Types Of Backflow Prevention Devices
Types Of Backflow Prevention Devices
Dual Check Valve (DCV) – Low Hazard, usually non-testable
A dual check valve is a simple device with two internal one-way valves. It’s typically used for low-risk scenarios (nuisance but not health-threatening). Many residential water meters in Victoria include a built-in dual check valve as basic protection.
TESTING: Dual check valves are generally not testable in the field – they are a sealed unit. They provide minimal protection and are usually replaced if suspected faulty. If your property only has a small 20–25 mm meter with an in-built dual check, no annual test is required. However, adding any higher-risk feature to the property may require an upgraded device.
Double Check Valve Assembly (DCVA) – Medium Hazard, testable
A double check valve has two one-way valves (check valves) in series, plus test ports for connecting testing equipment. It’s used in situations that could endanger health but are not life-threatening. Most commercial and industrial properties with moderate risk, and fire services on some buildings, will have a DCVA installed.
TESTING: During an annual test, the plumber will isolate the device and use a differential pressure gauge to check that both valves seal properly. If either fails, the device must be repaired or replaced.
Reduced Pressure Zone Device (RPZD) – High Hazard, Testable
RPZDs contain two check valves and a pressure-monitored relief valve. They’re used in high-hazard scenarios where contamination could be deadly or severely harmful. These are found at hospitals, chemical sites, and even in homes with high-risk plumbing features (e.g. bidet sprays).
TESTING: Plumbers attach test hoses and simulate back-pressure and siphonage to ensure both check valves and the relief valve operate correctly. If the relief valve discharges during the test, that’s expected – it’s doing its job.
Atmospheric Vacuum Breaker (AVB) / Pressure Vacuum Breaker (PVB)
AVBs are used on fixtures like taps or irrigation outlets and are not testable. PVBs are testable and typically used in irrigation and laboratories.
TESTING: PVBs are tested using a gauge. AVBs are visually inspected to ensure air inlets function.
Registered Air Gap or Break Tank – High Hazard (alternative method)
These are non-mechanical systems that rely on physical separation to prevent backflow. For example, a pipe that stops above a tank’s overflow level is an air gap.
TESTING: These require visual inspection annually to ensure no bridging or alteration has compromised the gap.
Summary: Medium and high hazard scenarios require testable devices by law. Low hazard setups use simpler devices but may need upgrades if risk increases. A qualified plumber can confirm the correct device and ensure compliance.
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