HEALTH AND SANITATION
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Table 2: Standards and codes applicable to catchment and conveyance network
Table 3: Control equipment for make-up water systems
Solenoid valve
Automated shut-off valve that activates
(opens or closes) automatically when turned
on. When connected to water level sensor, it
provides seamless mains backup in the event
of no rainwater or electrical interruptions, for
consumer convenience and comfort. •
When selecting control equipment for the
make-up system, the issues listed in Table 3
must be considered. •
Sizing
All control equipment must be appropriately
sized. Of particular concern for top-up-based
systems is the sizing of the top-up drainage
piping. This pipe must be sized according to
gravity flow, not pressurized flow, to prevent
water backing up the pipe. In addition, all
valves and backflow preventers must also be
sized to be the same diameter as the pipes to
which they are connected. Many water level sensors (such as float
switches) must be rated to handle the power
of the device they are controlling. For instance,
if a float switch controls a solenoid valve or a
pump, it must be rated to handle the power
needed to operate the valve or the pump. Float
switches and solenoid valves act like typical
light switches; however, they differ in that
these actions can take place whether power
is connected or not. To differentiate between
these two operating conditions, the terms
‘normally open’ (N/O) and ‘normally closed’
(N/C) are used.
Electrical
Most control components of a dual-system require
an electrical supply to operate. When designing
the electrical system for the RWH system, the
following must be taken into consideration:
• The electricity supply source: national
grid, solar power, dual source (grid and
solar power).
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•
•
The operating voltage of the pump
(generally 220V), solenoid valve and
other relevant components.
The power requirements of the pump (in
watts), solenoid valve and other relevant
components.
Power rating for float switches and
electrical wiring.
All equipment must be certified and
installed in accordance with the relevant
South African Electrical Codes.
CROSS-CONNECTIONS AND BACKFLOW
PREVENTION
Whenever rainwater and mains water are
interconnected, the mains water must be
isolated from the rainwater system by a
May 2019 Volume 25 I Number 3