Friday, 4 March 2016

The building of a flamethrower.

Over the past year or so, I have been ocasionally working on a homebuilt liquid fuel flamethrower, just on and off, whenever I had some spare time or money to buy parts. Today I finally finished it enough to do my first testing on the sucker. No flames yet, just some underwhelming water spraying, but enough to prove that its all coming together.

Thats the beastie there. Built from an aluminum frame backpack, an old SCBA tank, a paintball tank and accompanying remote line, and some misc. high pressure fittings and hose. I haven't got the propane torch on the wand in this picture cause I've yet to finish the final mount for it, but its together enough to finally allow me to do a proper pressure test on the whole thing. 

Safety has got to come first when you are building something like this. 800PSI, Gasoline, mistakes and sloppy work do not mix very well.  So I am taking it slowly, making sure things are done right. Anyways, I got it done enough for a pressure test. I filled the fuel tank with water, screwed on the valve assembly at the top, laid it down on my concrete front steps and ran the remote line to the air tank inside:

When I actually run gasoline or diesel in it I will be using a 20Oz CO2 paintball tank as propellant to ensure an inert environment in the fuel tank and all the lines right up to the nozzle. Both fuels will not burn in a liquid form, only the vapours burn, but the CO2 ensures that there is absolutely positively no chance of a flashback into the tank. Safety first. But CO2 is expensive and I am just using water for the moment, so I am safe to use my paintball HPA tank instead. The scuba tank I used to fill my HPA tank didn't have very much pressure in it, so I only managed to squeeze in about 1000 of a possible 3000PSI:

Doesn't really matter for the pressure test because it has a regulator that takes it down to 800PSI anyways, I just did not have the volume to keep the tank at that much pressure for very long. 

With that all set up, I ask that you please direct your attention to the video below. Exceedingly poorly filmed iPhone first person flamethrower pressure testing:

As you can see from that video, (sorry for the shakeyness and the general poor filming quality, I'm a tinkerer, not a film student) my remote line disconnect had not seated all of the way and was leaking a bit. I fixed that up and tried again:

Mostly leak free. Most importantly, the fitting that I tapped and O-Ring'd into the bottom of the tank held beautifully,  but there were two of the NPT connections I had not tightened up enough and had very small leaks. This would be exactly why you always test with water first.
The JIC union right off of the bottom of the tank sealed up nicely, it was just the two joints at the coupler. I have since taken them apart, re-doped them and re-tightened them to a tighter fit. At the time of writing I have not re pressured them back up to see if they hold now. 

Couple of things to note about the video, first, again sorry for the terrible quality, trying to film and do stuff at the same time is rather difficult with no proper equipment. And second note the totally underwhelming spray coming out of the gun. This is do to a couple of things. Most notably that the propellant tank was as I mentioned only filled to 1000PSI. So after the very first shot, which I didn't even get in the camera lens, the pressure in the whole system dropped to probably drastically less than 500PSI. When a CO2 or properly filled HPA tank is used, it should keep the system at a fairly constant 800PSI throughout the entire full to empty cycle of the fuel tank. And second, I did not have any sort of restriction at the tip of the wand, it was shooting at as full of a volume as a 1/4" pipe could muster. If I were to reduce the size of the opening from which it sprays, it would shoot less volume but much farther. 

Those things said, if you take a look at this video from this guy: (absolutely no relation or endorsement or anything besides me finding his video on youtube and thinking it was reletively neat) you will see that his stock flamethrower shoots water about the same distance, and flames much, much further. So even with it as it is, it should shoot some decent flame. 

Anyways, thats it for now, be safe out there and have fun!