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My 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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My Piston

Unread postAuthor: jor2daje » Thu Feb 19, 2009 12:18 am

So i decided to make my own large-ish coaxial, this is my first try at a semi big piston.

Just wondering if you think this piston will work, the gun Im planning will probably be irreversibly sealed so i want to know if you think this might work.

My piston is just a cork with some tape to make up area, some innertube is epoxied to the end.
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Unread postAuthor: starman » Thu Feb 19, 2009 12:29 am

It looks fine in and of itself...the cylinder it works in is just as critical. They have to fit well together and parameters just as piston throw and the sealing face of the barrel have to be up to par as well.

In any case, it isn't a good idea to build a non-servicable piston.
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Unread postAuthor: jor2daje » Thu Feb 19, 2009 12:33 am

Ok well its a really nice fit with the cylinder, my barrel will hopefully be like 8mm or so, should i use a different sealing face or can i seal dirrectly on the barrel, my concern is that the thin barrel will cut the rubber.
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 19, 2009 12:39 am

jor2daje wrote:my concern is that the thin barrel will cut the rubber.


A legitimate concern, the solutions i found to this problem are either have the sealing face on the barrel itself, likethis launcher, or epoxy a sleeve to the barrel at the breech end to enlarge its external diameter.
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Unread postAuthor: starman » Thu Feb 19, 2009 12:41 am

That's why you need to make your piston serviceable. It isn't uncommon for the seal to need replacing after some time, especially the thinner the barrel material.

Use some 1/8" neoprene rubber if you can find it. McMaster has it here.
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Unread postAuthor: jor2daje » Thu Feb 19, 2009 12:42 am

Could I maybe use one of the tools used for enlarging pipe to try to roll a sort of lip over on the back of the barrel so it has a larger surface area.
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Unread postAuthor: john bunsenburner » Thu Feb 19, 2009 4:41 am

maybe you could cout an O-ring so it has a little p on one side and slide it over the barrel, this too would needs replacement but like this you spare the acctual rubber, depending on what is sheeper make your decision, if you are using neoprene then maybe my idea works if inner tube then its not worth the O-rings.
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