7
Figure 4
Installation
FloPlast AF32 or AFE32 valve
FloPlast AF32 or
AFE32 valve
32mm
40mm
40mm
(a) installation to prevent self-siphonage
(b) installation to prevent induced siphonage
Up to five wash-basins
50mm minimum
6.2 To contribute to the ventilation of the underground drain and to minimise the effects of excessive back pressures
when a drain blockage occurs, the branch or main drain serving a stack or stacks fitted with a FloPlast valve may require
a venting point upstream of the stack connection. Guidance is given in Table 3 and Figure 5.
Table 3
Air admittance valve disposition
Number of
Dwellings
Up to three stories in height
Multi-storey domestic dwelling and non-domestic buildings
1 – 4
Additional drain and venting not required
Conventional drain venting to be provided if more than one
such building, each equipped with the valves, is connected
to a common drain which is not itself vented by means of a
ventilation stack or discharge stack not fitted with a valve.
5 – 10
Conventional ventilation (open-topped discharge
stack) to be provided at the vent stack at the head
of the installation.
11 – 20
Conventional ventilation (open-topped or dis-
charge stack) to be provided at the vent stack at
the head of the installation and at mid-point of the
system.
