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Gas Cannister Formats and types

The information below is transcribed with full acknowledgement, and with thanks, to Roger Caffin's Australian Bushwalking FAQ at; http://bushwalkingnsw.org.au/clubsites/FAQ/FAQ_GasStoves.htm#Canister

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.

 In Australia all stoves and canisters are subject to the Australian Gas Authority (AGA) for licensing.

•  The (French) Gaz Bleuet puncture-type C206 canister 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 canister cannot be removed from the burner, which is a real disadvantage. Well, actually, it can be removed from the stove while there is still gas in the can, but the result can be a fireball or an explosion as the remaining gas escapes. No, there is no way of stopping the gas from coming out. 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 hazard is so bad that the French authorities are getting a bit unhappy that this design is still for sale, even in France.  

• The screw-thread or ""Epigas"" canister was pioneered by the UK firm Epigas (well, actually, their precessor), and is now probably the most common type around most of the world. Epigas themselves were subsequently bought out by Coleman of America. The canister 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. 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 canisters. The thread is explained below as well. Canisters and burners are sold by Epigas, Primus, Coleman, MSR, Snow Peak, Kovea, Caribee, Trekka and a whole range of others 9including the Chinese, who make a lot of the stoves as an OEM factory). The 220 g canister, at 30 g/day, lasts us about 7 days reliably in summer. The taller 450 g canister lasted us about 2 weeks in poor weather in the Pyrenees (measured over three trips of 6, 8 and 12 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 canisters at some hardware stores, at exaggerated prices, and I believe such canisters 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 canisters. These are mentioned again below (3 points down, under 'Gasmate'). Other brands exist I believe, such as Markill. 
   
• The Easy-Clic CV series of CampingGaz canisters look almost identical to the screw-thread ones but they have no thread. They fit pretty much 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 canisters have reasonable availability in Australia, but they are most widely available in France. Why did the French have to be different? (Well, truth be told, i think the Easy-Clic connection is more reliable than the screw-thread one. I have had the thread on the stove strip off after much use: this wouldn't happen with the French system.) Unfortunately the Easy-Clic Campingaz stoves have a relatively clumsy mechanical design and are rather heavy. 
   
• The Coleman liquid gas PowerMax canisters (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 canisters 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. 
    
   
  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 canisters 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 canister clips inside the stove body. The canisters 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'. (Actually, it just liquifies and won't boil off vapour below -0.5 C. The actual freezing point is at -138 C: a bit colder. My thanks to Bernhard Kuemel for pointing out my misues of 'freezes' here.) 
    
    
  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 rigid dip tube pointed 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 need 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. 
   

 

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. 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.

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. Sources for the adapter include the following.

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 (Sitro Group, Victoria, Australia). 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. Thes

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 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 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 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.

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).

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 Jetboil stoves of some notoriety are theoretically made by Primus, although i suspect primus in turn have sub-contracted the actuall manufacture to Kovea - see their Alpine stove..

The valves in these canisters appear to be 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 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. But some Chinese canisters 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 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. 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.

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 in general 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.

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.

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.

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 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-Ring	ID	OD	Thickness
BS006	1/8"" (3.18 mm)	1/4"" (6.35 mm)	0.070"" (1.78 mm)
BS011	5/16"" (7.94 mm)	7/16"" (11.11 mm)	0.070"" (1.78 mm)
BS108	1/4"" (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. 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. 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.)

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 fiedl 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.

• 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 canister will be under a significantly higher pressure, and this may well take the canister coose to its safety limit on a hot day. I think this is far too dangerous to even consider. Refilling with the stock butane/propane mix would not alter the internal pressure.
  • The canisters are designed to handle the pressures involved with the designated gas mix, with a safety margin.  The safety margin is meant 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 by repeated filling.
  • It is possible that that canisters made for walkers might might have a lower safety factor compared to canisters made for home/workshop/car-camping. The latter would certainly get banged around a lot more. Walkers, I imagine, treat their gas canisters 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 canisters 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 canister was made from aluminium, while only the base was steel. The Coleman PowerMax canisters 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. On the other hand the narrower tube on the Powermax does allow for a thinner wall - a physics/engineering factor. Here we do seem to have a significant difference in design approach from the workshop/caravan steel LPG bottle.
  • Just where do these canisters 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 canisters 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 canisters. 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 canisters. 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 canisters - partly becasue they are narrower.
  • Summary for engineering strength - but purely my guesses of course. I imagine the butane/propane canisters might survive being filled with pure propane in cold weather, all other things being equal, and with good care, but I don't know what sort of safety margin they would then have. Not enough in my opinion to try it. I might be game to try refilling a canister with a commercial isobutane/propane mix if I really had to. Would I bother anyhow? Probably not, unless for some reason I needed some of the very small 100 g canisters for a special trip.
• Mechanical Reliability Issues
  • The thread on the screw-thread type of canister 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? Especially 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. The pin inside the stove connector 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 canisters 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 been 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 canister 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 canister. 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 (and/or the jet 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 not do it. Note however that Coleman do sell heavier propane bottles and stoves specially designed to go on those bottles. They are heavy but good for snow use.
  • 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 size of jet? I do not know, but I believe it should be so.
  • 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 on a cold day, then you stuck it in the sun, the expansion of the liquid could easily burst the canister. How to gauge this? I would suggest weighing the canister several times during the refill process would 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.)

Conclusions

I might try 'topping up' a small (100 g or 220 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!