OW TO INSTALL IT

Different types of water wheels--The impulse and reaction
wheels--The impulse wheel adapted to high heads and small amount of
water--Pipe lines--Table of resistance in pipes--Advantages and
disadvantages of the impulse wheel--Other forms of impulse
wheels--The reaction turbine, suited to low heads and large
quantity of water--Its advantages and limitations--Developing a
water-power project: the dam; the race; the flume; the penstock;
and the tailrace--Water rights for the farmer.

In general, there are two types of water wheels, the _impulse_ wheel
and the _reaction_ wheel. Both are called turbines, although the name
belongs, more properly, to the reaction wheel alone.

Impulse wheels derive their power from the _momentum_ of falling
water. Reaction wheels derive their power from the _momentum and
pressure_ of falling water. The old-fashioned _undershot_, _overshot_,
and _breast_ wheels are familiar to all as examples of impulse
wheels. Water wheels of this class revolve in the air, with the energy
of the water exerted on one face of their buckets. On the other hand,
reaction wheels are enclosed in water-tight cases, either of metal or
of wood, and the buckets are entirely surrounded by water.

The old-fashioned undershot, overshot, and breast wheels were not very
efficient; they wasted about 75 per cent of the power applied to them.
A modern impulse wheel, on the other hand, operates at an efficiency
of 80 per cent and over. The loss is mainly through friction and
leakage, and cannot be eliminated altogether. The modern reaction
wheel, called the _turbine_, attains an equal efficiency. Individual
conditions govern the type of wheel to be selected.

_The Impulse, or Tangential Water Wheel_

The modern impulse, or tangential wheel (so called because the driving
stream of water strikes the wheel at a tangent) is best adapted to
situations where the amount of water is limited, and the head is
large. Thus, a mountain brook supplying only seven cubic feet of water
a minute--a stream less than two-and-a-half inches deep flowing over a
weir with an opening three inches wide--would develop two actual
horsepower, under a head of 200 feet--not an unusual head to be found
in the hill country. Under a head of one thousand feet, a stream
furnishing 352.6 cubic feet of water a minute would develop 534.01
horsepower at the nozzle.

Ordinarily these wheels are not us