- Last updated:
- 21 Feb 2020
It is important to refer to the manufacturer's instructions prior to installing a backflow prevention device.
Installers need to check the valve is installed in the direction of flow. An RPZD must be installed in the horizontal position. some DCV can be installed either horizontally or vertically, so it is important not to get these confused. Any valve with a swing check must be installed horizontally. RPZD must be installed a minimum of 300 millimeters above ground level.
It is recommended that DCV and testable single check valves are installed above ground.
If they must be installed in pits below ground, adequate access must be provided for testing, maintenance, removal and replacement of the device.
Resilient seated isolating valves must be installed immediately downstream and upstream of backflow prevention devices for testing purposes.
If the valve train is for firefighting purposes, the isolating valves must be locked in the open position. Property isolating valves should not be used as the downstream isolator or the appliance isolating valve as the upstream isolator, as they are not designed for testing purposes.
Line strainers must be installed to all backflow prevention devices, except for devices used for firefighting. Line strainers prevent particles of grit from damaging or becoming lodged in the seats of check valves and causing failure to the backflow prevention device.
To do this effectively line strainers must be installed in the correct direction of flow and the line strainer elements must comply with table 4.2 of AS/NZS 3500. The strainer screen will collect material in the strainer at the lowest point of the screen and allow cleaning without residue falling back into the pipe work.
Backflow prevention devices must be able to be removed for repair or replacement. Barrel unions should be used to allow the valves to be disconnected.
To prevent damage to backflow prevention devices they should be supported properly and there are a range of clips and supports available for this purpose. Installers should also consider if the backflow prevention device will be subject to tampering or vandalism, as a cage or cover may be required.
Backflow prevention devices must be tested every 12 months, so you need to ensure adequate access for testing purposes. It is recommended that the device be installed 100 millimetres from any wall. If you need to install a backflow prevention device in a plant room or other location where access is restricted, you will need to consider carefully the location for testing and maintenance purposes.
Guidelines for backflow prevention are available on council’s website.