A water mill is a structure that harnesses the energy of flowing water to drive a mechanical process. It typically incorporates a water wheel or turbine to convert the movement of water into usable power.
The Fundamental Concept
Water mills convert the kinetic energy from moving water or the potential energy from falling water into mechanical rotational energy. As water flows or falls, it exerts force upon the water wheel, causing it to turn. The amount of energy that can be harvested depends on both the quantity of water and its velocity.
Essential Parts of a Water Mill
A water mill system relies on several interconnected components. Water is supplied from a source such as a river, stream, or mill pond. A water channel, often known as a head race, leat, flume, or penstock, diverts this water to the mill.
The water wheel, a large rotating part equipped with blades or buckets, is central to the system. An axle or shaft connected to the wheel extends into the mill structure, transmitting power. Within the mill, a basic gear system transmits and modifies this power for various mechanical applications. Sluice gates are often used to control the flow of water to the water wheel.
How Water Interacts with the Wheel
Water interacts with the mill wheel in distinct ways, depending on the wheel’s design. The undershot wheel is driven by water flowing beneath it, pushing against its paddles or blades. This design harnesses the kinetic energy of fast-moving water and is suitable for flat areas with a large volume of water and a low “head,” or vertical drop. Undershot wheels are less efficient, typically 20% to 60%.
In contrast, the overshot wheel utilizes the potential energy of falling water. Water is directed over the top of the wheel, filling buckets or compartments along its rim. The weight of the water in these buckets causes the wheel to turn due to gravity, pulling the heavier side downwards. Overshot wheels are more efficient, achieving 60% to 90% efficiency, and are well-suited for smaller streams with a significant height difference.
A breastshot wheel represents an intermediate type, where water strikes the wheel around its midpoint.
Converting Rotation into Useful Power
The rotational motion of the water wheel is converted into usable power. The main shaft, directly connected to the water wheel, transfers this rotation into the mill building. A gearing system, often involving components like a pit wheel, wallower, and spur gears, modifies the speed and direction of this rotation. These gears increase the rotational speed from the slow-turning water wheel to a rate suitable for the machinery it powers.
This transmitted power was applied to various tasks. Water mills ground grain into flour, operated sawmills, and pumped water. They were also used for textile production, metal shaping, and wire drawing. The power could be further distributed to various machines within a factory using systems of belts and pulleys.