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A non-mechanical backflow prevention device with a permanent unrestricted air inlet, the device being installed so that the flow of water is in a vertical downward direction.
Maximum permissible fluid category against which a Type DC arrangement 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 5
Note: arrangements incorporating Type DC devices shall have no control valves on the outlet of the device, they shall be fitted not less than 300mm above the spillover level of a WC pan, or 150mm above the sparge pipe outlet of a urinal, and discharge vertically downwards.
Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: backflow prevention arrangements