Mechanical Technology March 2015

⎪ Pump systems, pipes, valves and seals ⎪

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

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.

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. q

try, solids in underground dams need to be prevented from settling

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-

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

Mechanical Technology — March 2015

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