Type AD – Air gap with injector

A non-mechanical backflow prevention arrangement of water fittings with a horizontal injector and a physical air gap of 20 millimetres or twice the inlet diameter, whichever is the greater. 

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

Backflow by back pressure: fluid category 5

Backflow by back siphonage: fluid category 5

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