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Ideas for piston

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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Unread postAuthor: Fnord » Thu Mar 05, 2009 7:05 pm

By far the best piston I've ever made was just a solid hunk of rubber with a floating oring.

You'll want to use a bench grinder* to reshape it to the size you want(rubber round stock is often uneven), but after that it'll last freaking forever. The most you'll need to do is grease it occasionally.
A dremel works for a floating oring groove.

*maybe there's actually a proper tool for the job, but it works for me :)
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Unread postAuthor: jmeyer1022 » Thu Mar 05, 2009 7:08 pm

Thanks for the help hubb, I looked through numerous pages last night and did some searches most of which I've tried or just don't seem of interest. I appreciate the help guys, I wrapped some duct tape on my 1 1/4 coupling which helped alot, I tried doing this before except with painters tape and it had little effect not sure what it is with the duct tape but its helping a large amount. Still open for suggestions though =)
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Unread postAuthor: psycix » Fri Mar 06, 2009 4:55 pm

From what I read it just seems like your pistons are WAY not tight enough in your pipe. Usually when people with piston troubles say that their piston is pretty tight, there actually is ONE HELL OF A GAP.
The piston has to be as tight as possible, without experiencing significant friction ofcourse.
You've got a big pilot valve, which is good. I think that this is the reason your pistons actually even work. With a smaller pilot valve they probably wouldn't even have worked.

A tip on enlarging your piston diameter with duct tape:
The tape has to be wrapped PERFECTLY.
One wrinkle and it is ruined.
Note that the tape has a limited lifetime.

The problems ranged various from to big of equalization, to much drag, and just structurally weak.

Are you making equalisation holes in your pistons? If you are, then stop doing that, it is only needed on 100% airtight pistons. Which is certainly not the case.
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Unread postAuthor: jmeyer1022 » Fri Mar 06, 2009 6:19 pm

Thanks for the reply, I've fixed my piston coupling piston up I'll show you a diagram of it and the changes I made. Also it was wrapped in PAINTERS tape.
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Alright that's what my old piston looked like, it fit super loose inside the 2" pipe. The new one is same exact thing except it's duct tape rather than painters tape. The 2" steel washers are epoxied onto the coupling, before I believe air was getting inside of it and not sure what but just doing weird stuff. So with the epoxy no air is getting between the washer and the coupling. I cut up a tennis ball for a bumper, before my bumper was some weird foam which I believe did absolutely nothing because every 10-15 shots I'd have to take it out and re-tighten the bolt/nut. I also smothered this baby in lithium grease. I appreciated the tips. The piston now actuates as low as 18ish PSI. Weather says its suppose to be 55 tomorrow so I'll be busting out the video camera and anything I can destroy.
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Unread postAuthor: psycix » Sat Mar 07, 2009 10:30 am

Any pictures of the piston and the fit in the pipe?
Maybe you should look for something that fits closer to the 2" pipe then that coupling. Try endcaps and pipes of other sizes. Or something completely different like a deodorant can.
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