Backflow preventers come in many shapes and sizes. The three main categories of backflow assemblies are:
1.) Double Check Backflow Preventers
Double check backflow preventers consist of two check valves, four test ports, and two shut-offs and are commonly found in green rectangular irrigation boxes at ground level. These are also occasionally installed in crawl spaces, garages, and unfinished basements.
2.) Reduced Pressure Backflow Preventers
Reduced pressure backflow preventers are composed of two check valves, a relief valve assembly, a sensing line, four test ports, and two shut-offs. These are required to be installed above ground – both indoor and outdoor – and sometimes in insulated hot boxes.
3.) Pressure Vacuum Breaker or Spill Resistant Pressure Vacuum Breakers
Pressure vacuum breakers consist of a single check valve, an air inlet, two test ports, and two shut-offs. These devices are required to be installed above grade, and are almost exclusively found outdoors.