Type AUK1 – Air gap with interposed cistern

A non-mechanical backflow prevention arrangement consisting of a cistern with a Type AG overflow and an air gap; the spill-over level of the receiving vessel (WC pan or other receptacle) being located not less than 300 millimetres below the overflow pipe and not less than 15 millimetres below the lowest level of the interposed cistern. 

Maximum permissible fluid category against which a Type AUK1 air gap is accepted as adequate backflow protection:

Backflow by back pressure: fluid category 3

Backflow by back siphonage: fluid category 5

Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.  

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