Mt Whitney Zone Forums General Discussion Stoves

Ken, absolutely right. The original mixes were butane only. Butane will not vaporize below 31F, and you need to be at least 10 degrees Fahrenheit above that for your stove to have enough power to work right. In other words, you really can't use butane below 40F, and that's the very lowest you can go. And what happens to a canister after you run it for a while? It gets colder than its surroundings. So even if the outside temperature was 40F, your canister would quickly get colder than the surroundings, and your flame would get smaller and smaller and smaller...

Needless to say, 100% butane went over like a lead balloon and gave canister stoves a bad name for many years. Then people started getting smart. They added propane and made a mix. Propane vaporizes down to -44 F. That's right minus 44. Brr. Now, the propane as it would vaporize would drive the stove. Problem of course is that propane burns off faster (it's a bit more complicated than this, but this is a good approximation) rate than the butane, so toward the end of the canister's life, all the propane would be gone, and you'd be back to square one with a stove that barely functioned at 40F (which isn't particularly unusual even in summer as any Sierra hiker knows). Then they got really smart. Certain chemical processes can "bend" (not a precise scientific term here folks, but close enough) the butane molecule into what's called an isomer. The isomer has the same chemical formula (C4H10), but it's different geometry gives it different properties, one property is that the point at which it vaporizes goes from 31F to 11F. Huzzah! We're saved. lol But seriously, that 20 degree Fahrenheit lower vaporization makes a big difference in practical terms out in the field in real world conditions. Even at the very end of the canister, you should still be able to cook even if the temperatures are approaching 20F if you keep the canister warm. If the canister falls below 20F, you're not going to get much more than a flickering candle flame.

Probably WAY too much physics and chemistry for one day, but hopefully a few will find this interesting.

Told you I was a stove nerd,

HJ

Oh, yes indeed. A very favorite stove of mine to this day. Of all the stoves produced in the 1950's only the Svea 123 is still produced today.

Oh dear me. You have made Hikin' Jim the stovie very sad. That is no way to treat a work of art. Just fill the little dimple (depression) around the burner column with white gas or better still alcohol and ignite. That's it. Do not douse. You could ruin the valve.

Hmm. Well, there are good alky stoves and bad ones. And they are slow, but they're very light and there is nothing to go wrong on them. They have their place, but they're not as straightforward as a conventional canister gas stove. Call them an acquired taste.

HJ

A "stovie"! Cool.

I think I will dig out the Sveas and pay them some attention (I truly love them; they are so beautiful)

I always thought that the "douse" method had to bee overkill, as it seemed like we were on teh verge of a 'meltdown'. It was truly amazing how you could finely tune the flame on such a simple contraption. The models that I have (I think they are still in the box after moving...along with the 2 Sierra Cups) were bought in the early 60's and they never failed. Rich bought 2 of them because he was afraid that they would be discontinued (like a favourite pair of shoes.)

I think that the alky stoves really required a certain confidence in their supreme simplicity (one must beelieve in the concept) I think that I was very nervous about the fact that if I spilled some juice, I may not notice if I had a runaway flame...!

The physics and chemistry of the stoves is really interesting reading (uh-oh...letting on my very nerdy background)

Jim, I was bitterly disappointed that you were not present on a stove thread for the first few days. How was this possible? My faith in your stove-radar is restored!

Ditto! I felt sure when I mentioned your name you'd appear instantly like a genii!

I was up in the eastern Sierra. A guy has got to go hiking once in a while!

HJ

Bee,

Be very careful with a stove that hasn't been fired in a long time. The gasket on the tank cap may have hardened in which case it won't hold pressure anymore.

HJ

Apparently there is a titanium o-ring available that is a perfect replacement for the Svea gasket. So common a guy found one at Charlotte Lake last week . . .

Uhh, WAY too late now to "correct', but this thread was better suited to "Stove Heads", e-r-r, "Gear Heads"!

Very interesting, thanks! I assume this is what's referred to as isobutane?

Also, if propane vaporizes down to -44F, why not fill the canister 100% with propane, and forget about the butane completely?

Good question. After all, a common backyard grill or a two-burner Coleman camp stove uses propane and works in shivering conditions. But pick up the empty fuel can and it's heavy. The answer to your question is simple. Propane has a high vapor pressure under normal conditions (that's why it works so well) and therefore requires a very strong and heavy container. The can itself is heavier than you would want to carry in your backpack. Going to the next lower vapor pressure simple hydrocarbon, butane, reduces the strength and weight requirement for the can. The problem there is that, as discussed by Hikin Jim, the vapor pressure of butane gets too low to be useful as the temperature gets cold. The butane isomer, isobutane, has a slightly higher vapor pressure and adding a little propane (20% or so) makes a mixture that is fine-tuned for the vapor pressure/strength-requirements. So we end up with something of a compromise: a fuel that has a vapor pressure that is just high enough to be useful under most backpacking conditions, in a can that is not too heavy to carry.

Sexiest WZ thread ever!

lol.

For those who aren't in on the inside joke, I lost my wedding ring recently on a Sierra backpack. I posted that I had lost the ring on several forums (including this one and Facebook). Someone recently found the ring and remembered my post. He contacted me... and I now have my ring.

HJ

Exactly. The isomer form of butane is isobutane, and any time you're out in weather that's going to be below 50F, then it's worth your while to only get brands with isobutane. "Plain" butane does not work well for canister gas stoves in cold weather.

Ah! The classic question. Well, think about a pot on the stove that's gently boiling. Then you open up the burner on full, the boil goes wild, and the lid practically jumps off the pot. What's happening here? The higher above the boiling point in terms of temperature, the more vigourous the boil, and the greater the vapor pressure. Propane vaporizes at -44F. If one is at, say, +100F, one is some 144 Fahrenheit degrees above the boiling point of propane. The vapor pressure is so high that a thin walled steel canister (such as those used for backpacking) cannot safely contain the pressure. Therefore, in the US, you won't find more than 30% propane/70% butane (or 20% propane/80% isobutane) mixes. They just won't meet safety standards. That's the simplest answer I can give. Physicists and chemists among you will no doubt point out that smaller, lightweight canisters that would contain 100% propane are possible, but such canisters would not be as affordable as the current cheap steel canisters commonly used today. However, if anyone wants to provide me with a titanium canister for me to experiment with, I am all ears.

HJ

Very well put and quite correct. Thank you, Glenn.

HJ

Smart is sexy? lol.

Well, I hope it helps. There is SO much confusion and misinformation out there about stoves.

HJ

Bzzzt! I'm sorry, but thank you for playing:

" Well, think about a pot on the stove that's gently boiling. Then you open up the burner on full, the boil goes wild, and the lid practically jumps off the pot. What's happening here? The higher above the boiling point in terms of temperature, the more vigourous the boil, and the greater the vapor pressure."

Nope: turning up the temperature on the burner does NOT raise the temperature in the pot that is already boiling. It increases the heat input, and therefore the rate of vaporization but without closing the vessel and increasing the ambient pressure, it certainly does NOT increase the temperature of the boiling water. That is already determined by atmospheric pressure plus the weight of the lid and can't be increased by just adding heat.

Try that piece of it again, maybe with a pressure cooker instead of a loose lid.

Sheesh, Salty, cut a guy some slack. lol.

Yes, liquid water will not go above it's boiling point for a given atmospheric pressure. However, in terms of liquified gas in a canister, this statement is correct:
The higher above the boiling point in terms of temperature, the more vigorous the boil, and the greater the vapor pressure.

HJ

Mmmmmmmm . . . nope, not buying. The boiling point is a function of pressure, so as the pressure in the vessel goes up so does the boiling point. Boiling point is by definition the point at which vapor pressure equals atmospheric pressure. By definition "the higher above the boiling point in terms of temperature" with respect to a liquid in a canister, is a contradiction in terms. Until the canister fails, of course. It should read "the higher the temperature, the greater the vapor pressure". Has nothing to do with the vigor of the boil. That's a function of heat rate, not temperature of the fluid.

;-)