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Something bad happened, help needed :)

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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Something bad happened, help needed :)

Unread postAuthor: chinnerz » Sun Jan 17, 2010 2:21 am

i was in the process of zeroing a scope when i heard a thump, my rifle didnt shoot at all after that, however i kept hearing a successful discharge noise when i pulled the trigger.

on a closer inspection i discovered this:

Image
By chinnerz2, shot with NO SPAMMING ALLOWED at 2010-01-16

my piston had separated into the 2 parts it was made from. does anyone have any idea as to why this happened? and what are the steps in preventing this from happening.

Edited by jrrdw.
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Unread postAuthor: jor2daje » Sun Jan 17, 2010 2:46 am

Use something better to fasten you sealing face to your piston like a screw or better glue. Also you should change your piston so its something you can tap thread into and screw your sealing face one.
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Unread postAuthor: jrrdw » Sun Jan 17, 2010 7:33 am

What exactly is your piston made of and exactly how did you put it together?
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Unread postAuthor: chinnerz » Sun Jan 17, 2010 8:05 am

the piston is cast from hot glue, with a 2-3 mm black rubber seeling face. Made it by first casting the piston the mixing up some araldite and attaching the face then putting it in a clamp over night
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Unread postAuthor: dewey-1 » Sun Jan 17, 2010 8:48 am

One thing I notice is that the piston length is to short for the material used.

Make the length of the piston 3/4 to 1.5 times your inside dimension ID.

Your picture shows a length of about 1/4 of ID. Due to its short length, the pressure deformed the piston outer edge and caused it to rotate.

Another solution is to make the piston of stronger materials such as epoxy or HDPE, UHMWPE.
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