My First Air Piston Cannon

[micquai]

This is my first attempt to build an air piston cannon.
It has two 3"x 24" air chambers and a 1 1/2" x 32" barrel. I made the barrel removable to accommodate different sizes. The air chamber is also removable.
The air valve is made from a 2" PVC tee with a 1 1/2" x 3 1/2" piston made from 1 ½” PVC pipe.. The piston seals to the 2" tee with 3 o rings and also seals to the barrel with an o ring.
It is about 90%completete. I finally got most of the bugs worked out of it. I had trouble keeping the O rings on the piston. I finally used some epoxy to secure them to the grooves. I used a 1 inch Rain Bird sprinkler valve to trigger the piston. It seems to work OK, but the potatoes fragment.
After reading many of your posts I’ve learned a lot. I realize I’ve made some mistakes. I appreciate everyone’s knowledge and expertise.
Thanks!!

[mattyzip77]

You could probably cut back on the pilot volume. The short socket depth of the bell reducers tell me they are probably dwv and not rated. Other than that looking good. Can we see a pic of the piston?? I love the double chamber idea!! One more thing. get rid of that hose and it will pilot better and faster!!!

[micquai]

Here are some pictures of the piston. It's 1 1/2" pvc. I used a router table and a v-groove bit to cut the oring grooves. The piston is hollow. I thought the lighter the better. A 1 1/4" cap fits inside the piston almost perfect. I glued it in the back and filled the voids with hot melt glue then glued on a piece of red rubber for a bumper. It seals nicely to the inside of the 2" tee. Where the piston and barrel meet I glued a 1 1/4" coupling inside the piston and let it stick beyond the end of the piston about 1/2 the thickness of the oring then I used epoxy to secure the oring to it.
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[jackssmirkingrevenge]

Not bad!

The design can be tweaked for better efficiency but even as-is it should be quite a power house

One thing you can do is cap the open end of the piston, as while having it hollow makes it light, the internal volume contributes to pilot volume which reduces valve opening speed.

[Mr.Tallahassee]

Wow that's a close ratio. That thing must snap when it opens. I would be concerned by the excess dead space in the piston itself but it probably doesn't hurt performance too much.
EDIT: NOT Ninja'd by JSR. Actually, the open end is the barrel side from what I read. The coupling was on the barrel side.

[jackssmirkingrevenge]

EDIT: NOT Ninja'd by JSR. Actually, the open end is the barrel side from what I read. The coupling was on the barrel side.

Right you are, in that case it is extra dead volume and not extra pilot volume, but still extra

[PotatoEnemy17]

Awesome cannon! Give us damage pics!

[archie370]

Wow they are some sweet pistons man Wish i had your skill

[Technician1002]

I used a router table and a v-groove bit to cut the oring grooves.

If you ever need to replace the piston, I found square cut grooves to work well. The V may apply excess pressure on the piston cylinder and cause binding. Check the How To section for info on O rings on pistons.
Use a good bumper. I had trouble with PVC pistons either breaking or breaking the plug behind them.

[micquai]

I finally finished my cannon . Here are some finished pictures.
I built a base so you can move the cannon horizontal and vertical. I added sights and two grips with a trigger on the right side. I also cut a muzzle brake in the barrel. Everything seems to work OK.
Many thanks to all of you for your expert advise.

[jrrdw]

Try and get some video of it in action. Looks good.

[micquai]

Hey Guys,
A word of caution. I don't want anything like this to happen to any of you. My pvc cannon exploded this afternoon.
I was trying to see how much damage the cannon would do and it blew up. The cannon was shooting through 2 sheets of 1/4" luan plywood and a piece of 3/4" particle board. I kept increasing the pressure to 100 psi and it blew apart. The piece with the piston in it flew back and hit me in the head. I was lucky I had eye protection on. I only suffered a gash above the right eye and I will probably have a black eye in the morning. Don't let anyone tell you that pvc won't explode. Enclosed are some pictures. Guys please be careful this could happen to anyone of you.

[jrrdw]

That sucks balls!!!

[tigerblues28]

BURN THE MOTHER %#@&-ER.

Glad you're okay and seemed to walk away from it. This is a good warning to everyone. Thanks. Were you using a bumper?

With Cold weather around for a lot of folk be careful with that brittle PVC!!


Ehh. What woman doesn't like a good ole' shiner right?



Nick

[Technician1002]

Possible cause of failure may be related to the cannon support on the air chambers and the barrel recoil was unsupported except by the vertical pipe. This torqued the rear of the cannon and it let go. Possible future fix is to support the barrel against recoil by supporting it directly on the mount and let the air chamber float. Some bonding between barrel and air chamber ot prevent torque on the rear wouldn't hurt. PVC doesn't like to be flexed often. It cracks and breaks.

The double break seems to supprt the parts were stressed there, not just in the pilot from the piston. Improper bumper usualy results in shattering of the plug/female fitting of the pilot.