My dad believes that if I use propane or MAPP gas in a hybrid or even a simple combustion (PVC or steel or aluminum), and ignite it, the whole gun will explode into tiny pieces. Even if I use the reccomended amount of fuel for my size of cannon.
Anyone care to give evidence that he is wrong?
Posted: Sat Apr 12, 2008 8:04 pm
by benstern
The maximum combustion pressure of Propane is around 150 psi. It rarely ever gets to this in normal combustions. Pressure rated PVC will work with this as well a half inch thick walled steel pipe used for air conditioning and heating ducts.
This is just another case of parent ignorance, it happens somewhat often.
Posted: Sat Apr 12, 2008 8:05 pm
by mopherman
simply tell him that the average pressure of a 1x propane ignition is close to 90psi for a very short period of time. Then tell him that pressure rated pvc is more than enough to handle that pressure and temperature. Its written right on the side of the pipe.
Posted: Sat Apr 12, 2008 9:07 pm
by miskaman
Thanks, I'll see what he has to say to that.
Posted: Sat Apr 12, 2008 9:10 pm
by Blitz
Plus, it's only exposed to that kind of pressure for milliseconds of time.
Posted: Sat Apr 12, 2008 9:12 pm
by potatoflinger
My parents are the same way, they won't let me build a combustion gun, but they will let me build pneumatic cannons. (which I think are more fun anyway).
My advice is that you just build a pneumatic, as long as you use pressure rated parts.
Posted: Sat Apr 12, 2008 9:20 pm
by miskaman
potatoflinger wrote:My parents are the same way, they won't let me build a combustion gun, but they will let me build pneumatic cannons. (which I think are more fun anyway).
My advice is that you just build a pneumatic, as long as you use pressure rated parts.
Eh, combustions are cooler I think. And the weird thing is, I can build a combustion made to be used with hairspray, just not propane or MAPP.
Posted: Sat Apr 12, 2008 9:43 pm
by starman
Just tell your parents that there are real live parents (ie. me) that design and build combustion cannons....and lets his children shoot them. Truthfully, if it were that volatile, Spudfiles (and Spudtech before it) could not exist openly.
Seriously, if he would like to email or telephone, I would be glad to talk. Just PM me and lemme know....
You could use D_Hall's HGDT tool to mock up a gun and show him the pressures in the chamber and barrel involved. Download it here and run it:
1x and even 2x guns stay well within the pressure limits of even sched 40 PVC.
Posted: Sat Apr 12, 2008 10:25 pm
by DYI
Ask him if the engine block of his car explodes into tiny pieces when he starts it up; it's essentially a full auto, 8x hybrid.
Or you could always show him one of the hybrids on here, or _Fnord's test of SCH 40 2" steel at 11x hybrid mixes, which still couldn't come close to breaking the pipe.
Or, if he's a scientific type (which he probably isn't, if he believes what he says), you can always get into the low density and bond strengths of propane compared to solid explosives, the studies that show its DDT runup distance to be over 10 metres in ideal conditions, and the fact that, since it contains no oxidiser, it's impossible to overload fuel.
Posted: Sat Apr 12, 2008 11:21 pm
by Velocity
Blitz wrote:Plus, it's only exposed to that kind of pressure for milliseconds of time.
As compared to milliseconds of what ?
Posted: Sat Apr 12, 2008 11:25 pm
by Blitz
Well, since you called me on it, you tell me.
Posted: Sat Apr 12, 2008 11:34 pm
by trae08
just show him a you tube video of someone using mapp or propane in a cannon....
Posted: Sun Apr 13, 2008 6:08 am
by psycix
Parents with a lack of knowledge mots of the time think that its an "explosion" and thus its dangerous.
But its isnt a explosion, its a deflagration, just a normal buring process of the gas.
People are scared of fire and most of the time think that pneumatics wich use air are undangerous.
(though WE know pneumatics can be more powerful then combustions )
Posted: Sun Apr 13, 2008 6:22 am
by sniper hero
I can't add something an the other forum members
but "the recomended amount of fuel"
to little fuel will give no ignition or low power shot and too much won't ignite at all because there is no oxygen.
Posted: Sun Apr 13, 2008 8:37 am
by SpudFarm
[youtube][/youtube]
this is a pressure test of a 5" steel pipe with 7mm thick walls.. everyone thought it would be quite unsafe at 10x mixes.. that was because of it's large areal and "thin" walls.
Larda proved them wrong with this 2610psi test..
2610psi are equal to a 24x propane mix..
Larda put it this way when i had doubts.. "a plastic soda bottle has 0.34mm thick plastic walls and can take 150 psi" that made me thinking..
i am a metric guy just search "....mm in inch" om google
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