Page 29 - trends in automation

Wasser an der Walküste: nährstoffrei-
ches Meerwasser für die Meeressäuger, zu
wenig Trinkwasser für die Menschen.
There 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 during the South African
winter, providing a huge attraction for
the thousands of tourists 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
measures, 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
regulator to be able to apply more force –
there is no need for costly maintenance.
A further advantage is that the
compressed air is available even if
the power fails, since in addition to a
compressor there is also an air reservoir
for generation and preparation.
Reliable actuators
The Overstrand Municipality replaced
the butterfly valves at the filter
basins with pneumatic actuators and
positioners 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
Hermanus on the Cape Whale Coast: Nutrient-rich sea water for sea life, but not enough drinking water
for those on land.
Photo: Jean Tresfon
/Flickr
Issue 23 trends in automation
Synergies 26 – 27