The Background
Severn Trent Water’s Little Eaton Water Treatment Works is a vital facility that helps provide clean drinking water to Derby and the surrounding area at a rate of up to 80 megalitres a day – more than 900 litres a second.
The river intake at Little Eaton has several large pumps which supply water from the River Derwent to the treatment works.
Selwood customer nmcn – formerly known as North Midland Construction – was commissioned to replace the mechanical screens which usually prevent debris from the river entering these pumps.
To enable the removal of the existing screens while maintaining an uninterrupted water supply, nmcn called upon Selwood’s pump rental specialists to overpump from the river to the rising main pipeline that feeds the treatment works.
The Challenge
Because the works were taking place within the water inlet area, the only available space to position the temporary pumps was on the riverbed itself. Once in position, Selwood’s team needed to connect them the existing rising main in a lower level of the main pump building.
The only access to this building was through a standard-sized door – so the task at hand was to install a pipe large enough to meet the required flow, but small enough to fit through the door and connect to the existing 600mm pipework.
The Solution
Selwood’s team chose the Sulzer J 604 ND 10” pump for the job, because of its ability to provide the 231 litres per second required over static head. Friction losses needed to be kept to a minimum because of the oversized pipework being used.
A total of five of these pumps were used – four duty and one on standby – to achieve a total flow of 924 litres per second.
The pumps were installed on the riverbed with fish basket strainers to prevent fish and other items entering the works. They were then attached to 12” outlet pipework “risers”, a distance of approximately 15m. Once on solid ground this pipework was manifolded first into 500mm pipework, to a flowmeter which enabled the team to check the flows provided, and then through the doorway into the pump building.
Once in the building the pipework was immediately enlarged to 600mm for a distance of 15m to reduce any friction losses. This larger pipework was attached to the existing rising main via a non-return valve on the lower level within the pump room.
The Delivery
The riverbed was uneven, with large rocks and logs present, which meant there was an element of trial and error in the placing of the pumps.
As the water level was high during the site survey and scoping work, Selwood’s team had presumed a distance of three metres from the river bank would be enough – but it became apparent during installation that a distance of six metres out was required to sit the pumps securely.
A 30-ton crane was used to install the units and for any lifting outside the building. An existing gantry crane was used for internal lifting.
Time
Installation took 4 days to complete. The project was commissioned and started pumping in June.
The Outcomes
NMCN were able to complete the work replacing the screens on schedule, while the Selwood pumps ensured an uninterrupted supply to the Little Eaton water works.
www.selwood.co.uk
You can see coverage of the operation here:
www.youtube.com/watch?v=NxnQdDn_Uc4
