SpudFiles

Go with the second picture. The first one is pointless since the added area is equaled with pressure behind it as well. This could even rip off your sealing face or such too.

Leave room behind the piston for a bumper. Without one things will break.

In the Wiki, there is a section on Piston Valves that covers the forces on one that hold it closed and the force and pressure in the pilot required to open it. This force goes down as the piston OD is reduced to nearly the same diameter as the valve seat. As these sizes become close to the same, pressure in the pilot area from blowby (eq pressure) will hold the piston closed to lower pressures and piston friction becomes critical. The upside is they are fast when they do pop open. You don't want these sizes too close to the same as it makes the valve unreliable and subject to not firing.

http://www.spudfiles.com/spud_wiki/inde ... Piston_valve

i made my piston kinda like that i didnt use a washer tho i had a peace of some white plastic i think its nylon it was 2mm bigger than my part it slide in
i drill press lathed it down but not the end so it has a in built washer

it aslo let me use a bigger barrel port

Ok, I'm going to go with the second picture and the bumpers going to be a couple rubber gaskets

Use number 2

Just make sure the piston is a good fit in the bushing, and you will be more than fine.

Pic 1 would probably not work very well.

Thats what I heard, the pistons cast in a plug so it should fit in the bushing nice, I was just worried there would be no air to push it back