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More introductions of Francis Turbine

Francis turbine is one of the most widely used water turbines arounfd the word .The water flows radially into the impeller and generally flows out along the axial direction. it has a wide range of water heads (30 to 700 meters), a simple structure, reliable operation, and high efficiency, has been chosen and used by more & more electrical utilities, new energy developers etc.

Structural characteristics of Francis Turbines
The flow of water through the impeller is radial, and the outlet mechanism is radial. The opening of the guide vanes can be adjusted with the change of load. The impeller is composed of an upper crown, a lower ring, and a certain number of streamlined blades fixed in the middle. The introduction chamber is generally a metal volute or a concrete volute. The suction tube consists of a straight cone diffusion, a specially shaped elbow tube, and a diffusion section. The elbow section of a small unit is called a bent pipe, which is divided into different forms such as equal section and variable section.

Francis turbine has a compact structure, high efficiency, and can adapt to a wide range of water heads. It is currently one of the widely used water turbine models in various countries around the world. When the water flows through the working wheel of this type of turbine, it enters radially and flows out axially, so it is also known as a radial axial flow turbine.
It is suitable for the range of water head from 30 meters to 700 meters, with a simple mechanism, stable operation, and high efficiency, but it is generally used in the medium water head range (50 meters to 400 meters). The single machine output ranges from tens of kilowatts to hundreds of thousands of kilowatts. At present, the maximum output of this type of water turbine has exceeded 700000 kilowatts. It is the most widely used type of water turbine. A 700 MW unit with a single unit capacity in China has been put into operation in the Three Gorges Dam, and an 800 MW Francis turbine has been adopted in Xiangjiaba Hydro Power Plant.

Components of a Francis Turbine
The structure of the francis turbine is simple, and the main components include the volute, seat ring, guide system, top cover, runner & impeller, main shaft, guide bearing , bottom ring, draft tube, etc., which also indicates the flow direction. A snail shell is a water diversion component, resembling a snail shell, usually made of metal material with a circular cross-section. The seat ring is placed between the volute and the guide vane, consisting of an upper ring, a lower ring, and several columns, and is directly connected to the volute; The column is wing shaped and cannot rotate, also known as a fixed guide vane. The water guide mechanism is composed of movable guide vanes, speed control rings, crank arms, connecting rods, and other components. The runner is directly connected to the main shaft and is the rotating component of this type of turbine. The runner is composed of an upper crown, a lower ring, a discharge cone, and several fixed blades. The shape and matching dimensions of each component vary depending on the water head used. The tailpipe is a water turbine discharge component that directs the water flow from the outlet of the turbine downstream. It is generally a curved elbow shape, and small turbines commonly use a straight conical tailpipe.