Specific Installation Guidance

B​ackflow protection

T​ype AB air gap: unrestricted discharge from weir overflow

To be considered as providing fluid category 5 backflow protection, in addition to maintaining a suitable air gap, the water pathway to a Type AB air gap overflow, and discharge from the weir itself, must be unrestricted.

If the overflow is located close to another surface, such as a wall or other installation behind, in front or below the overflow, the gap between the discharge point and these surfaces must be sufficient to accommodate full discharge unimpeded. One way to demonstrate this is to ensure there is a clearance equivalent in shape and size to the weir overflow which is maintained to the air break to drain or floor level.

That is to say a clearance equivalent in shape, size and orientation to the ‘letterbox’ shape of the overflow is maintained to either floor level (so any discharge flows freely i.e. is not restricted by surfaces) or an air break to drain.












To improve this information please give us your feedback >
Your Feedback


Uncontrolled if downloaded. This is informative, non-statutory guidance and intended for general guidance purposes only; it is subject to change.

Compliance with this information should not be relied upon as guaranteeing no enforcement action will be taken by water undertakers. Water Regs UK accepts no liability for loss, indirect or consequential loss arising from or in connection with this guidance document.