Type DUK1 – Anti-vacuum valve combined with a single check valve

A mechanical backflow prevention device comprising an anti-vacuum valve with a single check valve located upstream. 

Maximum permissible fluid category against which a Type DUK1 device is accepted as adequate backflow protection:

Backflow by back pressure: fluid category 2 

Backflow by back siphonage: fluid category 3

Note: Type DUK1 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