Piston valve not opening: Help!

[daniele tn]

Hi, I have got a problem with the small metal piston gun that I built.
It was actuated by a ball valve, thanks to your help I upgraded it using a modded sprinkrel valve instead.
The proble was that the valve was too big for the gun (1 inch compared to the 1/2 inch gun) and that it could sustain only 15 bar.
So I thought to build a piston valve.
The problem is that the piston doesnt open when I open the pilot valve (ball valve)
This is a crappy diagram that I made in paint:



What I think is the problem is that the washer that seals the barrel is large like the tee I use (1/2)
Making that modification could help?
(making the barrel enter the tee and using a smaller washer)
Or could the problem be a too small pilot valve(3/8 ball valve)?
Thank you

[MRR]

If the the diagram is accurate then you have a bad sealing face to piston diameter ratio.
The diameter of the piston has to be bigger than the diameter of the barrel that you are sealing.

[tghhs]

http://www.spudfiles.com/forums/piston- ... t8157.html

The piston needs to be bigger than the bore, because it needs a surface area for the opening force to act on.

[daniele tn]

Thank you so much.
I thought that was the problem but I wasnt sure.
Thank you both

[i-will]

That only half the problem. Your piston is backwards. the end with the bigger surface area is gonna be pushed by the pressure. In your first design the pressure is actually forcing the piston to seal against the barrel (it has the greater seal diameter). If the seal on both ends is the same diameter (like the second den) then its not gonna move at all (equal force on both ends). this is my favorite type of piston and I've made the same mistake long ago. it's all about the surface area of the actual seals.

[daniele tn]

It works exacly like that, just had to think a bit to find out.
I changed it and now it works, but I still have leaks from the barrel.
I use a neoprene washer as sealing face, but it doesnt seal properly, do you know a way to fix that?
And also, the bigger the difference in sealing surface and pilot surface the faster will be the opening?
If yes, do you think 15mm pilot and 10mm barrel diameter is enough?
Thank you