Flamethrower Plans. Critique?

[Moonbogg]

Dude I don't like this. I suggest going to an army surplus store and buying a real one and asking them how to use it.

[Ragnarok]

I'm surprised a moderator hasn't brought down the BAN-HAMMER on this thread by now.

Me, not so much. Mod activity has been very low recently.

Anyway, this isn't really ban-hammer territory. This is what loctite* is used for.

Gasoline would weaken the pvc and make it rubbery. PVC is soluble in gasoline.

I mentioned this in the last thread. This is a common myth, which was nicely busted on the old Spudtech forums.
http://www.spudfiles.com/spudtech_archi ... f=6&t=7896

Not soluble in petrol, nor permeable to it either. Bear in mind you can buy PVC petrol cans...

*Thread locker, in case you're thicker than two short planks.

~~~~~

@c11man: Now, I don't advocate taking risks. But equally, that doesn't mean that you should blow them out of proportion. It pays to be reasonably straight with these things, because if someone thinks you're exaggerating, they'll completely dismiss what you were saying.
This is fairly simple psychology. If it sounds implausible, it gets written off completely as false.

It's not often I say this, because people tend to take it the wrong way, but I use basic psychological techniques in my post writing - I write my posts in such a way as to make them more likely to be accepted, taken in and understood by the reader than if I had presented the same information in another manner.
Quite often, I'm surprised how many other people are prepared to waste lots of the effort and time they've put into posting by using things which make the contents less likely to be accepted. Simple things like bad spelling/grammar or unnecessary profanity can bring this curse down on a post.

Now, on the PVC hybrid thing (i.e. what you were saying the other day), I really can't agree. PVC hybrids can be done perfectly safely without them failing. Again - and I quote you verbatim: "it could fail after 3 or 30 shots but it WILL fail" - you were giving what is a possibility as being guaranteed.
Yes, anything will fail eventually, but there's no reason this can't be beyond its working lifetime. Off the top of my head, I can't think of more than a very small handful of PVC hybrids that have gone ground-zero, and some of those were deliberately being destructively tested.

Any unbelievable exaggerations or twisting of the truth (even if it may be true in the most pedantic sense) are unlikely to give your posts any credit, and I'm sure you don't want what you've taken time writing to be devalued by such things.

[c11man]

ok fine i promise to stop exaggerating. i might have a comple more implausible posts but i will work on it. i also have to admite that i am not the most educated on some (most) topics. i just try to sound smarter...

[boom_o_matic_2.0]

boom_o_matic_2.0 wrote:
I'm surprised a moderator hasn't brought down the BAN-HAMMER on this thread by now.

Me, not so much. Mod activity has been very low recently.

Anyway, this isn't really ban-hammer territory. This is what loctite* is used for.

Quote:
Gasoline would weaken the pvc and make it rubbery. PVC is soluble in gasoline.

I mentioned this in the last thread. This is a common myth, which was nicely busted on the old Spudtech forums.
http://www.spudfiles.com/spudtech_archi ... f=6&t=7896

Not soluble in petrol, nor permeable to it either. Bear in mind you can buy PVC petrol cans...

*Thread locker, in case you're thicker than two short planks.

~~~~~

wow I didnt realize that. I always assumed it would "eat up" the pvc.

I'll go sit in my corner now and watch everyone who knows what they are talking about. lol

[c11man]

aw come on. just as long as you dont start cutting yourself while in that corner

[boom_o_matic_2.0]

aw come on. just as long as you dont start cutting yourself while in that corner

nope. just writing poetry by candle light and listening to pink floyd.

[mik3v]

ok I"m suprised a moderator hasnt brought down the BAN-HAMMER on this thread by now. lol. plus too gasoline would weaken the pvc and make it rubbery. PVC is soluble in gasoline. not only is there a risk of combustion, there is just a risk of it popping like a big flamable balloon. if you wanna do it, use a different pressure source AND different fuel. the whole design is a flop. sorry dude

thanks for your concern but we did some tests to be sure.
we took a piece of pvc and stuck it in a 5 gallon bucket filled with gas for a week. and no change.
thanks though

[mik3v]

It seems like you've got this week's sardonic wit brigade.
No offence guys, but a little less sarcasm (particularly on the repeat points) and a little more useful input would benefit the forum.

Also, c11man - you seem to have a habit of assuming the worst possible scenario to be the probable scenario. Yes, there's a chance it could combust - that does not mean that "[his] tank will go boom". Could and will are very different.
I wouldn't recommend mixing compressed air, fuel, unrated PVC and ignition sources either, but I'm not going to say it's certain that explosions are going to follow.

~~~~~

mik3v. My best advice to you is Google for Roland Tower's creation (But I'm not going to give a direct link, sorry). It's got a decent set of build instructions with it.

Still, like suggested, propane (preferably regulated) is a better pressure source for a flamethrower than compressed air. Indeed, military flamethrowers will use either pure nitrogen or propane to reduce the risks of ignition. Nothing with oxygen in it.

Good tough pipe is also a must.

Thanks for your imput. im tired of people jumping to conclusions and assuming they are soo much smarted and have to rip on us.

So far, we have soldered copper pipes and fittings together to assemble the gun and the trigger valve that is supposed to be for an air compressor. We have built the PVC tank and that is how far we are. We have pieces that we havent installed yet to have a hose from the PVC fuel tank to the bottom on the gun. We also have bought parts for the propane that fuels the pilot light. We are still working on what parts to use and how to do so to add either propane or compressed air into the PVC.
We also have a fuel port in the top of the tank in addition to a gauge to tell us the PSI in the tank.

sooo... we are having trouble with getting a tight seal with the brass parts screwing into the tank. And finding parts to be able to add propane to pressurize the tank....

[Technician1002]

It seems like you've got this week's sardonic wit brigade.
No offence guys, but a little less sarcasm (particularly on the repeat points) and a little more useful input would benefit the forum.

Also, c11man - you seem to have a habit of assuming the worst possible scenario to be the probable scenario. Yes, there's a chance it could combust - that does not mean that "[his] tank will go boom". Could and will are very different.
I wouldn't recommend mixing compressed air, fuel, unrated PVC and ignition sources either, but I'm not going to say it's certain that explosions are going to follow.

~~~~~

mik3v. My best advice to you is Google for Roland Tower's creation (But I'm not going to give a direct link, sorry). It's got a decent set of build instructions with it.

Still, like suggested, propane (preferably regulated) is a better pressure source for a flamethrower than compressed air. Indeed, military flamethrowers will use either pure nitrogen or propane to reduce the risks of ignition. Nothing with oxygen in it.

Good tough pipe is also a must.

Thanks for your imput. im tired of people jumping to conclusions and assuming they are soo much smarted and have to rip on us.

So far, we have soldered copper pipes and fittings together to assemble the gun and the trigger valve that is supposed to be for an air compressor. We have built the PVC tank and that is how far we are. We have pieces that we havent installed yet to have a hose from the PVC fuel tank to the bottom on the gun. We also have bought parts for the propane that fuels the pilot light. We are still working on what parts to use and how to do so to add either propane or compressed air into the PVC.
We also have a fuel port in the top of the tank in addition to a gauge to tell us the PSI in the tank.

sooo... we are having trouble with getting a tight seal with the brass parts screwing into the tank. And finding parts to be able to add propane to pressurize the tank....

I have always been uncomfortable with pressurized fuel in this type application because the fuel container is Flammable, leaks are common, and if dropped, PVC may shatter under pressure. Can I recommend a safety pressure vent? In case of a hazard the pressure can be quickly blown off in a safe direction.

On a smaller scale, a gas coleman lantern tank and pump may be a safer fuel container. It's metal and contains a pump.

[rikukiakuchiki777]

I once gave this a thought, but after a few minutes of research I found PVC was soluble in gasoline, so I'm surprised you have not done the same. How much have you actually researched? I would definitely recommend forgetting flamethrowers, even though countless people on youtube have done it successfully. I think we're a long way overdue for some horrible, homemade flamer related death.

Anyway, I know its wrong to encourage this (and I'm contradicting myself) but out of curiosity, could a propane tank attached to a high flow blowgun (one with the long 'barrel') with a small nozzle work? I don't know the pressure of an LPG tank, but if it was high enough, say 120psi, a decent flame size might be produced. The cons of something like this is that gas fires are a lot safer than something like liquid gasoline fires, and there is little to no chance of combustion inside the actual tank.

But again, fire is bad, don't do it.

[smiley_666]

ok, i might be completely wrong, but could you not have a separate pressure vessle (propane tank) and the petrol tank. you have the petrol tank non-presurised and have the petrol 'feed' into the propane via a venturi.
saves having to try and make the petrol tank air-tight and avoid pressurizing it as well (should stop being warned about it exploding so easily)
hang on, ill draw it up in paint...

here we go;



as for performance, i have no idea at all, but it shouldnt be that hard to make...

[jimmy101]

PVC is soluble in gasoline.

No it isn't. PVC has "fair" to "excellent" resistance to gasoline depending on the type of gasoline.

http://www.pvc4pipes.org/faq/chemical-r ... -pipes.htm
http://www.rutlandinc.com/industrial/RP ... .Chart.pdf

[inonickname]

I'm going to go out on a straight line here and say that using any gas that is an aid or sufficient to support combustion as a pressurizing agent for gasoline is a bad idea.

There are better ways to do it, so I'll try start your brain ticking.

You need a check valve between the gun and tank, as well as a main valve. Just a safety factor.

To force the gasoline out you could use a springloaded piston or venturi to draw vapor- though then you would end up with more of a torch.

Some water guns (super soaker CPS) used a rubber diaphragm as a chamber, so the elastic energy of the rubber kept enough pressure on the water to keep enough power up.

Just ideas, but at the very least pressurize the chamber with an inert gas.

[MrkSutter]

I too am working on flamethrower project, so here's my two cents:

1. Each time before using the gun, check to make sure there aren't any structural faults in the tank. Do this by pressurizing the tank at low PSI and spraying soapy water on the exterior--if you see new bubbles forming on the tank, it would be best not to fill it with gasoline at high pressure.

2. Use an inert gas to pressurize the tank, not propane or air. Propane is not inert, and if the tank happens to fail while the gun is operating, you may find propane and petrol spewing into the air around you and catching on fire. If a CO2 filled tank fails, the danger is far less because the CO2 will tend to choke off any potential ignition.

Also, when the tank gets empty during operation, there is usually a "suckback" effect which pulls air and flame back up into the gun. I know people who have nearly been killed because the suckback went all the way back into their tanks (which were filled with air). Even if you pressurize with propane, there will still be some air left in the tank when the gasoline is all used up, and there will also be some propane left; propane mixed with air and flame = explosion + 3rd degree burns!

With CO2, the chance of a tank exploding is very small.

3. Good luck!