Read each of the following descriptions of how and why water wheels were gradually replaced by turbines, and then use the information to write a letter back to Catherine explaining how her factory works.

A list detailing what must be included in the letter is provided in the print materials for this lesson.

Click on a tab to display information on the descriptions.

Horsepower and Torque

A water wheel is like any kind of engine; it develops two kinds of power – horsepower and torque. Horsepower is a measure of the speed the water turns the wheel and therefore how fast machines connected to the wheel can be turned. The faster the river is rushing downstream, the more horsepower it can provide to the machines connected to the wheel. Torque is a measure of the force the water delivers to the wheel and therefore how much weight it can lift or friction it can overcome. This force is determined by how much downhill travel the water is experiencing at that moment, and that travel is called the river’s head. Head is measured in feet, indicating the difference in elevation between how high the river started and how low it ends up. For example, water pouring off a desk onto the floor has a head of about 60 cm, while water poured from your outstretched arm when you are standing would have a head of 1.5 to 2 meters. The water you poured while standing would impact a water wheel with more energy than the water from the desk, allowing the water wheel to transfer more torque to its machines and therefore to do more work.

Weaknesses of Water Wheels

Water wheels worked well enough for centuries, but during the industrial revolution as human needs for mechanical power grew, certain drawbacks became apparent. First, the water is only pushing in one direction - down. If the wheel has 12 slats, only three or four are being pushed against by falling water at any one time, in the meantime, the other slats are useless. In addition, the force required to turn the un-used slats back up to the top took away energy that could have been turning machines. Second, if the bottom of the wheel gets submerged, the wheel stops turning and becomes useless. There cannot be any depth of spilled water around the wheel; therefore the water must be evacuated quickly. Third, since the pouring water impacts the wheel near its top, much of the water’s head is wasted. It would be better if it could build force before hitting the slats. All of these drawbacks meant that water wheels never exceeded 75% efficiency; that is, they never transferred more than 75% of the river’s power to the machines, and it was often closer to 60%.

A New Technology – Turbines

Turbines were invented in the 19th century specifically to overcome the weaknesses of water wheels. In a turbine, the wheel is placed on its side, and the water is dumped inside it using a pipe. The water wants to exit the wheel, and does so through the hollow slats, turning the wheel as it goes. In this way, the water is pushing against all of the slats at once. In addition, the water is able to fall a greater distance since the turbine lies flat at the bottom of a basin or waterfall. The turbine works underwater, so there is not as pressing a need to evacuate the spilled water, and the turbine is often made of iron, not wood, so it requires less maintenance. The turbine can convert up to 88% of the water’s energy into usable mechanical energy and does so more reliably than water wheels could.

Catherine’s Cotton Factory and Its Turbines

Catherine’s factory was famous nationwide because it was an example of a factory built in, by, and for the Southern states and because it used all of the newest, most expensive equipment. Prior to the building of this factory, Southern industry had been seen as poor, unsophisticated, and backward. This factory, built in the same town as the very important U.S. government rifle factories, was seen as a first step in changing Southern manufacturing. The factory had two brand-new turbines in its basement, each almost two meters in diameter. The turbines used water brought from the Shenandoah via a specially dug underground Inner Canal and had access to over four meters of head. On average, they generated 60-70 horsepower for the machines, depending on the speed of the river. The turbines were connected to a central axle that traveled straight up through the center of the factory and fed power to secondary axles that ran along the ceiling of each room. The turning motion of these axles was transmitted to the individual machines via smaller axles or leather belts. (see Fig. 4 – Virginius Island Cotton Factory). The machines were completely dependent on the turbines and, therefore, the river. If the river ran dry or the turbines broke, or the central axle malfunctioned, all work stopped. There was no back-up coal, wood, or animal power.