Engineering, Technology, and DIY
Build a Flamethrower with PVC and Copper Materials
Two summers ago, Dmitriy, Rich, and I found ourselves bored one Saturday. What are three guys with a little cash and a lot of time to do? Go to the hardware store, of course! Walking up and down the isles, searching for inspiration, led us to our eventual project: flamethrower.
Learn how a flamethrower works and how we built ours after the jump…
Conceptually, a flamethrower isn’t a very complex system. A combustable liquid fuel is held under pressure in a tank usually mounted on the back of the user. One can use a variety of fuels depending on the goals and restrictions. We used denatured ethanol for a clean burn, but one could use gasoline for a better result (but it also eats through PVC). The fuel then travels down a hose controlled by some sort of trigger or valve. An ignition source, often a small propane flame, is situated such that the stream passes through and is set aflame. A nozzle is used such that the fuel stream is kept thin enough ignite and prevent dripping, while thick enough so that it doesn’t completely combust before reaching the destination. HowStuffWorks has a great interactive diagram that will help eliminate any confusion.
- 1.5ft, 3″ diameter pressure rated PVC
- 3″ diameter PVC threaded female end couple and matching cap
- Schrader valve, threaded
- 0.5″ to 3″ PVC couple (series of couples), the 0.5″ end female threaded
- 0.5″ threaded male-male copper couple
- 1ft, 0.5″ flexible metal sheathed hose
- 2 0.5″ sweat ball valves, one female-female threaded, one solder-male threaded
- 2ft, 0.5″ copper pipe
- 0.5″ copper solder-male threaded couple (may need solder-female + male-male)
- 0.5″ to 0.25″ metal couple
- 0.25″ to 0.125″ nozzle
- 0.125″ (slightly smaller) semi-soft tubing
- Propane torch
- Air pump (e.g. car tire pump)
Construction was fairly simple. The 3″ PVC pipe was used for the fuel tank. On the other was the cap, which we tapped and screwed in the Schrader valve. This would allow us to refill the flamethrower, as well as easily pressurize it. On one end was the 3″-0.5″ couple system, which would have been much simpler if we could find a single couple to do that. Into that, the male-male couple was screwed, which allowed for the sheathed, flexible tube to be attached.
The copper pipe became the barrel. The solder-male valve was attached to one end, which would then be connected to the a ball valve (for fuel cutoff), and then the fuel tank hose. The solder-female couple was attached to the other end to allow the nozzle setup to be attached.
The nozzle that we ended up using consisted of a sweat ball valve for the trigger, the 0.5″-0.25″ couple, and the 0.25″-0.125″ nozzle. We found that that was still too wide of a stream, so we stuck a slightly tighter tube on the end to give us one a bit thinner. This apparatus was then attached to the end of the barrel with a male-male couple.
Use and Testing
After loading the denatured alcohol into the fuel tank, a car air pump was used to pressurize up to 80-100psi. The fuel cutoff valve was opened and the torch was lit. Opening the nozzle valve let the fuel ignite and shoot.
All in all, it works extremely well for something thrown together on a whim. In the future, it would be interesting to use an all-metal construction such that we can use more aggressive fuels without worrying about the fuel tank dissolving. It would also be nice to have a portable, controllable pressurization mechanism.
Click to see the full set of photos from the build process
The very existence of flame-throwers proves that some time, somewhere, someone said to themselves, You know, I want to set those people over there on fire, but I’m just not close enough to get the job done.
– George Carlin