My sprinkler valve leaks water as soon it shuts off. By checking online and going to Home Depot first I installed new inside parts, that didn't solve the problem. then I was told that I had to replace the whole valve, so I did and it's still doing the same thing. Anybody know what's going on or how to fix it?
The most likely issue going on here is that the sprinkler piping down stream from the valve is at the same elevation or higher elevation than the valve itself. Water left in the line is flowing back through the anti siphon air gap in the valve and resulting in what you see as a "leak".
Normally sprinkler valves are meant to be installed so that they are eight to twelve inches above the highest elevation of the watering circuit to prevent this problem.