Flamethrower design
Posted: Wed May 30, 2007 7:57 pm
This is a rough sketch of my design for a flame thrower. It's made of PVC and brass parts and fittings, and will be pressurized with propane.
First, a disclaimer. This isn’t the normal legal mumbo jumbo, so please read it. The whole thing.
This drawing and parts list is offered for educational, informative, curiosity-quenching purposes only, and is NOT intended to be used for anything remotely illegal.
Neither the author(s) nor the owner(s) of the website this document are posted on take any accountability or responsibility for anything you may do with this document.
By reading any further, you're acknowledging your consent to the above terms.
This document assumes you have some experience with building things, such as potato cannons, airsoft guns, R/C, or other hands/on, mechanical experience. You need to understand basic gas laws (such as what an oxidizer is, what upper and lower explosive limits are, etc….). You also need to know how to solvent weld PVC properly, and how to drill/tap for a fitting.
If you do not understand basic gas laws and PVC construction, please don’t attempt to build something resembling this. The community does not want to see “15-year-old goes out in a fireball attempting to build a home made flamethrower” on the evening news. It gives the rest of us a bad rap. So, in this document, I’m not going to baby-step you through anything. You’re expected to understand the basics, and if you don’t, you shouldn’t be attempting this.
The basic principal of a flamethrower is similar to an industrial-strength super-soaker. Pressurize a fuel (we’ll be using denatured alcohol) with a non-oxidizing or inert gas, and light it on it’s way out the “barrel”.
This drawing should be reasonably self-explanatory.
In this design, the fuel chamber is pressurized with propane. Pressurizing the fuel chamber with a flammable gas may seem counter-intuitive to some people, but it’s actually a safety feature. The upper explosive limit of propane is just over 10.0%. If there’s more than, say, 20% propane in any given atmosphere (Such as the inside of our fuel chamber), a spark could not ignite it – there’s not enough oxygen (or another oxidizer) to support combustion. Pressurizing our chamber with propane up to 60+ psi ensures there’s not enough oxygen inside the chamber to allow combustion. To further improve safety, check valves and pressure gauges are installed in both the tank and the “gun”, along with a fuel gauge and pressure pop-off safety valve on the tank. Additionally, using propane is more convenient than using CO2 or another inert gas, because when your propane tank runs out, you can just grab a new one from the hardware store for $3 (You’ll want to stock up….). With CO2, you’d have to go to a paintball store to get it refilled all the time.
MAKE SURE TO STOP FIRING when pressure starts to get low (below, say, 20psi) or when fuel runs out. Trying to continue firing on low pressure or an empty fuel tank could create conditions that could support a back flash up the hose and into the tank, although this is very unlikely.
DO NOT use any DWV (drain, waste, vent) parts for this device. NSF-PW, pressure-rated PVC ONLY. MAKE SURE to solvent weld (prime and glue) the pipe and fittings properly. Your life could literally depend on the air-tightness of your solvent welds. If you don’t know how, Google “how to solvent weld” and read up on it.
Short pieces of pipe are used to connect the 4” 90˚ pieces. The sections of 4” should be long enough to completely bottom-out in the fittings.
Pretty much all of the small parts here are going to be ½” brass fittings. They’re reasonably cheap and widely available. Anywhere you need to insert a brass fitting into the PVC, do so where a pipe and fitting overlap (where there are two layers of PVC. This gives the threads more to grab onto, and reduces the chance of cracks, etc….) Carefully drill and tap the hole, and use some epoxy on the threads to be sure. Again, your life could potentially depend on the air-tightness of your work.
The fuel gauge is simply a lab-type Pyrex glass or Lexan tube that runs inside the oval tank to allow you to see the fuel level. Make sure the tube you get can handle AT LEAST 125psi of pressure and preferably closer to 200.
The propane system is simple. You’ll need a propane tank adapter, like this: http://www.bcvids.com/store/product_inf ... ucts_id=39 and an adjustable regulator, which you should be able to find in any hardware store with the air compressor stuff. For the pilot light, you’ll just need a regular, $8 benzomatic propane torch.
Set the regulator to around 90psi. Play with the pressure to see what works best. Keep it under 120 (that pop-off safety valve will go off at 125….) and above 60 for sure. Higher is probably better.
The entire device should be pressure-tested using water (super-soaker style) several times up to 100psi before loaded with actual fuel. Leave it pressurized with water overnight to make sure it holds the pressure. If not, find the leaks and seal them with industrial-strength epoxy.
When selecting a fuel, make sure you use something that WILL NOT corrode or react badly to/with PVC. I would highly suggest filling a small section of PVC pipe with an end cap on one end with your intended fuel and leaving it overnight to test to see if it corrodes the PVC at all. If it does, obviously, do not put it in your tank.
Denatured alcohol is the fuel I use. It’s kind of expensive but works great.
If you want to backpack-mount the tank, just find an old metal-framed hiking pack and use hose clamps to attach it.
DON’T GET YOURSELF ARRESTED, START A FOREST FIRE, OR DO ANYTHING ELSE STUPID!!!
Here's the tank:
Here's the "gun":
If you have any questions let me know.
First, a disclaimer. This isn’t the normal legal mumbo jumbo, so please read it. The whole thing.
This drawing and parts list is offered for educational, informative, curiosity-quenching purposes only, and is NOT intended to be used for anything remotely illegal.
Neither the author(s) nor the owner(s) of the website this document are posted on take any accountability or responsibility for anything you may do with this document.
By reading any further, you're acknowledging your consent to the above terms.
This document assumes you have some experience with building things, such as potato cannons, airsoft guns, R/C, or other hands/on, mechanical experience. You need to understand basic gas laws (such as what an oxidizer is, what upper and lower explosive limits are, etc….). You also need to know how to solvent weld PVC properly, and how to drill/tap for a fitting.
If you do not understand basic gas laws and PVC construction, please don’t attempt to build something resembling this. The community does not want to see “15-year-old goes out in a fireball attempting to build a home made flamethrower” on the evening news. It gives the rest of us a bad rap. So, in this document, I’m not going to baby-step you through anything. You’re expected to understand the basics, and if you don’t, you shouldn’t be attempting this.
The basic principal of a flamethrower is similar to an industrial-strength super-soaker. Pressurize a fuel (we’ll be using denatured alcohol) with a non-oxidizing or inert gas, and light it on it’s way out the “barrel”.
This drawing should be reasonably self-explanatory.
In this design, the fuel chamber is pressurized with propane. Pressurizing the fuel chamber with a flammable gas may seem counter-intuitive to some people, but it’s actually a safety feature. The upper explosive limit of propane is just over 10.0%. If there’s more than, say, 20% propane in any given atmosphere (Such as the inside of our fuel chamber), a spark could not ignite it – there’s not enough oxygen (or another oxidizer) to support combustion. Pressurizing our chamber with propane up to 60+ psi ensures there’s not enough oxygen inside the chamber to allow combustion. To further improve safety, check valves and pressure gauges are installed in both the tank and the “gun”, along with a fuel gauge and pressure pop-off safety valve on the tank. Additionally, using propane is more convenient than using CO2 or another inert gas, because when your propane tank runs out, you can just grab a new one from the hardware store for $3 (You’ll want to stock up….). With CO2, you’d have to go to a paintball store to get it refilled all the time.
MAKE SURE TO STOP FIRING when pressure starts to get low (below, say, 20psi) or when fuel runs out. Trying to continue firing on low pressure or an empty fuel tank could create conditions that could support a back flash up the hose and into the tank, although this is very unlikely.
DO NOT use any DWV (drain, waste, vent) parts for this device. NSF-PW, pressure-rated PVC ONLY. MAKE SURE to solvent weld (prime and glue) the pipe and fittings properly. Your life could literally depend on the air-tightness of your solvent welds. If you don’t know how, Google “how to solvent weld” and read up on it.
Short pieces of pipe are used to connect the 4” 90˚ pieces. The sections of 4” should be long enough to completely bottom-out in the fittings.
Pretty much all of the small parts here are going to be ½” brass fittings. They’re reasonably cheap and widely available. Anywhere you need to insert a brass fitting into the PVC, do so where a pipe and fitting overlap (where there are two layers of PVC. This gives the threads more to grab onto, and reduces the chance of cracks, etc….) Carefully drill and tap the hole, and use some epoxy on the threads to be sure. Again, your life could potentially depend on the air-tightness of your work.
The fuel gauge is simply a lab-type Pyrex glass or Lexan tube that runs inside the oval tank to allow you to see the fuel level. Make sure the tube you get can handle AT LEAST 125psi of pressure and preferably closer to 200.
The propane system is simple. You’ll need a propane tank adapter, like this: http://www.bcvids.com/store/product_inf ... ucts_id=39 and an adjustable regulator, which you should be able to find in any hardware store with the air compressor stuff. For the pilot light, you’ll just need a regular, $8 benzomatic propane torch.
Set the regulator to around 90psi. Play with the pressure to see what works best. Keep it under 120 (that pop-off safety valve will go off at 125….) and above 60 for sure. Higher is probably better.
The entire device should be pressure-tested using water (super-soaker style) several times up to 100psi before loaded with actual fuel. Leave it pressurized with water overnight to make sure it holds the pressure. If not, find the leaks and seal them with industrial-strength epoxy.
When selecting a fuel, make sure you use something that WILL NOT corrode or react badly to/with PVC. I would highly suggest filling a small section of PVC pipe with an end cap on one end with your intended fuel and leaving it overnight to test to see if it corrodes the PVC at all. If it does, obviously, do not put it in your tank.
Denatured alcohol is the fuel I use. It’s kind of expensive but works great.
If you want to backpack-mount the tank, just find an old metal-framed hiking pack and use hose clamps to attach it.
DON’T GET YOURSELF ARRESTED, START A FOREST FIRE, OR DO ANYTHING ELSE STUPID!!!
Here's the tank:
Here's the "gun":
If you have any questions let me know.
