"An air gap" means a visible, unobstructed and complete physical air break between the lowest level of water discharge and the level of potentially contaminated fluid downstream (critical water level) within a cistern, vessel, fitting or appliance, hereinafter called a receptacle, that:
a. is not less than 20 mm or twice the internal diameter of the inlet pipe whichever is the greater; and
b. from which water discharges at not more than 15° from the vertical centreline of the water stream.
Follow the links below to get definitions of each of the recognised backflow prevention arrangements.
- Tap gap
- Type AA air gap – air gap with unrestricted discharge
- Type AB – Air gap with weir overflow
- Type AC – Air gap with vented submerged inlet and circular overflow
- Type AD – Air gap with injector
- Type AF – Air gap with circular overflow
- Type AG – Air gap arrangement with minimum size circular overflow
- Type AUK1 – Air gap with interposed cistern
- Type AUK2 – Domestic tap gap
- Type AUK3 – Higher risk tap gap
- Type DC – Pipe interrupter with permanent atmospheric vent