My First Pneumatic (1" Piston Cannon)

[jmadden91]

1" Piston Cannon

This is my First Pneumatic Spud Gun. It is obviously not 100% complete but it is firing pretty hard already at 50psi.

Gun Specs
Chamber - 55cm of 25mm PN12 PVC (Plus Fittings)
Barrel - 1m of 20mm Electrical Conduit
Valve - 25mm Piston Valve
Pilot - 20mm Ball Valve
Operating Pressure - 50psi (will go up to 100-120psi soon)

Valve Specs
Housing - 25mm Tee with 25mm Coupler
Seat - 20mm PVC slid into the Tee
Piston - Plywood Glued together on a bolt
Sealing Face - Sink Plug cut to size

Additions still needed
Paint Job
Barrel Support
Bolt Action Loading
Pressure Gauge
Modded Blow Gun Pilot (Will this be enough??)
Scope
Rifled Barrel
Higher Pressure!

With the Pump I have at the moment, 50-60psi seems to be the max i can get (useless 12v Compressor). At this pressure though it punches marbles through ply with no worries at all. With the shraeder in the chamber I have to hold my hand over the barrel until it builds up pressure to seal, which is annoying.

But here it is, any suggestions criticism etc will be appreciated.
Edit: oh and yes it is modeled from Big Bob's Cannon:
http://www.spudfiles.com/forums/viewtopic.php?t=14648&

Cheers, jmadden91

Whole Gun:




Piston and Pilot Area:


Pilot Valve:


Piston:






Damage

Entry:


Exit:
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[FORE!!!!]

how thick is that ply wood???

[jmadden91]

not very, bout 10mm

[FORE!!!!]

hey do us a favour and collect a bunch of newspaper make sure its about 70mm-80mm think and tell me if it goes threw it,in ur own time of course reason being i have made a similar canon but not with a piston vavle using a ball vavle...i wanted to see the difference in power

[THUNDERLORD]

...i wanted to see the difference in power

D_Hall's GGDT would be more accurate since the results are in FPS and will give you details for your exact design.

Been known for being very accurate when compared to chrony's too.
Srry no link...got to sleep...new job tommorrow. 8)

[Technician1002]

I have to hold my hand over the barrel until it builds up pressure to seal, which is annoying.

Wow, I almost forgot that part of my little 1 inch piston cannon. With a 1 inch barrel, I could seal it with my thumb, give a couple strokes on the pump and pop out my thumb which would seal the piston. Those were the days.

I almost forgot that was one of the reasons to build a newer valve that is more reliable and less fussy to get to work.

You will want a proper bumper or your piston might not bother stopping at the pilot valve. PVC is brittle and doesn't take a pounding very long.

Limiting the piston travel to reduce the speed it can pick up helps reduce the impact force. Letting it move no more than 1/2 the diameter of the valve seat is recommended. 1/4 the diameter is the minimum distance. Longer travel distance can let the piston pick up excessive speed and break things.

[jmadden91]

It has a bumper, just a little bit of rubber that sits nicely in the reducer attached to the pilot valve. Also limits travel of the piston to about 10-15mm which sounds about right

[jmadden91]

Sorry to double post, but could anyone help me model my gun with GGDT? I have no idea what to put for things like the flow coefficient of the valve, the friction of the marble etc etc.

Any help would be greatly appreciated,
Cheers, jmadden91

[Hubb]

Nice. Most people don't go with a piston valve for a first cannon, but yours turned out nicely.

Allow me, if you will, to make suggestions for improvements. First off, you asked me about a sprinkler valve. If I were you, I would keep this piston valve and make it work. Save the sprinkler valve for another launcher.

Next up, you said that you ain't getting a good seal with the piston. This is a simple fix. Check this out. I need to update that post, as I have now successfully tried this mod and it works quite well, even with sprinkler valves.

Another suggestion is to drop the metal hardware on the piston and go with nylon hardware. These pieces can usually be found at any credible hardware store, usually right next to the steel ones. It will cut the weight of the piston significantly and you will gain a slight increase in performance.

Lastly, you should probably add a barrel support. It will add strength and increase durability to the launcher. More information can be found through search and "Improving the Barrel" (linked in my sig).

Considerations:
- Consider a breech loader. With marbles, you'll probably want a detent of some sort. If that is the case, I can help you further if needed. Otherwise, I'll leave it at that.
- Consider dropping the ball valve for a blowgun. This will aid in a more comfortable shooting platform. Complete modification instructions can be found in "The Sprinkler Valve" (linked in my sig).

*As far as GGDT is concerned, I don't use the program as religiously as others do, but it is a very good program. Sorry I can't help.*

[jmadden91]

Thanks for the info mate, all those things are coming, just have to fix a few leaks then it will get bolt action loading, a blow gun etc. Its got a barrel support now. What is the best way to go about sealing the bolt though? Just O rings? thanks again mate