Irrigation Backflow Device Installation (AVB/PVB)
The following illustrations show the correct installation for the most common irrigation backflow devices. There are significant installation differences between the atmospheric vacuum breaker (AVB) and the pressure vacuum breaker (PVB). One of the most common mistakes is that an AVB is installed like a PVB with a valve after the device. This can cause the device to fail. If you have this incorrect installation, please call a knowledgeable plumber/landscaper to correct your irrigation system.
Illustrations from USC FCC-HR 10th edition