Cross Connection Prevention
Pipes located above ground within buildings should be colour-coded (150mm approx.) to BS 1710
- Applies to:
- industrial, commercial buildings or houses use water other than wholesome
- all water fittings, including cisterns and valves
- taps are particularly important
- Supply pipes colour-coding:
- Water supplier's wholesome water - blue
- Hot distributing water - red
- Reclaimed grey water - black
Mechanical
- Water Supply (water fittings) Regulations 1999 - covers backflow prevention
- http://www.rwc.co.uk/ - about backflow prevention
- Back-pressure devices that positioned downstream of the device (B,C and E families)
- BA - RPZ valve
- DA - Anti-vacuum valve e.g. storage cistern with submerged inlet (category 3, not acceptable for back-pressure)
- MUST be fitted on MIN 300mm up stand above the discharge point
- MUST have no valve or restriction on its outlet
- DB - Pipe-interrupter e.g. garden irrigation system (category 4, not acceptable for back-pressure)
- DUK1 - Anti-vacuum Valve with Check Valve e.g. special applications (Back-siphonage 3, back-pressure 2)
- HA - Hose Union Backflow Preventor NOT allowed on new installations! (Back-siphonage 3, back-pressure 2)
- HC - Diverter with Automatic Return. Integral with domestic appliances e.g. bath/shower combination tap (category 3, not acceptable for back-pressure)
- HUK1 - hose union tap with double check valve e.g. replacement only existing hose union taps (category 3)
- LA- Pressurised Air Inlet valve e.g. special applications (category 2, not acceptable for back-pressure)
- LB - pressurised air inlet valve with check valve (Back-siphonage 3, back-pressure 2)
- Positioning
- Only HA and HUK1 (categories 2 and 3) can be located outside
- For category 4 should have line strainer and service valve fitted upstream
Non-mechanical
- Back-siphonage devices that positioned prior to the device (A,D and H families)
- Air gaps:
- AA - e.g. cattle trough (unrestricted discharge)
- AC - with vented submerged inlet e.g. silencer pipe (category 3)
- AD - with injector e.g. in-built into washing machines (category 5)
- AF - with circular overflow (unrestricted discharge) e.g. CWSC (category 4)
- AG - MIN size circular overflow e.g. CWSC type AUK1 (category 3)
- AUK2
- 1/2G = 20mm
- 3/4G = 25mm
- > 3/4G = 70mm
- Category 3
- AUK3 - e.g. washbasin in a hospital, kitchen sink
- DC interrupter
- MIN 300mm between DC and spill over level of the urinal bowl with Pressure Flushing Valve
- MIN 150mm between DC and the outlet
- AB - weir overflow for boosted water supply
