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some questions concerning psi of propellants and pvc pipes.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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some questions concerning psi of propellants and pvc pipes.

Unread postAuthor: ghostink » Mon Jul 27, 2009 1:08 am

looking for approximate estimations.

how much psi can a 'not rated for pressure' 3" diameter pvc pipe at one foot length hold safely?

at what psi will the chamber explode and the fragments go flying?

what's the psi of the following propellants when ignited in combustion chamber?

right guard
aqua-net
propane
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Re: some questions concerning psi of propellants and pvc pip

Unread postAuthor: inonickname » Mon Jul 27, 2009 4:30 am

ghostink wrote:'not rated for pressure'


I believe your answer lies there. However, there isn't much of a risk with a 1x spray and pray if you take care of the gun.

As the aerosol propellants aren't metered the pressure hasn't been determined.

However, I think metered propane was recorded near to 120, but a much lower figure would be usual. Also, pressure is lost rapidly as the gas cools.
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Unread postAuthor: FORE!!!! » Mon Jul 27, 2009 4:43 am

Even if the pipe ses that its not pressure rated it probly is, Most pipe is rated to some kind of pressure,Before sale to the public,,,and from my source ,basic hair spray when detonated creates about 100psi+ of pressure but dont hold me to it.
its only when the pipe becomes brittle should u worry about it exploding..
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Last edited by FORE!!!! on Mon Jul 27, 2009 4:50 am, edited 2 times in total.
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Unread postAuthor: inonickname » Mon Jul 27, 2009 4:46 am

FORE!!!! wrote:Even if the pipe ses that its not pressure rated it probly is, All pipe is rated to some kind of pressure,Before sale to the public,,,and from my source ,basic hair spray when detonated creates about 100psi+ of pressure but dont hold me to it.


1. Your hairspray does not detonate, it deflagrates
2. It does not produce 100+ psi

And no, not all pipe is pressure rated.
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Unread postAuthor: MrCrowley » Mon Jul 27, 2009 4:48 am

Even if the pipe ses that its not pressure rated it probly is, All pipe is rated to some kind of pressure,Before sale to the public,,,and from my source ,basic hair spray when detonated creates about 100psi+ of pressure but dont hold me to it.

When it says it's not rated for pressure, they mean exactly that. Of course it can hold some pressure, that'd probably be part of their testing to make sure the pipe can widthstand certain scenarios. But the pipe could blow up as low as 20psi, or as high as 150psi. That's the thing, no one knows (with out any data and tests anyway).

It should be safe in a hair spray combustion though, they only create about 40psi of pressure, not 100psi. But it's your own risk. Just buy rated PVC if you're that worried. It's so cheap in America.
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Unread postAuthor: Technician1002 » Mon Jul 27, 2009 4:55 am

ABS is much less likely to shatter when it fails. Thick wall cellular foam is very tough. I did a pressure test on it. I did not test to failure as was my intent. It didn't fail below my test pressure.

http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html
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Unread postAuthor: MrCrowley » Mon Jul 27, 2009 4:58 am

Technician1002 wrote:ABS is much less likely to shatter when it fails. Thick wall cellular foam is very tough. I did a pressure test on it. I did not test to failure as was my intent. It didn't fail below my test pressure.

http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html

Pity he's using PVC :wink:
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Unread postAuthor: FORE!!!! » Mon Jul 27, 2009 6:01 am

"my appologies" after a bit of searching i found this. scroll down to testing new plumbing pipes, about half way. http://books.google.com.au/books?id=hde ... t&resnum=4

basically dwv stack sytems are pressure tested to 5 psi before inspection,
but as most things are underated for safty ,how much do u think u could safley stretch it to?
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Unread postAuthor: Technician1002 » Mon Jul 27, 2009 6:02 am

FORE!!!! wrote:"my appologies" after a bit of searching i found this. http://books.google.com.au/books?id=hde ... t&resnum=4

basically dwv stack sytems are pressure tested to 5 psi before inspection,
but as most things are underated for safty ,how much do u think u could safley stretch it to?


I haven't tested to failure. I have had it to 100. I test evey year to 85 and operate under 65.

All I can recommend is test it.
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Unread postAuthor: jimmy101 » Tue Jul 28, 2009 12:48 pm

Couple things;

All common aerosols fuels, from RightGaurd to pure propane will pressurize a closed chamber to about the same maximum pressure if the mixture is correct. That maximum pressure is about 120 PSIG.

That 120 PSIG of pressure won't last very long in a closed chamber. Heat loss will bring the pressure back near atmospheric in less than 1 second.

Combustion spudguns rarely excceeds 60~70 PSIG when firing, many guns don't even get that high. Peak pressure mostly depends on the friction between the ammo and barrel, the mass of the ammo and the diameter of the barrel. Even though the chamber was going to get to ~120 PSIG, movement of the ammo lowers the peak pressure.

Cellcore PVC typically will work OK for a metered, 1x propane fueled, combustion spudgun without any safety problems. Pressure rated is of course preffered but doesn't appear to be absolutely necisary.
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