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Mini M203

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Velocity » Fri Sep 01, 2006 11:05 pm

Thanks for the suggestion PVC arsenal. I am still considering whether to use a diaphragm valve or a piston valve. I am leaning towards the piston valve, just because I have built many of them, and easily can pull one together. Also, I am worried that I will have trouble getting a floating diaphragm to reseat properly.

I will probably go for a diaphragm/piston hybrid; It will essentially be a very, very, very short piston (or you could call it a diaphragm reinforced with PVC rod)
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Unread postAuthor: ProfessorAmadeus » Fri Sep 01, 2006 11:29 pm

Thats a great gun. Very small. I havnt ever had any luck with diaphragm but pistons are easy. A end cap, o-ring and sealing face.
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Unread postAuthor: killagorrila99 » Sat Sep 02, 2006 12:03 am

i got a good idea, you could conceal it in a larger spudgun... lol nice idea aye! anyway its a sweet gun
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Unread postAuthor: PVC Arsenal 17 » Sat Sep 02, 2006 10:50 am

This actually uses a fixed diaphragm. The flexible sheet of rubber is pinned between the barrel and the plug. It does not float.

It actually started out as a piston gun. It's 1 1/4" so I could use a 3/4" cap for the piston. I didn't like how it turned out so I made a fixed a diaphragm instead. A piston would take up valuable chamber space on a gun so small.
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Unread postAuthor: Shrimphead » Sat Sep 02, 2006 11:40 am

CPVC is actually used for hot water applications. I'm not sure if they make not-rated cpvc or not.
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Unread postAuthor: PVC Arsenal 17 » Sun Sep 03, 2006 5:23 pm

So is that why CPVC is used on combustions? Because of heat tolerance?
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Unread postAuthor: thrasmussen » Wed Sep 13, 2006 7:15 pm

mind uploading a diagram of the internals.
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Unread postAuthor: PVC Arsenal 17 » Thu Sep 14, 2006 2:30 pm

There really are no internals besides the diaphragm. Just a sheet of rubber from a tub stopper.

The diaphragm sits fixed between the plug and the barrel which runs through the inside.

Image
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Unread postAuthor: thrasmussen » Thu Sep 14, 2006 2:48 pm

Many thanks :D
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Unread postAuthor: PVC Arsenal 17 » Sun Sep 17, 2006 5:30 pm

today I blew my second diagphragm. I had it to around 100 psi and it burst.

If you make it with sink stoppers stay below 90 psi.
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Unread postAuthor: carlbelcher » Sun Sep 17, 2006 5:39 pm

That's freakin awesome, I love compact clean guns!
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Unread postAuthor: potatocannoneer » Sun Nov 05, 2006 11:55 pm

i know nothing about diaphragm cannons could someone please post some plans
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Unread postAuthor: PVC Arsenal 17 » Wed Nov 08, 2006 7:38 pm

I quote myself:

This gun is called a coaxial. This means that a smaller pipe runs the length of a larger diameter one. Floating inside the larger pipe is a piston or a diaphragm that presses up against the inner pipe which is the barrel. When the gun is pressurized from behind, suction pulls the piston against the barrel and seals it. Meanwhile, air leaks by into the larger pipe. This is the "pressure chamber"

So... Now you have a sealed barrel inside a pressurized "shroud" To fire it, air from behind the piston is exhausted and the piston is pulled back due a strong suction. When it moves back, the seal with the barrel is broken and a new one is made behind it. The prevents the air in the chamber from exhausting as well. Instead it all rushes out through the inner pipe, propelling the projectile.

This is quite a common design that continues to prove itself through time. It is one of the powerful designs around and it can be made easily by the average builder. The "pipe within a pipe" concept makes it very compact and self contained.

Contrary to what most people say, I think this is the best design to build as a beginner. With experience you will get a nack for them and they will get better and better.

Basically what you need to look for is:

2" pipe
1/2" pipe
2" coupling
2" female adapter
2" x 1/2" slip bushing
2" x 1/2" threaded bushing
1/2" ball valve.
1/2" tee
1/2" x 1/8" bushing
1/8" tire valve
Rubber sheet


Glue the female adapter to one end of the 2" and the coupling to the other. Glue in the slip bushing to the coupling. Let all this dry. Cut out a sheet of rubber for diaphragm valve (rubber pipe cap) so it fits into female adapter. Thread in the bushing vertically with the rubber sitting on the inside over it. now, get a length of 1/2" pipe and slide it all the way through the 2" pipe via slip bushing till it firmly presses on the rubber sheet. mark it and glue. let it dry. Assemble the bushing, then tee, then tire valve, then ball vave. put PTFE tape on all threads. Fill it with the tire valve and fire by opening the ball valve.
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Unread postAuthor: potatocannoneer » Thu Nov 09, 2006 12:00 am

thank you so much man that is really helpful
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Unread postAuthor: POS » Thu Nov 09, 2006 5:51 pm

the rubber sheets, what are they used for, and how thick are they ? Can't realy find something around here, or I probably look in the wrong place.
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