Quote Originally Posted by slow_runner View Post
After isolating stages he discovered that a gland seal was passing. He has sorted that by resorting to using 3(?) smaller O rings.
This is an early FX 3 stage pump and is a bit different to the available drawing.
http://www.fxairguns.com/wp-content/...d-partlist.pdf
The second / third stage piston (#11) has two internal O ring seals that it appears weren't up to it; there was enough room for another to be fitted to the stack and this seems to have done the trick.
Job done.
Thanks for all your suggestions