Turbine and Pump Maintenance

• Hydraulic turbines are classified as either reaction turbines or impulse turbines referring to the hydraulic action by which the pressure or potential energy is converted to rotating or kinetic energy. The reaction turbines include the Francis and the propeller types, while the impulse turbines are represented by the Pelton type turbine. Impulse turbines convert all available head into kinetic or velocity energy through using contracting nozzles.
•  The jets of water from the nozzles act on the runner buckets to exert a force in the direction of flow. This force, or impulse as it is referred to, turns the turbine. Impulse turbines primarily are used for heads of 800 feet or more, although they are also used in some low-flow, low-head applications. Water flow to an impulse turbine is controlled by a needle valve.
•  The position of the needle valve is controlled by a governor to change speed or load. A moveable deflector plate, controlled by the governor, is positioned in front of the nozzle to rapidly deflect the water away from the turbine during a load rejection
• . The head pressure in a reaction turbine is only partially converted to velocity. While the reaction turbine obtains some power from the impulse force from the velocity of the water, most of its power is a result of difference in pressure between the top and bottom of the runner buckets. The Francis turbine is very similar in construction to a volute pump with a closed impeller (see figures 1 and 2).
•  Water entering the spiral or scroll case is directed to the turbine runner by the guide vanes and the wicket gates. The wicket gates, controlled by the governor through hydraulic servomotors, control water flow to the turbine. A propeller turbine is similar in appearance to a boat propeller. Water is directed and controlled in much the same manner as with the Francis turbine. A variation of the propeller turbine is the Kaplan turbine which features adjustable blades that are pivoted to obtain the highest efficiency possible at any load.