Page 311 - 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

the critical water level that would determine the position on the cistern of the
float-operated valve and the distance between the float-operated valve and
the overflow.

Type AUK1 air gap with interposed cistern

This is a non-mechanical backflow prevention arrangement consisting of a
cistern incorporating a type AG overflow and an air gap. The spill-over level of
the receiving vessel is located not less than 300 mm below the overflow pipe
and not less than 15 mm below the lowest level of the interposed cistern. It is
suitable for protection against fluid categories 5 for back siphonage and 3 for
back pressure.

Type AG air gap Warning pipe

15 mm minimum
Contaminated water

Interposed cistern or
recepticle such as a
WC pan
Suitable for protection against fluid category:
3 Back 5 Back Outlet
siphonage
pressure
p Figure 5.69 AUK1 air gap

This arrangement is most commonly found on WC installations, with the WC
pan being the receiving vessel containing fluid category 5 water. A conventional
domestic WC suite consists of a 6 l/4 l dual flushing cistern, a part 2, 3 or
4 float-operated valve with an AG air gap and overflow arrangement. This
creates an AUK1 interposed cistern or, in other words, a cistern that can be
supplied from a mains supply or another protected cistern without the need
for additional backflow protection.

Type AG air gap

Overflow

300 mm
AUK1 air gap
Spill-over level

p Figure 5.70 AUK1 air gap on a WC cistern
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