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piston cannon question

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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piston cannon question

Unread postAuthor: Pilgrimman » Sun Apr 27, 2008 5:51 pm

I am in the testing stages of my new piston golfball gun, and something weird is happening. I know the gun works because the golfballs fly a long way, but what happens is, I can hear the pilot, but it is very quiet. A bow and arrow probably makes more noise firing than my gun. Does this mean my gun is super efficient or something? One theory I have is that the piston doesn't hit the back of the tee because it gets stopped by friction. (The back of the valve is a very tight fit)


Thoughts?
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Unread postAuthor: jrrdw » Sun Apr 27, 2008 5:59 pm

Do you have any problems resealing the barrel after a shot? Is the gun loud out the muzzle? I've read where a proper chamber barrel ratio makes little to no noise. You must have a small pilot volume, very little air to make noise with.
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Unread postAuthor: Pilgrimman » Sun Apr 27, 2008 6:22 pm

1. I have to push the piston back in manually to reseal it.
2. The muzzle makes no noise I can hear. All I hear is the QEV piloting.
3. The pilot volume is (ballpark) 6-8 in^3.

I thought it might be because the gun is efficient that it makes little noise, but I sure didn't design it with efficiency in mind!
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Unread postAuthor: jrrdw » Sun Apr 27, 2008 7:06 pm

Are you filling from the pilot chamber? If not, put a spring behind the piston. With just enough tension to push it forward. I have a spring and fill from the pilot chamber. Got any pictures we can look at? I ask a lot of questions, don't I ? Are we there yet? :P
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Unread postAuthor: mark.f » Sun Apr 27, 2008 9:57 pm

I'll attempt to answer your question just because your avatar says Led Zeppelin. :P

What size cannon is this? Almost every single cannon I made that used a piston valve with smaller than 1" porting was pretty dern quiet.

The best resolution here is to just chrono the rounds and see if they're hitting where you want them to. If they're going as fast as your goal was, then it doesn't really matter how loud the cannon is.
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Unread postAuthor: Pilgrimman » Mon Apr 28, 2008 1:23 am

I'll post some pics as soon as I get access to the digital camera. I wasn't planning on posting this until all the testing is done, but I guess curiosity got the better of me :wink:

@jrrdw I fill from the pilot chamber, but there are two reasons the piston doesn't move forward: 1) The piston is a tight fit, and 2) My pump is very low flow. Also, I plan on using a spring eventually, but I am more worried about other aspects right now. I'll definitely keep that in mind!

@ markfh11q The cannon is roughly 3' of 2" chamber with a 5' 1 1/2" SDR 21 barrel. The porting is 1.7". My goal was to make a piston cannon that works, so 1 fps or more is my speed goal :D

I'm starting to think that jrrdw was right, and my cannon just happens to be very efficient. Thanks for the help so far!
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 28, 2008 1:32 am

Almost every single cannon I made that used a piston valve with smaller than 1" porting was pretty dern quiet.


Depends on the pressure, my 6mm mini pistons are extremely loud at 400 psi :roll:
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Unread postAuthor: ghostman01 » Mon Apr 28, 2008 4:09 am

jackssmirkingrevenge wrote:
Almost every single cannon I made that used a piston valve with smaller than 1" porting was pretty dern quiet.


Depends on the pressure, my 6mm mini pistons are extremely loud at 400 psi :roll:


Pistons ? how many you got ???? lol
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Unread postAuthor: psycix » Mon Apr 28, 2008 6:00 am

I think your cannon is indeed very efficient.
The C:B ratio is kinda low, and I suppose your not on really high pressures?
Because youve got such a big barrel on a relatively small chamber (on low to mid pressures) it doesnt make much sound.

If you want to get it noisy, increase pressure and enlarge the chamber.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 28, 2008 6:29 am

ajdevi92 wrote:Pistons ? how many you got ???? lol


I made quite a number of 6mm piston designs, mostly high pressure (300-400 psi) and with differing barrel lengths, chamber sizes and piston configurations.

Here's one with a 7 inch barrel:

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And here's what the internals looked like, 100% seal syringe plunger piston and a non-return valve. These days I tend to cast my pistons out of epoxy though, it's a tight enough fit for good performance and also removes ne need for the complications of extra valving.

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