High Risk -
Reduced Pressure Zone Assembly (RPZA) - must be tested annually

Moderate Risk -
Double Check Valve Assembly (DCVA) - must be tested annually

Low Risk -
Dual Check Value - not testable

Air Gap (AG)

• The vertical distance between the end of a water supply outlet (i.e. a hose, a tap) and the vessel or container the water is discharged into.
• Provides an adequate space between the contaminant and water supply.
• If well designed and properly maintained, is the best available protection against backflow.
• Can be used for extremely hazardous installations, in particular for the filling of tanks for chemical applications in the agricultural areas (see best practices for rinsing and filling fertilizer tanks [PDF - 155 KB]).

Reduced Pressure Zone Assembly (RPZA)*

• Two independently acting check valves separated by a reduced pressure zone.
• Installed as a unit between two shut off valves.
• Each check valve is fitted with a test cock for periodic testing.
• Can be used for health hazards (i.e. toxic material) and severely hazardous connections (i.e. medical/dental facilities, industrial plants and agricultural operations).

Double Check Valve Assembly (DCVA)*

• Two internally loaded check valves, force-loaded or internally weighted.
• If one check valve fails to close the other will prevent backflow.
• Each check valve is fitted with a test cock for periodic testing.
• Can be used for all non-health hazards (non-toxic) connections (i.e. fire sprinkler, irrigation systems).

Hose Connection Vacuum Breaker (HCVB)

• A spring-loaded check valve seals against an atmospheric outlet when the water supply is turned on.
• The HCVB vents to atmosphere when it is turned off, protecting against backsiphonage conditions.

Dual Check Valve (DuC)

• Two independently acting, spring loaded check valves.
• Usually does not have shutoff valves and may or may not be equipped with test cocks.
• Should only be used to isolate non-health hazards and is intended for single family homes.