Instructables
Picture of Start a fire with air
To do this we need to make a firepiston, which is a device for starting cook, camp and signal fires with air.

Firepistons seem so high tech that it's hard to believe they were not developed at MIT or Carnegie Melon under a top secret DARPA contract with unlimited funding. Since the firepiston is also given credit for Rudolf Diesel's invention of his Diesel engine it is quite surprising that the firepiston was not invented by Diesel himself or by one of his contemporaries or the likes of Ben Franklin and other European and American pyro based device inventors of the 16th, 17th and 18th centuries.

What historians note is that the firepiston was most likely invented in conjunction with the invention of the blow gun by prehistoric South East Asians since firepistons are normally found in the possession of those who use blowguns. The need to dislodge the internal partitions at each connecting joint inside a length of bamboo by ramming a rod or piston through the membrane, and in the course of doing so, rapidly compressing the air thereby setting dust particles or the membrane alight, is the reasoning behind co-invention.

I was so amazed at the technology and the science behind it that after building my own firepiston to prove to myself that the science and technology was real I could not resist sharing the science, technology and construction of my first firepiston with you by creating this instructable.

Here then is a description of how to make your own working firepiston to see first hand for yourself that the science and technology do in fact work. I left lots of room for improvement in materials, workmanship and degree of completeness for possible use in the field, if going beyond a demonstration is what you want to do.

 
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Step 1: So how does a firepiston work, anyway?

Picture of So how does a firepiston work, anyway?
A firepiston can set an ember to burn as a result of energy being concentrated into a smaller and smaller space by compression of air resulting in a corresponding increase in the air's temperature.

The principle of increasing temperature by method of compressing air is explained by the Adiabatic process in which the internal energy of a gas must increase when a mass of air is rapidly compressed (or the volume of space containing a mass of air is rapidly decreased). The resulting increase in internal energy results in a rise in the temperature of air sufficient to light an ember, just like the pressure produced by an ice skater's blade is sufficient to increase the internal energy of the ice, which turns ice under the blade into water.

You can envision the effect in a 2D graph (below) with pressure as the ordinate (vertical) and volume as the abscissa (horizontal) and the adiabat or curve of constant entropy as the inverse relation curve. (Black lines are the curves of constant entropy.)

Rapid compression by a factor of 25 to 1 produces sufficient internal energy to send the air temperature to 800 degrees Fahrenheit. This temperature is sufficient to ignite a piece of char cloth for use in kindling a fire.

After several tries and some fine tuning (better sealing with more lubricant) I was able to produce embers with char twine using the apparatus I constructed.

Step 2: Materials and tools

Picture of Materials and tools
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In general you want a material that will allow a cylinder to be bored smoothly with approximately an 1/4" ID which is around 6" deep and sealed on one end. Incidentally, If you do the math then you will see that it is the ratio of the height of the uncompressed space to the height of the compressed space that determines the height of the cylinder. In other words if you want .25" of char cloth to be ignited and you need a compression ration of 32 to 1 (instead of 25 to 1) to do it then the height of the cylinder will need to be 32 times .25 or 8", plus a little extra room to insert the piston.

The piston is a rod that fits snugly inside the bore of the cylinder using a gasket or seal of some type to make it air tight. The bore and the piston must be perfectly straight and smooth to achieve and to maintain an air tight seal while it is being operated to produce an ember.

Natives might collect woods and cutting tools and keep at least one firepistons under construction in various stages of completion to be able to go from start to finish within minutes, hours or days.

To speed up some of the process required for construction requires use of a 1/4" by 6" brass nipple with an end cap filled with JB Weld and an aluminum or oak dowel to construct two test pistons. The pistons require a 1/4" OD O-Ring (or slightly larger diameter that can be filed down to fit) to act as an air tight seal. Natives would use fibers of some sort and perhaps anything from animal fat to earwax as a sealing lubricant. We can use lip balm or Petroleum Jelly.

I used a 1/4" power drill and a piece of dowel wrapped with an inch long sheet of tissue paper soaked with a solution of water and Bar Keeper's Friend (Oxalate acid) to polish the inside of the brass nipple to a mirror finish. (On the larger 3/8" nipple I'm working with now the inside of the nipple is much less smooth and straight requiring various grades of sandpaper to hone it smooth before polishing.)

I used a hack saw blade, a glass file and the threads on a bicycle wheel spoke to fashion the seat for the O-ring in both the aluminum and in the oak dowel. A 1mm bit was used to drill the hole in the char twine box. (Commercial units have a much deeper cylindrical hollow to hold more char cloth better.)

Originally I used a temporary piston stop made by using a pair of vice grips clamped around the piston shaft where the handle would be attached to the piston shaft to keep the char twine from striking the bottom of the bore. This worked but it appears that commercial makers of firepistons hollow out the end of the piston much deeper to provide greater room for more char cloth and allow the end of the piston around the hollow to serve as the piston stop, rather than using a shaft pin or the handle as the piston stop. BTW - commercial versions can run upwards of $50, but some come with all of the amenities such as char cloth and lubricant.

Step 3: Polishing the cylinder

Do not use cylinders with a weld seam left inside but only nipples that have been bored smooth at the factory. Otherwise you will have to bore out the inside of the pipe to remove the excess material remaining after the seam was welded.

I used a 1/4" power drill and a 1/4" oak dowel with an inch wide piece of damp tissue wrapped around it for polishing. I used various grades of sandpaper for honing first since the nipple was dented or had internal high or low areas resulting from the equipment used to keep the nipple from slipping while the threads were cut.

The tissue was dampened with a solution of water and Bar Keeper's Friend (oxalate acid), inserted into the nipple and spun by the drill. The nipple can become quite hot so wear rubber or leather gloves to prevent pain and give a better grip on the brass. Also, stop frequently to add water or more solution to help keep things cool. Adjusting the width and amount of tissue wrapped around the dowel will help to optimize the fit and lower the degree of friction. The more you polish the better, but 10 minutes or less should be enough if your last job of honing was with extra fine grit sandpaper.

Step 4: Putting on the end cap

JB Weld is used to fill in the space where the nipple does not reach the bottom of the end cap. If the space is not filled the O-Ring will expand in this space and release the air pressure too soon as well as get caught in the space.

The end cap is set down like a cup and filled halfway with "steel" and half way with "hardener." They are mixed with a matchstick or toothpick. Then the nipple is held upright and the bottom end threaded into the end cap and tightened. Once tightened the nipple and end cap are either hung by a string or stood up so the JB weld will set with a flat and horizontal surface on the inside to stop the piston and to eliminate all unintended air space.

The hard part comes next - waiting the full 16 hours for the JB Weld to set completely.

Step 5: Cut the hollow and the seat

On the very end of the piston a hollow is cut using a rounded or squared end drill bit. The hollow may also include 1mm or 1/16" hole, drilled in the center for a total depth of no more that 1mm or 1/16" to help hold the char cloth or twine better. Commercial versions may use a slightly deeper (3/16") hollow with no center hole and with the O-Ring set back behind it for practical use in the field.

For construction of this firepiston I just wanted to see if it the limits of the science and technology that might keep it from working. I tried several other configurations. You can experiment with all sorts of arrangements, including a double O-Ring configuration. Feel free to experiment and learn everything you can in case you ever really need to make one of these out in the field!

I cut the seat for the O-Ring next by placing the other end of the piston in a 1/4" power drill and using a hack saw blade, glass file and the threads of a bicycle wheel spoke as lathe chisels.

The O-Ring is and seat are next lubricated and the O-Ring is slid on and the O-Ring fitted to the inside diameter of the cylinder.

Step 6: Test the fit of the piston and O-Ring

While it should not be difficult to insert the piston and O-Ring into the nipple there should be obvious resistance from air pressure and the piston should spring back when released. If not try a little more lubricant.

If the piston can not be inserted then remove all lubricant from the shaft and O-Ring, slide the O_Ring up onto the shaft past the seat, put the piston back in the drill and spin the O-Ring on some sandpaper to reduce the outside diameter of the O-Ring a very small amount each time.

Re-lubricate and re-seat the O-Ring and try again. Repeat this process if necessary.

Step 7: Add handles

Since I was not planning to use this in the field (just yet) but rather testing compression ratios I used vice grips as an adjustable piston stop and for the piston handle and a towel to hold the cylinder. For field use you can used pieces of wood with a hole drilled in them the size of the outside diameter of the piston and the outside diameter of the cylinder and secure them with epoxy.

Step 8: Insert char cloth and test

Char cloth is cotton or denim cloth that has been placed inside a closed container, like an Altoids tin or capped nipple, with a small hole drilled in it about 1mm or 1/16" in diameter to allow gases to escape. The container is heated in a fire to drive off water and other volatile compounds. I found also that setting a piece of twine alight after inserting it in the hole and letting it burn down and then capping it just before the flame went out produced enough char twine on the very end to be set alight by compression, although for a much shorter period of time.

( Here is an instructable for making char cloth in the field for use with a firepiston...)

A piece of char cloth is inserted in the recess of the piston head and the piston is inserted into the cylinder. A rapid motion is used to drive the piston forward with great force and then withdraw immediately (but with some slight delay).

When withdrawn a small ember should be found which must be nurtured if used to set a piece of tinder alight in order to build a fire.

Do a Google search on the keyword "firepiston" and you can find hundreds of sites on the internet that discuss how to use a firepiston and find videos that show the glowing ember and how it is used to light tender and start a fire. If you have an Adobe Flash Player or add-in you may also be able to view this.

Mine works but until I put on handles I'm not going to develop an operating technique. I have learned that a slight delay after plunging rather than a sort of very rapid bounce worked much better. Experiment.

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VentureScout2 months ago

I like it!

nbenson11 year ago
Could you just not use a push bike pump with the metal ball nozzle? They get rather hot :)
Fred826645 years ago
Cool I will have to try this out,Is this the same principle that some Diesel Fuel engines start up ( the ones that do not have glow plugs ) ?
Glow plugs heat up the engine when You start up a diesel. Thats all they do. Once the engine is hot, the pistons compresses the fuel and that plus the little bit of heat makes it work. I also do not know of any diesels without glow plugs, but it could be possible in hot areas. I'm a teenager thats a nerd and does nothing with trucks and I can tell you that. Sorry I did that. It just bothered me. and yes, its kind like that, but this isnt as powerful as a diesel and a lighter is easy to me compared to this. Just saying.
cool I like to see the younger generation thinking about other things then sex drugs and rock and role. there all good ,but I am in my 40s I know about the glow plug thing probably be for you was a twinkle in your dad's eyes. ( not meant to make ya feel bad ) older farm tractor did not use glow plugs some of the old Mac trucks and military vehicles did not use glow pugs. I think the use of glow plugs came in around the 60s ,I could be wrong on that thought as well as my thought that friction created the heat to light up the diesel fuel

by all means continue to feed your mind better things then drugs and Challenge current technology make it bettermake new ! (lol my life in some old folks home may be much better by you doing it lol)
You are correct. Not all diesels do have glow plugs... Early diesels were just cranked over repeatedly, which created enough heat due to the compression to start the engine. However, cold weather made it hard to start the engine especially when high compression/high speed diesel engines appeared. Glow plugs were the most successful method of starting diesel engines in cold weather. Some of the methods used before are solid fuel blocks that were fitted into the cylinder head (rudementary glowplug), intake heaters (increase incoming air temp), and introducing ether into the intake. Some example of pre glow plug diesel engines are: - Field Marshall tractors (large single cylinder 2 stroke diesel) which used a solid fuel block, and then later a stogun cartridge style started which ignited fuel in the cylinder. -Stationary diesel engines, like Petter's and Lister's, which are low speed engines that didnt need glow plugs or heater - I believe that the Detroit Diesels featured the ether intake system. Hope that helps. By the way, I'm 19, but have been interested in old engines since I was born :P Old tractors that used TVO still produce the nicest smell :)
Yes this dose to you young lad you have my honers. you have done well in your studying and investing your knowledge to better living and only 19 at this point of time. I can see much more grate things coming from your efforts in the years ahead of you ! keep it growing
Thank you.
He obviusly wasnt talking to you.
A youtube video of a Petter PAZ1

http://www.youtube.com/watch?v=Xp3gIpKnswQ

You just crank the engine over and then flick the decompression lever...causing the engine to rapidly compress air causing heat...
dkop14 years ago
I love my fire piston. I got mine from Wilderness Solutions, (the "Scout" model)
and it's never failed me. It did, however, take me a long time to learn how to turn that ember into a roaring blaze. I've never had problems lighting a fire, but I was accustomed to using flint and steel, or ferrocerium rods.
Any suggestions on natural tinder for fire pistons though? all I've ever used is char-cloth.
This is something I'll have to do in the future. It combines technical things with fire which is an irresistible combination. It'd make a great grill ignitor (I like to grill with real wood)
I dont know if you have heard of this,not very technical,but take paper egg cartons fill with sawdust or dryer lint then pour melted wax into each section,when cooled seperate them,they will each burn about ten minutes,a little longer if useing sawdust.
Yeah, actually knapweed and grass clippings work well for that also.  There's actually an instructable on it.
I take a paper towel, fold it 4 times so its like 1 inch wide ( you have to tear the paper towel) and then soak most of it in wax. leave a little bit without wax so you can light it. they burn for like a candle.
 Have you tried nitrate soaked paper? if it doesnt blow it up, you might get a open flame? Nice lighter with nature fuel possible if you fuel ran out.
spylock5 years ago
This is where Ive been making my mistakes,I didnt fill the cap,none of the other people told me of this step,thanks.
I've been looking through all the info on the net on fire pistons and how to make them. I have to say for how simple they look they are fiendishly difficult to make. I finally ordered one so I had a starting point LOL. I'm getting closer now, the current prototype works but not consistently enough for me. Hopefully after a few tweaks it'll be solid and I'll post my own instructable. Another thing I noticed is that some of the materials listed in various fire piston how to's aren't easy to find. For example the longest brass nipple I can find is 4", other people used copper pipe but I can't find anything smaller than 1/2" so its been a challenge just to get the materials let alone getting it to work. Its all fun stuff though!
forlack5 years ago
Digging into that website Melon gave down there in the comments, NASA gives you two formulas based on the laws of entropy that you can use to calculate the temperature due to volume changes.

The first is to calculate the pressure change due to the compression ratio (or volume change)
p2 / p1 = (v1 / v2) (gamma)

Knowing that you can then use the second formula which relates pressure change to temperature change.

T2 / T1 = (p2 / p1) ( (gamma - 1) /gamma)

"Gamma" is just a number that depends on the gas. For air, at standard conditions, it is 1.4. (this is a simplification)

For the full workout go to http://wright.nasa.gov/airplane/compexp.html.
Now obviously this has some simplifications, but it should get you a good approximation. Plus their breakdown is for pistons in general which is good.

BTW Temperature is in Kelvin. Using the above equations and with the following:

Compression ratio of 25:1; initial temperature of 25c. The final temperature will be equal to 807c...pretty hot.
How did the potassium nitrate saturated coffee filters work? Back in high school we used to make smokebombs with that stuff and we'd soak newspaper in a saturated solution of potassium nitrate to act as a slow burning fuse.
sharlston5 years ago
any more ideas please email them to mattyts@live.co.uk this is so cool
K.hall866 years ago
have you experimented with a stainless rod?? the stainless would have more resilience, although you would need more advanced cutting tools. although you might also need to experiment with the width of the o-ring grove...i can see the grove depth and width playing a key role in this. i would assume that the optimum grove width and depth would be the diameter of the ring. that way the ring would have no "slop" in the thrust direction, and it would also guard the ring from trying to roll out of the grove....i am of course assuming a lot here...lol you might try making a piston in very large scale at first....large diameters have tons of structural integrity..it might help work out the kinks in the small scale experiments...
n0ukf K.hall866 years ago
Have you ever tried to work with stainless? it's tougher to cut than regular mild steel (which is tougher cutting than aluminum)
watermelon (author)  K.hall866 years ago
I use to carry stainless steel mini mess kits. It is not until you add things up that weight becomes a factor. Aluminum rod has enough strength and corrosion resistance plus workability to make it an excellent material for the job, especially for field use were weight is a factor. Commercial units use a variety of materials. The purpose of testing various configurations is to optimize your own personal firepiston to match the characteristics you need - like building a bow to match your height and strength.
i have tried to make own out of pvc i saw on a website but i cant get it to start the tinder any one got any suggestions
watermelon (author)  chi chi chippy6 years ago
You can always make the length longer to gain a greater compression ratio, but PVC is not a material I would use due to the temperature at which it begins to soften and the low pressure at that temperature required to deform it. Clear polycarbonate, however is often used to make demonstration models. You might also consider making one out of a chunk of wood or a piece of bamboo. The lignin which binds the cellulose fibers in wood together is very resistant to degradation.
SPININSPUR6 years ago
has anyone come up with one small enough to be put on a key chain. How small can one be made so that the compression aspect is not compromised.i would like to make one as small as possible to carry.
you can make one as small as you want but the smaller, the less tinder (char cloth/twine)you can use. i mean ive seen one as thin as a pencil.
Kinnishian6 years ago
Very nice guide. But I think explanations are overcomplicated.

Just for one simplification that anyone with some algebra could understand involving why it gets so hot.

Use the formula PV=nRT

Where P = atmospheric pressure. V = volume of gas (air). n = atoms of gas in mols. R = gas costant .0821 and T = Temperature in kelvin.

Keeping in mind P, n, and R remain the same anyone can determine T with simple algebra.

You can use suggestion or not it's still a good guide.
watermelon (author)  Kinnishian6 years ago
The math is quite a bit more complicated than juxtaposing the Equation of State for an Ideal Gas, as the Adiabatic process involves the Laws of Thermodynamics and must include the Enthalpy Equation. (See Entropy of a Gas)
Hmm....Alright :-) My mistake then. We covered the basics of gases earlier, and now we're into enthalpy and entropy. But, I don't think we've put them together yet. My favorite class it tis... Is the difference in the mathematics considerable? Oh, and I suppose we just started trying to determine the K constant for entropy. But I don't understand that yet. Maybe I should go do my homework now :p.
watermelon (author)  Kinnishian6 years ago
Detroit would most likely hire an engineer at a high wage who could model a firepiston mathematically.
...=/

I was just trying to ask how accurate 'my method' would be?

And you know. So, right, thanks.
watermelon (author)  Kinnishian6 years ago
Sometimes in school teachers will make it seem like if you learn only what they are teaching at the moment that you will know everything there is to know and that there is nothing beyond unless you come up with it. Then all of the sudden its like walking off a cliff when you find out they only scratched the surface. The pressure, temperature and volume relation of a gas is important to know but that is far from all there is. Check out air conditioning and refrigeration systems. A repair technician could probably help you to understand what happens with temperature when a gas is compressed at various ratios. Those are the guys I would ask.

so incredibly true there
Easier than that. You need a compression ratio of about 25:1 Calculate the volume of the cylinder. V Calculate the volume that remains with the piston fully in. Vc V:Vc should be 25:1 or more. Note that the wider the cylinder and the smaller the tinder hole, the shorter the stroke length. Nearly any materials can and have been used to make these. The ones for sale on the net are art pieces-like custom knives. When the British first found these, they couldn't believe that they hadn't been invented somewhere 'civilized' as they found them pretty much everywhere the blowgun has been invented. They were just becoming very popular in Europe when the match "lucifer" was invented. Despite the then major disadvantages of the match (early ones tended to light TOO easily, like in your pocket!) Once you've got one they have a number of advantages over the standard lighters ('flint' & steel) in that they are wind and waterproof--if you're not actually under water, it will ignite, and more reliably than most lighters. No fuel to buy as nearly anything that is fluffy and burns will ignite.
Senseless6 years ago
Dang nice Instructable. It reminds me of an old pump design that let's you lift a small volume of water ten feet using a larger volume of flowing water like from a stream but without the need for it to drop like a typical dam system uses to generate force. I can't remember the name of the thing it's been around since the 1800's or so. This will bug me all weekend now trying to remember what it was called LOL.
We call this a 'waterfall bong', check out youtube for more.
Hi Senseless, it's a hydraulic ram if I'm not mistaken:

Hydraulic ram
Thanks! That's it exactly! I'll be able to sleep tonight LOL. It's like getting a song stuck in your head...
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