_Hydraulic machinery_ may be broadly divided into
1. Motor machines, and,
2. Pumps.
_Water motors_ may be divided into
1. Water wheels,
2. Turbines, and,
3. Water pressure engines.
_In hydraulic motor machines_ a quantity of water descending from
a higher to a lower level, or _from a higher to a lower pressure_,
drives a machine which receives energy from the water and applies it to
overcoming the resistances of other machines doing work.
_In the next general class_, work done on the machine by a steam engine
or other source of energy is employed in lifting water _from a lower to
a higher level_. A few machines such as the ram and jet pump _combine
the functions of both motors and pumps_.
_The subject of water wheels is but a continuation of much that has
been illustrated and defined in the historical introduction_ to which
is now added the following summary.
In every system of machinery _deriving energy from a natural water-fall
there exist the following parts_:
(1) _A supply channel_, leading the water from the highest accessible
level, _to the site of the machine_; this may be an open channel of
earth, masonry, or wood, or it may be a closed cast or wrought-iron
pipe; in some cases part of the head race is an open channel, part a
closed pipe.
(2) _Leading from the motor_ there is a tail race, culvert, or
discharge pipe delivering the water after it has done its work.
(3) _A waste channel_ placed on or at the origin of the head race by
which surplus water, in floods, escapes.
(4) _The motor itself_, which either overcomes a useful resistance
directly, as in the case of a ram acting on a lift or crane chain,
or indirectly by actuating transmissive machinery, as when a turbine
drives the shafting, belting, and gearing of a mill. With the motor
is usually combined regulating machinery for adjusting the power and
speed, to the work done.
The great convenience and simplicity of water motors has led to their
adoption in certain cases, where no natural source of water power is
available. In these cases, an artificial source of water power is
created by using a steam engine to pump water to a reservoir at a great
elevation, or to pump water into a closed reservoir in which there is
great pressure.
Water flowing from the reservoir through hydraulic engines gives back
the energy expended, less so much as has been wasted in friction.
Where a continuously acting steam engine stores up energy by pumping
the water, while the work done by the hydraulic engines is done
intermittently,—this arrangement is considered the most useful.
NOTE.—“Wherever a stream flows from a higher to a lower level it
is possible to erect a water motor. The amount of power obtainable
depends on the available head and the supply of water. In choosing
a site the engineer will select a portion of the stream where there
is an abrupt natural fall, or at least a considerable slope of the
bed. He will have regard to the facility of constructing the channels
which are to convey the water, and will take advantage of any bend in
the river which enables him to shorten them. He will have accurate
measurements made of the quantity of water flowing in the stream,
and he will endeavor to ascertain the average quantity available
throughout the year, the minimum quantity in dry seasons, and the
maximum for which bye-wash channels must be provided. In many cases
the natural fall can be increased by a dam or weir thrown across the
stream. The engineer will also examine to what extent the head may
vary in different seasons, and whether it is necessary to sacrifice
part of the fall and give a steep slope to the tail race to prevent
the motor being flooded by backwater in freshet time.
In designing or selecting a water motor it is sufficient to consider
only its efficiency in normal working conditions. It is generally
quite as important to know how it will act with a scanty water supply
or a diminished head. The greatest difference in water motors is in
their adaptability to varying working conditions.”—ENCYC. BRIT.
[Illustration: FIG. 110.]
_Water wheels_ are large vertical wheels driven by water falling from
a higher to a lower level: they are motors on which the water acts,
partly by weight, partly by impulse. _Turbines_ are wheels, generally
of small size compared with water wheels, driven chiefly by the impulse
of the water. Before entering the moving part of the turbine, the water
is allowed to acquire a considerable velocity; during its action on the
wheel this velocity is diminished, and the impulse due to the change
of momentum drives the turbine. Roughly speaking, the fluid acts in
a water-pressure engine directly by its pressure, _in a water wheel
chiefly by its weight causing a pressure_.
_A flutter-wheel_ is shown in Fig. 110. This is a water wheel of
moderate diameter placed at the bottom of a chute so as to receive
the impact of the head of water in the chute and penstock. Its name
is derived from its rapid motion, the effect of which is to cause a
commotion of the water like “the fluttering” of a fowl.
_Impact Wheels._—The simplest and most imperfect of the horizontal
wheels are the so-called impact wheels or impact turbines, such as
shown in Fig. 111.
[Illustration: FIG. 111.]
They consist of 16 or 20 rectangular blades fastened to the wheel at
an inclination of 50° to 70° with the horizon. The water is brought on
through a race of 40° to 20° inclination, so that it strikes at about
right angles upon the blades.
These wheels are used in falls from 10 to 20 ft., where a large
number of revolutions is necessary, as in grain mills, where the
moving millstone is hung on the vertical shaft of the wheel, hence
intermediate gearing is unnecessary. These crude machines are found in
Southern Europe, North Africa, in the Alps, Pyrenees, and in Algiers.
They are about 5 ft. in diameter, and the blades are 15 inches high and
8 to 10 inches long (measured radially).
[Illustration: FIG. 112.]
Fig. 112 shows an “_undershot water wheel_.” In this style of wheel,
the work is done by impact alone, as the running water acts only on a
few immersed buckets on the under side of the wheel.
In the _breast wheel_, Fig. 113, the water is admitted on a level or
slightly above the center of the shaft, so that the water acts by
impact and weight.
[Illustration: FIG. 113.]
NOTE.—“_A weir_ is a dam erected across a river to stop and raise the
water, as for the purpose of taking fish, of conveying a stream to a
mill, of maintaining the water at a level required for navigating it,
or for the purposes of irrigation.”
For facilitating the computation of the quantity of water flowing
over weirs, Weir Tables, are used, based upon approved formulas, of
which “Francis’ Formula” is perhaps the most reliable. These tables
are applicable to the subject of water wheels but cannot be printed
in this work.
[Illustration: FIG. 114.]
Fig 114 represents an _over-shot water wheel_ (F G H L, with axis at O)
in which the water flows upon the top of the wheel at _h_, in the same
direction in which it revolves, therefore the impact of the water is
utilized upon the upper buckets H, a, b, after which the weight of the
water acts in the buckets c, d, e, F, e´, d´ and c´. At b´ the buckets
begin to overflow and empty themselves as shown at a´. It will be seen
that the water acts upon almost one-half the circumference of this
wheel, thus realizing the greatest mechanical effect with the smallest
quantity of water.
_The current-wheel_ is perhaps the first application of the force
of water in motion, to drive machinery. In the first century B. C.,
water-wheels for driving mills were used in Asia Minor and on the
Tiber. In the former case we suppose, but in the latter case we know,
that these were current-wheels.
[Illustration: FIG. 115.]
_The tide or current wheel_, (Fig. 115) erected in the vicinity of
the north end of London Bridge, and subsequently under its northern
arch, was erected by Peter Morice, a Dutchman, in 1582, and operated
force-pumps which supplied a part of London with water. The stand-pipe
from the pump was 120 feet high, and conducted the water to a cistern
at that height. The amount raised was about 216 gallons per minute. The
wheel worked sixteen pumps, each 7 inches in diameter, and having a
uniform stroke of 30 inches.
During the seventeenth and eighteenth centuries the works were extended
from time to time, and occupied one after another of the arches. In the
first arch of the bridge was one wheel working sixteen force-pumps. In
the third arch were three wheels, working fifty-two pumps. The united
effect was 2,052 gallons per minute, raised 120 feet high.
In 1767 Smeaton added wheels in the fifth arch. Steam-engines were
added about this time to assist at low water and at neap-tides. Thus
the matter remained till 1821. Stow, the antiquarian and historian,
describes the works in 1600; and Beighton in 1731 gives an account of
them at that date.
The water-wheels at that time were placed under several of the
arches. The axis of these wheels was 19 feet long 3 feet diameter.
The radial arms supported the rings and twenty-six floats, 14 feet
long by 18 inches wide. The axis turned on brass gudgeons supported
by counterpoised levers, which permitted the vertical adjustment of
the wheel as the tide rose and fell. On the axis of the wheel was a
cog-wheel 8 feet in diameter and having forty-four cogs; meshing into a
trundle-wheel 4-1/2 feet in diameter and having 20 rounds, or pins and
whose iron axle revolved in brasses.
The axis of the trundle was prolonged at each end, and had quadruple
cranks which connected by rods to the ends of four walking beams 24
feet long, whose other ends worked the piston-rods of the pumps. The
axis of oscillation of the lever supporting the wheel, and by which it
was adjusted to the height of the tide, was coincident with the axis
of the trundle, so that the latter engaged the 8-feet cog-wheel in all
conditions of vertical adjustment. Cranks operated one end of the beams
while pumps were attached to the other end.
[Illustration: FIG. 116.]
Fig. 116 exhibits an _overshot water wheel_ employed at Laxey, Isle
of Man, for driving the pumps which drain the mines at that village;
these have an extreme depth of 1,380 feet. The wheel is 72 feet 6
inches in diameter, 6 feet in breadth, exerts a force of about 200
horse-power and is capable of pumping 250 gallons per min. from a depth
of 1,200 feet. Its crank-stroke is 10 feet. The water for driving it is
conducted by pipes from a reservoir on a neighboring hill, and ascends
in the column of masonry shown to the left of the wheel. (Knight Vol.
III.) An extra crank appears to be shown in the foreground of this
reproduction of an old drawing.