Type AUK3 – Higher risk tap gap

The height of an air gap between the lowest part of the outlet of a tap, combination fitting, shower head or other fitting discharging over any appliance or other receptacle, and the spillover level of that appliance, where a fluid category 4 or 5 risk is present downstream. 

Maximum permissible fluid category against which a Type AUK3 tap gap is accepted as adequate backflow protection:

Backflow by back pressure:  not acceptable for protection against back pressure from any fluid category 

Backflow by back siphonage: fluid category 5

Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: backflow prevention arrangements