Upright Canister Stove Thermal Feedback into the Canister

Discussion in 'Stove Forum' started by Reflector, Sep 22, 2020.

  1. Reflector

    Dec 26, 2013
    Denatured Alcohol Pointless Ban Land (California)
    elI've noticed a few times that I have some canister stoves that get particularly warm if not hot on the valve body that screws onto the canister. At the same time I run all my stoves on straight butane (the $0.75-1.25 a long can kind) and on refilled canisters as the butane runs low, the chilling causes the canister to lose pressure making the output a lot less on all my unregulated (of which, I own 4) stoves.

    So putting two and two together, I had experimented a little with a Snow Peak Gigapower 2.0 since it gets ridiculously hot with the windscreen set on it. I had inverted the stove with the valve off briefly on a less than half full can and left it like so for a minute and found that output recovered quickly, even if the can chilled. I hadn't continued experimenting with that until just recently.

    I found out that the Snow Peak Gigapower 2.0 gets to around 125-135F on the valve body (IR thermometer, might be off) and that the LiteMax gets even hotter at 135-140F. Hot enough that if I touch the valve body briefly after shutting the stove it'll be of the burning kind of a sensation where a reflexive withdrawal from a far too hot surface. Not good for putting the stove away quickly after use given I can't unscrew it for several minutes.

    However on inverting the canisters and listening closely I could hear a sort of bubbling sound, which confirmed that indeed heat does transfer from the threads of the valve (and not the shoulder of the canister) into the butane. Still, it was a slow process and only the LiteMax seems to pour tons and tons of heat into the butane, enough to cause the canister to rise 5F in around a minute or two. Too slow but I was able to make a container go from 60F to 90-98F with coaxing over several minutes.

    Recently I found out that shaking the (inverted) canister with attached stove makes heat transfer fast. Real fast. How fast? The Gigapower 2.0's valve bodyat around 130F will take a minute to drop 10F. On gently sloshing the butane up and down, I found that I could get the valve body from 125F to 105F in around 15-20 seconds and conversely the (mostly full) butane can went from 88F to 96F. Yes the canister feels a little warm (nothing more than above room tempreature to the touch) in the process.

    This is helpful because butane also has a far lower pressure at the same temperature when compared to isobutane mixes (or butane+propane mixes) found in regular canisters. At 70F, butane has less than 20psi of pressure while a 70/30 propane-butane mix (comparable to 20-80 propane-isobutane) is at a little over 35psi. At 90F and 100F, pure butane respectively has a pressure of 30psi and a little under 40psi. The 30/70 propane/butane mix would be at over 65psi and almost 80psi! To get the low, low 20psi of pressure out of a 30/70 mix would need the canister temperature at below 40F...

    Butane has a far, far lower operating pressure meaning that the safety margin is far higher but respectively it suffers from canister chill a lot easier. As far as I am aware, the 4 to 16oz threaded canisters are to be rated to 130F (~55C) which means that the pressures are far, far in excess of 90psi (=110F, pure butane is 45psi!). At that point the canister itself would be too hot to touch with a bare hand anyways.

    So for anyone who finds the idea of an "Alpine Bomb" or "Moulder Strip" (direct thermal feedback into the canister with a little piece of copper) a bit too hazardous when using refilled butane in a canister, then a warm stove body might be sufficient with a little bit of shaking to warm the butane up inside to get it sufficiently above ambient for normal operation. That aside, it seems that the lower pressure of butane makes it far safer in operation as well.

    Also cassette stoves (as in the stoves that the long butane canisters are used for) do use direct thermal feedback in a form of a copper strip that runs up to the burner head (and sometimes is exposed to the flame directly) and then runs back into the canister. Of course, they also have a safety mechanism that will disconnect the canister from the stove and thus shut it off to prevent continual thermal feedback. Using bare handed touch would suffice if monitored given that there isn't that much heat being put in by the stove body thermal feedback method. The Alpine Bomb and Moulder Strip being another matter (touch the canister often...) due to varying construction and degree of thermal feedback.

    As to the specifics of the stoves warming up, it seems different throttle settings on stoves that have warm throttle bodies varies. On the Gigapower it will heat up at low to medium settings. On the Litemax it heats up quicker the higher the throttle setting. On the Pocket Rocket 2 I know it most certainly will heat up at low throttle settings. For some stoves it seems low throttle settings cause a lot of thermal feedback because the flame isn't "lifted" off the burner head. The Coleman Exponent F1 is also a heat monster, it heats up to stupid hot levels for the valve body that Coleman put a bunch of plastic around it to prevent it from becoming an outright burn hazard. In contrast: It seems all the regulator type stoves (at least the ones I own: Soto Microregulator, Soto Windmaster, MSR Pocket Rocket Deluxe and a Kovea V1) have cool valve bodies that don't become outrageously hot and untouchable.

    I assume a mix of warming the canister up (for actual cold weather use) by keeping it underneath clothing, using it to warm a little water until it becomes lukewarm to the touch followed by setting the canister into the water to "soak" some of the heat up before inverting the stove and shaking it would allow for butane to operate in fairly chilly conditions. As long as there's enough pressure to get the stove started and to get it to warm some water to allow for that heat to boost the pressure a little then it should be sufficient to bring it to near room temperature.

    I hope this was helpful for anyone who was wondering if thermal feedback from the canister stoves. It seemed weird that the valve bodies would heat up so much, perhaps the designers were actually trying to use some thermal feedback to allow for them to operate at lower temperatures.