An Archimedean revolution on the Isle of Sheppey
The Isle of Sheppey on the Medway estuary is home to a revolution in screw pump technology. The Isle of Sheppey has long been a fantastic place for nature to thrive, providing large habitats for birds and other wildlife. On the South-East of the Island two land drainage pumping stations had reached the end of their asset lives and needed to be replaced.
Out with old, in with the new
The two existing pumping stations each housed two submersible pumps with operating capacities totalling 2,700 litres per second across the stations. Each station managed the levels within its own catchment. The two pumping stations were also overseen by different organisations. Bells pumping station was owned and operated by the Lower Medway IDB. While Mocketts pumping station was an Environment Agency asset.
Due to the two pumping stations reaching the end of their asset lives simultaneously. The Lower Medway IDB and the Environment Agency agreed to jointly fund a single new pumping station.
There were two criteria which were of particular importance to both the Lower Medway IDB and the Environment Agency. The pumps at both Bells and Mocketts pumping stations were known to suffer blockages. Therefore, it was imperative to reduce the chance of blockage. The safety of eels was also paramount as the habitat within the drains on the Isle of Sheppey is excellent for European eels. It is a fantastic natural source of food for the birds.
With these criteria, the revolutionary Fish Flow Innovations screw pumps supplied in the UK by ACE were selected. While the screw pumps are revolutionary in terms of land drainage, they parallel the original design by Archimedes himself. A key feature of the design is that the whole outer drum is sealed to the helix within. Thus, removing any leakage and subsequently any chance of runback. This eradicates the pinch point that is known to damage fish. While removing the possibility of energy loss that occurs in open trough systems due to run back. To further ensure fish friendliness, a patented leading edge is used. This glides through the water rather than striking it. The stillness of the water around the intake is efficient and ensures a passable system for eels.
1.75 tonnes of water pumped per second
To future proof the station, the pump capacity was increased. Therefore, the new pumps needed to have a joint capacity of 3,500 litres per second, meaning each pump had to lift a staggering 1.75tonnes of water per second. The volumes and lift capacity dictated the pumps dimensions at 2.5m diameter and 10.5m screw length.
The screw pump design also ensures it can operate at varying flow rates and speeds. Running it slowly will not cause efficiency losses as with open trough designs. The new pumps at Bells and Mocketts are operating between 11.2 and 23.3 RPM. This is a
The low speed, the large space between the flights and the rotating drum also remove any chance for blockages to develop. Which was a crucial feature for both the Lower Medway IDB and the Environment
ACE would like to thank the Lower Medway IDB, per second Agency and the principal designers at Peter Brett Associates who did a fantastic job. Not only designing the asset but also managing the contracts.