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First canon and got some questions

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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First canon and got some questions

Unread postAuthor: mtbkr5 » Mon Jan 29, 2007 9:46 pm

Hey guys

one of my engineering projects this year requires me to launch an egg approx. 50 yards, so i decided to make a compressed air canon. doing some research i stumbled across this forum. i made the canon and man is it cool. the only pic i have now is from my cell phone and is not a close up.

the canon worked great for testing. i was shooting approx. 20 ounces of water at 60-80 psi and it was traveling maybe 20-30 feet.

my setup:

2" by 2' pvc for the chamber
leads down to a 3/4" sprinkler valve
leads up to a 1.5" 4' long barrel (had to keep the barrel 4' long [it was the only required thing for the project])


the thing is that i wired up a toggle switch for the valve, but the switch did not work and i had to use the little manual lever on the valve.

the major problem however is that the sprinkler valve does not hold air anymore. i think i might have exceeded the max. psi it can handle.


if anyone knows what could be the problem i would appreciate any help or ideas of other valves.



and sorry for the long write up.
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Unread postAuthor: Insomniac » Mon Jan 29, 2007 9:54 pm

The valves can hold around 125 psi, so I doubt you exeeded its max pressure. Try taking the valve apart and putting vaseline on the rubber diaphram.

Is the pipe and fittings the gun is made out of pressure rated?

Oh and although this shouldn't matter for the project, you can make the gun MUCH more powerful by pnumaticly modding the sprinkler. (it makes the valve open much quicker, and the valve no longer needs the solenoid to work)

http://www.spudfiles.com/forums/viewtopic.php?t=305& heres a link on how to mod a sprinkler valve.

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Unread postAuthor: mtbkr5 » Mon Jan 29, 2007 9:57 pm

pneumatically modding the sprinkler? o.O

you mean bypassing the solenoid and using a type of trigger?
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Unread postAuthor: mtbkr5 » Mon Jan 29, 2007 10:05 pm

oh sorry nvm i found the how to mod the valve.

but thanks for the help!
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Unread postAuthor: Insomniac » Mon Jan 29, 2007 10:05 pm

All the solenoid in a sprinkler does is open a tiny little valve to let out the air above the diaphram, and the higher pressure below the diaphram pushes it up, and opens the valve. Pnumatically modding, is where you cut a hole in the top of the sprinkler valve and attach a blowgun or a small ballvalve. The larger valve lifts the diaphram much quicker than the weak little solenied can, and makes the valve open faster. Faster valve= faster projectile. There is a link in my first post explaining how to mod a sprinkler.

An added bonus with a modded valve is that you don't need to mess around with batterys for the solenoid.
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Unread postAuthor: mtbkr5 » Mon Jan 29, 2007 10:40 pm

sweet i will be making that new trigger tomorrow.

and just a question, how much psi do yall think i need to shoot the egg 50 yards? i do not have much to base it off of so i need an estimate. the final grade for the project is 3 parts: accuracy, distance and then there is a "save the egg" part where you try to get the egg not to break but that is not any fun.
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Unread postAuthor: Insomniac » Mon Jan 29, 2007 10:52 pm

80 psi will do it easily. Make sure the egg fits the barrel well, if it doesn't you will need to put a spud in first to seal the barrel off, then the egg on top.

Are your fittings and pipe pressure rated???!!!!!!!!!
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Unread postAuthor: A-98 » Mon Jan 29, 2007 10:53 pm

if your using a PC look up GGDT in the spud wiki.

as for the "save the egg" are you allowed to build custom catching units? i would go for trash bags filled with packing peanuts.
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Unread postAuthor: joannaardway » Tue Jan 30, 2007 9:17 am

Vaseline is the last thing you want to use to grease the diaphragm. It slowly eats at rubber. Try silicon grease (more expensive, but much better).

As for the required range, then just experiment with a few eggs and different pressures. Choose a pressure that consistently beats that range, then just use that.
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Unread postAuthor: medievalman » Tue Jan 30, 2007 9:03 pm

and for the "save the egg", put it in some kind of looseish fitting soft shell when you fire it, and catche it in the previous ideas of garbage bags filled with packing peanuts. good luck!
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Unread postAuthor: mtbkr5 » Tue Jan 30, 2007 9:04 pm

ok yeah thanks for the help guys

when i was getting the parts i told the guy what i was doing and he was real interested and i told him i needed all pressurized (except after the barrel) so the parts are all pressurized.

and as for the silicon grease i have a can of it so i will try that.

before i go and take apart the valve is there anything i need to know before i do so. is anything going to come flying out of the thing that i wont be able to put back together?

i did not get a chance to get the things for the blowgun trigger so that is to come later.
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Unread postAuthor: medievalman » Tue Jan 30, 2007 9:11 pm

nothing should come out except the diaphragm, and thats supposed to be removable. if something else comes out, that's why it isnt working, lol. just make sure that when you put it back together, you tighten the screws down, ALOT as these are what is making it airtight.
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