Type DC – Pipe interrupter with permanent atmospheric vent

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