Modded Valve too weak for pilot?

[deusXmachina]

I am currently working on a large piston valve, which is piloted by a modded sprinkler valve. It is a 1" inline made by Champion (it's pretty much comparable to RainBird) which is tapped 3/4" and can be vented either electrically via rainbird, or pneumatically. When I fire at 60 psi, the chamber pressure has to drop significantly before the piston actually fires. The 1" pilot tends to make a loud, squawking noise, not quite honking but still rather unhealthy sounding (even with white lithium lubrication), for about .75 sec until the piston goes. I feel like I'm missing something totally obvious here so any advice is appreciated.

[hi]

If that happens then your piston probly isnt tight enough in the chamber. Try wraping in painters tape, i had that problem, I wrapped the piston in tape and now it works. As for the honking noise, your diaphram is leaking, you need to plug up the solinoid hole with epoxy and just use a blow gun or ball valve.