Wasser an der Walküste:
nährstoffrei-
ches Meerwasser für die Meeressäuger, zu
wenig Trinkwasser für die Menschen.
T
here is no shortage of nutrient-rich
water on the Cape Whale Coast.
This area of the coast gets its name
from the great southern whales
that migrate there from the Antarctic dur-
ing the South African winter, providing a
huge attraction for the thousands of tour-
ists who come to watch them. On shore,
however, water is a scarce resource. The
Preekstoel water treatment plant gets its
fresh water from groundwater wells and a
reservoir dam in the city’s mountainous
interior where the water level has been
continuously dropping in recent years.
This drop in the water level is due to the
decreased winter rainfall as well as the ever
increasing demand for water caused by
the brisk building activity. The water supply
authority of the Overstrand Municipality
had to take action, deciding to upgrade
the Preekstoel water treatment plant built
in 1974 and add more automation to
increase efficiency.
Pneumatics instead of electrics
“
As part of the modernisation mea-
sures, the Overstrand Municipality
decided to replace electric actuators
for opening and closing butterfly valves
or ball valves with pneumatic ones,”
explains Coen Pretorius, sales engineer
at Festo Cape Town. “We were able to
convince the authorities that pneumatic
automation technology can reduce
investment, installation and operating
costs in comparison with electrical
installations by more than 50% in some
cases,” he adds.
Pneumatic drives remain maintenance-
free for the duration of their service life.
Since process valves are irregularly
actuated in water technology, residues
or build-ups can occur that result in
significantly higher breakaway torques.
The overload protection of pneumatics
is an important feature here. If the drive
comes to a standstill, the pressure can
be easily increased at the pressure re-
gulator to be able to apply more force –
there is no need for costly maintenance.
A further advantage is that the com-
pressed air is available even if the power
fails, since in addition to a compressor
there is also an air reservoir for genera-
tion and preparation.
Reliable actuators
The Overstrand Municipality replaced
the butterfly valves at the filter basins
with pneumatic actuators and position-
ers from Festo and installed control
loops with flow and level sensors. The
butterfly valves and slide valves in
the sand bed filters and ultrafiltration
plants of the Preekstoel water treatment
plant are now equipped with pneumatic
actuators of the type DLP and DAPS. The
linear actuator Copac, or DLP for short,
is the ideal solution for shut-off, safety
and control slide valves. It acts directly
on the slide gate and ensures that various
positions can be approached accurately.
Its high corrosion resistance also means it
can be used without any problems out
in the open without being affected by the
salty air of the Cape Whale Coast.
Hermanus on the Cape Whale Coast:
Nutrient-rich sea water for sea life, but not enough drinking water
for those on land.
Ph t
o
o: J
ean
s
e
r
T
fon
/
Fl
ickr
2.2012
trends in automation
Synergies
38
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