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Design on a Coaxial Piston Cannon

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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Design on a Coaxial Piston Cannon

Unread postAuthor: Atattack » Thu Aug 25, 2011 6:30 pm

Wanted to get some experienced spudders thoughts on my design. After posting some questions on here I have a pretty good idea of how my cannon will look and wanted to get some feedback.

Will be a coaxial piston cannon with a 4" x 48" Schedule 40 galvanized steel chamber. Using a 4"-2" reducer at top of chamber to taper down to fit 2" barrel. I will have the option to add to the barrel length since I threaded the ends but will be 55" long initially.

I will use this valve to vent the pilot chamber.
http://store.gaugemagazine.com/34gc450x ... valve.aspx

The piston is going to be made of UHMW and be 3.9" diameter and be 3" long. I'm using 1/2" thick neoprene sheet on end of piston to seal barrel. Thanks again to all the posts for info on this and just wanted to get some feedback before putting it together.
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Unread postAuthor: mattyzip77 » Thu Aug 25, 2011 7:11 pm

Seems like kind of a pricey valve, but if you got the loot, so be it.Have you considered a bigger valve? You could get a 1 1/2 inch one for the same price on e bay! Just a thought! Seems like a promising cannon, cant wait to see the finished goods!! :D
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Unread postAuthor: Lockednloaded » Thu Aug 25, 2011 7:15 pm

Will be a coaxial piston cannon with a 4" x 48" Schedule 40 galvanized steel chamber. Using a 4"-2" reducer at top of chamber to taper down to fit 2" barrel. I will have the option to add to the barrel length since I threaded the ends but will be 55" long initially


Co-axials require some less then standard parts. A standard reducer will not allow the barrel to extend into the chamber to make it a co-axial gun.

Maybe get some diagrams drawn, a picture's worth a thousand words :wink:
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Unread postAuthor: Atattack » Thu Aug 25, 2011 7:49 pm

I am having a machine shop bore out the reducer and weld it to the pipe, probably should have put that in the post. Don't have ability to do a pic now lockednloaded. Matty the valve I linked to will only be a valve to realease pressure in pilot chamber. The gun will be a coaxial piston gun, figured this valve would be large enough and allow me to fire remotely.[/img]
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Unread postAuthor: jsefcik » Thu Aug 25, 2011 8:19 pm

i did read the entire topic
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Last edited by jsefcik on Thu Aug 25, 2011 9:04 pm, edited 1 time in total.

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Unread postAuthor: Gun Freak » Thu Aug 25, 2011 8:20 pm

jsefcik wrote:make sure its pressure rated!!!!!

I'm pretty sure galvanized steel is pressure rated.
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Unread postAuthor: mattyzip77 » Thu Aug 25, 2011 8:29 pm

Atattack wrote: Matty the valve I linked to will only be a valve to realease pressure in pilot chamber.[/img]

It keeps going and going and going,Yes I thought that, however i was thinking maybe eliminate the piston valve all together and use the big 1 1/2 inch qev. I should have said that before, my apologies dude!! If you just want a qev to pilot it, you can get one on e bay for alot cheaper money, or even at mcmaster.com
EDIT this was supposed to post to previous post, however my dog was chasing my dragon and pulled the wire hooked to my labtop causing it to fall to the floor and make the double post,my apologies!
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Last edited by mattyzip77 on Thu Aug 25, 2011 9:05 pm, edited 1 time in total.
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Unread postAuthor: jhalek90 » Thu Aug 25, 2011 8:37 pm

... Dog+laptop+dragon....LOL!

On topic again:
I can't wait to see this thing built.
What psi are you thinking?
Anything less than 200 and you might as well use PVC.

Just a warning...200 psi on a 3.9" piston and it might shatter.
Consider a aluminum piston, and a damn good bumper.
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POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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Unread postAuthor: Atattack » Thu Aug 25, 2011 8:38 pm

The largest size I was able to find at mcmaster was 1" qev. I might have missed it though. That was the reason I went to a piston valve. No need for apologies matty, appreciate the insight. Plus I did a solenoid because I wanted the ability to remote fire the cannon.

Also that solenoid valve is pressure rated to 450psi and all the fittings and pipe are schedule 40 galvanized steel so I'm not sure what the pressure rating is but I'm sure it is higher than 450 psi.
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Unread postAuthor: Atattack » Thu Aug 25, 2011 8:42 pm

Jhalek, piston is made of umhw, going to but a 1/2" neoprene pad on both sides of piston to protect it. You guys think that should be enough? Going to use it @ 200 psi mainly. Probably take it to 400 to see how far it will go just not very often. Just gonna have trouble getting that large of a chamber that high. Gonna use a helix compressor to get to 200 for most of the shots. Some parts are at machine shop now as I don't have a lathe or equipment to bore out bell reducer, looking forward to it.
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Unread postAuthor: saefroch » Thu Aug 25, 2011 8:44 pm

Build yourself a good piston valve, it'll probably offer better performance than a QEV, since they typically have smaller passages inside that will limit flow more than the port on a homemade piston valve with the same pipe thread attachments.

The valve you linked would work fine as an exhaust valve, but there are many cheaper options.
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Unread postAuthor: Moonbogg » Thu Aug 25, 2011 8:46 pm

That sounds like a beefy cannon. Does the piston just fit in the chamber ID and press against the barrel toward the back of the cannon? That could be a good hybrid design also. You might be building a hybrid and just don't know it!
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Unread postAuthor: Atattack » Thu Aug 25, 2011 9:10 pm

Moonbogg, I don't have the ability to post a pic right now but I followed the diagram for coaxials on the sticky titled piston valves explained. The piston will seal against the barrel when pressurized and slide back 1.5" when exhaust valve is released. Would be cool if had capability to be a hybrid. This is my first cannon so still learning. Is more of a mortar due to it's size.

I know valve is expensive. But wanted valve with 400 plus psi rating. May have been others with similar psi cheaper I just didn't find em.
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Unread postAuthor: Lockednloaded » Thu Aug 25, 2011 9:18 pm

Atattack wrote:Moonbogg, I don't have the ability to post a pic right now but I followed the diagram for coaxials on the sticky titled piston valves explained. The piston will seal against the barrel when pressurized and slide back 1.5" when exhaust valve is released. Would be cool if had capability to be a hybrid. This is my first cannon so still learning. Is more of a mortar due to it's size.

I know valve is expensive. But wanted valve with 400 plus psi rating. May have been others with similar psi cheaper I just didn't find em.


Tell us your problems with the pictures, most people can help with computer stuff around here.

The piston ideally doesn't need to retract more then 1/2" by the d/4 rule, but I'd at least shorten your travel to 1"
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Unread postAuthor: Atattack » Thu Aug 25, 2011 9:34 pm

This is a very rough sketch, the elbow on the back of the end cap is 3/4" and I am going to add another elbow to that so it basically makes a 180 and runs up the chamber where I will have the valve to fill it up, a pressure gauge, and also the solenoid valve to release it. Thanks for the rule on d/4. Was unaware of that rule, good to know.

Also, I changed the design on the piston from a cup to a solid cylinder due to the end cap and reducing the amount the piston will travel, hard to explain but figured if I put a big pad on end cap for piston to bounce off of this would help out.
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