Type DA – Anti-vacuum valve (or vacuum breaker)
A mechanical backflow prevention device with an air inlet which is closed when water within the device is at or above atmospheric pressure but which opens to admit air if a vacuum occurs at the inlet to the device.
Maximum permissible fluid category against which a Type DA device is accepted as adequate backflow protection:
Backflow by back pressure: not acceptable for protection against back pressure from any fluid category
Backflow by back siphonage: fluid category 3
Note: Type DA device shall have no control valves on the outlet of the device and be fitted on a 300mm minimum Type A upstand.
Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: backflow prevention arrangements