Bedford Pumps Ltd, a leading manufacturer of large submersible and conventional pumps to the water and wastewater industry, has just completed a contract in excess of £1.25 million ($1.89 million US) with Yorkshire Water for the refurbishment of the Don Valley Sewage Pumping Station, a job that provided a connection to Bedford Pumps’ past as well as a showcase for the company’s future.
BACKGROUND OF DON VALLEY SPS
Don Valley SPS is part of a £78 million ($118 million US) investment from Yorkshire Water for Blackburn Meadows Wastewater Treatment Works. Blackburn Meadows is the second largest treatment works in the United Kingdom at a colossal 78 acres, treating 79 million gallons (298.62 million liters) of waste from a population of 457,000 daily.
The Don Valley Pumping Station site originally housed five A P E Allen mixed flow vertical spindle units to lift sewage 70.21 feet (21.4 meters) to the inlet works. These pumps were at the end of their working life and no longer able to cope with the demands of the pumping station. As a result sewage debris often entered the River Don during heavy rainfall.
HISTORIC CONNECTION
Historically Bedford Pumps was formed as a company in 1987 by former members of the Pump Department of NEI (W H Allen), who produced the original units. As a result the Allen pumps were originally designed by present Bedford Pumps’ staff, and the proposed units have been manufactured with a similar ethos, to the same exacting standards.
Bedford Pumps have replaced the original units with six conventional shaft driven volute pumpsets. The pumps are of a centrifugal, mixed-flow design and have far greater solid handling capabilities than their predecessors. All the pumps are designed to handle untreated raw sewage, and the largest of the six pumps has a solids handling capacity of 8.46 inch (215 millimeter) sphere.
DELVING INTO DETAILS
An equally important consideration with respect to blockages is the operating envelope. The pumps have been carefully selected to operate between +/- 25 percent of best efficiency flow. Operating outside this range tends to increase the possibility of blockages. The pumps have been selected to meet this stringent requirement, whilst also taking account of overall efficiencies.
The station has been designed within a wet well sump that is divided into two halves. Each half is a mirror image of the other and is designed to function with one half operational and one half isolated. Bedford Pumps units must therefore provide sufficient total pumping to achieve the entire full flow to treatment (FFT) from one half of the wet well only. Bedford Pumps achieved this criteria by suggesting that each half of the sump houses an identical set of three pumps, of varying sizes. The pumps are installed in a vertical configuration.
GETTING TO WORK
The largest pump has a duty of 31,730 gallons per minute (2000 liters per second) at 85.3 feet (26 meter) head driven by 645 kilowatt 6.6 kilovolt motors. The next size down operates at 23,797 gallons per minute (1500 liters per second) at 89.9 feet (27.4 meters) head powered by 505 kilowatt 6.6 kilovolt motors. The smallest pumps run at 13,485 gallons per minute (850 liters per second) at a head of 93.18 feet (28.4 meter) from 300 kilowatt 6.6 kilovolt motors.
All of the units have been designed to operate efficiently over a wide range of flows and heads. Various combinations of operating units have been evaluated in order to achieve good efficiencies within the entire operating range, and the optimum number/size of units has been defined for any condition.
The decision to use high voltage motors (6,600 volt) was taken to reduce cable sizes and to limit the variable speed drives were supplied by ABB.
The pumps are fitted with a fabricated steel support plate to support the units on supports either side of the unit. Suction and discharge flanges are bolted directly into the pipework, this arrangement allowing the rotating element to be removed for routine maintenance whilst leaving the casing in situ.
The one-piece mixed-flow impeller is capable of handling the solids and fibrous material found in normal sewage applications. After machining, it is hand finished where the surfaces are inaccessible to the cutting tool and dynamically balanced, to exacting UK standards.
Bedford Pumps worked in close collaboration with ETM (j.v. Aecom and Galliford) to overhaul the Don Valley site. Yorkshire Water state that this investment will “treat more waste water, more efficiently and to a higher standard.” ■
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ABOUT THE AUTHOR
Lucy Ogden is the marketing manager for Bedford Pumps Ltd. For further information, email her at lucyo@bedfordpumps.co.uk, call 01234.852071, or visit the Bedford Pumps website at www.bedfordpumps.co.uk.
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MODERN PUMPING TODAY, June 2013
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Inside Don Valley Sewage Pumping Station Clean Up
