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Best 3/4 Bore Cannon Possible

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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Best 3/4 Bore Cannon Possible

Unread postAuthor: BeaverRat » Fri Jul 30, 2010 2:32 am

Hello,
I have a couple questions for you guys here... I will be making a cannon with a 3/4 inch barrel, and a 2 inch chamber. I am wondering what the best possible valve power-wise for this would be. I am mainly going for pure performace here - I don't really care about efficency, so I will be using a 2:1 C:B Ratio.

Here are some ideas I had

-1 inch modded sprinkler valve (too expensive to go bigger)
-3/4 inch QEV
-Barrel sealing piston valve (what size tee should I use with 3/4 valve seat?)

Thanks
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Unread postAuthor: Mr.Sandman » Fri Jul 30, 2010 2:37 am

The Qev and piston valve will be your best choices. But if you have the right tools, you can make the piston valve more effective and stronger.
A qev is basically a commercial piston valve with a thin rubber diaphragm. In my opinion, you should make it yourself, nothing beats the satisfaction of something you make working!
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Re: Best 3/4 Bore Cannon Possible

Unread postAuthor: jackssmirkingrevenge » Fri Jul 30, 2010 2:54 am

BeaverRat wrote:I am wondering what the best possible valve power-wise for this would be. I am mainly going for pure performace here


Well, the best possible valve is not to have one, but this limits your choice of projectiles. A burst disk valve offers performance that is practically just as good and allows freedom of choice in terms of projectiles, though it's a bit more involved when it comes to reloading.
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Unread postAuthor: Crna Legija » Fri Jul 30, 2010 10:47 am

if you do build your own piston valve use 1'' tee
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Re: Best 3/4 Bore Cannon Possible

Unread postAuthor: velocity3x » Fri Jul 30, 2010 10:54 am

BeaverRat wrote: I don't really care about efficency, so I will be using a 2:1 C:B Ratio.


I found out the hard way that building pneumatics with a C:B larger than 1:1 is the wrong thing to do but...... that's just my opinion.
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Re: Best 3/4 Bore Cannon Possible

Unread postAuthor: jackssmirkingrevenge » Fri Jul 30, 2010 10:58 am

velocity3x wrote:I found out the hard way that building pneumatics with a C:B larger than 1:1 is the wrong thing to do but...... that's just my opinion.


Not everyone runs at the same pressures you tend to though ;)
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Re: Best 3/4 Bore Cannon Possible

Unread postAuthor: c11man » Fri Jul 30, 2010 11:13 am

velocity3x wrote:
BeaverRat wrote: I don't really care about efficency, so I will be using a 2:1 C:B Ratio.


I found out the hard way that building pneumatics with a C:B larger than 1:1 is the wrong thing to do but...... that's just my opinion.


its not rare for some of my launchers to exceed 3:1 ratio with some barrels. high C:B ratios is not a problem unless the volume and pressure of gas is very high as in your creations
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Re: Best 3/4 Bore Cannon Possible

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Unread postAuthor: BeaverRat » Fri Jul 30, 2010 11:41 am

Oh, I forgot to mention, it will run at roughly 150 PSI. I think I will go with a piston valve actuated by a modded sprinkler valve.

With the barrel porting of 3/4th inch, will a 1 inch tee be the propper ratio, or do I want to go with maybe a 1.25 inch tee?

Also, anyone have any ideas for a nice piston for a 1 inch tee?
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Unread postAuthor: Technician1002 » Fri Jul 30, 2010 11:45 am

You do want a large CB ratio for low pressure low force launches. I have not posted much about it here due to being busy shooting and a large (100+) gathering. Launching eggs with a small chamber and high pressure breaks them. A long barrel, low pressure, and high flow can get some fantastic ranges with raw eggs. This was a hit at a local egg drop engineering contest. We threw eggs over the building and landed them on the roof of the building on the other side of the parking lot. I wish we had video of the shots, but we don't.

In the 3 gallon launcher with a 2.5 inch barrel and foam sabot, the max an egg will take is about 15 PSI without breaking. Around 20, they pretty much all break.
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Unread postAuthor: clemsonguy1125 » Fri Jul 30, 2010 11:58 am

BeaverRat wrote:Oh, I forgot to mention, it will run at roughly 150 PSI. I think I will go with a piston valve actuated by a modded sprinkler valve.

With the barrel porting of 3/4th inch, will a 1 inch tee be the propper ratio, or do I want to go with maybe a 1.25 inch tee?

Also, anyone have any ideas for a nice piston for a 1 inch tee?

What material are you using for your gun,pvc, if so Id stay below 120 PSI, I used a 1 inch yee for my 3/4 porter and the piston was a 1/2 Inch CPVC coupler wrapper in tape and filled with hot glue, washers were epoxied to both end and a toy "popper was epoxied to one washer. A ty popper is like a rubber bowl that you invert and set on a table, they then pop into the air
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Unread postAuthor: BeaverRat » Fri Jul 30, 2010 2:07 pm

Why did you fill it with epoxy? It seams to me that would add unecissary weight which would slow down opening times... Isn't a 1/2 inch coupler strong enough?
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Unread postAuthor: clemsonguy1125 » Fri Jul 30, 2010 4:37 pm

I actually filled it with hot glue, it was mainly because I was afraid it would shatter at higher pressures(100 psi)
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Unread postAuthor: BeaverRat » Fri Jul 30, 2010 6:36 pm

Ok, I actually decided to use a 1/2 PVC coupling. It's a really close fit, so I will just sand it down a bit... If I set the 3/4th inch porting at the dead center of the tee, will that give enough flow?

Thanks
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Unread postAuthor: clemsonguy1125 » Fri Jul 30, 2010 8:33 pm

Yes, as long as your pistons not to long
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Unread postAuthor: BeaverRat » Sat Jul 31, 2010 2:14 am

why would it matter how long the piston is? I can set the piston travel pipe at whatever length i want...
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