Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | JUNE 2014 | 23 The main pump hall at Bray Gravels a er all the pumps had been reinstalled and commissioned A er more than three decades in service, the pumps at South East Water's Bray Gravels pumping station were reaching the end of their life. However, when an ROI calculation showed refurbishment was a better option than replacement, it led to a major overhaul of the water transfer pumping capability. South East Water's Bray Gravels pumping station has an essential role to play in supplying fresh water to around 300,000 homes immediately to the west of London. Built more than 30 years ago, the pumping station draws water from boreholes close to the River Thames at Maidenhead and pumps it to the Surrey Hills and Crowthorne Reservoirs some 10 miles away. However, although continuing to supply water to these reservoirs, by 2011 the three Weir two-stage high-head split volute water transfer pumps, which by now were obsolete, had become unreliable and inefficient. A major contributing factor was the fact that since installation in the early 1980's, the demands on the pumping station had changed, exposing the pumps to fluctuating operating regimes. Consequently, at different points over the years each of the pumps had been run off the true pump curve, to detrimental effect. This became apparent when, in late 2011, AxFlow was called out to one of the three pumps, and discovered substantial wear and component South East Water pump refurbishment Work at Bray Gravels pumping station secures supply Project focus ● Reverse engineering key to success ● Matching old with new meant bespoke solutions ● Initial work led to full refurbishment John Dixon MaNaGER axFloW WINdsoR BasE ● A er 30 years the transfer pumps at the pumping station were inefficient, unreliable and, by now, obsolete ● Failure of two remaining motors when one pump was removed for repair posed a very real risk to supply ● The return on investment calculation showed that the most cost-effective solution was to undergo a comprehensive refurbishment, despite the challenges that presented, rather than replace all three pumps • Drivers • Challenges 1 ● The logistics challenge: Each pump and motor had to be dismantled and removed to AxFlow's service base – a process complicated by the fact they were installed before the current pump house was built ● The engineering challenge: a replacement suction impeller had to be rough cast using a sand pattern before being machined to the original dimensions "At different points over the years each of the (three) pumps had been run off the true pump curve to detrimental effect"

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