A Type AD air gap, sometime call a ‘jump jet’ is a non-mechanical backflow prevention arrangement comprising of a horizontal injector which ‘jets’ water into a cistern, vessel, fitting or appliance fitted (receiving vessel) and an air break to drain open to atmosphere.
A Type AD 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 applicable to a Type AD air gap is given below:
The air gap is an unobstructed and complete physical break between the terminal point of the injector and inlet orifice of the receiving vessel. Measured horizontally it must be no less than 20 mm or twice the internal diameter of the supply whichever is the greater.
The air break to drain must be open to atmosphere and capable of draining the maximum flow rate without submerging or coming into contact with the inlet.
The inlet must not come into contact with any splashing, drips or run off from the receiving vessel.
Type AD air gap installations should be inspected, and as necessary maintained every 6 months (BS EN 806: 5)
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