propane cylinder high flow discharge unit

[51K]

So a while back I saw a demo of a high volume propane discharge / fireball unit. Actually, the piece fired and discharged a large cloud of propane but failed to ignite the propane. I was really impressed by the idea. So just a little while ago I decided to make one of these fireball generators. Below are 2 photos of the propane popper in progress:

http://www.hot51.com/pics/pyropopper.jpg

and

http://www.hot51.com/pics/pyropopper2.jpg

The concept is that the propane can just barely slides into the 4 inch internal diameter pipe. The needle ram piece (which has not yet been welded together in the photos) slides into the other end of the pipe. You put a black powder charge doped up with some titanium or magnesium chunks in a film canister behind the ram and screw on the endcaps. The unit is fired electrically and the black powder charge flings the needle/ram unit forward which cores a hole in the bottom of the propane cylinder which then discharges propane at a HIGH rate. Since the breaking charge is doped up with the titanium chunks, it will throw sparks through the same vent holes the propane flows through and walla - a big fireball. I have not tested this assembly yet but will post up pics when I do. I figure I may have to add a second ignition source outside the pipe for guaranteed ignition of the propane.

I did not invent this concept but it sounded like a fun idea. I wouldn't be suprised if this type of thing has been posted here before but I figured I would give a review of mine here anyway.

[meselfs]

I made something like this out of PVC when I was 12. It shot propane firebal about 2 meters, very simple.

Just be careful about this: the explosion could cause the valve to remain open.

[51K]

I am talking about blowing a 2 inch diameter hole out of the bottom of the canister and dumping out all the propane in about a second. Basically a one second burn of a pound of propane.

[meselfs]

Oh, my error. Sorry.

[NightStalker]

This ota' be fun! :)

Be sure to get video, eh? ;)

[Sparky]

Hmm, 51K, you weren't by chance at the PGI convention in Wyoming last year were you? I saw something just like this there, as part of a Hollywood pyrotechnics class. They used it when a smallish, clean fireball is needed and hence gasoline is not suitable to make the fireball. The device that I saw seemed to be very reliable, I'm surprised you saw a failure. I guess in the movie business it has to be reliable.

[51K]

I saw it at that class that was given at another location. The break charge popped the bottle open but failed to ignite the propane so I really don't know how big the effect should be. Sounded like a neat idea.

Anyway, I have tentatively scheduled a couple test shots in Reno this weekend. There is a gun show and machinegun shoot this weekend. Hopefully we will have success and I will post up a couple video clips. Leaving in a few minutes so I won't probably get back to the web till after the weekend. I will probably have the pipe on the table at the show so if you see it, stop by and say hi.

[mongo blongo]

I would use slow burning stars instead of chunks of metals in the charge since the metals require oxygen to burn. I'm not saying it won't work but stars would be much more reliable. Can't wait to see this thing go off :) Good work!

[nbk2000]

This would be just the thing for pre-positioning as a vermin-clearing device in a building, in case of vermin invasion.

Like a thermobaric, only cheap and easy to make. :)

[51K]

Took the thing up to the reno machinegun shoot to test fire. First bursting charge was coarse chunk commercial black powder (the type usually used in lifting aerial shells), one film can in volume. The charge did move the piston but only caused a dent in the bottom of the propane cylinder. For the next charge, I got a small water bottle and cut it in half to hold the black powder. The second charge was doped up with some magnesium chunks for added spark effect and the charge was the same coarse black powder, say about the size of .177 pellets you fire out of a pellet gun. The second charge was probably 4 film cans in volume and shot with electric match like the first.


Yeah - so let me tell you a little story about pressure forming sheet metals with explosives....
:rolleyes:

The charge ignited and showered the area with sparks. The piston blew a big hole in the bottom of the cylinder and all the propane dumped out through the holes and produced what appeared to be about a 20 foot in diameter fireball. No earth shattering kaboom, no fear of god and hellfire, no little dump of adrenaline - just one big non scairy fireball and no lingering aftertaste ala black rolling cloud like a gas bomb - er, I mean gas powered special effect - would give.

I was pretty much not impressed. But the fun was just beginning. The bursting charge mashed the propane can so bad it flowed in an elastic state and mushroomed into the $30 end cap so although I could eventually unscrew the endcap from the pipe body, still to this day I have not been able to beat the propane cylinder free of the endcap. It mushroomed into a space just behind where the threads are cut into the end cap and will NOT come loose. Prolly have to cut it out in chunks with a dremel.

So to sum it up if you have need of about a 20 foot fire ball with no lingering cloud or liquid fuels to possibly contaminate your blasting area, this thing works just fine.

I ended up monetarily in the thing close to $130 including the pipe and two endcaps, and probably two to three hours drilling and deburring holes. 4 inch internal diameter heavy wall pipe with threading is expensive.

Kinda makes me start doing the mental calculations on how much 400 mesh aluminum and chlorate I could have bought instead.

Anyway, I have video that I need to edit down to a manageable size and will post up a link when I have it available.

[nbk2000]

A 20' diameter fireball with little noise, no smoke, and you're complaining?

Well, I guess since you were doing it as a special-effect project, that's understandable. But, as a weapon, this'd be great!

In an enclosed space like a room/parking garage/tunnel, this'd be great for burning out vermin. :)

How about using a plastique ring (with half-cylinder liner) around the canister, magnesium chips 'frosting', and blowing that?

The explosive will cut the cylinder clean in half, instantly dumping the gas, and the burning magnesium does the rest.

To prevent the cylinder from getting squashed in the endcap, make a steel plug that fits in the pipe, which has a funnel shape to it, and that should act like a bullet-trap does.

[51K]

I am sure the occupants of a room or enclosed space would feel pretty unhappy about the thing.

Bringing me to another item I had been thinking about building but as yet is still in the concept phase. This would be a backpack portable 'high volume high speed mold decontaminant'. A metal stand with electronically controlled valves that operate a small oxygen and a small acetaline tank, blowing both through some sort of mechanical mixing vortex. The controller would run the tanks for a pre set amount of time and then the barbecue sparker would spark. If you are talking about launching pieces of a structure on the cheap, or giving the occupants a whoa shit, this would seem the ticket. I am thinking if it was built like a brick shithouse you could just wait till the pieces stopped falling and then go back and dig it out of the rubble. I haven't looked into the mechanical costs of such an item but I am sure it would be a hundred times more exciting than the propane popper. I would also think this would be a LOT safer for the operator than trying to fill a big plastic trash dumpster liner with an oxy acetalyne mix as you could put a delay in the circuit and leave before the two started to mix.

[meselfs]

I'm thinking: what if you had a really slow burning compostion to surround the tank, maybe even sugar/saltpeter, & let the pressure resulting the heat rupture the cylinder. Some magnesium in the mix should guaruntee ignition of the propane.

I don't think oxy-ethyne is a good plan. Ethyne is a bit more unpredictable then most think...
But oxy-propane would work great.

In fact, if propane will not react with oxygen even under pressure, what if you joined an oxygen cylinder to a propane cylinder and let them diffuse.
Definitely, the mixture would be far to rich, but it would be much more powerful then propane alone.

[51K]

The slow heating till it pops sounds pretty good in a situation where it is safe to let fly with some metal pieces at high speed. I would get the boot for sure at the pyro events I go to - permenantly. Sounds like something I will have to try somewhere in the middle of nowhere.


An oxygen and acetalyne mix pops GREAT. Maybe the term I am looking for is fantastic or BEAUTIFUL. In any event, do a search in the forums for oxy/acetaline mixes. Maybe I just suck at spelling but I think it is acetaline. The mix is used in welding/cutting torches.

[nbk2000]

Acetylene.

.............................

[meselfs]

The slow heating till it pops sounds pretty good in a situation where it is safe to let fly with some metal pieces at high speed. I would get the boot for sure at the pyro events I go to - permenantly. Sounds like something I will have to try somewhere in the middle of nowhere.


An oxygen and acetalyne mix pops GREAT. Maybe the term I am looking for is fantastic or BEAUTIFUL. In any event, do a search in the forums for oxy/acetaline mixes. Maybe I just suck at spelling but I think it is acetaline. The mix is used in welding/cutting torches.
I realize that...

... I own a cutting/welding torch :-P

Even without oxygen flow the ethyne will make a pop sound when ignited.

The heat of formation for propane is negative, but for ethyne it is (very) positive, which accounts for the all the energy.

But ethyne can be unreliable. Probably, it's safe enough... but still keep in mind that it just might turn on you.