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Thread: Fire Piston Optimal Size, Material and Seal

  1. #1
    Junior Member
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    Oct 2014
    Shenandoah Valley VA

    Default Fire Piston Optimal Size, Material and Seal

    I have seen several videos about making fire pistons using plastic, wood turned or carved by hand, aluminum etc. The sizes vary a lot.
    What is the optimum size for a primitive backpacker for a fire piston, what material, what seals?

  2. #2
    Senior Member WalkingTree's Avatar
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    Jun 2015


    You'll probably get some better information from others than from me, but...whatever else, it needs to have an adequate compression ratio. Some sources say 18 to 1, and some say 25 to 1. However, many will say that they've never given the ratio a thought, and never had a problem getting a homemade piston to work. Though I suspect that this is just because it usually works out that different people typically design and build one of such dimensions that it accidentally has this ratio, because I don't think that it's that hard to accidentally get this ratio from a design that someone would conjure up.

    Other than that, what is 'best' might be subjective. Might not really be a 'best'. There's a bit of flexibility with materials and design. You just need to imagine the piston being able to plunge fully and smoothly, yet not be loose and is a little tight - much of this being according to the o-ring seal (and a trace of lubrication) and needs to be straight. Cylinder and piston need to match well. Needs to seal, yet be amenable to being plunged quickly. Pretend that you'll always have some 'leakage', so it needs to plunge and reach ignition compression faster than the leakage would prevent this. On that note, for keeping the compression ratio in mind while designing, I figure that you'd want to design in a 'little extra' or a little higher ratio...this would make it 'forgiving' and let a slight lack of skill or experience still result in ignition. Would also compensate for seal leakage to some extent if a build wasn't perfect unknowingly.

    Beyond that, I think that this is something which is on the one hand not too difficult to build effectively, while on the other hand is a matter of 'holding your tongue just right' while making and while using, versus there being a single perfect material or design.
    Last edited by WalkingTree; 04-19-2016 at 03:20 AM.
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  3. #3
    Super Moderator crashdive123's Avatar
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    Jan 2008
    North Florida
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    I honestly don't know if there is an optimal size. For backpacking - small and light. I have only made one and used 1/2" copper pipe.
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