Francis Turbine

This demonstration turbine provides a simple low cost introduction to the Francis inward flow reaction turbine showing its construction, operation and performance. A tapering, spiral shaped volute conveys water to the runner via a ring of guide vanes that are adjustable in angle to vary the flow through the turbine. Water enters the runner tangentially at the periphery, flows radially inwards through the blades towards the hub then exits axially via a draft tube. Power generated by the turbine is absorbed by a Prony friction brake consisting of a pair of spring balances attached to a brake belt that is wrapped around a pulley wheel driven by the runner. The load on the turbine is varied by tensioning both spring balances which increases the friction on the pulley wheel. Brake force is determined from the difference in the readings on the two spring balances and the torque calculated from the product of this force and the pulley radius. The head of water entering the turbine is indicated on a Bourdon gauge and the speed of rotation is measured using a non-contacting tachometer (not supplied). The volute of the Francis turbine incorporates a transparent front cover for clear visualisation of the runner and guide vanes.