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TECHNICAL
Schematic diagram of RPZ cut away.
b. a double check valve shall be incorporated as close as is
practicable to the point of discharge; or
c. a combined check valve and vacuum breaker shall be so installed
that the vacuum breaker is at least 300 mm above the spill-over
level of the receiving appliance.
Look at section 7.4.3.3 above and think about Nikki
spouts in baths. It clearly says here that for fittings
that discharge into for example a bath, there must be
a gap between the outlet and the spill-over level of the
appliance (not the overflow outlet level — the spill-over
level means the rim of the bath) with a certain vertical
distance separating them.
A Nikki spout does not have this gap, so we need to
install either ‘b’ or ‘c’ as above. How many of us do
this? As a side note, in Annexure D of SANS 10252-1
(D.1.6.1), it says that if the terminal water fitting already
has a backflow prevention device incorporated within the
fitting that is suitable for the hazard generated, we need
not install additional backflow prevention. Given that a
single check valve is not a suitable backflow prevention
device, how many of us have actually installed Nikki
spouts that comply?
In essence, our role here is quite simple: we need to
determine the hazard level and from that, we need to
decide on the type of backflow preventer we need to
install, if any. Note that a break tank with an air gap is
also a suitable means of backflow prevention, but not
September 2018 Volume 24 I Number 7
Figure 1: Typical backflow prevention set-up.
easily employed. Note also that if there is no break tank,
the two most common backflow prevention measures
are given in table 12 — either an RPZ valve or a double-
check valve. Not a single check valve, as this is not
considered a backflow preventer.
In many cases, it is not enough to simply install a
backflow preventer on the main incoming supply —
we need to prevent cross-contamination within the
premises as well. That is to say a section or process
within an installation that constitutes a hazard must be
isolated from the rest of that installation, so the backflow
preventer(s) must be installed immediately upstream of
the process or area. Have a look at Figure 1.
You will notice that all parts of the installation
downstream of the backflow preventers are deemed
to be non-potable (NP). Therefore, multiple backflow
preventers are required in these cases.
Backflow prevention devices must be tested and
maintained according to manufacturer’s details, but
these intervals shouldn’t be more than 12 months. In
Annexure D of SANS 10252-1 (D.3.6.3), it states that
if there is no such maintenance programme in place
(again, this onus is on us as installers), that backflow
preventer shall not be employed, and the standard air
gap requirements shall apply, as this set-up is pretty
much maintenance-free.
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