07 November 2008

Micro Gas Stoves

Micro Gas Stoves

Micro Gas Stoves image

When it comes to pure lightweight cooking nothing beats ultra light cartridge stoves - making them the only real choice for fast ascents and lightweight trips into the mountains. With a featherweight cooking set up, using the lightest pan, stove and 100g gas cartridge, the whole lot can weigh less than many stove units alone.

Modern cartridge stoves are so simple to use, just turn the knob, press the ignition button and you’re away, with the fuel turning to gas at atmospheric pressure without the need of priming. This convenience is a real boon when tired or when cooking in cramped places where you know you shouldn’t use a stove, yet are forced to by circumstance (in a bothy bag for example), where a flame-throwing stove could spoil more than just your supper. Cartridge stoves are also simpler than liquid fuel stoves, often being nothing more than a simple valve with a flame spreader attached to the top. It is for this reason that cartridge stoves are so much lighter than their liquid gas counterparts, as they are simply a mechanism for allowing the factory compressed butane/propane gasses to be released from the cartridge. Liquid stoves on the other hand are heavier because they must contain, pressurize and release the fuel from its raw state and its fuel storage systems (fuel bottles) are designed for reuse - unlike a gas canister - and so are more heavily constructed. Most small cartridge stoves are also only designed for minimal cooking, not banquets, so again the designer can save the extra grams needed by a workhorse stove.

Most super light gas stoves are roarer burners, producing a roaring flame like a welding torch. This flame hits a flame spreader that deflects the flame so you don’t just end up with a red hot spot in your pan or even have it melt a hole straight through it. Often the cooking performance of the stove is entirely dependent on the quality and design of this flame spreader, with bad designs best saved just for boiling water and good designs able to be used for the odd Alpine fondue (if you don’t own a Trangia). One downside with the simplicity of cartridge stoves is that although they’re simple, when they break they stay broken, with any fault beyond a simple blockage impossible to repair. For this reason if buying a gas stove for red-blooded days out then make sure it’s a good quality design that won’t let you down.

AVOIDING A GAS DISASTER

The pros and cons of a cartridge stove are generally down to the cartridge itself. It is the cartridge that gives the designer the ability to make a stove as light as a screwgate karabiner and it is the cartridge that gives it its instant ignition. Unfortunately, as in everything, there is a price to be paid for this convenience, in that the stove is totally dependent on its cartridges. If travelling beyond the reach of outdoor shops they can be hard to find and this can be a problem in itself. They are also more expensive per minute to run than liquid gas and the cartridge must be carried and disposed of once empty. Damaged or tampered-with canisters and the gas within them is also quite common, especially in the developing world, resulting in unwanted dramas in high camps. I can remember once building Joe Simpson (name dropper), a modified Markill Stormy hanging stove for a trip to Pumori. While on the mountain he had huge problems with the stove, the diagnosis being that the gas they’d bought in Nepal had been refilled with gas AND water. The gas would burn off first as it was lighter than water and, once burnt off, you’d be left with what you thought was a half full canister. On his return I did make what I thought to be a very funny joke, remarking that although this had ruined his trip at least he could now write a book called Stormys of Silence. I don’t remember him laughing.

The most common cause of damage to the cartridge is to the valve where the threaded nipple is either compressed or dented. Even slight damage can stop the stove from connecting properly to the cartridge, which often gives the user the false impression that the stove is broken, as the cartridge is obviously full. This kind of damage can take place while the canister is stowed away in your ‘sack or even before it was bought. So it’s well worth checking your cartridges when you buy them and then packing them carefully so they won’t be damaged from outside knocks (it’s a good idea anyway as you don’t want a punctured gas canister in your ‘sack… especially if you’re smoking at the time).

If your canister has a damaged nipple here are two possible ways of solving the problem.

* If the nipple is compressed, screw on the stove as tight as you possibly can. This should pull the nipple out far enough for the stove’s piercing pin to penetrate far enough into the canister’s valve.

* If this doesn’t work then do the same but have the stove turned as you do so. Be careful as this will result in gas pouring out once it engages the cartridge.

Another problem is that although all cartridges should conform to a CE norm, there can be minor differences even from the same brand (due to the fact they are made in hundreds of thousands and in several factories), sometimes resulting in one cartridge that’ll work and another that won’t.

Both of these problems can affect the high tech stoves more than their more basic cousins, as the better stoves are made to much finer tolerances, even though this isn’t sometimes matched by their fuel source. This has been a common problem with the MSR Pocket Rocket on 120g cartridges and the Snow Peak GigaPower on some non Snow Peak cartridges. My advice is that you should screw on and test all your cartridges before a big route and if in doubt always take a spare. It is also a good idea to carry several smaller cartridges rather than one big huge one (2 x 250g cartridges instead of a single 450g for example), so if you do get a dud you have another option.

WINDSHIELD WARNING

Many manufacturers of tower type burners (where the stove is screwed directly on to the cartridge) recommend that you don’t use a windshield. The reason for this is that the heat build up can be so high there is a good chance you could cause the cartridge to explode.

I can remember once telling a guy from MSR how I’d used copper pipe to heat my gas cartridges in the Alps and how the cartridge had got so hot its O-ring had melted. The guy just looked at me and said “Dude (he didn’t actually say dude), you’re not even supposed to leave a gas canister in a hot car.”

Any user knows that without a windshield you’re just wasting fuel, as a windshield can knock a minute off a stove’s boil time. Nevertheless the warning is warranted in this case. The best thing to do is arrange the windshield into a U shape, allowing excess heat out, but keeping the wind off. If the wind is blowing from several different directions enclose the stove but make sure you keep a good gap around the edge’s pan (one inch), or better still modify your windshield by cutting one-inch serrations along the bottom. If you don’t own a windshield then the MSR windshield (available as a spare for around £10) is well worth buying.

MAKING THE MOST OF YOUR FUEL

For mild weather cooking a standard mid-sized 250g cartridge should last two people between four to five days. For winter use where snow has to be melted you’ll use double that. Fuel efficiency is primarily down to maximizing heat output (using a windshield and not overloading the stove’s heat output) and the type of cooking it’s expected to do. Food that requires no simmering or lengthy cook times will extend the life of your fuel greatly. Food like Supernoodles, couscous and Smash are staples of the gas frugal cook. Try and mark on the pan how much water is needed for different foods so you don’t end up heating one litre of water when half the amount would have been sufficient. When using micro burners it’s a good idea to keep your pans small so the flame heats the whole cooking surface. If it’s cold, once the Propane has burnt off you’ll see a drop-off in performance. If you are unable to warm the canister it’s best not to overload the stove by trying to heat lots of water, as the water may cool faster than you can heat it. This scenario sees you sitting for half an hour for two litres of water to boil when you would be better cooking four half litre pans of water instead.

A good way to extend your fuel is to have cold or just warm drinks (not boiled), like fruity power drinks, as you don’t gain much from a hot drink apart from a morale boost and having spare gas is a bigger morale boost on a climb than heating water only to let it cool again before drinking.

COLD WEATHER PERFORMANCE

For long winter trips where you’d be forced to cook many meals below zero I would personally use a liquid fuel stove running on white gas. This is because white gas isn’t as affected by the cold and these stoves are more efficient at melting lots of snow, plus performance remains constant. Nevertheless if you’re doing a short winter trip, or a winter climb with two or three bivvies most people will opt for a cartridge stove.

At sea level Butane vaporizes at a temperature above -1°C. This decreases with altitude gain (as air pressure is reduced) so it’ll vaporize at -11°C at 1,000ft (3,050m) and -19°C at 20,000ft (7,000m). This might not sound too bad, but this temperature is not only dictated by the ambient temperature, but more importantly the temperature within the cartridge itself. As the liquid fuel vaporizes it expands 270 times its volume, causing cooling (like in a fridge). You can see this when ice builds up on a cartridge even in mild weather. This means that unless you’re high on K2 Butane is a poor mountaineering fuel for general use.

Propane on the other hand vaporizes at -42°C at sea level and is obviously an awesome cold performer. Unfortunately Propane must be stored under much higher pressures, making it impossible to manufacture easily portable, lightweight, pure Propane canisters.

A way around this is to blend the two fuels (80/20 or 70/30 butane/propane) to increase cold weather performance while maintaining a portable cartridge. When the cartridge is full this works great for cold conditions, unfortunately the more volatile Propane burns off faster (even if you shake it up). Add to this the fact that performance drops by 50% as the pressure drops and you see why cartridge stoves seem amazing when first fired up on a fresh cartridge (in the shop), but seem less effective on their 10th brew on the Walker Spur.

MSR Iso Butane is another blend that has been introduced, which increases the amount of Propane to its maximum level in order to increase the stove’s mountaineering performance.

If cooking in an enclosed space like a tent porch in winter this isn’t a great problem as the ambient temperature soon rises and all you need to do is insulate the cartridge from the ground. Due to the unstable nature of tower cookers you need to be careful if propping the stove on top of something, but a small square of wood or, better still, something like Primus’s folding support (30g/£4) is a good option.

If you are camping or bivvying keep the next morning’s canister in your sleeping bag so it’s warm for the first brew and swapping between two canisters (putting one in your jacket) can also reduce the effect of cooling. Some people mistakenly think that insulating the canister with foam will improve its performance but this only increases the rate at which it cools as no ambient heat can warm it (even if it is super cold outside it’ll be colder in the canister).

If forced to cook outside on an open bivvy then you need to stop the cartridge freezing. As mentioned above a windshield can help warm the cartridge, or you can pop the cartridge into the water every now and again as you’re cooking. Another option is to place the canister in the pan lid and let it stand in half an inch of cold water, topping it up as you heat the water in the pan above (you’ll need a second lid which can just be made of tin foil). Many climbers in the past played around with copper tubing that ran through the flame and back down to the canister, but this has largely fallen from favour, with climbers preferring to use the above methods or just use white gas stoves if it’s that bad. Hand warmers can also be used very effectively, but this is either an expensive option with disposables and heavy with reusable models.

I’m sure it goes without saying that all the techniques mentioned above can be extremely dangerous if common sense and judgment aren’t used when mixing highly volatile gases with heat.

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