The Principle Operation of a Pressure Vacuum Breaker Backflow Prevention Device Assembly – No Water out-of-the-box
No Water – The PVB out of the box, the check valve is closed and the air inlet valve is open. The check valve spring is keeping the check valve closed and the air inlet valve spring is keeping the air inlet valve open. Supply or inlet pressure will open the check valve and close the air inlet valve.
In this exploded view of a typical PVB note the location of the check valve, air inlet valve and springs.