A waterwheel is a type of device that takes advantage of flowing or falling water to generate power by using a set of paddles mounted around a wheel. The falling force of the water pushes the paddles, rotating a wheel. This rotation of a wheel can be transmitted to a variety of machines through a shaft at the center of the wheel. These wheels are generally large and composed of wood or metal with many blades or buckets along the edge of the wheel to capture the power of the moving water.
Waterwheels are usually positioned vertically over a water source. This means that the axle is positioned horizontally. This axle transfers the energy from the falling water to a drive belt or a system of gears that then operates some sort of machine. These wheels require some source of falling or flowing water, and these sources can include streams or rivers. Sometimes special ponds known as mill ponds were created by damming a flowing stream. This creates a special channel known as a mill race from the pond to the waterwheel.
Although waterwheels are not used widely today, hydroelectric dams function on the same basic principle of using the power of flowing water to move machines known as turbines.
Overshot wheels are a type of waterwheel that can be built if there is a significant height drop in the river or body of water being used to move the wheel. Generally, these are built on the side of a hill as a drop of at least 4.5 meters.
In this type of waterwheel, the water exits the flume above the wheel itself. The water then falls down onto the blades of the waterwheel, pushing the wheel forward. The fact that water is introduced at the very top of the wheel means that the water falls the greatest distance, making the wheel highly efficient - from 80-90%.
In areas that have little to no slope, undershot waterwheels are the only type of waterwheel that will work. Since there is almost no drop in the water, these wheels are inefficient compared to other types. This is because the waterwheel relies on there being large quantities of water moving quickly to move the wheel. Because of this, the wheels tend to be built on large, strong rivers.
In this type of waterwheel, there is no flume. Instead the water rushes along the bottom of the waterwheel, spinning it backwards compared to the water flow. This spinning motion occurs because the water pushes along the blades that are in contact with the surface of the water.
Breastshot wheels are used where there is a moderate drop in the height of the water. Generally, breastshot wheels are used if there is a drop between 1.8 to 2.4 meters. These waterwheels were particularly important in the Industrial Revolution, and during this time period the wheels tended to be made out of iron. These wheels can be made to be very large to increase their power output.
In this type of waterwheel, water flows onto the wheel about half way up and pushes the blades of the wheel downwards as it falls. The water then continues to flow underneath the wheel, pushing it more as it flows forward.