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Old April 15, 2007, 09:12 PM   #1
rugerdude
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Air cannon question

Okay, so a friend of mine and I built a "spud gun" that we will use to launch confetti and such for an upcoming performance where we will be "playing" (basically acting like we are plating) a song by Rammstein (asche zu asche).

Anyway, we have a nice tank and everything works okay, except we can't get any sort of real pressure. Our solenoid valve won't open if we put more than 80 psi in the tank, and even at that pressure, it's pitifully weak.

Our tank is 4" pvc, and that gets necked down to 1" to go through the valve, and then it goes to the barrel which it 3" PVC.

When we fire it, it won't depressurize all at once, instead it takes a couple seconds to fully discharge (and makes a funny honking noise).

Is the pressure loss because we're necking it down, or is the valve to blame?

Would a butterfly valve work better? Would it be expensive (We've already put 70 bucks into it)?

Thanks in advance!

Sorry to the mods if this ins't gun related enough, but I figure if air rifles are okay...
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Old April 15, 2007, 09:34 PM   #2
Maser
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Why can't you make a real spud gun that uses hairspray and a BBQ igniter? If you're worried about the confetti catching fire, you can always go to any hobby shop that sells model rocket supplies and buy some fireproof wading.
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Old April 15, 2007, 09:38 PM   #3
WeedWacker
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I know a guy who hooked up a small propane tank with tubing and valves to some PVC piping and took a stun gun and hooked the power supply up as an ignition system. Launched the spuds about 200 yds easy
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Old April 15, 2007, 09:42 PM   #4
rugerdude
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This will be going off in a school auditorium......see why pyro is a no-no?
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"The SKS is a rifle, made the way they should be, out of a heavy block of crappy commie steel, set in an inletted semi-reshaped 2x4."

Not my quote but I agree completely.
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Old April 15, 2007, 09:51 PM   #5
oystermick
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It's the valve. The "necking down" should create a Venturi effect and increase the the air speed.
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Old April 15, 2007, 10:10 PM   #6
pipoman
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This is an award wining hedge ball cannon. It works on air pressure.





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Old April 15, 2007, 10:15 PM   #7
pipoman
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I know you were trying to save some money by going with a 1" valve but I think that is your problem. I think you need a larger valve. 4" to 1" is way too dramatic IMO.I think you need at least a 2" if not larger (depending on the size of the tank).

Or maybe going with 1 1/2 valve and 1 1/2" pipe to the end. The problem may be that the 3" pipe would require more pressure than a 1" opening can supply.
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Old April 16, 2007, 12:17 AM   #8
Mike Irwin
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Be VERY careful taking PVC (I'm assuming that's what you used) to pressure. Make sure you have pipe that is rated for the pressure you want.
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Old April 16, 2007, 07:14 AM   #9
rugerdude
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our pipe is rated for 220 psi in the tank, and our smaller pipes are something like 150, so we're fine in that respect. Our pump will only give out about 80psi anyway.

Looking around on the internet at others who have built air cannons, it seems to be a valve problem.
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"The SKS is a rifle, made the way they should be, out of a heavy block of crappy commie steel, set in an inletted semi-reshaped 2x4."

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Old April 16, 2007, 08:23 AM   #10
DesertShooter
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My first guess would be the valve. The strange "honking" sound (more like passing wind?) is probably due to the valve fluttering.
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Old April 16, 2007, 08:32 AM   #11
Csspecs
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Solenoid valves are the problem, I have a few launchers we use as bazookas when we play airsoft, what we have is a 1 1/2 inch brass 1/4 turn valve and a galvanized 1 1/2 air tank about 18 inches long (Lowe's has them already threaded for like 5.00 each)

We can throw a Nerf football about 200 yards at 140 psi and with a paper shot cup we can also throw cracked corn about 50 yards with 80 psi. Whenever you are making a launcher you want to remember that if you drop it or fall on it that PVC WILL shatter and become basically a pipe bomb. You want every part that contains the air to be METAL and to be threaded together not glued.

If you are trying to shoot confetti you will find that you want ALL the air out the barrel at once. Here is a good design for a valve (go down to "How a 'quick exhaust valve' pneumatic cannon works")

http://www.xinventions.com/main/spud..._gun_works.htm
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Old April 16, 2007, 08:56 PM   #12
rugerdude
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I fixed the problem by just going with a ball valve, and a shot cup. It works very well now, thanks.
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