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.

Contents
        (Previous page)
    Stoves Home page 		        (Subsequent pages)
Fuel Efficiencies - technical details
        Gas Stoves (this page) Technical details of stoves and their use
  • Safety - what not to do
    • Carbon Monoxide - Myths and Facts
    • Hydrocarbons - another hazard
    • Isobutane canisters - a caution
  • Relative Costs of Stoves
  • Jet Sizes for different fuels
  • Wind and Radiation shields
  • Smart tricks to improve stove use
  • Maintenance of your stove
    • Dirty and bisbehaving needle valves
  • Fuel Quantities used
  • Stove Operation Times
  • Names and contents of fuels
  • Transporting stoves and fuel on planes
  • FAQs on stoves elsewhere on the web
Butane/Propane mixtures - technical details

Gas Properties - Summary

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

In practice, the 70% n-butane / 30% propane canisters are fine for warm weather with an 'upright' stove, while the 70% isobutane / 30% propane canisters (eg Kovea) are good for cold weather, but not very far below freezing. The 80% butane / 20% propane canisters 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 canisters simply didn't work in the snow. (A technical note here: the butane is still vaporising, but the vapor pressure is less than one atmosphere, so nothing comes out of the canister.) 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 (or maybe it was just a long time ago). 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. Strange hissing noise from just behind me ... This design has been superceded by the resealable canister: these allow you to remove the stove and pack the sealed canister 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 the canisters contain a mix of n-butane and/or iso-butane with 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. 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 (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 and Solutions. 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. You could also read The Effect of Cold on Gas Canisters at Backpacking Light. That does require a subscription though. (Disclosure: I wrote the article.)

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! 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 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 (see below under Smart Tricks), 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.

Safe operation of Upright Gas Stoves

If you want to use your stove in cold weather you need to 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. Their only concern is to prevent a customer from ever thinking of suing the company. The instructions which come with some stoves seem to be more than 50% hazard warnings - which few people ever read anyhow! Mind you, some of the damn fool things I have seen people do with canisters and stoves might make you understand the mindset of the lawyers.

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. What applies in America pretty well sets the standard for the rest of the world. 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!). That is safe. 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 - Upright Canister

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, with the canister sitting upright. In this they are 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 - actually, most 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. Don't try it.

Remote Canister Gas Stoves - Inverted Canister

A variation on the conventional upright gas stove treats the liquefied gas as a liquid fuel - like petrol or kero. (The similarity is extreme, as we explain elsewhere.) The gas canister is inverted 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. Some physics required.

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 ...)(Updated in 2011: it seems Coleman have discontinued the Powermax canister as well. Sigh.)

I think the special Powermax canisters once contained an excellent 60% butane / 40% propane mix, although the amount of propane seems to be less today. It is not actually specified. 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. There is a picture of the insides of a Powermax canister showing the pickup tube below. For availability of the stove and canister (not easy), you will now have to try eBay. 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 rather 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, but check MSR) 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!)(Update 2011: I have seen reports that MSR may actually release a remote canister stove designed to work with an inverted canister. About time! Update 2012: Whisperlite Universal)

Help: I can't get my Powermax to work!

This is a well-known problem, with an easy fix. First, check the tiny O-ring around the central pin on the connector. Is there 1 O-ring or 2? There's a pic here to help. The early models of the Xtreme had 1 O-ring, and many users did complain they could not get a connection between Canister and connector. I chased this up with Coleman who admitted they had heard of the problem but were not able to reproduce it (in the lab).

A key feature of every report was that users had the problem *in the field*, but not back at home (and not in the warmth of a lab). The source of the problem was the tiny O-ring: in the snow it got cold, which made it hard, so it would not compress easily, so you could not (easily) push the canister into the connector far enough to get it to mate. I passed this info on to Coleman, who re-engineered that latest (and last) batch of adapters to take 2 O-rings, stacked. That gives the connection more compressibility, and it is easier to get it working.

So if you have this problem in the cold all you have to do is push harder *before* you turn. Once you have done it a few times you will get to know how much force to use. In the cold it does require a bit of 'male force'. Of course, it does help to warm the connector up a bit first - hold it in your hand just a bit. So play with it in a warm room first, to learn what the connection feels like. Then move into the cold.

Ah - and carry a couple of spare O-rings in your maintenance kit! They are kinda crucial.

Alternatives, of the DIY form

Note added in 2014: also read the next section entitled My Ultra-Light Winter Stove for all canister styles to see just how far I took the MYOG concept!

However, this is not the end of the story. You can turn many other remote canister 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 canisters placed upright. The manufacturer does not go so far as to recommend you tip the canister 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. (I believe this stove was originally designed to be used with an inverted canister; MSR just never marketed it that way. I think their lawyers got nervous.) The Primus Gravity II EF works most excellently in the snow with the canister inverted, and so do many others like it. I gather that Primus does (or did) actually mention this possibility somewhere, although they advise great care while tipping the canister upside down (which is good advice). That stove (or its predecessor the Gravity EF) doesn't work quite so well with Shellite, and works poorly with kero in my opinion. Making genuine multi-fuel stoves is hard. Why bother?

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. However, the smaller and lighter Primus EtaExpress emits an incredible amount of CO in use: an absolute death hazard!
Note added early 2009: the Primus EtaPacklite is a much lighter version of the EtaPower concept, works well, and has a low CO emission. Consider this stove for winter trips.
Note added mid-2009: the Primus Spider Express is the guts of the EtaPacklite, without all the extra weight. Now we are getting pretty good!

You can also stick an upright stove on the Brunton Stove Stand and run the canister inverted. In the photo here my Snow Peak is happily working away. However, a caution is imperative here. The Brunton Stove Stand does not have a preheat tube. There is nothing to stop this arrangement from flaring badly, and dangerously. My original solution was to attach a small brass block over the inlet tube (red arrow) and a strip of copper up from that to the flame (blue line). This acts as a 'heat shunt'. I start the stove with the canister upright, wait maybe 10 seconds while the flame heats the shunt and the heat travels down to the brass block, and then I turn the canister upside down - gently, and at low power. The heat travelling down the shunt will make sure the liquid fuel is vaporised before it gets to the jet. It works fine for me, but no responsibility is accepted if you do this yourself. There is a full article about this at Backpacking Light.

A caution is in order here. When you turn the canister upside down the needle valve will now be throttling liquid fuel, not gas. The liquid fuel will expand into gas at about 250 times the volume. If you are not careful you may find that the stove will suddenly roar a little too fiercely! So before you invert the canister, just turn the stove down to a gentle low. It may pick up a bit even so when you invert. Once the canister is inverted, regulate the stove as normal. You may find the valve slightly more sensitive.

Another word of caution is in order about the use of inverted canisters. The fuel in them may contain some gunge, and this gunge can get on the needle valve. (Normally such gunge sits at the bottom of the canister after all the propane and butane has evaporated off.) If this happens, and it has done so for me, you may need to clean the valve. A photo of a 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 uncertain. I cleaned it off when I got home, but uyou could clean it off with a bit of toilet paper in the field. Just make sure you have the tools (eg spanner) with you to remove the valve, and even do a practice run at home first.

A good question has been just what id that white gunge seen in the photo. Initially I thought it might be the odorant the suppliers have to add to the fuel so you can smell any leaks. However, that stuff is volatile. I now believe it is traces of low-grade paraffin in the fuel. Yes, this can easily happen. Try using summer diesel in mid-winter in the mountains (in a diesel car of course), and you will find the filter blocking up due to the paraffins in the fuel. You have to buy 'winter diesel' if you want to park your car in the snow for any length of time. How do I know this? Experience!

If you want more information about stove maintenance, there is an excellent article covering all aspects of the subject at Backpacking Light. I know the article is excellent, because I wrote it myself ...

Inverting a canister

How do you tip a canister upside down in a stable manner is of course a good question. One method which the author has used is to fit the canister 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 canister, 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.

More recently, on a 6-week trip through Switzerland, I took one of my experimental stoves and ran it off an inverted 230 g canister the whole time. I didn't take any supports for the canister: I just tipped it upside down once the stove was going and leant it up against one of my joggers or whatever was handy. This worked perfectly well. The moral of the story is that you should always consider doing without all the 'extras' they try to sell you.
Theory - how it all works

Why does the liquid feed idea work so well in the cold? There are two reasons. The fuel 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 (virtually) 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 behind the jet 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 + stove. It has a 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 canisters

No-one is ever satisfied with convention, are they? So there are also canisters 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 steel 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 canisters 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. Note however that these stoves are always, by design, quite heavy.

The other use appears to be for use with remote-canister 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! (There is a solution in fact.) 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.

My Ultra-Light Winter Stove for all canister styles


Image courtesy Douglas Frick

Eventually I got tired of the heavy weight of the traditional winter stoves, even the gas ones, and began to wonder whether I could do better myself. I also got tired of the problems we had finding screw-thread canisters when we went walking in the European mountains. Often the only ones we could find were either Bleuet (which I do not trust any more) or French Campingaz, which has a different connector. So, a long project (as in several years) started, to develop my own winter stove, with a number of key requirements. The project was a success, and was initially written up at Backpacking Light. The success including selling a large number of the stoves (heading for 100 in early 2014). A full write-up (extracted from BPL) comes in three parts: the initial concept; years of experimental work; and the successful result.

Canister Formats

The gas canisters 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 usually be swapped around with (almost) no problem. This is despite bleatings by some manufacturers that you must 'only use our canister on our stoves'. It is interesting to note that the Kovea screw-thread canisters actually have a notice on the side saying 'This cartridge is compatible with any good quality and approved threaded appliance'. Kovea make both stoves and canisters 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 canister onto a stove not designed for it. This is discussed under Isobutane. In Australia all stoves and canisters are subject to the Australian Gas Authority (AGA) for licensing.

 

Interchangeability of canisters between brands

You may find that the instructions with your gas stove warn you to use only canisters 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 canisters are interchangeable. For that matter, I understand that all the canisters are made by just a few 'third party' companies who have the necessary gear. For instance, Dae Ryuk Can Co in Korea makes canisters 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 canisters which bear a label saying "This canister is compatible with any good quality and approved threaded appliance". That's honesty. The Kovea canisters 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 canisters sold in Australia have to meet the requirements of Australian Standard 2030, which I think just refers across to the European Standard EN417 in a single page. 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.

Update 2010: I recently bought some canisters at a reduced price from a local (Sydney) shop. The labelling claimed it was suitable for Primus and a couple of other known brands. The percentages of butane, iso-butane and propane were quoted to at least one decimal place, and were 'kinda strange' (something like 24.89% propane). I tried this canister out upright and it worked fine. But inverted it released so much dirt/dust that my stove blocked up within 30 seconds - several times. My suspicion is that the canister was a Chinese clone: unfiltered and dirty gas, ridiculous accuracy claimed for the composition, and very low price. I returned the canisters and got my money back. Caveat Emptor.

Using Screw-thread stoves on Campingaz canisters, and other swaps

It is in fact possible to make an adapter to allow a screw-thread stove to go on a CampingGaz canister, 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 canister 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 can be found at some gear shops in Europe but you need to search. In 2013 I did find them at Edelrid in Europe, and they are now widely available on eBay and Amazon

You can also get adapters to convert the old puncture canister to take screw-thread stoves, and to adapt spray-can butane canisters to lie on their side for screw-thread stoves. Some places stock several sorts. I don't trust the puncture canisters, after a few bad experiences, and they usually only contain butane. The pressure pack adapter is rather heavy. Frankly, I reckon it is best to get the right things at the start if you can. [2014: availability is falling. The puncture design is a known safety hazard (the seal can leak) and thr design is being deprecated.]

Finally, it is possible to make an adapter to put a screw-thread on a PowerMax canister so you can use those lovely Powermax canisters to drive a different remote-canister 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 canisters are no longer available as production has ceased. Those of us with stocks are hoarding them carefully.

There is one place where interchangeability can be slightly hazardous, and that is with canisters containing straight isobutane. This gas is in principle a valid alternative to the standard butane/propane mix. I have seen it in two different canister formats: an MSR one of straight isobutane which looks like a spray can, while another was standard screw-thread canister. Both of these canisters had the standard Lindal valve screw thread fitting. The advantage of isobutane is that it boils at -12 C 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.

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 Easy-Clic 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.

I then spent about 5 years developing a connector which could handle screw-thread, Campingaz and Powermax, plus a winter stove for inverted canister use. This works just fine (like, very safely and reliably) and has been sold to >100 enthusiasts, mainly via BPL. See http://www.backpackinglight.com/cgi-bin/backpackinglight/caffin-evolution-of-winter-stove for more details. I use the stove all the time.

Standards: EN 417, EN521 and Lindal valves

I had to hunt around to find the technical details for the valve and the screw thread used on these stoves and canisters. The often-quoted European Standard EN 417 Type 200:1996 is effectively the governing standard world-wide for the safety requirements for pressurised canisters, 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 canisters 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 canisters with a total capacity of between 50 ml and 1 000 ml, ..."

So 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 canisters, 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 canisters, and Standards dislike specifying commercial details.

Anyhow, lots of manufacturers state that their canisters 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 canisters 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 canisters, and that those factories supply the brand name companies. For instance, we know the MSR canisters come from the Dae Ryuk Can Co 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 canisters 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 early Jetboil stoves of some notoriety were theoretically made by Primus, although I understand Primus in turn have sub-contracted the actual manufacture to Kovea - see their Alpine stove. Later Jetboil stoves were made in China - with hiccups.

The valves in these canisters are all made by the Lindal Group of Germany, probably as part number B188. An unused B188 valve unit from Lindal is shown to the right here, upside down. The blue bit is inside the can. I have opened up (empty) canisters of many brands, and the valve inside has always looked the same. I suspect the Lindal company is the only Western source for these valves - I have not been able to find alternatives in the West. There is a possible exception with some Chinese canisters. There does not seem to be as much respect for international copyright and patent laws in China (no respect at all, actually). But some Chinese canisters have been found which don't mate properly with the stoves either, and have been shown to leak sometimes. You have been warned!

A sample unused valve assembly (from Lindal) is shown 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 canister 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 canister is called 'resealable'. Part F is the blue bit in the previous photo. The disk D is pushed down by a pin located inside 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. In some cases (eg Coleman Powermax) the blue pin is actually a tube and the gas goes up inside it. In most cases there is a hole in the stove body for the gas near the blue pin. Given the millions and millions of spray cans around the world, this valve would seem pretty reliable in sealing (even if the flow does sometimes get blocked up).

What is the thread on the canister?

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 canisters 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 canisters. But then, a close inspection of the thread on various canisters 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 short-term problem in my opinion (or apparently in the opinion of either the manufacturers, who would have some liability concerns, or the Standards Authorities).

However, the inadequate thread-form does present a long-term problem, in that over the years the brass thread on a stove base will wear out as it rubs on the steel canister. This means the stove will no longer seat properly on the Lindal valve. That in turn means the pin won't depress the valve, so no gas will come out. This isn't a safety hazard per se, but it does mean you should check your old stoves for wear on the thread. One of mine died this way after 6 weeks in France - half-way through a three months trip. I had to quickly buy a new stove.

Measuring a range of stoves and canisters I have found that the pitch is 28 tpi, which is finer than the standard 7/16" UNF pitch of 24 tpi. However, there is also a (not very common) UN Extra Fine (UNEF) series, and the 7/16" UNEF thread has 28 tpi. So that's what the thread is: 7/16" UNEF. I was able to buy a tap locally (Goliath brand) but it wasn't all that cheap. I also bought the taps and dies from e-taps in America, even though they do not list the size. (Marvelous what you can do with an NC grinding machine!) I have made various stove fittings and can confirm that they work just fine on all the canisters I have tested. My thanks to Dag Karlsen of Norway for early assistance with this.

If you don't want to actually machine a 7/16" UNEF thread, you may be able to use an existing one. Robert Woodcock wrote:

While looking for 7/16 UNEF nuts/fittings/taps (I'm trying to connect some brass tube to a canister for a hobby steam turbine project), I found that 7/16 UNEF just so happens to be the same thread used for *another* system originally designed to be difficult to find parts for - wireless ethernet RP-TNC connectors. I just took apart a RP-TNC-to-SMA adapter, and once the guts were removed from it, it threaded onto an MSR IsoPro 8oz (227g) canister perfectly.

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 on many stoves the thread on the jet seems to be M4.5 x 0.5 , which is a Metric Fine thread. 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. Once again, I was able to buy the taps and dies at a quite reasonable price from e-taps in America. Note that you need to buy both the Starter and the Bottoming (Finisher) tap, or at least the Finisher tap, to get the right finished size. Curiously, the giant Dormer/Sandvik do not list this size, nor do they list the UNEF sizes.

However, some stoves have a bigger diameter thread or a coarser thread, and there does not seem to be any common standard for these. For instance, recent stoves from Fire-Maple in China use an M6 x 0.75 thread, The large size allows them to put a small sintered brass filter inside the threaded section. This is meant to prevent the jet from getting blocked, which is a good idea until the filter gets blocked. Then you are really in strife! In some cases it may be necessary to drill the metal filter out and replace it with some tissue - and to change that every year or so. At least, that is field-maintainable.

It's easy enough then to make the thread on the outside of a jet. Making the hole in the middle of the jet is more tricky, as we are talking about a very fine hole. Typically the hole will be between 0.25 mm and 0.35 mm, depending on the stove and the fuel. However the fine drills for the hole are available. The Dormer A100 series are good, and they start at 0.20 mm. The Dormer A720 micro-drill series go even finer but seem to be double the price. Mind you, drills this fine are very expensive and break easily. Don't try to use an ordinary drill chuck for them! A precision Swiss lathe helps, or a Lorche lathe, or some real ingenuity with a custom assembly on the lathe saddle. If you get your lathe set up correctly, it is possible to drill the hole in a few seconds per unit.

But be careful before trying to swap jets between stoves. As mentioned above, not all stoves have exactly the same thread. I found several jets in my collection which look similar but have a coarser thread. I am not sure what stove they come off though! So if the jet does not go in easily, don't force it. And some spare jets which are commercially available have smaller holes than you need: they are meant for gas lanterns rather than stoves. The lanterns need a much smaller gas flow. Finally, even quite similar stoves may have slightly different sized jets (eg 0.28 mm vs 0.32 mm), and usually the stove is optimised for just the one size of jet.

What is the O-Ring on the Stove?

Underneath the stove, inside the screw-thread fitting, there is a crucial O-ring. This seals against the top of the threaded spigot or nipple on the canister. If this is missing you risk have gas going everywhere. It can fall out: I have lost one O-ring in the field. Fortunately I always carry spares. You should always check that this O-ring is in place when you take the stove OFF the canister. Later on is too late! If you hear lots of gas escaping (or smell it) while you are putting the stove on a canister, check the O-ring again. A brief hiss as you do up the connection is common, but not a sustained hiss.

I always carry several spares. For most stoves th O-ring is a BS011, and if you buy some you should buy them in Viton rubber, not a cheaper version. However, some of the Primus stoves use a BS108 O-ring instead. This is a bit fatter than the BS011, which is not a bad idea. I suspect you could use a BS108 O-ring in place of a BS011 if desperate, but you might need to screw the stove down much harder to get gas flow. This would make the brass thread on the stove wear out quickly. You should be able to buy these O-rings at good hardware, engineering or auto parts shops. If in doubt about the size, take the stove with you.

The Coleman Powermax canisters do have a Lindal valve, but they have a very different O-ring arrangement, as shown here to the left. Note: there may be one or two O-rings on the central pin/tube. Older versions have one O-ring; newer versions have two. The O-ring is a BS-006. They too can fall off, so carry spares.

The actual sizes of these O-rings are as follows, in case you need to measure them to identify them. Since they are an imperial size (BS = British Standard) the primary dimensions are imperial.

O-RingIDODThickness
BS0061/8" (3.18 mm)1/4" (6.35 mm)0.070" (1.78 mm)
BS0115/16" (7.94 mm)7/16" (11.11 mm)0.070" (1.78 mm)
BS1081/4" (6.35 mm)7/16" (11.11 mm)0.103" (2.62 mm)

Origins of the Resealable canister

How did the resealable canister come about? 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 canisters when some bright spark there a) got tired of the Bleuet canisters and b) realised that the existing Lindal B188 valve was rated for both propane and butane because they are sometimes used as a propellant for paint or hairspray. Of course, they then had to decide what shape to make the new canister - or should they just use an existing canister? Again, I suspect they decided they needed a lower, more squat shape for stability, similar to that of the Bleuet canister, and someone obliged.

Why did the French subsequently come up with a different connector on their CampingGaz canister - which was otherwise virtually identical to the standard screw-thread one? A silly question: would the French accept anything British? The French CampingGaz Lindal valve 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 canisters for the CampingGaz stoves: they can't get the valve. (Actually, not true. You can get them from Lindal.) That, or there isn't the international market demand for the French design. It figures, although I am actually disappointed about this. The CampingGaz fitting is, in my opinion, somewhat better than the Epigas fitting. It does not strip the thread on the inadequate thread form as happens with the Epigas version. But note the irony here: American Coleman now own both the original English Epigas company and the French CampingGaz company.)

Why hasn't Coleman discontinued the French design? Well, try buying a screw-thread canister in France, or adjacent European countries. Just not available. The CampinGaz Easi-Clik canisters are however widely available, along with the matching stoves, even in little shops in little towns on the big routes. Market demand! (Which means that if you are planning a trip to Europe, be prepared to buy a new CampinGaz stove when you get there.)

Where did the beautiful Coleman PowerMax canister 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 canister. 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 canisters 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. Oh, by the way: I think the Powermax canisters are made by Exal Corp of America. They do a lot of those sorts of aluminium containers.

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 canisters 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 canisters. You can't get this liquid feed from either the screw-thread or the the French canisters while they are upright. Putting a liquid feed into any 'upright canister' stoves would result in a fireball as the liquid gas came out the burner.

Gauging the Contents of a Gas canister

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 canister. People crap on about 'what to do with half-empty canisters'. This criticism is most often heard from the advocates of petrol and kero (or alcohol, in America). 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 canister at home on a small cheap digital scale. I know how much gas there should be in a new canister - typically about 220 - 230 g in the most common size. It is written on the side of the canister as 'Net Wt' or equivalent. The canister might weigh 350 g when new, so the empty canister should then weigh (350 - 220) = 130 g. Now I can work out how much gas is left in a canister after a trip just by reweighing it. I have recorded the weights of many empty canisters over the years: the light Primus ones were about 115 g, many more common ones weigh 130 - 135 g, and a few of the cheaper more tourist-variety 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 canister itself, you will quickly get to know what's going on. You can see my numbers on the Powermax canister 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.

In the field on a long trip I know I will use about 30 g of fuel per day for my wife and myself. Since I usually have the starting weight written on the can, I can easy guesstimate how much fuel is left. Shaking the canister serves as a very rough check on this too.

Refilling Gas canisters

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 canisters, obviously, and the resealable canisters are designed and authorised 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 canisters does come to mind. Zen Seeker has drawn my attention to a Japanese company which actually does market adapters designed for doing just 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.

Practical Considerations

One must never fill a gas canister completely full! There must always be some room for gas at the top. At the very least, if the canister was really full of liquid on a cold day, then you stuck it in the sun, the expansion of the liquid could easily burst the canister. And don't forget that even in the snow, a bright sunny day can heat your pack up quite a lot, especially at altitude.

How to gauge this? I suggest weighing the canister several times during the refill process is going to be the best way. You would of course need to know what a brand new canister of that type should weigh. (Yes, different brands, different weights.) Make sure you do not exceed the original purchase weight. The same would apply to 'topping up' a partially-full canister.

Are there any other ways to refill a canister so it is not too full? What you have to do is to keep some vapour space inside the canister. Ideally this should be fuel vapour, but it could be air. Having air inside the canister (well, oxygen, really) could theoretically make an explosive mixture inside the canister, but this is unlikely. For these gases to burn their concentration in air needs to be about 2 - 10%, which is quite low. So you could start with a really empty canister containing air and fill it while it is tilted over at an angle: this would leave some air trapped in the top-most portion of the canister. The trapped air would prevent the cylinder from overfilling.

However, while that method sounds good, there are several problems. What angle of tilt is required to get the right amount of compressed air to match the purchase weight? Working this out could take an awful lot of trial-and-error. How you replace the remaining fuel vapour in an 'empty' canister with air before you start refilling is another interesting problem.

I am left to wonder how it is done at a commercial can-filling plant, and whether they leave air inside the canister as well. If anyone knows, please tell me!

Conclusions

I might try 'topping up' a small (100 g or 230 g) canister with standard butane/propane mix from a large (450 g) one. This could be useful to add a bit to a half-full canister so I could be sure it had enough for a trip. I might do this a couple of times before throwing the canister out. Myself, I would not try using straight propane at all: there are 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 myths, 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. (Which is why alcohol is inefficient: each molecule also carries a heavy oxygen atom.)
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 even 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.

Gas Petrol
Stove $ 50 $150
Fuel $ 50 $ 5
Total $100 $155

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? Get things in perspective, folks.

The second common criticism of gas is the weight of the canister. 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 canister 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.

Gas Petrol
Stove 120gm 300gm
Fuel 220gm 250gm
Container 115gm 200gm
Total 455gm 750gm

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?

 

© Roger Caffin 2002- 2012