April 15, 2007, 09:12 PM | #1 |
Senior Member
Join Date: July 6, 2004
Location: Tulsa, Oklahoma
Posts: 1,443
|
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...
__________________
"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. |
April 15, 2007, 09:34 PM | #2 |
Senior Member
Join Date: May 21, 2006
Location: Mysterious Cities of Gold
Posts: 920
|
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.
|
April 15, 2007, 09:38 PM | #3 |
Senior Member
Join Date: December 13, 2006
Location: Body: Clarkston, Washington. Soul: LaCrosse, Wisconsin
Posts: 1,591
|
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
__________________
- Jon Disequilibrium facilitates accommodation. 9mm vs .45 ACP? The answer is .429 |
April 15, 2007, 09:42 PM | #4 |
Senior Member
Join Date: July 6, 2004
Location: Tulsa, Oklahoma
Posts: 1,443
|
This will be going off in a school auditorium......see why pyro is a no-no?
__________________
"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. |
April 15, 2007, 09:51 PM | #5 |
Senior Member
Join Date: December 11, 2004
Posts: 197
|
It's the valve. The "necking down" should create a Venturi effect and increase the the air speed.
__________________
"Americans have the right and advantage of being armed- unlike the citizens of other countries whose governments are afraid to trust the people with arms." - James Madison |
April 15, 2007, 10:10 PM | #6 |
Senior Member
Join Date: November 8, 2005
Posts: 897
|
This is an award wining hedge ball cannon. It works on air pressure.
|
April 15, 2007, 10:15 PM | #7 |
Senior Member
Join Date: November 8, 2005
Posts: 897
|
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. |
April 16, 2007, 12:17 AM | #8 |
Staff
Join Date: April 13, 2000
Location: Northern Virginia
Posts: 41,367
|
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.
__________________
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower. |
April 16, 2007, 07:14 AM | #9 |
Senior Member
Join Date: July 6, 2004
Location: Tulsa, Oklahoma
Posts: 1,443
|
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.
__________________
"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. |
April 16, 2007, 08:23 AM | #10 |
Member
Join Date: September 19, 2006
Posts: 67
|
My first guess would be the valve. The strange "honking" sound (more like passing wind?) is probably due to the valve fluttering.
|
April 16, 2007, 08:32 AM | #11 |
Senior Member
Join Date: December 21, 2005
Posts: 1,111
|
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 |
April 16, 2007, 08:56 PM | #12 |
Senior Member
Join Date: July 6, 2004
Location: Tulsa, Oklahoma
Posts: 1,443
|
I fixed the problem by just going with a ball valve, and a shot cup. It works very well now, thanks.
__________________
"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. |
Thread Tools | Search this Thread |
|
|