Wessex Water's Ashton Avenue sewage pumping station near Bristol was originally commissioned in 1970 and was targeted for renovation by Wessex Water because of pressure put upon the site by a rising population. This was resulting in unsatisfactory intermittent discharges of diluted sewage from the sewerage network, which was occurring both during and after heavy rainfall. £9.5m has been spent on upgrading Ashton Avenue to reduce this risk of flooding in South Bristol. During times of heavy rainfall a greater volume of storm water can now be safely taken away from homes in the area.
Water and wastewater pumps
Bedford Pumps, manufacturer of large, bespoke water and wastewater pumps, made and installed three storm pumps and two dry-weather flow (DWF) pumps for the site and, also refurbished three of the existing DWF pumps previously installed by the company in 1994.
One of the new DWF pumps replaces the original W H Allen pump installed when the station was first built. This is noteworthy as W H Allen was the company that facilitated the existence of Bedford Pumps, which was founded in 1987 by members of the former Pump Department at NEI (W H Allen) after the company closed its manufacturing plant in the town.
The company worked in close collaboration with the main contractor and Wessex Water to undertake the refurbishment of the DWF pumps. These units lift the foul sewage up into the southern foul water interceptor for onward flow to Avonmouth sludge treatment works for processing. They are each required to pump up to 650 l/s with a guaranteed head of 6.4 m.
The three new storm pumps are of the mixed-flow canister type having submerged motors. Each pump is rated at 2,625 l/s at a total head of 11.8 m, 440 kW, complete with variable speed drives. They replaced the original storm pumps from 1970, which were shaft-driven, axial flow with the motors at ground level. Condition monitors and canisters for the storm pumps were also supplied. Air release valves are included on the top of each canister and a novel ‘latch lift’ system ensures speed, efficiency and cost savings when accessing the pumps.
On schedule – under budget
Commented Mark Lloyds, Project Manager for Wessex Water: "During the design stage of the scheme, it became apparent that Bedford Pumps was one of only two likely suppliers for these pumps. Being a proven manufacturer of large pumps and the supplier of the original pumps gave the company extra credibility, and it was selected through a competitive tender process."
"The company worked closely with us on the integrated design and it has proven to be a successful contract all round”, concluded Lloyds. The project was completed ahead of schedule and under the original budget.
The pump design
Bedford Pump’s range of submersible axial and mixed flow bowl pumps, which find many applications, including storm water, have been designed as an efficient alternative to conventional shaft driven units. Their versatility allows a wide variety of installation configurations to be used without impairing performance. Two high quality, independently mounted seals in an oil-filled enclosure prevent water ingress to the motor, which is a squirrel cage induction design to BS 4999, Class F insulation. The motors are suitable for star delta, DOL, inverter or autotransformer starting. Thermal overload thermistors, embedded in motor windings, and seal leakage sensors, are fitted as standard. Other pump types are also available from the company.