• Water turbines convert flowing water to electricity.flowing water image by John Fatuzzo from Fotolia.com
  
  A water turbine is needed to capture flowing water and convert it into electricity. There are two main styles of water turbines: impulse and reaction. An impulse turbine operates in the air and uses the water's velocity to move the turbine's mechanism, while a reaction turbine is fully submerged in water and receives its power from the combined pressure and movement of the water. Within these categories, there are several different types of turbines. While all are able to convert flowing water to electricity, their mechanisms for doing so differ greatly.
  
  

Pelton

• A Pelton wheel is an impulse turbine that has  at least one free jet. The jets release water into an aerated space where it is caught by a series of buckets or cups located on the runner, the rotating piece of the turbine that is used to convert the water's energy into mechanical energy. Typically, these buckets are divided into two sections so they are able to deflect water away from the oncoming jets. A Pelton wheel also has a cutaway on the lower lips of the buckets, which allows a subsequent bucket to move ahead before it stops the water jet that has moved the previous bucket. As a result, the buckets enter the water jet more smoothly.
  
  

Turgo

• A Turgo water turbine is another impulse turbine, but this style features blades instead of buckets. A jet of water hits the blades to move the turbine and convert the water's energy into mechanical energy. A Turgo water turbine is similar to an airplane turbine because it has curved vanes that enclose the turbine's main hub. The vanes capture the water as it pours through the turbine, so the main hub begins to turn. The water enters this type of turbine on one side, flows across the vanes and leaves on the other side. Turgo turbines are typically smaller in diameter than Pelton turbines, but they are able to move at higher speeds.
  
  

Propeller

• A propeller turbine is a reaction water turbine that contains a runner with three to six blades. Water continuously flows over these blades so they turn and the water's energy can be converted to mechanical energy. As the name implies, it is similar to a boat propeller, though it operates inside a pipe. Some propeller turbines feature blades that may be adjusted, and are often used in large-scale hydroelectric power plants. Propeller turbines can also be used in areas where there is little vertical change in elevation between the water at the turbine site and the water downstream if there is a high enough volume of water passing between the two areas.
  
  

Francis

• A Francis turbine is another reaction water turbine, but unlike a propeller turbine, a Francis turbine's wheel assembly is fully submerged in water and covered in a pressure casing. The pressure casing is usually shaped like a spiral and tapers to a narrow tip so the water can be dispensed evenly throughout the runner. The runner in a Francis turbine typically has nine or more vanes, which are used to turn the runner. There are also guide vanes that make certain the water reaches the runner at the proper angle.