Hi there, here's a quote:
"PVB's must be installed such that the water supply to the sprinkler system goes through the PVB before supplying the sprinkler system valves. Furthermore, the device must be installed at least 12 inches or more above the highest sprinkler head or shrub riser."
It's the same for ASV's. But check with the city for local codes.
http://www.sprinklerwarehouse.com/detail.aspx?ID=585
Good luck!
If I can't fix it, it's broken!