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Piston Problems

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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Re: Piston Problems

Unread postAuthor: Anatine Duo » Sun Apr 13, 2014 2:45 pm

i promised never to seal up a piston with glue again...

can you hot glue and pin the endcap?

good luck!
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Re: Piston Problems

Unread postAuthor: jackssmirkingrevenge » Mon Apr 14, 2014 5:31 am

QEVs are cheap and easy to find... just saying :)
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Re: Piston Problems

Unread postAuthor: Suedo » Mon Apr 14, 2014 8:10 am

What do you mean by hot glue and pin? Do you suggest I bolt it in rather than glueing it?
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Re: Piston Problems

Unread postAuthor: Anatine Duo » Mon Apr 14, 2014 1:12 pm

Yes, you might be able to pin or bolt it together, and use the hot melt for sealing. If the piston needs maintenance (all of mine eventually did) then you pull the pins and warm it up to take it apart. Threaded connection is better but it depends what you have to work with.

Or glue it and hope you don't need to take it apart...
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Re: Piston Problems

Unread postAuthor: Technician1002 » Wed May 28, 2014 10:38 am

I've seen only one major detail left out of the above posts. The surfaces that come together to seal, must come together completely. Any surface uneveness will leave a relatively large leaky gap. The first order of business is to polish and true the valve seat. A wooden dowel the same diameter as the piston makes a good tool with a piece of sand paper glued on the end. I normally start with about a 75-100 grit. Use a sharpie to paint the valve seat and examine your early polish efforts. You may notice the high spots quickly lose the ink, but the low spots remain. Sand until a light sanding quickly removes all the ink. When that is achieved, switch to a 200 - 400 grit and sand until it is polished smooth.

If you have self stick sandpaper, the end of the piston can be then trued against the valve seat. By working the process in reverse, you can true the end of your piston before applying the rubber seal so it is true and flat. Add your rubber seal and test for leaks.

When I make pistons on the drill press I can skip this step as the finishing of the face of the piston makes it true to the bore.

See the making of my Mouse Musket for more info on truing your seals. My thread on making a small piston on a drill press shows the truing of the valve piston face.

Truing the face of my piston on a drill press. The cutting tool is passed under the piston shaving the face flat.
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Re: Piston Problems

Unread postAuthor: bravootome » Wed May 28, 2014 2:18 pm

Suedo wrote:What do you mean by hot glue and pin? Do you suggest I bolt it in rather than glueing it?


Myself i do not use any bolt for any of my 1000 pistons i made so far. Only lot of superglue. Bondo absorb the superglue, so you need to let it be absorbed for 1 min then add some more superglue and put the rubber. All this process must be made holding the piston upside down... or the glue will flow on the piston's walls .....
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