Coaxial Not Firing

[FreakyShotGlass]

Its been a while but I decided to finally make another cannon. But I have a problem the piston seals and pressure builds but when it comes time to fire all the pressure is released through the pilot valve which is a 20mm sprinkler valve. Is this because the piston is not tight enough and it will be back to the workshop to make a better one or is there something else at play?

[jackssmirkingrevenge]

Is this because the piston is not tight enough

Probably

[Gippeto]

Yup...the leading cause of "failure to actuate".

A distant second is likely surface area differential.

[FreakyShotGlass]

Ok I have it going now with a very tight piston but now it won't hold over 40 psi, past that it just leaks out of the barrel.

[Willdebeers]

You don't want it to tight, but not too loose. For the easy option, wrap it in tape until there is no play, but you can push it with your little finger.

[Demon]

To make the piston the more leak proof for cheap is to wrap around some very thin tape.