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Piston Failure Possibility?

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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Piston Failure Possibility?

Unread postAuthor: MrCrowley » Tue Dec 18, 2007 10:22 pm

I'm sure most of you are familiar with my SGA golfball gun, if not, tough.

Anyway I can't seem to find 'PVC plugs' in NZ, and I hear they are alot easier to seal the back of a tee then an end cap. So i've just glued an end cap on, can't be bothered trying to have a serviceable piston anymore with so many leaks.

The problem is i've threaded a 20mm nipple through the back of the end cap and it connects up to my pilot valve and fill valve etc but when the piston actuates i'm afraid it might knock the 20mm nipple out as that's the only thing it will collide with.

Since the end cap is only a few mm thick, it might not be enough to hold the nipple in over multiple firings.

I was thinking of putting a bolt in the end cap so the piston will get stopped by the bolt, but after a few firings I would say it would be bent as sh|t

I do have a bumper, but with so much force I doubt it will do that much.

Any ideas?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2007 10:27 pm

can't you get some thick rubber discs and cut out holes for the nipple as a bumper, in that way they never touch....
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Unread postAuthor: ShowNoMercy » Tue Dec 18, 2007 10:27 pm

Can you take the cap off as of now or is it glued on nice and good? Cause if it isnt could you run the nipple through the part where the cap and tee overlap? It wont look as good but you would have more to grab and have a less risk off hitting the piston.
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Unread postAuthor: elitesniper » Tue Dec 18, 2007 10:28 pm

cant you put a bolt with a some cushoning on the top?
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Unread postAuthor: ShowNoMercy » Tue Dec 18, 2007 10:29 pm

The force will still be along a single plane and will most likely split the piston.
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Unread postAuthor: MrCrowley » Tue Dec 18, 2007 11:04 pm

jackssmirkingrevenge wrote:can't you get some thick rubber discs and cut out holes for the nipple as a bumper, in that way they never touch....


That's not a bad idea, I think I might have something like that.
If not i'll just put two or three bolts in to share the force.

Do you think there is a high chance of it forcing the nipple out?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2007 11:08 pm

Do you think there is a high chance of it forcing the nipple out?


Experience shows that if you touch a nipple enough, even with a small force, it will eventually pop out. I'd advise against the bolt idea, as not only would the contact area remain small, but you're also drilling more holes into the endcap. You could also fill in the space with epoxy, with the added benefit of increasing strength and reducing pilot volume, though some sort of bumper would still be required.
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Unread postAuthor: MrCrowley » Wed Dec 19, 2007 12:03 am

Hmm yeah sounds good, i'll see what I can do.
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Unread postAuthor: EGOed » Wed Dec 19, 2007 3:47 am

Jacks idea is good , or you can also pour epoxy to build up the level of the endcap flush with the exposed nipple......Will you be able to relube your piston with it not being serviceable...?....I have noticed this is the only service that I have ever really had to do so far with mine.
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 19, 2007 3:49 am

EGOed wrote:Jacks idea is good , or you can also pour epoxy to build up the level of the endcap flush with the exposed nipple.


That's basically what I was suggesting.
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Unread postAuthor: EGOed » Wed Dec 19, 2007 4:16 am

Didnt see your second post Jack.....I thought the rubber discs would work well though in your first post.
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Unread postAuthor: jrrdw » Wed Dec 19, 2007 5:58 am

I'm in total agreement with the no bolt/s! The piston will bust the end cap with the bolt. Bumpers in your cannon are a must, i've read alot here at Spudfiles where members talk about tennis balls cut apart as bumpers.
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 19, 2007 6:06 am

jrrdw wrote:tennis balls cut apart as bumpers.


That works but is wasteful of pilot volume, a thick rubber pad is effective as well as maintaining efficiency.
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Unread postAuthor: jimmy101 » Wed Dec 19, 2007 1:11 pm

Jack's idea sounds like the only one that'll work.

You might consider Bondo instead of epoxy.
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Unread postAuthor: MrCrowley » Wed Dec 19, 2007 3:22 pm

I do have a bumper, but it's rubber, not necesarrily the softest stuff I would think it would still contain most of the energy.

I'll be spending the day in the garage so i'll see what I can come up with trying out JSR's idea.
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