3 minute read
Choosing a centrifugal pump just got easier
Almost 70% of the standardised pumps in use today operate at a constant motor speed and are usually combined with IE3 asynchronous motors. Pump manufacturer KSB has developed an alternative approach – a smart drive solution which aims to reduce the complexity of variants, while also increasing planning reliability for the engineering contractor. flow found out more.
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In applications which require fixed speed pump sets, the pump is usually adjusted to the design point by machining its impeller. “Our new MyFlow Technology marks a fundamental change to this concept,” explained Daniel Gontermann, Product Management Drives & Mechatronic Solutions at KSB SE & Co. KGaA. “With this new technology, the required head and flow rate can be adjusted via the motor by selecting an individual fixed speed, a capability which offers clear benefits to operators and OEMs.”
This new approach makes it possible to optimise pumps to meet specific system conditions after the production process. This does away with the need to trim the impeller during production to match the calculated design point. To make this advance possible, KSB has combined a cost-effective, motor-mounted minimum frequency inverter with its IE5 SuPremE synchronous reluctance motor and the latest generation of its Etanorm pump range.
Where the selection process traditionally involved using asynchronous motors alone, the exact adjustment to the required flow rate was achieved by first selecting a suitable pump and then fine-tuning it by reducing the impeller diameter. However, this required a wide range of pumps to choose from. For example, KSB’s Etanorm range alone is made up of 43 sizes, but now, with MyFlow Technology, only 18 sizes are needed to cover the same H-Q selection chart. In practice, fewer variants mean that pumps do not necessarily need to be produced on an order-specific basis, making inventory management much easier. The pumps can also be customised within a few minutes of receiving an order, or even once they are installed in a system.
Through extensive characteristic curve analyses and calculations, KSB’s development engineers have been able to prove that this reduction in the number of sizes brings no disadvantages concerning hydraulic efficiency or the pumps’ suction characteristics. Speeds ranging from around 1000 to 4500rpm can be set. This generally means that the same pump power output can be achieved with a smaller pump casing. Less material means lower costs for the pump’s hydraulic system and less space for storage. This also makes product data maintenance and inventory management easier for system operators.
Another technical advantage of this concept is the working principle of the IE5 SuPremE motors. They feature around four per cent higher efficiencies at the rated load point and significantly higher partload efficiencies than asynchronous motors. “At first glance the frequency inverter makes the new drive appear a little more expensive,” commented Daniel. “However, if you compare the real investment costs for the systems – with all of the components which have to be installed when using an asynchronous motor – the total costs are very similar.”
Contrary to asynchronous motors, which can only provide temperature-based information, the new drive used in the MyFlow system features a Modbus interface for communication with a higher-level control station. From a start/stop signal through to fault history, this interface offers complete transparency and remote access for Industry 4.0 concepts. This means that information such as the head, flow rate, electricity consumption, speed and much more can be viewed at all times.
The idea of setting the flow rate once the pump set has been installed, instead of basing this on a calculated design point prior to installation, is undoubtedly very appealing. It is no secret that generous safety allowances are incorporated during
the planning and installation stage. All parties involved in the selection process of a pump allow an additional margin.
During installation, it is often the case that the pipe diameter or the nominal diameters of the installed valves differ from the plan. This causes thepump’s calculated design point to deviate further and further from the real operating point. To accommodate this fluctuation safety margins of 10-15% are often used. As a result, in practice, many pumps do not offer energy-efficient operation.
Furthermore, even with optimum conditioning of the fluid handled, solids buildup can occur in a system, increasing flow resistance and causing the pump’s operating point to shift towards the shut-off head. With the speed adjustment feature integrated into the new drive-based concept, adjustments can be made at any time. Using a mobile app provided by KSB, the speed can be easily changed by making virtual impeller trimming adjustments.
SUMMARY
Robust and attractively priced asynchronous motors have primarily been the automatic choice for pumps with constant flow rates for well over 100 years. However, most system operators are unaware of the disadvantages associated with these motors. In the age of networking, communication and localised intelligence, perhaps now is the time to start questioning this traditional approach.
www.ksb.com
