What is a Type AA air gap?

A Type AA air gap is a non-mechanical backflow prevention arrangement comprising of an inlet which discharges water into a cistern, vessel, fitting or appliance (receiving vessel) and an outlet. Depending on the outcome of an assessment by the local water undertaker it can feed a single or multiple installations.

A Type AA air gap is rated by the Regulators as suitable backflow protection against both back siphonage and back pressure at the highest level of contamination risk, fluid category 5.

A summary of some of the key requirements for a Type AA air gap is given below:

1. The supply pipe and inlet control must be external to the receiving vessel and fixed so the air gap is maintained and unrestricted.

2. The air gap is an unobstructed and complete physical break between the lowest point of discharge and the spillover level of the contents of the receiving vessel. Measured vertically it must be no less than 20 mm or twice the internal diameter of the supply whichever is the greater.

3. The spillover level is the level at which the contents of receiving vessel spill over the top edge when the inflow of water exceeds the outflow through the outlet i.e. demand.

4. The spillover is unrestricted.

5. If the supply pipe feeding the inlet or the inlet itself comes into contact with the contents of the receiving vessel, for example due to splashing or foaming, then the air gap is considered to be compromised and must be increased to the point no contact occurs.

6. Type AA air gaps should be inspected, and as necessary, maintained every 6 months (BS EN 806: 5)