SpudFiles

hi guys

first time poster.

recently i built a pneumatic cannon, but cannot for the life of me get the valve to seal. i've pulled it apart and cleaned it several times to make sure there is no grit inside, and there are no cracks in the body, nor holes in the diaphram.

every time i try to fill it with air, it is leaking out through the barrel. strangely enough if i connect the valve backwards (ie with the flow arrows pointing in the wrong direction) it will seal with only a slight leak coming from the barrel.

any help would be appreciated.

cheers
darren

Are you filling it with a bike pump? If not, I just posted a The Sprinkler Valve thread. It should be able to help you.

man, super fast reply!!

i downloaded the zip file, but haven't read it yet.

yes, i am filling with a bike pump, could it be that there is not enough pressure in the first instance to create a proper seal?

heers
darren

That's exactly what it is.

Try moving your fill valve from the chamber to behind the diaphragm. If that doesn't work, then you will either need to use a compressor or you could place a ball valve between your sprinkler valve and the chamber. Fill the chamber, then open the ball valve to seat the diaphragm.

thanks for the quick reply and info, i'll have to go and modify my design a bit.

cheers
darren

You could also try to pump like a compressor on crack. The force that seals it rises equally along with the pressure.
Alot of guns do not seal on lower pressures, while they do on higher ones.

If it still leaks after you connect it to the compressor, try making the equalization hole smaller. I put epoxy over mine and then made the hole with a pin in the epoxy before it hardened.