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Francis Turbine

Francis Turbines are reaction turbines and are best suited in Low Head, high flow situations. The reaction turbine captures the energy of the water when there is not enough head to create a high pressure water jet. The reaction turbine operates in a fully flooded chamber and 'reacts' to the flow of water thru it. Axial flow turbines using Francis runners direct flowing water on to the blade of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). In this way, energy is transferred from the water flow to the turbine and they must be encased to contain the water pressure (or suction), or they must fully submerged in the water flow.

Francis Turbines in Small Hydro Systems are typically used with low head applications (30m - 100ft).  Flow through the turbine is controlled either by a large valve or by wicket gates arranged around the outside of the turbine runner. Differential head and flow can be plotted for a number of different values of gate opening, producing a hill diagram used to show the efficiency of the turbine at varying conditions.

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