Monday, 20 June 2016

Flamethrower details

In a previous post, I mentioned that I had been building a flamethrower on and off over the last year or so, and at the time of the post I had not completed it yet. I was also a little sparse on the details and pictures. Well anyways I have long since gotten it finished and actually revised the design slightly. So here are a few more details and pictures and whatnot of it all.
First off is this one. This shows most of the components of the flamethrower before it was assembled:
A quick picture of the tank as it is holding its very first pressure test:
And a closeup of the bottom showing where I drilled and tapped the bulkhead fitting into the tank.
Getting that hole was no easy task. I think I ended up turning a floor mounted drill presses table 90 degrees to what it normally is and using about 7 ratchet straps to secure it to the table at the right spot. But I got it made. You can see where I spent a bit of time with a sander, smoothing out any inconsistancies in the metal and removing all the paint where the o-ring seals.
Here you can see detail of both the torch mount, custom made from some scrap sheet metal, and the device that I made to prevent the fitting from turning in the bottom of the tank or coming loose. Hydraulic hose does not have any torsion at all to it. If you twist one end, the other one is twisting as well. I was worried that if I accidentally twisted the gun handle or whatever, my fitting would start to spin out of the tank or rub the o ring or any number of other bad things. So I took a piece of nice thick aluminum I had laying around, roughtly cut it to fit the bottom of the tank and extend out one side. Then I painstaikingly drilled and filed and drilled and filed and drilled and filed some more until I had a perfect hexagon that fit right over the fitting. I drilled a hole just on the side of the tank and secured a bolt thru it. Then hose clamped the bolt to the tank in exactly that position, effectively eliminating any possible movement.
Heres a picture of the flamethrower all completed and waiting to be used. In this shot I have a HPA tank hooked up instead of a CO2 tank because I believe I was again doing some water testing.
And this is how I store it. The barrel unthreads from the gun handle for ease of storage, the valve unthreads from the the top of the tank and the paintball remote line has a quick disconnect on it. 
I mentioned in my previous post that the spray coming from the wand was dissapointing in range, and so before I even tested it with fuel instead of water, I went to the hardware store and purchased several 1/4" caps to thread on the end of the barrel and drill different sized holes in to see which was the most effective.
I ended up using one with a hole this size:
It did work fairly well, I have some video that I will post later showing the flamethrower firing using this tip, but I found that as it shot out, the harsh reduction in size caused the water or fuel to spray out and atomize more quickly rather than coming out in a stream as is more beneficial to a flamethrower. Nonetheless it did work and produced some impressive flame, it just needed to be improved.
Princess Auto came to the rescue with a 1/4"x1/8" reducing coupling and a 1/8" small nipple. Both designed to be used in hydraulic systems and therefore rated to 5000PSI or so. The 1/8" nipple is a fair amount smaller inside due to the thick walls needed to contain such pressure and has nicely beveled ends on both ends that cause a much smoother transition for the fluid and therefore more stream and less spray. The smaller ID means less fuel flowing thru, and therefore perhaps slightly smaller flame but longer lasting. I can always drill it out if I find myself needing more flow. Here are a couple of pictures of the upgraded nozzle:
Gotta have the first person camera to capture all the fire coming out of this thing, so I cobbled together a mount from PVC and pipe clamps. This is the only piece on this whole build that is just kludged together without much care. Its a non critical part, and I wanted it to be easily customizable.
Here's what the buisness end looks like. I think it looks kinda threatening personally :)
And for the final picture of the day, here it is as it is sitting right now. The other two modifications that you can see are the shorter line running from the tank to the gun handle and the shorter propellant tank assembly.
When I was first designing and building my flamethrower I wasn't totally sure how long of a hose I would need between the backpack tank and the gun handle, and because I didn't want to come up short, I bought and used a 6' hose. Which did indeed work, as you will be able to see from the videos of it in action, but it was not optimal. First of all, I am a tall guy and the hose hung down and almost dragged on the ground, not very practical. But more importantly, the longer the hose the more line pressure loss you have due to friction and other things. I'm sure if you asked an engineer, they would be able to tell you exactly why. I just know that as short as possible is better. So having some practical experence under my belt, I settled on a length of 3' for my new hose. Its just about the perfect mix of length for manuverability, without being too long and having too much line loss. Also hangs to a much more reasonable height above the ground. The second mod also has to do with simplification and  line loss. The paintball remote line was quite long, and had the quick disconnect fitting on it. I already covered line loss, and the QD was a little finnicky. Needed to be presurized and then wiggled around to seal properly. And having to hose clamp the tank to the fuel tank and undo it every time you needed to change tanks got old fast. All those problems were solved by just buying a paintball ASA (the thing you screw onto the top of a paintball tank and just connecting it directly to the CGA346 adapter that threads into the valve. Less line loss, no finnicky o rings, and easy bottle changes.

To end this post off, here are the videos that I took while pressure testing once all the upgrades had been made. First one is pressuring it up and describing the modifications, second is from the first person camera showing the upgraded spray pattern. Enjoy!

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