Wilkins PVB leaking bonnet

The system is as follows: 5/8" meter - 70psi - 3/4" PVB to a 1" PVC mainline to Orbits manifold (I told my friend to get Rainbird valves and I would build him a manifold) - way under 15GPM per valve; With the mainline under pressure there are no leaks. When he opens a valve, the PVB has water draining from the bonnet area and there is not enough pressure to fully operate Rainbird popups (they spray only a foot or so). Could this be caused by debris somewhere in the bonnet area of the PVB?

The leak from the vacuum breaker prevents the downstream pressure from building up enough to "pop" the pop-ups. Repair the vacuum breaker.

A repair kit is avaliable that includes the bonnet and seals