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