Acetylene / propane powered cannon

[oldguy]

Was at a machine shop today way out in the sticks to get some things cut, machined & welded. Got to taking with the owner about BP. He said I have a cannon, but not the BP type, wanna see it? Hell yes, I said. He takes me out behind the shop & sure enough, there is a cannon on a carriage. Barrel was about 6 ft long, 4 inch diameter & 1 inch bore. Fired with percussion caps & charged with a acetylene / propane mixture. He pointed out an old junked 14 ft wide X 50 ft 2 bedroom trailer about a ¼ mile behind his shop (desert county & he owned a square mile). That’s our target. Old Betsy will hit it every time & shoot a ball right through it, like it was a paper bag. He was busy & had customers waiting, but next time I come out, he said he would fire it for me, when no one else is around. I didn‘t have my camera with me, but will on the next trip & get some pictures

 

 

[chipmunk]

My uncle had something like that but it was made out of PVC. Two piece construction so if the mix was to high the top part would fly off. Lantern lighter for ignition and used coffee cans for the projectiles. Had no problem with launching the can a good ohhhhh 2-300 yards

 

Used ether instead of acetylene, not really sure if it was safer but sure made one heck of a bang tho

Edited February 11, 2012 by chipmunk

[NightHawkInLight]

Quite a few people use ether and acetylene in PVC cannons, and both fuels are incredibly dangerous. The combustion pressure usually does not reach the listed bursting point of the pipe, but the rapid spike in which the gas reaches that pressure is enough to shatter the brittle PVC. It's like any other misused device, you can get away with it dozens of times without it ever failing, or it could be on the first try. Unless you're tired of not using your health insurance I suggest using a safer fuel such as propane, or build a cannon out of materials suited to the task - Pressure rated steel or aluminum. Even then, acetylene is not recommended.

[Arthur]

I think thre is a whole sub culture that plays with "spud guns", propellant frequently commes from aerosol can propellant so will be propane/butane.

[kevins]

My uncle had something like that but it was made out of PVC. Two piece construction so if the mix was to high the top part would fly off. Lantern lighter for ignition and used coffee cans for the projectiles. Had no problem with launching the can a good ohhhhh 2-300 yards

 

Used ether instead of acetylene, not really sure if it was safer but sure made one heck of a bang tho

 

 

PVC. dose not show up on X rays !!!!! If it blows up on you the doctors will have dig around in you

 

to find the fragments

 

 

[Mumbles]

Thats a myth that has been discredited by several people.

[kevins]

Thats a myth that has been discredited by several people.

 

 

Opps. still would not want to be around it.If it dose.

[Mumbles]

I completely agree. I also wouldn't want to take a chance that they're wrong.

[Timm]

I been kickin around the idea of twisting up another mini-hybrid cannon.. My first one could quite impress, and in fact would like to go smaller this time, maybe less "frankengun" haha

Anyway, my question is what is the best way to measure peak pressure in such a device?

 

Any sort of resettable gauge would clearly not work, would get its guts wrenched out from the impulse, and be innaccurate if the gas were slowed down enough to not do so, I'd imagine..

Is there anything to give me a good ballpark pressure reading without obscure/expensive piezo devices or transducers?

[NightHawkInLight]

Spudfiles would be the place to ask about that. I've never made a hybrid cannon myself. I seem to remember some people have used one way valves between the chamber and the gauge so that the gas gets trapped where it is readable. I don't think you would have to worry much about restricted gas flow, I think it will force its way in there just fine. To get an accurate reading you would have to check quickly after firing before the gas cools and pressure drops inside the gauge.

[dan999ification]

you could find the combustion pressure with burst disks.

it depends what "x" mix you intend to fire ,efficiency, when you plan to let the burst disk fail, how long the barrel is, weight of ammo,peak pressure is also determined by fuel mix, advanced combustion [fuel meter, chamber fan etc] normally around 120 psi with atm air pressure this figure multiplies by the amount of times you add another atm/ bar of air and fuel, [i think]

4x is around 480/500 psi with propane iirc.

if you use the correct pressure [3000psi] rated steel and stay under 4x mix peak pressure should not be a concern or present problems in small volume well proportioned chambers, the higher the mix, the longer your chamber go and bigger dia is when you get run up to ddt or chamber/breech/barrel failiures. pretty sure you cant get ddt on low mixes with the right c/b ratio and dia's,materials.

most guages need to be isolated from the combustion to prevent breaking, most valves seals will not take the pressure either, if you want to record combustion pressure you need a good [expensive] valve with high pressure rating and expect short life

 

i would look on spudfiles if your serious before you build one,they will welcome you with open arms[and correct me], the hybrid section needs new blood, too many noobmatics nowdays

sb15's tbma has evrything you speak of, and need

jsr has made his fair share of mini high mix hybrids amongst other dakadakadaka things.

 

 

previous posts:

iirc the peak combustion pressure of acetylene at atm is 500 psi and will smash most pvc cannons,as said even if it is rated above that [unlikely in chambers over 2" dia] the spike pressure will finish it, ive seen footage of it breaking welds in steel cannons, it should never be used by someone with a poorly designed/built launcher and incorect materials.

oldguy: maybe your friend has one of these:

an example of a modified "hail cannon" [hail cannons are used to redirect hail and rain away from crops] using a low x hybrid mix of acetylene and oxygen http://youtu.be/hDx-mQqzYNw just for fun.

 

dan.

[oldguy]

oldguy: maybe your friend has one of these:

dan.

 

It was made from what appeared to be Schedule 80 steel pipe.

It was mounted on an axel, with leaf springs & wheels, so it could be towed.

I should go back & take pictures of it.

[allrocketspsl]

Was at a machine shop today way out in the sticks to get some things cut, machined & welded. Got to taking with the owner about BP. He said I have a cannon, but not the BP type, wanna see it? Hell yes, I said. He takes me out behind the shop & sure enough, there is a cannon on a carriage. Barrel was about 6 ft long, 4 inch diameter & 1 inch bore. Fired with percussion caps & charged with a acetylene / propane mixture. He pointed out an old junked 14 ft wide X 50 ft 2 bedroom trailer about a ¼ mile behind his shop (desert county & he owned a square mile). That's our target. Old Betsy will hit it every time & shoot a ball right through it, like it was a paper bag. He was busy & had customers waiting, but next time I come out, he said he would fire it for me, when no one else is around. I didn't have my camera with me, but will on the next trip & get some pictures

 

 

 

yeah baby love to see those vids

[allrocketspsl]

I completely agree. I also wouldn't want to take a chance that they're wrong.

 

when i was 14 years young my friend and I made a pile of pool powder chlorine we lit it off it went huge flames in the middle of the alabama woods to put it out my buddy slap a piece of wood on it when it pslash like flare powder molten goo it landed all over my lower leg on my calves stuck and burn into my leg.didnt hurt at all till i got home went to the doctor he said thats the cleanest third degree burn he ever saw,five months of pealing the scab off to clean the wound.Maybe pvc beaing chlorinated isnt so bad,lol!