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| | Impeller and leading edge more critical than throughlet in achieving clog resistance - latest N-pump trial shows |
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Owned by Northumbrian Water, Cargo Fleet Sewage Treatment Works, situated on the bank of the river Tees, is a critical station, handling the domestic and industrial sewage of ¼ million people in the Middlesbrough area. Since commissioning in 1998, the original pumps had constant blockage problems until the N-Pump (1999 Pump of the Year and IWEX Innovation Award winner¹) was trialed mid 1999.
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The four existing 45KW pumps, installed in June 1998 during a major upgrade of the site, were equipped with impellers with a 120mm throughlet to cope with a dry weather flow of 40,000 M³/day for one pump and a maximum station flow of 93,000 M³/day with three pumps running. After initial blockage problems these were uprated by the manufacturer to 145mm - still with no improvement.
Based on site data it was estimated that the pumps blocked approximately 90 times in the first year of operation causing considerable expense and inconvenience to Northumbrian Water and its operational team. Following the launch of the N-Pump with its unique self-cleaning impeller, Northumbrian Water's consultants Entec UK approached us to see whether we could provide the solution to their problem.
In agreement with Northumbrian Water and Entec we decided to trial a 44kW N-Pump with a 90mm throughlet against the three remaining pumps, each with a 145mm throughlet, and assess the results. The size of the throughlet is currently considered to be an important aspect for inherent clog resistance in wastewater pumps - a larger throughlet being the current industry standard used in the UK. The N-Pump challenges this, as only a smaller aperture is required.
The N-Pump was installed earlier this year with the statement from John Maddison, Entec's resident engineer, that, "the pump would prove itself after the first storm". After a subsequent heavy downpour we discovered that the three 145mm pumps had all blocked but the N-Pump was still running - in fact the pump was passing so many solids that the screens down stream of the pumps could not cope.
The NP3300LT Pump has now been running as the main duty pump at Cargo Fleet for over 5 months, still without blockages. Following its successful performance the three remaining pumps have been replaced with N-Pumps.
Nigel Watts, Northumbrian Water's project manager with responsibility for the upgrade of the treatment works says, "By fitting the N-Pump at Cargo Fleet STW, Northumbrian Water has seen a reduction in the maintenance costs associated with the continual blocking of the pumps and, importantly, the elimination of inconvenience to our operational personnel who were regularly being called out-of-hours to attend the site.
"An additional problem, which has been solved by the N-Pump, has been the need to clear the sumps of floating mats of rags, which would always be left in the sump when the original pumps failed. These normally had to be fished out by an operator with a grappling hook. But the N-Pump passes these solids before they can even form, thereby keeping the sump clean at all times."
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Source: ¹ (as awarded at the Processing Pumps & Systems Awards and Turret Rai IWEX Innovation Awards respectively).
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Malcolm Jackson
ITT Flygt Ltd
Tel: 0115 940 0111
Fax: 0115 940 0444
Suzanne Baker
GSB Public Relations
Tel: 0121 454 2323
Fax: 0121 454 5702
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