River Dart Country Park archimedean screw installation
This is a testimonial from Mark Simpson of the River Dart Country Park talking about the successful installation of an Archimedean screw hydropower turbine. The fish-friendly hydropower turbine was designed and installed by Mannpower Consulting Limited.
What is and Archimidean screw?
TheArchimedean screw hydro turbine is a relative newcomer to the small-scale hydro world having only arrived on the scene over the last ten years. However, they have been around for many decades as pumps where tens-of-thousands have been installed worldwide, particularly in sewage treatment works. The same manufacturers that dominate the pump market are now the main suppliers into thehydropower market as well.
As the name suggests, Archimedes is widely acknowledged as the inventor of the screw back in 250 BC, though the credit has been wrongly attributed because they were actually in use in Egypt many years before then. Historically they were used in irrigation to lift water to a higher level and were generally powered by oxen, or even humans on smaller versions. The basic principle of an Archimedean screw pump is shown in the diagram above. If the handle at the top was turned in an anti-clockwise direction it would draw the water up from the lower level to the top.
When used as a hydro turbine the principle is the same but acts in reverse. The water enters the screw at the top and the weight of the water pushes on the helical flights, allowing the water to fall to the lower level and causing the screw to rotate. This rotational energy can then be extracted by an electrical generator connected to the main shaft of the screw.
Archimedean screws forhydropower are used on low head/high flow sites. They can work efficiently on heads as low as 1 metre, though are not generally used on heads less than 1.5 m (more for economic reasons than technical ones). Single screws can work on heads up to 8 metres, but above this multiple screws are generally used, though in many cases for heads above 8 metres there may be more appropriate turbines available with much smaller footprints.