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4" Piston ideas

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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4" Piston ideas

Unread postAuthor: Vanlandinghale » Thu Oct 25, 2007 11:58 am

I'm making a cannon for my work to shoot small pumpkins (or very large spuds) and I'm having some trouble coming up with what to use for the piston. I've searched all over the forum and havent been able to find any 4" pistons that I can actually make. Its going to be used in a 4" tee and be a chamber sealer. First I thought of using endcaps but then I thought they might be too heavy but I cant find any that fit anyway. The only other thing I can find that might work are some old paint cans that almost fit and could be wrapped in tape with a good sealing face on the ends. Would that seal well enough or do you really have to use O-rings? You forum guys seem to be geniuses at this so if you have any ideas I'd appreciate it.

Here's what I have so far( just dry fitted).

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Unread postAuthor: ALIHISGREAT » Thu Oct 25, 2007 12:00 pm

you should just take the design for a 2" or 3" pistonand upscale it.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 25, 2007 12:07 pm

The only other thing I can find that might work are some old paint cans that almost fit and could be wrapped in tape with a good sealing face on the ends.


Folks on here have used similar methods and it worked for them. You might want to epoxy some sort of reinforcement at the bottom of the can (like say an appropriately sized wooden disk) to prevent it from deforming.
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Unread postAuthor: unisonmind » Thu Oct 25, 2007 12:21 pm

Its going to be used in a 4" tee and be a chamber sealer.




if you want it to a chamber sealer you need o-rings but from your set up you could make it a barrel sealer for it there a little easier to make i think


and someone out there tell me if im wrong but i think barrel sealers open slower but have higher muzzle velocity
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Unread postAuthor: jrrdw » Thu Oct 25, 2007 12:33 pm

unisonmind wrote:
Its going to be used in a 4" tee and be a chamber sealer.




if you want it to a chamber sealer you need o-rings but from your set up you could make it a barrel sealer for it there a little easier to make i think


and someone out there tell me if im wrong but i think barrel sealers open slower but have higher muzzle velocity


From what i read, you hit the nail rite on the head.

Vanlandinghale Posted: 10/25/2007 12:58 PM Post subject: 4" Piston ideas

I'm making a cannon for my work to shoot small pumpkins (or very large spuds) and I'm having some trouble coming up with what to use for the piston. I've searched all over the forum and havent been able to find any 4" pistons that I can actually make. Its going to be used in a 4" tee and be a chamber sealer. First I thought of using endcaps but then I thought they might be too heavy but I cant find any that fit anyway. The only other thing I can find that might work are some old paint cans that almost fit and could be wrapped in tape with a good sealing face on the ends. Would that seal well enough or do you really have to use O-rings? You forum guys seem to be geniuses at this so if you have any ideas I'd appreciate it.


Also, i read where a few members mold them from hot melt glue sticks. Welcome to Spudfiles.
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Unread postAuthor: Fnord » Thu Oct 25, 2007 12:52 pm

A standard 1lb green propane tank is very close to 4" diameter. You could wrap it in duct tape or epoxy some oring to it for a good fit.
You could cut it down to size and fill it with foam if it's too big.

Be sure to use a good bumper.
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Unread postAuthor: Vanlandinghale » Thu Oct 25, 2007 1:07 pm

Thanks for the replies they've been helpful. I think I might try making it a barrel sealer. Heres my ideas so far

Image

Do you think this set up would work? The 3in" end cap fits right in the 4" barrel, if I put a slightly larger sealing face on would that keep it from going through or would it just break the sealing face? (I'm trying to make it out of parts I have already :roll: )

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Image

propane tank might work too if I can do it without blowing my self up...hmmm
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Unread postAuthor: Vanlandinghale » Thu Oct 25, 2007 1:33 pm

I was going to make it be interchangeable between 3" to 6" if I can find the right parts. Right now all I have is a 4" barrel.
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Unread postAuthor: unisonmind » Thu Oct 25, 2007 1:36 pm

do what i did with this 2'' tee valve but just make with 4'' parts and you can still use you 3'' cap as a piston http://www.spudfiles.com/forums/the-start-to-the-new-gb-cannon-t10049.html
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Unread postAuthor: jrrdw » Thu Oct 25, 2007 1:49 pm

Normally the barrel is smaller then the piston, to accommodate the sealing face and piston. If the piston is smaller then the barrel, i think your going to run into jamming problems or the piston is just going to shoot out through the barrel. As for the design, no, i don't think it's going to work.

Image

My piston is the same size as the outside of this 2" pipe.

Image

I trimmed down a end plug to fit inside of the pipe to build my sealing face. Then i just solvent welded it in there, then i solvent welded a 1" barrel/pipe for my barrel. Heres a video clip of it in action.

Click here to watch video clip.

Thats the way i did it. Other members of course have thier own building techneke. No matter what the size, they are built on the same princables, (basic barrel sealers). Mine is built in a cross.

Feel free to ask any questions. I hope this helps.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 25, 2007 2:00 pm

unisonmind wrote:and someone out there tell me if im wrong but i think barrel sealers open slower but have higher muzzle velocity


Muzzle velocity depends on a) how quickly the valve opens and b) how good your flow is. Barrel length is a factor too, a fast opening valve with poor flow will have an advantage over a slow opening valve would good flow if you're using a short barrel. The reverse will be true for a short barrel.
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Unread postAuthor: Vanlandinghale » Thu Oct 25, 2007 3:18 pm

Ok, thanks for the ideas guys. jrrdw your cannon is awesome, the shooting 10 superballs part is great!
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Unread postAuthor: jrrdw » Thu Oct 25, 2007 3:28 pm

Vanlandinghale wrote:Ok, thanks for the ideas guys. jrrdw your cannon is awesome, the shooting 10 superballs part is great!


Thanks, can't wait to see how yours comes out. Will be looking forward to it.
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Unread postAuthor: williamfeldmann » Thu Oct 25, 2007 3:42 pm

Are you still planning on a chamber sealer? You are not going to have very good luck using a 3 inch cap in that case at it isn't a tight enough fit even with o rings.

Chamber sealers need the orings and tight fit because they hold the pressurized air in and not out like a barrel sealer. I have used 3 inch caps in my 4 inch tee barrel sealer with good luck.
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Unread postAuthor: Acdcmonkey1991 » Thu Oct 25, 2007 4:12 pm

Not to be the bearer of bad news but that pipe is dwv, Im not sure if it is pressure rated but if its not....KABOOM!!! Just trying to watch out for you safety. Happy spuddin'
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