The fire piston is a unique method of creating fire, using nothing but compressed air to ignite tinder. A plunger is quickly pushed into an air-tight tube, compressing the air, raising the temperature, and igniting a bit of charcloth or other tinder set in the tip of the plunger. The key requirements for a fire piston to operate correctly is a straight, smooth bore and a plunger that seals the chamber air-tight. It is possible to create one yourself, but purchasing a kit gives the satisfaction of carving and customizing your own without the efforts of precision required for the inner workings.
The theory behind a fire piston is simple, yet very interesting. To create flame by simply compressing air is pretty cool. The compression chamber is full of air at a certain temperature. The air molecules are bouncing around, hitting each other and the sides of the chamber. As the plunger is pushed in, the space in which the molecules decreases, causing them to hit each other more often and forcefully, generating heat. The energy given off as heat is absorbed from the force of pushing the plunger.
If the plunger is pushed too slowly, the generated heat dissipates into the materials of the fire piston. But, by forcing a quick compression, the air heats instantly to over 700F which is enough to ignite tinder.
Fire pistons have historically been crafted from animal horn, bamboo, hardwood, or even brass. The keys for successfully making a fire piston are to drill a clean, smooth, straight bore and have a properly sealed plunger. The bore needs to be the same diameter the entire length or partway down, the seal will be lost and compressed air will escape. The plunger has a cavity in the end to hold a bit of tinder which is extracted after ignition. It also has a gasket made of fiber, leather, or thread wound around it's leading end to create the compression seal. This gasket is then greased with animal fat, shortening, or vaseline to improve the air seal.
High tech pistons are now available made from plastics. The use of a rubber O-ring as a gasket rather than twine makes a much better seal and better compression.
Each person has their own favorite way of operating a fire piston. I prefer to tightly hold the main chamber in my left hand, position the plunger about 1/4 inch into the main chamber, and then hit the end of the plunger with my right palm. I imagine that I am driving my palm down to the bottom of the main chamber to ensure I force the plunger all the way, increasing the compression. That last 1/4 inch of compression makes the difference between ember and nothing.
Then, immediately pull the plunger out and look for a glowing ember. If you wait too long to pull the plunger out, lack of oxygen extinguishes the ember. This is also a good way to extinguish an ember if you are doing demonstrations - just push the plunger back into the chamber and leave it.
Scouts love fire and fire pistons are great fun. They can be used to demonstrate alternate fire starting methods, as well as to 'spark' a scientific discussion about what is really happening. Being able to to say you can make fire from air beats making fire from two sticks any day. It's a great way to get Cub Scouts interested in Boy Scouts and I use fire pistons as a demonstration at local Webelos den meetings when I visit. Even scouts that think they know it all are often impressed by this new gadget.
I've also found that fire pistons are highly appreciated gifts since they are so unique. You can purchase a beautifully done fire piston from Wilderness Solutions and present it to an Eagle Scout. Or, buy kits for your scouts and have them assemble and carve their own custom fire piston. Wilderness Solutions has a specially priced Scout kit available with an O-ring gasket for better seal and compression.
There is also a more traditional kit available with twine gasket to wind on.
Tips to Remember:
- Have your tinder bundle ready before using the fire piston. Be able to quickly transfer the ember to more tinder immediately.
- Lubricate the string gasket occasionally. Vaseline works well for this. After a few attempts, the seal will weaken and you'll find that the vaseline will recreate the seal. If your firepiston has an O-ring gasket, you shouldn't need to lubricate it.
- Use a full stoke. Start with the plunger as far out to the end of the compression chamber as possible. The gasket should be just started into the chamber. This allows a larger volume of air to be compressed, resulting in higher temperatures and better ignition.
- Compress Fast. Hit the plunger quickly and forcefully so it compresses all the air in the chamber into the smallest possible area in the shortest possible time.
- High humidity makes ignition more difficult. Each compression attempt will be heating and drying the tinder, so multiple attempts may finally create an ember.
- Use a good tinder, such as charcloth, especially when learning how to use the fire piston.
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