I'll try to summarize as best as possible:
1. I started my sprinkler system about 2 weeks ago and it was fine. A while later I noticed one of the test cocks was leaking so I shut off my main water supply gate valve in the basement until I could fix the leak.
Leak is fixed.
Now, whenever I turn the system on, I get water gushing out of the breaker / backflow preventer. I know (kinda) it is not damaged since it worked just 2 weeks ago.
I have a ball valve and test cock on either side of the backflow device. I have tried many differnt combinations and it always results in water flooding out of the backflow device.
If the ball valve between the MAIN water supply and the backflow is open, and I slowly open the gate valve to the main water supply in the basement, it leaks.
If I close this same valve (between the main and backflow), then turn on the main then open the valve, I still get a leak.
I don't remember the combination I did 2 weeks ago or I would try that, but I seem to recall that the breaker leaked, and both test cocks were open - and when i closed the test cocks it stop gusing via the breaker.......maybe I will try that again.
The system was professionaly winterized and I am in Mich.
Close the PVB testcocks. Close the outlet-side ball valve on the PVB. Open the inlet valves all the way - part-way open will give you that gushing water. Then open the outlet valve on the PVB.