Napkin Diagrams

Engineering, Technology, and DIY

Build a Flamethrower with PVC and Copper Materials

Assembled flamethrower
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.

Construction

Exploded diagram of flamethrower parts

An exploded layout of the flamethrower components

Material List:

  • 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)
Assembled Fuel Tank

Assembled fuel tank with transfer hose attached

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.

Nozzle Setup

The completed nozzle setup

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.

This was the best video we shot (#3 of 3):

Other videos:
Video #2
Video #1

Conclusion

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

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11 responses to “Build a Flamethrower with PVC and Copper Materials

  1. Pingback: Tweets that mention Build a Flamethrower with PVC and Copper Materials « Napkin Diagrams -- Topsy.com

  2. Dmitriy December 3, 2009 at 12:37 pm

    Oh man you saved the build sheets on this thing? Awesome. We really needed to do more research on fuels.

    Also probably the delivery tube getting wider and then narrower cut down our range and propulsion strength considerably.

  3. Julie December 5, 2009 at 5:10 pm

    You just gain like 1,000 cool points in my mind.

  4. Julie December 9, 2009 at 2:20 pm

    ok, but how does this compare to the bacon flame thrower?

    http://www.popsci.com/bacon

  5. Gerrit Coetzee January 13, 2010 at 4:52 pm

    I can’t help but fear the combination of fuel and oxygen in a compressed tank. The ethanol may be alright but if you put gasoline in there you would be asking to die. No human is fast enough to close a valve before a backfire gets to the fuel tank. Maybe if you could fill it with another easily accessible gas like CO2, He, N…

    • Brian Bickerton January 13, 2010 at 5:06 pm

      Hey, thanks for the comment and concern. Safety is always an issue when working with combustibles. Given the pressure and size of the nozzel/barrel, it’s much less of an issue as long as you’re still firing. One would make sure to stop firing before it ran out too much.

      That said, safety is always a concern. If I was to do this again, I’d likely use steel instead of PVC to avoid any interactions with the fuel, probably set up an electronic-based safety cutoff, and potential inert gasses. Perhaps some sort of expanding/contracting bladder system could be employed such that the gaseous volume in the tank wouldn’t be a concern.

  6. vinny March 15, 2010 at 11:55 am

    for your pressurization problem you can use a tank of propane connected to the camber and when fully opened will pressurize the chamber to 100-120 psi and stay constant

  7. mike September 10, 2010 at 1:29 pm

    if you used something like a fire extinguisher canister loaded with nape, an easy recipe of styrofoam and gasoline, and a separate tank of compressed nitrogen or co2, yours would be backpackable, and military grade. you would also run out of fuel before you ran out of inert gas.

  8. Joe February 13, 2012 at 11:17 pm

    What is the name and where do you find the tip of that torch attachment?

  9. bobbobber September 1, 2012 at 7:07 pm

    Where was the .125 inch soft tubing used?

  10. krishikaseo1 June 8, 2013 at 5:11 am

    I Gone through your Website its really amazing.
    very good information on product i got know useful information thanks for this.

    PVC Ball Valves

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