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Pump systems, pipes, valves and seals
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Mechanical Technology — March 2015
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Above:
Xylem SA offers full service support, via the local Total Care and mobile servicing offerings.
Left:
Xylem’s signature Flygt ‘banana blade’ propeller has a large diameter and a backswept self-cleaning
design for non-clog performance.
blade’, which is a two-bladed impeller/
propeller made out of polyure-
thane. Developed for non-
abrasive sewage applica-
tions, this signature
Flygt propeller has a
large diameter and
a backswept self-
cleaning design
for non-clog perfor-
mance. “For sub-
mersible mixers in
the mining industry
we offer our three-
bladed stainless steel
propellers or, for highly
abrasive applications,
these are also available
in high chrome, a mate-
rial that has made us a
leader in South Africa
for submersible mixers
for the mining industry,”
Mitchell claims.
Sizing mixing systems
based on thrust offers
significantly more de-
sign flexibility. “Because
we can offer different
blade designs depending
on the applications and bulk
flow required, we can achieve far bet-
ter mixing and energy efficiency. We have
six sets of propellers with different blade
angles, which enable us to customise
solutions to best suit the specific applica-
tion,” he adds. “Simply put: by choosing
the most appropriate propeller design, it
becomes possible to get more mixing out
of a less powerful motor.”
Comparative tests done on top-entry
agitators in Xylem’s Swedish test facility
have shown that a Flygt mixer achieved
40% better energy efficiency under con-
trolled test conditions than its Swedish
competitor. “And better efficiency also
results in better reliability. Reliability is
about right-sizing, – matching the right
mixer to the application,” he notes.
Mixers are used wherever agitation is
required to deal with solids in suspen-
sion. In wastewater treatment plants for
activated sludge treatments and digester
mixing, for example, and for mixing
settled solids in sumps before pumping
the contents away. “In the mining indus-
try, solids in
underground
dams need to be
prevented from settling
so they can be easily pumped away
as slurries. There are also a variety of
applications in the minerals processing
plants,” Mitchell says.
“Our comprehensive portfolio of mix-
ers and agitators cover virtually every
requirement. Hundreds of thousands of
Flygt mixers and agitators are in service
worldwide, delivering efficient mixing
performance. Our top-entry agitators are
used when deep tank mixing is required
and Flygt TEAs deliver outstanding cost-
effective performance for applications
that involve all types of fluids, includ-
ing fibrous sludge with high dry-solid
content.
“Our solutions are engineered for
energy efficiency, hygienic handling and
ease of installation and service. These
agitators combine dry-installed drives
with submersible shafts and impellers,
which can have multiple impellers in
deep tanks.
Xylem’s top-entry systems use bigger
shafts to minimise flexing and vibra-
tion on cantilevered systems. “We also
have a patented levelling flange, which
makes it easy to adjust the shaft to its
true vertical position,” says Mitchell.
“For very deep tanks with long shafts
and multiple impellers, we can install a
bottom support called a shaft stabiliser,
This prevents shaft runout by fixing the
shaft end to the bottom of the tank with a
swivel coupling assembly.” He adds that
full service support, via the local Total
Care and mobile servicing offerings, is
available for mixing installations, as are
the necessary spare parts.
“Ours are engineered solutions,” con-
cludes Mitchell. “Our recommendations
result from the use of specially developed
and validated computational fluid dy-
namics (CFD) software, based on care-
fully selected, relevant models. Our own
testing facilities, as well as field-testing
and measurement of actual on-site per-
formance, has given us keen insight into
what works. Using this knowledge and
expertise, we are in a position to install
and maintain mixing installations of any
size and complexity,” he says.
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