Section 1: Low Head Turbines
Generally low head turbines are going to be of the reaction type. The water passing through a reaction turbine loses its energy, or pressure, as it passes the turbine blades. The turbine must be encased in a pressurized housing, and fully submerged in water. This is different from an impulse turbine which changes the velocity of the water. Water is directed at the blades of an impulse turbine with a high velocity nozzle, and the velocity of the water turns the blades. An impulse turbine can be open to the air, and only needs a casing to control splash. All turbine types can be classified into one of these two groups.