Type AG – Air gap arrangement with minimum size circular overflow

A non-mechanical backflow prevention arrangement of water fittings with an air gap; together with an overflow, the size of which is determined by measure or a vacuum test. 

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

Backflow by back pressure: fluid category 3

Backflow by back siphonage: fluid category 3

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