Type LB – Pressurised air inlet valve combined with a check valve downstream

A mechanical backflow prevention device comprising a Type LA anti-vacuum valve and a single check valve located downstream.  

Maximum permissible fluid category against which a Type LB device is accepted as adequate backflow protection:

Backflow by back pressure: fluid category 2

Backflow by back siphonage: fluid category 3

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