Water & Wastewater Treatment

24 | june 2014 | WWT | www.wwtonline.co.uk All the pumps re- quired new motors (le ) which had to be adapted. Initial inspection of one pump re- vealed substantial wear and compo- nent fatigue (be- low). Such was the damage that the suction impeller was eaten away Project focus: South East Water pump refurbishment to be found, but this was far from straightforward because the existing motors were fitted with European Standard shas, making it impossible to get an off- the shelf stop gap. AxFlow had to quickly locate a suitable motor in another part of the country and make the necessary modifications to allow it to be used on one of the pumps, thus preventing any impact on South East Water customers. However, the emergency prompted South East Water to initiate a programme to fully repair the two remaining pumps, putting the project out to tender. Sourcing compatible motors for the pumps then became a very real issue. A major difficulty when refurbishing older pumps is matching new to old. The existing motors were so old they were not suitable for running with inverters, because they did not have insulated bearings. However, because non- standard fatigue, largely attributable to cavitation. Such was the damage, that the suction impeller was eaten away. The choices were to purchase a full replacement unit or, if possible, carry out a comprehensive repair and rebuild programme. On analysis, the latter proved to have the best return on investment and so South East Water opted for refurbishment. The initial programme of works included replacing the pump bearings, motor bearings, mechanical seal, propsha, universal joints, gaskets, efficiency liner, dismantling the motor and testing the windings, rebalancing the propsha, shot- blasting, painting and reassembly. However, replacing the damaged suction impeller was more problematic than simply sourcing a replacement. It meant going back to the drawing board and using reverse engineering to create the part in line with the original specification. A new rough casting was made in bronze using new sand casting patterns. This was then machined to the same dimensions as the original impeller. AxFlow removed the dismantled pump and motors from site for the work to be carried out, before reversing the process for installation, testing and commissioning - not a straightforward task given the size and weight of the pump and motor. And a process further complicated by the fact the pumps had been installed before much of the current pump house had been constructed. However, the removal of one pump proved too much for an already struggling system. As a result of the two pumps running at high speeds and temperatures, both the motors burned out on the same day, leaving the station with a reduced capacity to transfer water and a very real risk of disruption to supply. A temporary replacement had "The removal of one pump proved too much for an already struggling system... the (two remaining) motors burned out on the same day" • Challenges 2 ● The capacity challenge: already worn and in need of repair, the two remaining pumps and motors failed when the third was removed for refurbishment ● The obsolescence challenge: the old motors could not be used with inverters, so replacements were needed. However, the new motors had larger sha s than their non- standard predecessors necessitating the manufacture of three bespoke couplings. www.wwtonline.co.uk | WWT | june 2014 | 25 ENGINEERED SOLUTIONS FROM BEDFORD PUMPS ENGINEERED SOLUTIONS FROM BEDFORD PUMPS ENGINEERED SOLUTIONS FROM BEDFORD PUMPS Land Drainage Flood Defence Fish Friendly Storm Water Potable Water (DWI/WRAS) Waste Water Irrigation Cooling Water Dock Dewatering/ Impounding Ballast Sea Water Transfer Man-Made Water Courses for Sports & Leisure Bedford Pumps are one of Europe's leading manufacturers of large submersible and conventional pumps to the water and wastewater industry Bedford Pumps Ltd Brooklands, Woburn Road Industrial Estate Kempston, Beds, MK42 7UH Tel: 01234 852071 sales@bedfordpumps.co.uk www.bedfordpumps.co.uk

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