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Cant get my piston sealing face air sealed

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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Cant get my piston sealing face air sealed

Unread postAuthor: Tobin » Tue May 17, 2011 1:58 am

Since I changed my piston from a melting glue piston till a aluminium piston (because the glue piston didnt handle more than 24bar) i cant get my sealing face sealed. I use a 2mm thick rubber gasket but it simply doesnt seal even thought ive tried many times with small changes to the piston. Cant really understand why because it sealed perfect before with the old piston, there the same kind of gasket was used placed on a metal disk. The qev is an 1 1/2 brass fitting with a 3cm wide piston.

This is why i need som tip about what materials you guys use as gasket and how you usually solve leaking sealing faces.
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Unread postAuthor: Major Collins » Tue May 17, 2011 2:22 am

i also had this problem , i say try neoprene as a sealing face or make a cone shaped sealing face so it closes up snugly against the barrel side.
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Unread postAuthor: Technician1002 » Tue May 17, 2011 4:40 am

It is essential that the face of the piston and the face of the valve seat meet. Any warpage of any part that prevents contact of the entire valve seat at low pressure will cause a gap that will leak.

I generally put sandpaper on the face of a piston and use the piston to lap the valve seat.

http://www.v6z24.com/howto/valvelapping
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Unread postAuthor: Hubb » Tue May 17, 2011 5:33 pm

Try this. More than likely, the sealing face of the piston against the exhaust is just slightly off square. This solution should fix that.
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Unread postAuthor: the unit » Tue May 17, 2011 6:05 pm

How is the sealing face attached, if it is screwed it could be leaking through the threads. Listen to the above advice as well.
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Unread postAuthor: Tobin » Wed May 18, 2011 2:13 pm

Problem solved, the rubber gasket was attached with a bolt one tha same way the most gaskets are, on the other side of the piston i had drillet holes to reduce the pistonweight, one hole went into the bottom of the bolt so air was traveling upside the bolt's threads and out :wink:
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