An impulse turbine, the most common type of small water turbine, works by using a pressurized water jet to turn a wheel called a runner. The runner then turns a shaft attached to the alternator or generator that generates electricity. While on a vastly smaller scale, this is exactly the same way the impulse turbines in some hydroelectric dams work.
There are three different types of impulse turbines: Pelton wheel turbines, Turgo impulse wheel turbines and Jack Rabbit turbines. These turbines differ based on the type of runner they use for generating kinetic energy.
The Pelton wheel turbine is the oldest and simplest type of impulse turbine. Attached to the Pelton's runner are several buckets, each with two curved cups. Despite their simplicity, Pelton wheel turbines are highly efficient in areas where water flow is relatively slow, but head, the vertical difference between the level at which the water enters and exits the turbine, is large.
The Turgo impulse wheel turbine is an improved version of the Pelton wheel turbine. While each of a Pelton's buckets has two cups, a Turgo's has three, making it spin twice as fast as the with the same flow rate and head value.
The Jack Rabbit turbine is a unique device that generates power under poor flow and head conditions. A Jack Rabbit turbine can function in slow-flowing streams with no head at all, though it only generates small amounts of power compared to the two other turbine types.