Page 309 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 5 Cold water systems

Head over weir

Air gap 2 × inlet diameter
Weir spill slot Overflow pipe
screened

Shut off level Warning pipe

Not less than 25 mm
TYPE AB air gap with Outlet
weir overflow
Suitable for protection against fluid category:

5 Back 5 Back
pressure
siphonage
p Figure 5.66 Type AB air gap
p Figure 5.65 Type AB air gap with weir overflow with weir overflow on a cistern

Type AD air gap with injector
This is defined as a non-mechanical backflow prevention arrangement of water
fittings with a horizontal injector and a physical air gap of 20 mm, or twice the
inlet diameter, whichever is the greater. It gives protection against back pressure
and back siphonage up to fluid category 5. This device is commonly known as a
‘jump jet’.

Air gap

Suitable for protection against
fluid category:
Outlet
5 Back 5 Back
pressure siphonage
p Figure 5.67 Type AD air gap with injector

The principal uses of this type of air gap arrangement are in commercial clothes
washing and dishwashing machines. It also has the potential to be used in
catering equipment such as steaming ovens.

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