official testing to get formal Approval from the Gas Authorities. I made one for myself, and it has worked very well. I had to cut up a CampingGaz cartridge to get the profile of the nipple, and it took two goes before I was happy. But it worked just fine across the Pyrenees twice. I have since discovered that commercial ones do exist, as shown to the left. That one is an "Adapter für Ventilkartuschen", model 92497 and may be found at the Vaude web site, albeit with some difficulty. Searching on the part number seems the best way. It is also available from some distributors. An identical unit was apparently found on the Markill website, but I don't have the URL. It may be the same thing as the Vaude one.

Sources for the Markhill adapter include the following. I think they all allow ordering via the web.
Au Vieux Campeur in France
Action Outdoors in the UK (thanks to Ed Geary)
Backpacking Light company in the UK (thanks to Ed Geary)

You can also get adapters to convert the old puncture cartridge to take screw-thread stoves, and to adapt spray-can butane cartridges to lie on their side for screw-thread stoves (Sitro Group). I don't trust the puncture cartridges, after a few experiences, and the pressure pack adapter is rather heavy. Frankly, I reckon it is best to get the right things at the start.

Finally, it is possible to make an adapter to put a screw-thread on a PowerMax cartridge so you can use those lovely Powermax cartridges to drive a different remote-cartridge gas stove - one with a preheat tube of course. However, such an adapter could create a real fireball with an upright stove, and no-one is silly enough to sell such a thing. (I made one, but no details.) Sadly, these Powermax cartridges are no longer available from many places around the world. They have almost disappeared from Europe and the UK, and not many shops in Australia still carry them. But Coleman Australia do still import them from America, and shops can still get them in for you as indicated above.

There is one place where interchangeability can be slightly hazardous, and that is with cartridges containing straight isobutane. This gas is in principle a valid alternative to the standard butane/propane mix. I have seen it in two different cartridge formats: an MSR one of straight isobutane which looks like a spray can, while another was standard screw-thread cartridge. Both of these cartridges had the standard Lindal valve screw thread fitting. The advantage of isobutane is that it boils at -12C which means it can be very useful in the snow. However, it seems to present some fuel/air mixture problems with some (not all!) stoves. The technical details of the hazard and how to cope with them are given at Isobutane, while comparisons of how the different gases work are given in the Mixtures page.

Standards: EN 417, EN521 and Lindal valves

I have attempted to find the technical details for the valve and the screw thread used on these stoves and cartridges. My understanding is that the much-quoted European Standard EN 417 Type 200:1996 is effectively the governing standard world-wide for the safety requirements for pressurised cartridges, but I don't believe that the standard actually specifies the thread (despite what many catalogues seem to imply). Zen Seeker reported that

The CEN (Conseil Européen pour la Normalisation) Standard EN417 Type 200 document refers to:
"Non-refillable metallic gas cartridges for liquefied petroleum gases, with or without a valve, for use with portable appliances - Construction, inspection, testing and marking" ... "which comply with the requirements of EN 521. This standard is applicable to cartridges with a total capacity of between 50 ml and 1 000 ml, ..."

So clearly EN417 is more concerned with the safety of the container than the details of the valve. However, from other sources I believe it does recognise the existence of our little gas cartridges, and makes some special exemptions just for them. Apparently they are too popular to be restricted by the preoccupations of the safety and legal gronks. The European Standard EN 521 issued in 1998 may specify the threaded fitting as it is meant to cover 'Specifications for dedicated liquefied petroleum gas appliances' with an emphasis on portable applications, but I have yet to read the actual Standard. Also, there are several other fittings available for these cartridges, and Standards dislike specifying commercial details.

Anyhow, lots of manufacturers state that their cartridges comply with EN417, but I suspect they have little idea of what they are talking about. I have asked a couple of well-known companies for a copy of the relevant parts of EN417, and they have replied to the effect that they don't have that information. In that case, how can they make that claim? The answer seems to be that while there are lots of different brands of stoves and cartridges out there, not that many of them are actually made by the company whose brand is on them. My understanding is that there are only a few factories in the world making stoves and filling the cartridges, and that those factories supply the brand name companies. For instance, we know the MSR cartridges come from Korea because the label says so, and I have also had confirmation that the Kovea canisters are also made by this company. I have also been told that Primus now has their cartridges made for them by a third party. If you look at the Snow Peak GST stoves, the Vargo Jet-Ti and the Kovea Camp 3, you will see that the brass valve assembly and base are identical, and the mixing column and the burner are nearly identical. All that differs are the pot supports. Kovea do advertise themselves as makers of stoves for other companies. You may find other brands and models using the same Kovea Camp 3 hardware as well. The Jetboil stove of some notoriety is actually made by Primus.

The valves in these cartridges appear to be all made by the Lindal Group of Germany, probably as part number B188. I have opened up (empty) cartridges of many brands, and the valve inside has always looked the same. I suspect the Lindal company is the only source for these valves - I have not been able to find alternatives in the West. There is a possible exception with some Chinese cartridges. There does not seem to be as much respect for international copyright and patent laws in China. But some Chinese cartridges have been found which don't mate properly with the stoves either, and have been shown to leak sometimes. You are warned!

A sample unused valve assembly (from Lindal) is shown to above upside down, and the cross-section is shown to the right. It is effectively the same thing you find on a pressure pack can of paint or fly spray - some of which are (or used to be) pressurised by butane or propane! The basic valve shell A is crimped onto the cartridge body. The outer black butyl rubber ring B (shown brown here) does the sealing there. The stainless steel spring E just visible inside the central blue polyamide cylinder F pushes a small (often red) polyacetal valve plug D against an inner black neoprene rubber valve seat C (shown pink here) under the metal top. This spring-loaded valve is why the cartridge is called 'resealable'. The disk is pushed down by a pin inside the the threaded part of the stove body when the stove is screwed onto the valve, and this lets the gas out. The position of the pin is shown as a solid blue line. Given the absolute millions of spray cans around the world, this valve would seem pretty reliable!

What is the thread on the cartridge?

Anyhow, what is the thread? The Lindal company specification for valve B188 says the thread is '7/16 NS', but this is misleading. The 'NS' refers to an old (American) National Standard thread type which was replaced by the Unified National Standard, now usually known as UNC (coarse) or UNF (fine).

The 7/16 means 7/16", which matches, sort of, with the diameter I have measured on several cartridges of about 0.415". I say 'sort of' because 7/16" is 0.437", which is some 0.022" (0.56 mm) bigger than the measured 0.415" on the cartridges. But then, a close inspection of the thread on various cartridges tells you they are all seriously under-size. This aberration is doubtless due to the thin wall of the metal behind the rolled thread, and does not present a problem in my opinion (or apparently in the opinion of either the manufacturers, who would have some liability concerns, or the Standards Authorities).

Measuring a range of stoves and cartridges I have found that the pitch is 28 tpi, which is finer than the standard 7/16" NS/UNF pitch of 24 tpi. However, there is also a UN Extra Fine (UNEF) series, and the 7/16" UNEF thread has 28 tpi. Taps and dies are available for it, albeit at a high price. I have bought both taps and dies, made various fittings, and can confirm that they work just fine on all the cartridges I have tested. My thanks to Dag Karlsen of Norway for assistance with this.

What is the thread on the jet?

If you disassemble a bushwalking or camping stove you will come to the jet. This is usually removable for cleaning. The 'seat' is usually about a 45 degree taper, and the thread is usually done up moderately tight to make it effectively gas-tight. (Be careful: you would look very silly if you stripped the thread!) I have examined a number of stoves of different brands, both gas and liquid fuel, and in general the thread on the jet seems to be M4.5 x 0.5 , which is a Metric Fine. That is, it has an OD of 4.5 mm and a pitch of 0.5 mm. I have made jets and tested them in some stoves with one of these dies, and it worked. making the hole for the jet is more tricky, as we are talking about a very fine hole. However, both the taps and dies, and the fine drills for the hole, are available.

But be careful before assuming that the stove you have is the same as mine. I found several jets in my collection which have a coarser thread. I am not sure what stove they come off though! And some spare jets which are commercially available have smaller holes than you need: they are meant for gas lanterns rather than stoves.

Origins of the Resealable Cartridge

How did the resealable cartridge come about? I understand it was first produced by the English firm Epigas. My suspicion is that the UK firm saw a market opportunity to upgrade from the old French Bleuet puncture-type cartridges when some bright spark there a) got tired of the Bleuet cartridges and b) realised that the existing Lindal B188 valve was rated for both propane and butane because they are sometimes used as a propellant. That's my guess: I have no other information. Of course, they then had to decide what shape to make the new cartridge - or should they just use an existing cartridge? Again, I suspect they decided they needed a lower, more squat shape for stability, similar to that of the Bleuet cartridge, and someone obliged.

Why did the French subsequently come up with a different connector on their CampingGaz cartridge - which was otherwise virtually identical to the standard screw-thread one? A silly question: would the French accept anything British? The French CampingGaz fitting is of course very similar on the outside, and identical on the inside, and it may simply be a custom variant. That would explain why no-one else makes cartridges for the CampingGaz stoves: they can't get the valve. That, or there isn't the international market demand for the French design. It figures. (But note the irony here: American Coleman now own both the original English Epigas company and the French CampingGaz company.)

Where did the beautiful Coleman PowerMax cartridge come from? Well, have a look at hair spray cans next time you are in a large supermarket or department store (or beauty shop). Or at the green Atsko Water Guard spray can shown here, next to a Powermax cartridge. Yep: they look pretty much the same, except for the groove around the Water Guard can - that's designed to hold the plastic lid on. In times past cartridges of this shape often used butane or propane as the propellant. By the time Coleman decided to use this format, the safety testing had all been done already. Case solved.

The Coleman PowerMax fitting is similar to the standard resealable connection, but without the thread, and it may be a variant of the model 'RT' valve found on the Lindal web site above. It looks very much like the French fitting. I did measure both the PowerMax and CampingGaz fittings and found the Powermax is slightly different (larger) in size, so you can't interchange cartridges there. But this incompatibility may be very sensible for both Coleman and the user, as the Xtreme stoves are specially designed for the liquid feed from the Powermax cartridges. You can't get this liquid feed from either the screw-thread or the the French cartridges while they are upright. Putting a liquid feed into any 'upright cartridge' stoves would result in a fireball as the liquid gas came out the burner.

Gauging the Contents of a Gas Cartridge

One of the more common criticisms of the whole gas concept is that it can be hard to tell how much fuel you have in a cartridge. People crap on about 'what to do with half-empty cartridges'. This criticism is most often heard from the advocates of petrol and kero. It is true that you can measure exactly how much petrol or kero you have put in the tank, although in practice I suspect most people just fill the tank up. This adds extra weight of course. But it is really true that you can have no idea how much gas you are carrying? Of course not.

The method I normally use is to weigh the cartridge at home on a small cheap digital scale. I know how much gas there should be in a new cartridge - typically about 220 - 230 g in the most common size. It is written on the side of the cartridge as 'Net Wt' or equivalent. The cartridge might weigh 350 g when new, so the empty cartridge should then weigh (350 - 220) = 130 g. Now I can work out how much gas is left in a cartridge after a trip just by reweighing it. I have recorded the weights of many empty cartridges over the years: the light Primus ones were about 115 g, many more common ones weigh 130 - 135 g, and a few are up around 150 g. It all depends on the metal used for the tank. But if you start off by recording the new weight each time with a felt-nib pen on the cartridge itself, you will quickly get to know what's going on. You can see my numbers on the Powermax cartridge in the picture above.

However, I recently found another method for doing this, in the "Gear Talk Archive" for Sep/Oct 2000 on an American web site, from someone who signed himself as 'Barn'. He suggested you should float both an empty canister and a full canister in water and mark the water lines. Transfer the full and empty lines to the canister you take to the field. As the canister empties you can measure the remaining fuel level by floating it in water and noting where the water line is relative to the full line and empty lines.
Obviously you should be using the same canister for all these measurements. They won't let you fine tune your predictions along the lines of so many grams per day, but the method works in the field.

Refilling Gas Cartridges

Let me make it very clear right at the start that I am not advocating that anyone should do this. You can't do this to the puncture cartridges, obviously, and the resealable cartridges are designed for 'single use'. However, since other tourist-type LPG gas bottles can be refilled, the purely academic question of whether one could refill one of the resealable cartridges does come to mind. Zen Seeker has drawn my attention to a Japanese company which actually does market adapters designed for doing this. In essence, they are similar to the adapters available for other gas containers. I would add that the web site is in Japanese, and the Babblefish translations Zen suggested are a sight to behold. Machine translation of the Japanese language is not at a high state of evolution right now!

What are the issues with refilling? The following comments came out of a discussion with Zen on refilling and whether one could use a large LPG bottle (mainly propane) for the refills.

• Engineering Strength Issues
• The pressure inside a container of straight propane is going to be much higher than for the typical 70% butane / 30% propane mix as the propane is so much further above its boiling point. This means that if you refill with straight propane the cartridge will be under a significantly higher pressure. I don't know what the actual figures are right now. Refilling with the stock butane/propane mix would not alter the internal pressure.
• Any object such as a cartridge is going to be designed to handle the pressures involved with the designated gas mix. There is more on this in the Technical pages under safety. But the cartridge is also going to be designed to have a safety factor, to allow for consumer misuse and abuse. This should give you some room for safety - but you have no way of knowing when you have reduced the safety factor to one.
• It is possible that that cartridges made for walkers might might have a lower safety factor compared to cartridges made for home/workshop/car-camping. The latter would certainly get banged around a lot more. Walkers, I imagine, treat their gas cartridges with great care. But this is a guess - I don't know, and would the legal gronks even contemplate it?
• I note that the older Primus cartridges are lighter than say the common Coleman ones, although their latest ones seem to be from a new manufacturer, and to be heavier. Sigh. The lighter weight was because the body of the Primus cartridge was made from aluminium, while only the base was steel. The Coleman PowerMax cartridges are made from a very light gauge aluminium alloy as well. I imagine the aluminium might be as strong as the steel in tension but perhaps less robust against bangs etc from outside. Here we do seem to have a significant difference in design approach from the workshop/caravan steel LPG bottle.
• Just where do these cartridges come from anyhow, and who designed them? I don't know, but the safety standards EN417 and EN521 mentioned above obviously played a part in their design, somewhere in history. But not all cartridges were custom-designed for our bushwalking stoves. I have a 'spray can' of MSR isobutane - it looks like a quite ordinary spray can, made of much thinner steel than the cartridges. If you buy a modern sleek anodized can of hair spray or of Water Guard you will end up with something pretty well identical to the Coleman Powermax cartridges. So how much 'design' and how much 'expediency' has gone into all this is anyone's guess. But it would seem that the spray cans and hair sprays are much lighter than the screw-thread cartridges.
• Summary for engineering strength - but purely my guesses of course. I imagine the butane/propane cartridges might survive being filled with pure propane for some time, all other things being equal, and with good care, but I don't know what sort of safety margin they would then have. I might be game to try refilling a cartridge with a commercial isobutane/propane mix if I really had to, but I would not try doing it with straight propane. Would I bother anyhow? Probably not, unless for some reason I needed some of the very small 100 g cartridges for a special trip.
• Mechanical Reliability Issues
• The thread on the screw-thread type of cartridge is not fully formed. This means it is not as strong as one might hope. It will last for one filling of course, and probably for several fillings, but in principle one would have to be careful not to cross the threads and also to look for wear. On the other hand, the Lindal valve thread is steel, while most stoves I've seen have brass threads. It is unlikely that the stove will damage the canister.
• Steel is stronger than brass, so surely the brass thread on the stove will wear out first? Especiually as the steel thread only grips on the tip of the brass thread. The answer is yes: I have actually worn out the thread on a stove so that it would no longer stay attached to the thread on the canister. That could have been a real disaster for our dinners as the system is so designed that the gas won't come out unless the stove is screwed down firmly. There is a pin inside the stove connector which has to depress the valve in the canister: it was no longer able to do so. This is a fail-safe design. Fortunately I was able to buy another stove the next day.
• The CampingGaz and PowerMax cartridges do not have threads. Does this mean they might have a longer life? An interesting thought. Did the French look at the original Epigas connection and decide it would be unreliable in the long run, and so came up with something stronger? I have a feeling they may have ben right - but they don't have the market.
• The Lindal valve construction looks pretty good, but is specified for one filling only. I imagine it too has a safety factor, but it doesn't have infinite life. On the other hand, how many spray cans fail at the valve in real life?
• The safety of the whole thing depends on the O-ring seal between the stove and the surface of the Lindal valve. I have noticed that these Lindal valves, while apparently 'tin-plated', do develop corrosion after a while. Too much of this and you may well find the O-ring no longer seals perfectly. The hazard is obvious, and increases with time. This risk is serious: the canister has been designed for a finite life (unlike the solid brass LPG fittings).
• All the above being said, I have used a single Lindal valve unit in my home-made adapter (CampingGaz cartridge to SnowPeak stove) for several years and over 6 and 8 week trips in Europe. That's just the Lindal valve assembly, not the whole cartridge. I did make sure the surface of the valve assembly was occasionally wiped with silicone grease, which seemed to have stopped most corrosion. And the thread on the adapter has survived most excellently. A pity that the thread on the stove died while we were in France for 3 months.
• Chemistry differences
• Propane burns with a different flame velocity and oxygen mix compared to butane (and isobutane). I have already noticed that the straight Isobutane gas is not always reliable on some stoves. The isobutane flame can 'lift off' from some small burners, which could lead to one hell of a safety hazard. I was able to control this by throttling the air supply down when using the straight isobutane, thereby reducing the overall gas flow rate out of the burner head. Given that the pressure from straight propane would be higher again, I suspect the air-hole sizes on the stoves would not be suitable, and that all sorts of flame problems would arise. When we changed the (Australian) domestic gas supply from coal gas to LPG all the burners in every household stove had to be changed; I suspect the same problems would arise here. So trying to substitute straight propane could be a serious safety hazard, especially in warm weather, and I would be extremely careful, even doubtful.
• In going from petrol to kero to gas, one has to change the size of the jet. Should a stove burning straight propane use yet another smaller size of jet? I do not know, but I believe it should be so.
• One must never fill a gas cartridge completely full! There must always be some room for gas at the top. At the very least, if the cartridge was really full on a cold day, then you stuck it in the sun, the expansion of the liquid could easily burst the cartridge. How to gauge this? I would suggest weighing the cartridge several times during the refill process would be the best way. You would of course need to know what a brand new cartridge of that type should weigh. (Yes, different brands, different weights.)

Conclusions

I might try 'topping up' a small (100 g or 220 g) cartridge with standard butane/propane mix from a large (450 g) one. This could be useful to add a bit to a half-full cartridge so I could be sure it had enough for a trip. I might do this a couple of times before throwing the cartridge out. Myself, I would not try using straight propane at all: there seem to be too many risks. But I am not going to make any recommendations here apart from 'be damn careful'. What you do is YOUR responsibility!

Efficiency of Gas - dollars and grams

The full details of this are given on the Fuel Efficiency page. We summarise here. Contrary to some widespread stories, gas is as efficient or slightly more efficient in energy per weight than any of the other fuels. A gas stove can boil water as fast as any other stove around. The reason is that both the heat and the weight of the fuel come mainly from the carbon atoms in the fuel - no matter what form they come in. Gas has the disadvantage that it comes in a special metal container which cannot easily be refilled (without one of the above adapters) and which has to be paid for, but it has the advantage that it is very safe and easy to use. Some stoves even have a piezo-ignitor: turn, click and cook! Such couth luxury! With a gas stove you might have the kettle boiling before a liquid fuel stove is burning properly. To be sure, the fuel costs a little extra, but when you factor in the low cost of the stove itself (say $40-$50 vs $150-200 for a petrol or kero stove), you find that gas is very attractive for a long time. For example, let's look at the costs for a total of 30 nights over a year or two for the average walker. The figures are based on the author's experience with fuel consumption.

After that, who is counting the cost of the fuel - compared with the cost of everything else? How much did the fuel for your car for all the trips cost for instance?

The second common criticism of gas is the weight of the cartridge. However, once again the actual figures give a different story. Let's look at a trip lasting 4 nights but take enough fuel for an extra night just in case. A single full gas cartridge of 220 g is far more than the 150 g I would need for 5 nights, and a single MSR fuel bottle would be quite enough.

That's assuming a Coleman Peak Apex II stove for petrol and a cheap K-mart stove for gas. Seems to be a different story, doesn't it? It gets even better when you use a light 75 g stove. One wonders if the fact that the liquid fuel stoves are so much more expensive compared with the gas stoves (higher profit margin in the shops) has any bearing on the way the stories get pushed around?