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Radially split case versus axially split case

Olga Sallangos reports that initially KSB's radially split case pump was something of an outside choice when it came to the selection of the high pressure pumps. "Axially split case pumps have a reputation for being simple to maintain as they are quick and easy to open, which is why they were considered. However, when we went to KSB we saw at first hand the energy efficiencies that could be achieved with the HGM-RO pump and also just how little maintenance would be required compared with an axially split casing type pump. We were also delighted to learn that spare parts would be advantageous in economic terms.

KSB will be providing us with a 20 year maintenance contract, which in any case is normal with manufacturers axially split case pumps. We prefer to work with manufacturers who are prepared to provide lifetime maintenance. At the time of the evaluation, we asked all potential suppliers to provide a list of all the spare parts that we would need to keep in the plant and we also compared the costs."

The HGM-RO is a duplex design pump offering a very short bearing span which provides high stiffness. As a result, it is smooth running and has a low vibration level i.e. <2.3 mm/s as per ISO 10816-3 group 3. The minimum shaft deflection allows a smaller clearance gap for high efficiency. It is suitable for RO systems which have to push aggressive saltwater in large volumes often at pressures up to and exceeding 110 bar. With the HGM-RO, users have the availability of flow rates up to 1150 m³/h and discharge heads of 950 m.

When compared with a conventional axially split pump, KSB's radially split case pump design is recognised as having considerably improved efficiencies, which contribute to reduced energy costs. The inclusion of internal, product lubricated fibre composite plain bearings enables a short bearing span to be realised. This reduces vibration levels and consequently wear rates. Designed for hydrodynamic operation, the bearings offer an service life of 40,000 hours. The bearing design eliminates the need for maintenance-intensive grease lubrication and bearing temperature monitoring.

Dismantling the axial thrust balancing system is a very simple and straightforward operation and does not require the pump to be completely opened up, a procedure which for an ASMP requires the use of a crane. It is the pump's suction stage impeller design in combination with the free axial inflow that gives the excellent suction characteristics. Only one mechanical seal is fitted, this being on the drive end and it can be easily accessed. This capability is an essential element in contributing to lower maintenance costs and repair times, which can be as much as 50% lower than pumps with external bearings and two mechanical seals.

KSB's involvement did not stop with the supply of the RO pumps; in fact a total of 25 pumps have been supplied for the plant, these coming from KSB Halle, KSB Pegnitz and KSB Chateauraux and including models for the Omega V, Omega, Multitec-A and CPKN Series. According to Olga Sallangos, even though many of the existing pumps were still performing adequately after eight years, the tender stipulated replacement pumps. Several factors dictated the requirement for new pumps; the principal being the new design of the plant meant that the existing pumps in key areas, such as seawater intake, could not provide the required flows and pressures. Furthermore, because the refurbished plant has to provide 20 years service it would not have been economical to have started replacing pumps well into the life of the new plant.

With the commissioning of the new plant at Dhekelia, the inhabitants of Cyprus will be assured of a continuous supply of high quality potable water for many years to come. Importantly, this will come from a plant that has been purpose designed to produce water economically and efficiently. For KSB, the decision taken by Caramondani Desalination Plants Ltd to specify the HGM-RO pump, together with pumps for many other duties throughout the plant, is a resounding vote of confidence in the Company's capability within the field of reverse osmosis desalination.

Contact
Bryan Orchard
E-mail: orchard@primex.co.uk

Christoph P. Pauly
Email: Christoph.pauly@ksb.com
www.ksb.com

Olga Villa Sallangos
Email: cdp@cytanet.com.cy
www.caramodani.com

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