crispyjones

I am 98% certain that serves the same purpose and you should just fill it in. That square hole is the outlet to a passage that leads to the upper part of the valve, I assume it's a metal pipe like the old one but I can't see. You can confirm by blowing in one end or the other to see where the air comes out.When uses for its designed purpose (water) the sprinkler valve must vent the water from above the diaphragm after the solenoid has turned on, so it vents it into the outlet water pipe via that passageway. We are modifying it to vent to atmosphere through the air valve instead.

Thanks for the heads up. Can't wait for the big royalty check ;)

If you caught a peacock or hen with this net gun I would definitely add the video or picture to my instructable!

Thanks for ideas FrankC19. Do you have any links to the stuff you build, and I am interested in the carbon fiber valve.