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combustion/pneumatic thought (probably a bad one)

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combustion/pneumatic thought (probably a bad one)

Unread postAuthor: hi » Sat Apr 14, 2007 5:13 pm

would it work if i had a chamber and valve set up like a normal sprinkler valve pneumatic, but had a plug to spray fuel into.

the idea is that you spray fuel into the chamber, like a normal combustion, then fire it like a normal combustion, but the sprinkler valve holds the pressure back.

then when you want to fire you open the sprinkler valve and fire. the idea is that it is precharged and you can just carry it. my only problem with it is that even if it was 100% air tight, would it contract again, or would it stay pressurized?

call me an idiot, but i thought it would be cool, dont exactly know why.
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Unread postAuthor: dippydodo03 » Sat Apr 14, 2007 5:19 pm

if you used pvc, it would explode. if you use steel pipe, it would most likly explode as well. you would basicly be making a gas powered pipe bomb.
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Unread postAuthor: jssizzle » Sat Apr 14, 2007 5:20 pm

I had the same idea once, but I would always get this eerie feeling that something was going to go wrong with a contained explosion. Theoretically it might work, I heard somewhere that combustions only reach about 50-70 psi, but I think that it might get higher when not escaping through the barrel. Another issue would be the sprinkler valve . . . I don't know it it would close with a burst of pressure like that, maybe putting a ball valve in front of it would solve the problem. Cool idea.
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Unread postAuthor: Velocity » Sat Apr 14, 2007 5:34 pm

No, it probably would not explode, even in PVC pipe. However, the explosion would not be held; it would soon drop to 0 PSI, and when you opened the sprinkler valve, nothing would happen.
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Unread postAuthor: experament-u2 » Sat Apr 14, 2007 5:37 pm

it wouldnt work because the combustion is just a short peak of pressure before it cools down....at least im pretty sure thats right
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Unread postAuthor: frankrede » Sat Apr 14, 2007 6:09 pm

dippydodo03 wrote:if you used pvc, it would explode. if you use steel pipe, it would most likely explode as well. you would basically be making a gas powered pipe bomb.
Now why would you make such a statement like that?
You have nothing to back it up, and you truly are an idiot.
Maybe pvc would break after doing something like that several hundred times, over time weakening the pipe, but I guarantee steel wouldn't
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Unread postAuthor: Hawkeye » Sat Apr 14, 2007 6:39 pm

Frank, Maybe it was a bit of a broad exaggerated statement he made but it probably isn't a good idea to be calling anyone "truly an idiot" when they are likely just looking out for the well being of someone.
You had a little mishap of your own if I recall correctly.
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Unread postAuthor: boilingleadbath » Sat Apr 14, 2007 9:00 pm

You get about 100 psi from a combustion, so safety isn't an issue... but, as previous posters have said, the pressure generated by combustion is due to the increased temperature of the gases.

This means that, as the gasses cool, the pressure will return to about normal.
How long this takes will depend on several different design parameters, but won't be very long either way (a few seconds at most).

This means that the only advantage of this design is (possibly) increased performance, in which case you'd be best off using a burst disk with a high bursting pressure.

Also note that the sealing of the valve is complicated, because you'd have to pressurize the pilot to at least (25 psi?), in a few miliseconds. Not impossible, but it'd require enlarging the equalization hole considerably - with a correspondingly larger vent valve.
Again, a firm reason to go with the burst disk.
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Unread postAuthor: From_Hamsterdam » Sat Apr 14, 2007 11:17 pm

I read some were that after the explosion it produces a vacuum and sucks stuff back in. because all the oxygen has been consumed.

Might have been on spud tech. some one fired a combustion in to a lake with the tip under water, I cant remember why. But the spud gun was quickly filled with water almost pulling him in.
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Unread postAuthor: SpudBlaster15 » Sun Apr 15, 2007 12:08 am

Yes, a vacuum is created, but not because "all of the oxygen has been consumed" The vacuum is created due to the rapid contraction of heated gases as they lose heat energy to the chamber/barrel walls, and atmospheric air. The vacuum displacement is usually equivalent to the barrel volume.
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