Homemade Flamethrower
 

I've been lurking around here for quite some time, but haven't posted anything becuase I didn't have anything to say. Well, I made something I could talk about.

<a href="http://dotd.net/fire/flame.wmv">flamethrower!</a>

Note: I don't know how well my host can hold up. They're pretty pathetic at times.

The fuel tank is a 20lb tank, not 30 as the video says (typo, too lazy to correct it).

I've fueled and fired this thing 5 times so far. It is quite a sight to see in person. I usually fill the tank a little over halfway, to maintain pressure. With the compressor attached to it, it can maintain pressure for the full burn time. That video only shows the tank pressurized to about 90psi tops though. Maximum is 135psi.

The hose is a Buna-n hydraulic hose and all connections have gas-safe (as I was told, and as experiments in a bucket of gas have proven) threadlocker on them. Everything is rated for at least twice the pressure it is under.

The fuel tank has an air inlet and gas outlet at its top. A pipe internally extends down to the bottom of the tank to siphon the gas out.

The gun assembly is a pressure washer gun with about 12" of brass pipe that terminates in a check valve, then the nozzle (1/4" nozzle in this video). The gun was also left partially open in a bucket of gas for 24 hours and the seals did not degrade at all.

Since this thing is essentially a fuel air bomb, flashback is a huge concern. I haven't been able to find a flashback arrestor for use with a liquid like gasoline. Any suggestions on where to get one?

Total cost: Under $160.

Beyond that, any ideas for improvement?

Disclaimer: This is probably one of the most dangerous things you could ever make. Don't make one, don't try to make one, don't think about making one.


EXTRA DISCLAIMER!!

If ANYONE of you is stupid enough to try this, don't come crying back here.

This is probably one of the MOST dangerous things I've seen posted, because one simple mistake or screw up and you've made a full air bomb that can demolish a house or you've set yourself on [b]fire[b], which as I understand, is a particulary painful way to die (I hear that survivors actually wish they had died).

So please, don't make TFP the next example of "Guy does something stupid he read about on the internet, so lets censor the internet".

-lebell


EXTRA, EXTRA DISCLAIMER!

Original poster here. Once I saw the above disclaimer, I thought it prudent to add this bit extra:

If something went wrong with this device, it WOULD explode. And the above disclaimer's statement about a house being demolished is entirely true, and maybe even conservative about this thing's destructive power.

Taken from http://home.earthlink.net/~jimlux/energies.htm:

Gasoline has an combustion energy of about 47.4 MJ/kg, so a simple calculation will show that the cup (170g) will release about 8MJ when burned. When vaporized and mixed with air at the optimum ratio (stoichiometric), the mixture will occupy about 2100 liters, or a sphere some 0.80 m in radius. Assuming the mixture is ignited at the center of the sphere, it will take about 2.5 milliseconds for the flame front to propagate to the outer edge. This makes the assumptions that the flame front moves at the speed of sound (probably reasonable), and that the sphere of mixture doesn't expand appreciably due to the heating in the middle (probably very optimistic). So, 8 MJ in .0025 seconds is 3200 MW, or 3.2 GW


3.2 GIGAWATTS. That site states that a 3000lb car hitting a concrete wall is only 2.1 MEGAWATTS. This fuel tank exploding will incinerate you.

DO NOT DUPLICATE THIS PROJECT!!

That is completely awesome, i would also be very concerned about flashback though.

IIRC, a flashback arrestor is composed of 2 concentric tubes, one smaller in diameter than the other. The inner tube is perforated, the outer tube is not and at least 1/4" of free air space separates them. The inner perforated tube is usually a little shorter in length than the outer tube. Sometimes there are 2 concentric perforated tubes surrounded by a non-perforated one. The flammable material is ignited just beyond the solid outer tube. I doubt you can buy it ready made but it is an easy part to fabricate to be sure.

soundmotor

holy fucking shit!


your my new hero...


if you need anything welded for this thing, shoot me a PM, I'll do it up.

I believe that type of arrestor would be used for things like Oxy/Fuel torches, natural gas lines, etc. Gasoline, being liquid, is a very different animal. I'm not even sure that flashback is possible if the fuel line is 100% filled with fuel (ie, no oxygen for combustion).

Flashback would occur if the nozzle got blocked, the hose got a leak, or, worst case scenario, I kept squeezing the trigger when the gasoline stream became atomized (becuase its almost out of gasoline). For the latter situation, a giant explosion is almost certain, in my mind. Atomized gasoline, under high pressure with a large supply of oxygen? It'd be like being inside an engine cylinder, only much more devastating.

Truth be told, this thing is terrifying to operate. But its so much fun! :D

I think that if I can keep the fuel from atomizing (by releasing the trigger before it starts to), I won't have a problem of sudden rapid expansion of my personal self.

The only solution that I've been able to come up with would be installing some kind of float valve inside the tank that would safely shut off flow somehow when the fuel level dropped below a certain level (like the overfill device in propane tanks, or your toilet).

Another solution would be to use a nonflammable gas, like nitrogen or carbon dioxide, to pressurize the fuel tank, rather than regular shop air. I like this idea much better, but, as with everything I do, price was more of an issue than safety. I wonder how much it costs to rent/fill an N2 cylinder from Airgas.

It doesnt cost that much, 20 bucks for tank rental and 30 for a fill I think? Working with high pressure bottles can be a chore in and of itself tho, you;ve gotta regulate that down somehow...

WTF!?...You gonna go find an enemy bunker to take out now? :lol:

That's awesome. I want one.

Do they not include a regulator with the cylinder rental? A regulator for this setup would be at least $70.

Flame cannot propagate through perforated tubes; again IIRC. This is the same type of arrestor you would see on old style, squatty metal gas cans. It doesn't matter if the flame is feeding on a gas or a liquid it will not pass on. The best bet would be to find an image of a WWII flamethrower arrestor and compare. Once in a great while, Numrich has nozzles for sale BTW.

If I recall my HS chemistry/science, you are correct in your assertion that "I'm not even sure that flashback is possible if the fuel line is 100% filled with fuel (ie, no oxygen for combustion). " It will only combust where exposed to oxygen. However, using nitrogen as the propellant intuitively makes sense to me and does indeed seem far safer than shop air. Why not use a nitrogen tank from a paintball system?

soundmotor

It feels pretty good to be in the company of smart, sick, bastards BTW!

:D

soundmotor

I'll certainly look into the arrestor you described. If I can't find one, the way you described it made it sound like I could fabricate it, with some good technicals on it.

When you say Numrich has had nozzles, what exactly do you mean? Complete flamethrower gun assemblies?

Also, the paintball system sounds good, but a bigger cylinder sounds better. I'm not a paintballer, nor have I had much experience with compressed gas bottles. Would one of those small N2 paintball tanks have the volume to feed the flamethrower?

Hehe, thanks.

At least we know that out deaths will probably make it beyond the obituary section.

ROTFLMFAO!

soundmotor

The nozzle meaning the part with the handles & trigger that the tank hoses connect to. As far as the paintball tank goes, I'd investigate one of the backpack sized ones. They are about as large as small fire extinguisher. The amount of volume it would hold would be directly relative to how much fuel you want to shoot I'd imagine???

Standard disclaimer, we are of course speaking in a purely educational/theoretical fashion, ahem......

soundmotor

I'll be on the lookout for any parts. Getting to see one would be of GREAT help. I've looked all over for technical drawings, or even detailed explanations of the workings of these devices. But everything I've found has either been incomplete, speculation, or total junk.

I've thought about scrapping the current pressure washer design and making one from scratch. I think I could do it in a week if I had a lathe. (one of which, coincidentally, I'm planning on building - Not a Gingery one though. Those are too small.)

I just searched around for paintball N2 stuff, and for the prices, I might as well get a regular N2 setup. It would probably allow me to be a bit more flexible with setup.

/right, thought exercise only

Always buy paintball support items used. Lots get in & get out but not until after they've bought all the toys with dad's money.

Semi OT -

As far as a lathe, I looked at building one too & also looked at the Gingery approach. First you stake a claim, then you mine the bauxite, then you smelt it into raw aluminum.....

In the end, I started checking used machinery prices & discovered that you can find a used South Bend, Atlas, or Monarch with loads of tooling for $600 or so. Just a thought. Believe me, I am all for self-reliance but I'm also for having more time to build end use projects, not the projects needed to complete the end-use ones if that makes sense?

soundmotor

I'll check out the paintball approach.

As for the lathe, I'm just beginning to look into it. I was looking at making it out of heavy steel tube, although getting everything straight would be "more than a bitch." $600 is a lot for a poor college student, but it might be the only way to aquire one.

As for using tools instead of building tools, hey, what else am I going to build, a homemade battle tank with rotating turret and working gun? (yes)

pretty nice... I made a back-strap version... lasts for ~30 seconds of continuous flame(u dont do that though). PVC tank... pressurized w/ compressor... regular (steel?) plumbing pipes for handle and nozzle with soem brass fittings to top it off. Uses denatured alcohol instead of gas... burns a lil slower and flames look better... plus it wont dissolve my tank... i always wanted to make a metal tank version though.

OH HELL YEAH

oooh, {envious}

holy fuck that is awesome, but dangerous, i dont know if id have the balls to try it out lol

That is freekin awesome!!!

when you get that regulater or whatever you want to a test without you holding it

Man that is awesome. It sounds juvenile (me complimenting it) but I truly is an Awesome creation. Very dangerous also, but hey, if that's what you like doing, that's what you like doing.


You should make some targets made out of milk jugs of gasoline or something that will explode when you "flamethrow" them. That would be fucking sick.

thats fucking unbelievable man. Its like movie star shit, really nice work. Keep it up!

That's some crazy shit. I can imagine Arnold scorching an entire army with that bad ass thing.

wow... just wow

That is what Macgyver would make if he had those tools to work with.
That's awesome dude.

They're not that small, and I'm sure if you wanted more volume you could rig up a system to use a small battery of tanks.

Thats Crazy, Ill Stick with my hand-held flamethrower (WD-40 and a Lighter)

Holy CRAP that was amazing...You don't by chance live near Wilmington, DE do you? :D There's a special delivery I'd like you to make out that way....hahaha.

dashdot are you a Dr. Strangelove fan? just wondering. Oh and nice flame thrower.

That's amazing! Just stop while you're ahead dude!

Thanks for sharing

Next week on FOX!
Watch as crazy white people do stupid shit that they shouldn't do on ... When Honkies Attack!!!

j/k
It's pretty awesome that you got this to work without killing yourself and harming a bus load of orphans and 12 nuns in the process.

Woah, I should check back more often. Thanks for the comments. I haven't had any time to work on it since January because they won't let me have power tools in my dorm room. But I have done a little thinking.

Regarding the use of paintball equipment: I decided to get a gas conversion kit for my little flux core welder, so with a high pressure regulator and hose, I should be able to use that.

I'm also going to be on the lookout for an old compressed gas bottle to use as the fuel tank, and up the pressure to maybe 250psi. Jelled fuel too. That should result in a significant rise in the violence level of this device.

I've met a guy with a lathe and mill who's willing to teach me some machining and help with making a new gun assembly. The pressure washer gun works and has proven to not leak, but for reasons of lingering doubt and also asthetics, I'd like to have a nozzle specifically for this purpose. Also, this would allow for a greater flow rate (30 gal/min should be good :eek: ).

I'm certainly going to continue working on this thing over the summer, but I've got a few other projects that need to be done first (A logsplitter and a big roof over a dog pen. WTF? I'm a computer science guy. What's wrong with me?)

I'd also like to build a "tank-like" vehicle. If anybody would like to donate parts, like engine, hydraulic pump/motors, or TRACKS, I'd be grateful. Hell, I'll let ya have some time on the 'thrower :D

Indeed I am.

A Lotek Approach

soundmotor

WOW!! Is that you in the video?! I can't believe you had the balls to build your own flamethrower, let alone actually fire it. That's damn impressive.

No, it is not me. However, the results are so impressive that I'll certainly try it. I'd bet you'd get even better results if you mixed the washer concentrate with light oil such as Marvel's Mystery or WD-40. The washer concentrate is probably solvent enough to mix with it. Likely, it would eat into the plastic and ruin the soaker after a few times. But, golly, it would be a great ersatz, "Get out of my effing yard!" device should you find yourself in danger of being over-run by zombies.

:lol:

soundmotor

I thought the same thing when I saw this. I must say I appreciate the music. The flamethrower was alright too, I guess. [/understatement]


Now, unless I'm mistaken (which I may be - don't take my word for it) the gas tank can't simply "combust." If you fuck up a seal, the most you'll have is unintentional discharge, in the wrong direction. Now that could be pretty bad too - imagine, if you will, being shot in the back by your own tank. However, the ball of death described as above shouldn't happen. Gas doesn't work like that - it has to be misted into a piston chamber to explode correctly, and that doesn't change if it's in a backpack.

Disclaimer: I'm just some guy. Like I know what I'm talking about.