Dec 28, 2000

Pumps Give Stormwater the Shaft

At Work on Pumps

As part of an extensive scheme to further improve bathing water standards in the Brighton and Hove (England) area, a project for the diversion of stormwater is now in full operation. Located in Brighton Blackrock, the scheme involves a stormwater overflow into a six-meter-diameter storage tunnel stretching to Hove and providing a capacity of 147,000 cubic meters.

The Bedford Pump Co. was awarded the contract for the pumping installation part of the project by Southern Water. This involved the design of the system, the manufacture of the four main storm return pumps, the commissioning of two grit pumps and the installation and testing of the complete system including motors, cables, pipework, valves, steelwork to support pipework, guide rails and lifting equipment. The latter was essential to the project as the main pumps had to be easily retrievable for maintenance and service and lowered back to the base of the shaft for automatic connection to the discharge pipework.

Submersible Volute Pumps
Yield Optimum Return
Four Bedford SV submersible pumps operate in the 40-meter vertical shaft to return the stormwater to the existing sewer when the flow subsides.
These submersible volute pumps were essential to the project as the specification demanded pumps that could operate at an immersed depth of 39 meters with the added capability of reverse rotation from the full static head in the rising main pipe. Further influencing the choice was the reduction of running costs from increased overall efficiency, suction performance, low maintenance requirements and long service intervals.
The pumps are controlled by a PLC programmed with the pump outputs at the various shaft levels and inputted with data regarding the flow in the interceptor sewer and the level in the shaft. The system starts and stops the pumps, emptying the sewer as quickly as possible within the allowed constraints of 4 m3/s peak flow.

Stormwater Control
In the event of a storm, the PLC monitors the level in the shaft until the interceptor flow is equivalent to one pump’s output. The first duty pump then is automatically started. As the flow in the sewer abates, the second and third duty pumps will operate until the tunnel is emptied, maintaining a total flow not exceeding 4 m3/s in the interceptor sewer.
Also in the pumping station, two KSB grit flushing pumps handle grit-laden sewage washed into the base of the shaft during flushing and periodic cleaning. Each pump, operating with impellers made of Norihard material, is designed to deliver 65 L/s against a total head of 44m with a static head of 42m and a friction loss allowance of 2m.

An Uplifting Performance
The design of the system incorporates the ability to raise and lower the pumps from the sump at the base of the shaft to the access floor to facilitate ease of service or maintenance. A floor-controlled electrical radial crane can be operated from any position and is installed to retrieve and return the pumps using guide rails. An automatic coupling system allows the raising or lowering of the pumps above or below the fluid level without the need for permanently attached lifting chains and wires.

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