SpudFiles

OK,Now my new copper piston valve cannon is ready and it has a blowgun as a pilot valve but it has a one problem. It works fine pressures
between 2-4bar but no any higher pressures,for example,when I put in 8bar and press the blowgun,the air just comes out without the valve openes. My tee ID is 32mm and a piston is 50mm long and a barrels diameter is 20mm,OD 22mm.What is the problem?

Post some pics of the inside of your valve so we can see the sealing face location and so forth. Also the clearance specs from outside piston diameter to inside of piston cylinder.

That is not worth it anymore. I found the problem that was too slow pilot valve, now it works like a dream

Yeah swap the blow gun for a 1/4" QEV or a 1/2" ball valve and it will do wonders.

OK...I think still that my pilot valve is not enough for that, so I have to grow up my pilot ID to almost 1cm and then comes to the 1/2" ball valve.

Don't worry a 1/2" ball valve wont waste any air, it will only increase performance.