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Thread: Fire Piston Optimal Size, Material and Seal

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    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?
    Bigbob


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    Senior Member WalkingTree's Avatar
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    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 02:20 AM.
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    Super Moderator crashdive123's Avatar
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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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    Thanks, compression ratio is probably the answer, assuming well made such as on a lathe and good seal. Why this ratio?
    Bob

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    Senior Member Antonyraison's Avatar
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    I also honestly do not know, I have seen one or two, never used one, never attempted to make one.
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    Senior Member WalkingTree's Avatar
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    Quote Originally Posted by bigbob View Post
    Thanks, compression ratio is probably the answer, assuming well made such as on a lathe and good seal. Why this ratio?
    Bob
    https://en.wikipedia.org/wiki/Fire_piston

    A side thought I just had: I've noticed that sometimes when a person pulls the piston back out, the tiny ember can pop off of the end, which either ruins that attempt or is just another thing momentarily that has to be dealt with. I'm thinking this is because, no matter what, you often wont have exactly the same air pressure in the cylinder as when you started...not still equal to the outside atmosphere but instead a tiny bit less (unless instead due to the ignition physics it's the other way around). And it kind of sucks it off as you pop it out. (Watch the dirty minds) So this is something to keep in mind either in designing the end of the piston or when operating it.
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    Junior Member SurvivalGeek's Avatar
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    I bought the item below (Fire Piston) from Amazon and never could get it to work correctly. Its was difficult trying to get the correct amount of pressure to create an ember. After a few hundred tries (and after destroying two rubber O-Rings - lubricated with vasoline petroleum jelly like the instructions requested - which are required to operate the fire piston) and I still had issues creating an ember using char cloth. It's not worth it my opinion. Carry a Bayite 1/2 inch by 6 inch ferro rod ($14 on Amazon) with you. That particular size ferro rod will give you thousands of strikes yielding bright sparks. Bayite makes several different ferro rods and are the best quality and price available in my opinion.

    The bad things about the fire piston is it requires a particular type of tinder to create an ember and requires rubber O-Rings to operate. If you don't have the O-Rings, the fire piston won't work.

    If all else fails, try starting a fire using the primitive "Fire Saw" method. See the "King Of Random" demonstration on YouTube on how to use the "Fire Saw" to quickly make an ember using two pieces of wood.

    Sincerely,
    SurvivalGeek

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