Type ED – Non-verifiable double check valve
A non-verifiable mechanical backflow prevention device consisting of two single check valves in series, which will permit water to flow from upstream to downstream but not in the reverse direction.
Maximum permissible fluid category against which a Type ED device is accepted as adequate backflow protection:
Backflow by back pressure: fluid category 3
Backflow by back siphonage: fluid category 3
Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: backflow prevention arrangements