Guide vanes (orange) around a water turbine runner. (Source: © Filipp / stock.adobe.com)

Fixed or adjustable blades that direct water onto the turbine runner in order to make the most efficient use of the energy of flowing water. Guide vanes are usually located around the perimeter of the runner and direct water onto the turbine blades. Their function is to ensure that water is distributed smoothly and evenly on the blades. If they are adjustable, they open or close depending on the actual flow.