Look at a mill or factory erected on the side of a stream. The water will usually be found confined by a wall of earth or stone. The water runs from the stream through an opening called a canal and then to the water wheel. The difference in height between the canal and the river represents the fall or pressure of water which moves the machinery in the mill. In case of floods the water can run freely over the dam, without affecting the mill.
Falling water is a source of energy that supplies power to operate mills, factories, electric power plants, etc. Many factories and mills are located on the borders of rivers in the valleys of hilly communities. The water draining the hills rushes with considerable force down the rivers. The energy of this water is utilized by allowing it to run over an overshot water wheel (Fig. 44).
Fig. 44. - Overshot Water Wheel.
The most effective method of utilizing water power is by means of a wheel called a turbine. The river is dammed, and the water is conducted through a canal which runs alongside the mills. The water is allowed to pass through a cylindrical tube to a penstock which surrounds an iron case containing the turbine or rotating wheel (Figs. 45 and 46). By means of a connecting shaft the wheel may be made to operate a dynamo. Where there is current and little elevation, the energy of the water may be utilized by means of an undershot wheel (Fig. 47). The force of the current strikes against the lower part of the wheel.
Where the water is delivered under considerable pressure its power may be utilized to run lathes, sewing machines, and other light machinery. A common rotary water motor is employed, and is attached to the faucet. The water striking against the cup-shaped fans attached to the axle of the motor causes it to rotate. The axle is attached to a shaft which is connected directly or by belts to the machines. The motor is enclosed in a metal case with an opening in the bottom to allow the water to escape into the sink or outlet.
Fig. 45. - Use of Turbine.
Fig. 46. - Turbine Wheel.
Fig. 47. - Undershot Wheel.