Showing jet of water striking cups. Wheel illustrated is
very powerful, but principle of small wheels is the same

In general, the turbine type of wheel is best adapted to low heads, or falls, and the use of comparatively large volumes of water, and the impulse wheel is best adapted to the use of a comparatively high head, or fall, and a comparatively small amount of water. There are certain intermediate conditions for which the manufacturers of each type claim their wheel is best suited and in such instance a study of local conditions is always necessary to determine which type of wheel is best adapted.

The development of a water power by means of any kind of a waterwheel results in the conversion of the energy of the falling water into mechanical power which is exerted in a more or less rapidly revolving shaft. In order to apply this power of the revolving shaft to some useful purpose, there are several methods which may be used. The shaft may be directly connected to the shaft of an electric generator, or dynamo, to generate electric current, or it may be directly connected to a machine which it is desired to operate, provided the machine, or dynamo, is required to operate at the same speed as that of the wheel shaft. This is frequently not the case, so that under ordinary conditions the shaft of the wheel is fitted with a pulley, which in turn is connected by belt to another pulley on the machine which is to be driven.

Motor-driven Mangle

By using pulleys of different diameters on the shaft of the waterwheel and the shaft of the machinery to be driven, the speed of the machine may be several times more or less than the speed of the waterwheel. For instance, if the waterwheel revolves 200 revolutions per minute and it is desired to operate a machine, connected by belt, at a speed of 1000 revolutions per minute, a pulley of comparatively small size, say four inches in diameter, is placed on the shaft to be driven, and a pulley of five times the diameter, or twenty inches, is placed on the shaft of the waterwheel. This causes the shaft of the machine to revolve at a speed five times as great as the waterwheel. If the speed of the waterwheel is greater than that required for the machinery to be operated, then the reverse operation is followed out, placing a small pulley on the shaft of the waterwheel and a larger one on the shaft of the machinery to be driven. If the speed of the waterwheel is to be magnified more than about six times, it usually requires the installation of a countershaft and another series of pulleys in order to avoid the use of very large and very small pulleys. A pulley which has a very small diameter does not operate satisfactorily without considerable loss of power, and a very large pulley is objectionable on account of the space which it requires.

When a water power is once developed it may be applied to practical use either near the place of development or at a considerable distance. If it is to be used for power only, and not for lighting, and can be used where it is developed, there is no need of converting it into electricity. But if it is to be used for lighting, or for power to be applied at a considerable distance from the water-power site, then it becomes necessary to convert the power into electricity, in which form it may be most conveniently transmitted from one place to another. This requires an electric generator, or dynamo, to be driven by the waterwheel, and a transmission line, preferably of copper or aluminum wire, to carry the current where it is to be used. In order to reconvert the current into power at the end of the transmission line, where the power is to be used, it is necessary to run the current into an electric motor, the shaft of which is made to revolve by the action of the electric current. This motor may then be connected directly, or by belt, gears or chain drive, to the machine to be driven.

It should be borne in mind that in each of these steps of changing from water power to electric current, in transmitting the current over the wires, in reconverting it into power, and in transferring this power from a motor to a power-operated machine, there are losses of energy. These losses vary considerably in different instances. Assuming, for illustration, that a water power, whose theoretical power is ten horsepower, is required to drive a power machine at a distance, the efficiencies and losses will be somewhat as follows:

Waterwheel, efficiency 80%, Loss 20%, generates 8.0 horsepower.
Connections,“95%,“ 5%,transfers7.6“
Dynamo,“90%,“10%,generates6.8“
Transmission,“90%,“10%,transmits6.2“
Motor,“90%,“10%,develops5.5“
Connections,“95%,“ 5%,delivers 5.0“

Therefore, only five horsepower would be actually delivered to the machine to be driven. This amounts to only half of the theoretical power of the falling water which is actually realized in useful work of the machine being driven. If the power from the waterwheel is to be applied directly without generating electricity a much higher efficiency will be realized.