Backflow Overview

I​nstallation of mechanical backflow prevention devices

Mechanical backflow prevention devices which, depending on the type of device, may be suitable for protection against backpressure or backsiphonage, or both, should be installed so:

1. They are readily accessible for inspection, operational maintenance and renewal
2. Except for Types HA and HUK1, backflow prevention devices for protection against fluid categories 2 and 3, should not be located outside premises
3. They are not buried in the ground
4. Vented or verifiable devices, or devices with relief outlets, are not installed in chambers below ground level or where liable to flooding
5. In line strainers are provided immediately upstream of all backflow prevention devices required for fluid category 4. Where strainers are provided, servicing valves are to be fitted upstream of the inline strainer and immediately downstream of the backflow prevention device
6. The lowest point of the relief outlet from any reduced pressure zone valve assembly or similar device should terminate with a Type AA air gap located not less than 300mm above the ground or floor level.

Additional information: