SpudFiles

Ok I built my first Piston Valve Gun, pumped to 200 PSI and when piloted all the air burst through the back, nothing into barrel. I dont know what im doing wrong because the piston is able to move when i blow air and can move.

Here is picture

What size is the pilot? And the diameter of the piston?

the pilot area is 1 inch long and the diameter of the piston is about .25mm less then the OD of the tube

I meant the pilot valve, and the actual diameter of the piston.

the pilot is a standed bike tire valve. outer tube is 8mm, and the piston is about 7.5 mm

That's the problem, the gap around your piston is too large. Wrap some tape around it until it's a much closer fit. Them lubricate the heck out of it, and you'll be right.

will Vaseline be a good lubricant?

Yep, it won't break down the rubber. I used it before I got some decent grease.

ok so after messing with tiny peices of tape, i got the piston so its tight enough so too much air wont leak when piloted, but loose enough for air to get past to fill the chamber.
i used a small amount of epoxy for a low pressure test tomorrow, will post a video tommorow

id got with a bigger pilot even if it works tomorrow.

where are the pics???? Cant help you if we cant see the pics!!!

i had the same isseu with a schrader as a pilot... in the end i just made my own valve to pilot te bugger....