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of fuel (coal, wood, charcoal, petroleum, or gas), must be
employed. Such engines differ from those previously
described in being a constant expense for fuel and attention ;
but the great improvements which have been effected in recent
years, especially in the construction of small motors, has prob-
ably reduced this expenditure to a minimum. The simplest
machines are those which dispense with the use of steam.
These are the hot-air, gas, and oil engines. The competition
between the makers of these various types of motors, not only
amongst themselves, but with the makers of steam engines, has
resulted in all being brought to such perfection that it is often
a difficult matter to decide which form is the most desirable.
The hot-air engine is very compact and economical, requiring
but little fuel and skilled attention, but it is only adapted for
small works, where the h.p. required is from \ to 1. Its
only competitor under such conditions is the gas engine, and
as this is quite as economical in cost of fuel where gas is
reasonably cheap, and requires even less attention, it would
probably be selected where gas is available. The gas engine
is rapidly supplanting the steam engine in all but the largest
pumping stations, since they are not only more compact than
steam engines, but, with gas at a reasonable price, more eco-
nomical, when the great saving in repairs and in attendance is
taken into consideration. When once started they will run for
hours without any attention, and there is no risk of explosion
from neglect. " Oil " engines are of more recent introduction



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PUMPS AND PUMPING MACHINERY 353

and, owing to the cheapness of petroleum, are claimed to be
more economical than gas engines should the cost of gas be over
2s. per 1000 feet. It is also asserted that the cost of the oil
used does not exceed that of the corresponding amount of
coal required in driving a steam engine, when such coal can
be obtained at 10s. a ton. Where coal is more expensive
there is a saving in the cost of fuel, but in all cases there is
saved the wages of stoker and driver and the cost of water.
As the oil used has a high flashing point there is no risk of
explosion, and the danger from fire is reduced to a minimum.
In the best machines the vapouriser is heated by a small lamp,
taking about 5 to 7 minutes. As soon as the temperature is
sufficiently high the engine will start when the fly-wheel is
turned. The lamp is then extinguished, since the heat of
the vapouriser is afterwards maintained by the continuous
explosions. When once started the only attention required is
periodical lubrication and the occasional replenishing of the
oil reservoir. In fact, after being set in motion it requires
no more attention than the gas engine.

These engines are now made to work up to 25 h.p.,
and where gas is not obtainable there is no doubt that they
will be extensively employed.

In order to enable gas engines to compete with oil engines
where there is no public gas supply, plants are now made for
converting petroleum oils, fat and grease of all kinds, into gas,
and it is claimed that the gas so produced is cheaper than
coal-gas. Water-gas may also be manufactured and used for
this purpose. As the " oil " engines convert the petroleum
into gas in the vapouriser drop by drop as it is required, there
does not seem to be any advantage in or any necessity
for constructing a gasworks, unless gas is required for other
purposes besides that of supplying the motive power to the
engine.

Steam engines, except for large waterworks, are not likely
to be seriously considered as a source of power on account of
the comparatively large expense entailed in labour. For large

2 a



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354 WATER SUPPLIES

works, however, they continue to be the only practical and
efficient motors. In such cases, also, the compound condensing
engine will be used. For engines under 10 h.p. the saving
effected by the use of a condensing arrangement will not
compensate for the additional cost of the engine. The
pumps may be driven by a steam engine either directly or
through the intervention of a crankshaft and fly- wheel In
the former case the pistons of the cylinder and of the pump are
continuous, in the latter the piston of the cylinder acts upon
the fly-wheel and the pump piston is attached to the crank.
The crankshaft engine requires more space and stronger
foundations than the " direct " form, and as the latter are
now being made " compounding " and with high duty gear,
and are more compact, they will be generally preferred.

In calculating the horse power required for pumping a
supply of water, the chief factors are : (a) the quantity of
water to be raised, and (6) the height to which it has to be
lifted or forced. Besides this, an approximate estimate must
be made of the power which will be required to overcome the
friction due to gearing, and the passage of the water through
the pipes. The loss from friction in the pipes will depend
upon the nature of the surface of the pipe, degree of smooth-
ness or roughness, but more upon the diameter and velocity
with which the water is traversing it. It is of the highest
importance to have all the mains of sufficient diameter,
since the friction increases with the square of the velocity.
Thus the friction in a pipe discharging a certain number of
gallons per minute will be increased fourfold if the discharge
be only doubled. The friction also increases directly as the
length of the main. The main should always be of such
diameter that the velocity shall not exceed 2 feet per second
(Rawlinson). With this velocity the discharge from pipes
of different diameters is given in the following table. It will
be observed that the volume for any pipe can be calculated by
multiplying the square of the diameter in inches by the volume
discharged from a 1-inch pipe.



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PUMPS AND PUMPING AfACII/NERY



355



Diameter of Pipe.


1


inch


14


»»


2


>>


S


M


4


>>


6




8


»>


10




12


»>



Volume of Water <Uh<-)iai>piI |ht Minute
with a Velocity of '1 Feet per Hecoml.



4 1 gallons.


9*2


»»


16-4




87





65




148-0


»»


260*0




4100




690-0


tt







With pipes of such ample diameter the loss from friction is
very small and practically negligible.

An engine of one 1 actual horse power will raise 3300 gallons
1 foot high per minute, and any smaller quantity to a propor-
tionately greater height From the following simple formula
the h.p. required to pump any given quantity of water can
easily be calculated : —

OxH
3300



= H.P.,



where G = the number of gallons to be pumped per minute
and H = the height to which it has to be raised.

The allowance for overcoming the friction of the bucket or
plunger in the pumps, and of the movement of the water in
the pipes, and for raising the piston rods (when pumping
from a deep well), cannot be exactly calculated. It is better
to err on the safe side and allow 80 per cent for small engines
and 40 per cent for larger powers.

In all waterworks it is necessary to provide more pumping
engines than are actually at any one time required, in order
to provide for such contingencies as a break-down or laying-

1 By actual horse power is meant the actual power of an engine given
from the shaft or fly-wheel. The term "indicated" horse power, which
is frequently used, is the power given ofT in the cylinder, and is, of course,
higher than the actual or available power. Another term often employed
by makers of engines is *' nominal" horse power. It is a variable
quantity, and so misleading that it should be abandoned.



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3$6 WATER SUPPLIES

off for repairs. " In the case of small waterworks it is common
to have double the quantity of power needed, in the form of
two pumping engines, either of which is capable of doing all
the work. The reason for this is that the first cost would
probably be rather increased than otherwise, by subdividing
the work more, when the engines are very small, even although
the total horse power might be less. Then suppose the total
horse power needed were six i.Lp. 1 Two engines of six ih.p.
each would probably not cost more than three of three Lh.p.
each ; moreover, in work, the efficiency of the one pumping
engine of six i.h.p. would be greater than that of the two of
three i.h.p. each. Of course there is no hard-and-fast line
between small and large works, but it may be very roughly said
that it is not advisable to subdivide the pumping power into
more than two engines if, by so doing, separate engines of less
than ten i.h.p. each have to be provided. In the case of large
waterworks, the stand-by power need only equal one-third,
one -fourth, or, in the case of very large works, perhaps
one-fifth of the whole, there being, in such cases, three, four,
or five pumping engines" (Burton, The Water Supply of
Towns), Where engines are employed requiring the use of
fuel and attendance, it is desirable to have the machinery of
such power that the whole of the water required during
twenty-four hours can be pumped in a much shorter time. For
mansions, farms, etc., the engines may be sufficiently power-
ful to raise in eight or twelve hours as much water as will
serve for three or four days, thus necessitating pumping only
twice a week. For village water supplies pumping for from
four to six hours daily should suffice. For towns up to 20,000
inhabitants the pumps should raise in ten hours the whole
day's supply. For larger towns the pumping would probably
be continuous. Naturally the h.p. required will have to be
regulated by the quantity of water which has to be raised in
the given time.

1 Indicated horse power.



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CHAPTER XX

THE STORAGE OF WATER

Where a water supply is derived from the rainfall upon
any catchment area, it is obvious that, whether it is to meet
the demand of a single house, or of a whole town, sufficient
storage must be provided to tide over the longest periods of
drought ever likely to occur, and to equalise the supply
during a succession of dry seasons. The various ways in
which the amount of storage necessary is calculated, and the
opinions of various engineers and hydrologists thereon, have
already been recorded in Chapter XVII., where the amount of
water available from different sources has been considered.
The reservoirs used for the above purposes are called " im-
pounding" reservoirs, and when of large size they are
usually situated in a valley, or at the junction of two valleys,
where, by excavation and the construction of a dam, a sufficient
quantity of water can be collected.

The ground must be first surveyed to ascertain the
character of the impervious stratum and its distance from
the ground surface. If of rock, its freedom from fissures
(common in certain formations), through which the water
could escape, must, if possible, be determined. The presence
of an undiscovered fissure may result in the reservoir, after
construction, having to be abandoned, or in the expenditure
of large sums of money in detecting and attempting to remedy
the defect. The dam may be of masonry or of earthwork,
but the former is only applicable where there is a rocky



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358 WATER SUPPLIES

foundation. The latter can be constructed on rock, clay, or
other impervious strata, and is less costly than masonry. If,
however, the water is once able to penetrate it, the channel
will continuously increase in size and the dam will be
destroyed, whereas defects in masonry dams have not this
tendency to continuous increase and admit of being more
easily discovered and remedied. All vegetable matter should
be removed from the sides and bottom of new reservoirs,
otherwise these, by their decomposition, will give up organic
matter to the water, favourable to the growth of low forms of
life. To draw off the water a valve tower is provided, which
admits of valves being opened at various depths, so as to
avoid drawing either from too near the surface or too near
the bottom. A meter house may be required, in which to fix
the apparatus for recording the amount of water which is
passing into the mains, or the amount of compensation water
being supplied, or both, and a by-pass to allow of flood water
being diverted from the reservoir, and to prevent the water
rising above a certain level.

According to Kawlinson, the outer portion of the embank-
ment must be effectively drained, and if there are springs of
water in the puddle trench (as there usually are), these must
be collected and brought away. No form of culvert or other
works for drawing off water should be constructed within or
beneath or through the deepest made portion of the bank,
but the outlet tunnel, valve chamber, and works connected
with the drawing off of the water must be in the solid ground,
on the side of the valley. At the centre of the bank the
valve chamber should be formed. All pipes and valves should
be so placed as to be easily reached for repairs or renewals,
and it should be so arranged that no valve in the tier of
valves in the valve well need be worked under a greater head
than 10 or 15 feet.

In cases also where the water is derived from springs and
streams of variable flow, the supply sometimes falling below
that of the average demand, impounding reservoirs are



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THE STORAGE OF WATER 359

necessary to equalise the supply. The size will dc|>end upon
many circumstances, but will be chiefly influenced by tho
length of time during which the yield is below the average,
and by the extent of the fluctuations. Where river water is
impounded it must also be remembered that at certain periods,
following heavy rains, the water will be more or less turbid
or impure, and may have to be allowed to run to waste.
Where the average supply of a stream is more than sufficient
to meet all requirements, more or less storage is still required
to enable pure water to be supplied whilst the river is in
flood and its waters turbid and possibly polluted. Wherever
the water collected requires to be filtered before being
delivered to the consumer, reservoirs for "settling" are an
almost indispensable adjunct to the filter beds.

Such " settling " reservoirs retard the clogging of the pores
of the sand in the filter beds, and therefore enable the filters
to work for longer periods without cleansing. They should
be so constructed as to allow of emptying and cleansing, but
should not be too shallow, otherwise the water may become
unpleasantly warm in summer. A water depth of 12 to 16
feet is usually recommended. As generally constructed, with
sloping sides, the growth of algae is favoured. Vertical sides
are preferable.

Smaller or " service " reservoirs are often also constructed
in or near the place to be supplied with water, in order to
enable a constant average flow to be maintained to meet the
very varying demand during the 24 hours. These are especially
necessary where the water has to undergo a process of filtra-
tion, in order that the process may be uniformly continuous.
Without such a service reservoir, during the period of
greatest demand imperfectly - filtered water would pass into
the mains, unless filter beds of an otherwise unnecessarily
large area had been provided. These reservoirs are also
commonly used when water is raised by pumping. Without
such storage it is evident that pumping would have to be
continuous, and that the rate would have to vary with the



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360 WATER SUPPLIES

demand, whereas with a service reservoir the pumping
engines may work at a uniform speed, and for only a portion
of the 24 hours.

When the source from which water is derived is at a con-
siderable elevation, and long lengths of main convey the
water in different directions, as to villages and towns en
route to its ultimate destination, service reservoirs are often
constructed at elevated points, not only to break the pressure,
but to enable smaller mains to be used. Without these
reservoirs the mains would have to be capable of supplying
the maximum consumption, whereas with storage, the mains,
as far as the reservoirs, need only be capable of delivering the
average demand. As the maximum hourly consumption may
be twice the mean consumption, the difference in first cost,
where the mains are of any length, is very considerable.

Another very important advantage of such reservoirs is
that in case of fire there is a reserve of water instantly avail-
able. This is especially valuable in connection with the
supply of small towns, villages, mansions, and farms, since
the amount of water likely to be used in case of an outbreak
of fire would be a large faction of, or might even exceed that
of the whole capacity of the mains, whereas in large towns
the increased demand would only be a small fraction of
the average supply.

The amount of storage necessary and its character depends
upon the mode of supply, and whether by gravitation or by
pumping. Writing of these two classes of waterworks,
Burton, in his work on The Water Supply of Towns,
says: —

Gravitation works to be complete must consist of —

1. Either a high-level impounding reservoir, or a high-

level intake with a settling reservoir.

2. Filter beds.

3. A service reservoir near the impounding or settling

reservoir, or, if there is high land conveniently
situated, a reservoir as near as possible to the town



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THE STORAGE OF WATER 361

or within it, or one or more high-level tanks within
the town.
4. A distributing system.
A pumping system may consist of —
A. — 1. A comparatively low-level intake.

2. One or more settling reservoirs.

3. A set of filter beds.

4. A pumping station, with

5. A high-level reservoir or tank near or within the

town, holding enough to compensate for the inequality
of the consumption during 24 hours.

6. A distributing system.

B. — Where there is no land for a high-level reservoir, and a
high-level tank on an artificial support to hold enough
water to compensate for the variation in consumption
during 24 hours is considered impracticable.

1. A comparatively low-level intake.

2. One or more settling reservoirs.

3. A set of filter beds.

4. A low-level service reservoir.

5. A pumping station with engines pumping directly

into

6. A distributing system.

C. — When the intake is so low that the water will not
gravitate to any convenient place for settling
reservoirs and filtering beds, and there is room for
these only on low ground.

1. A low-level intake.

2. An intake pumping station with engines pumping

into

3. One or more settling reservoirs.

4. A set of filter beds.

5. Main pumping station with engines pumping into

6. A high-level reservoir on a high artificial support, and

7. A distributing system.

D. — The same as before, C, up to 5, but



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362 WATER SUPPLIES

5. A low-level service reservoir.

6. Pumping station, with engines pumping into

7. A distributing system.

The last case, as that of B, occurs where there is no
natural site for a high-level reservoir, and where a high-level
tank of sufficient size on an artificial support would be too
expensive, or is, for any other reason, impracticable.

Under peculiar circumstances modifications of these
systems may be and are adopted, and, of course, when the
low-level intake is a well or spring yielding water invariably
pellucid, the settling reservoirs and filter beds are dispensed
with, and the system is much simplified, the water being
forced directly into a high-service reservoir or even into the
distributing mains.

Impounding reservoirs must be of ample size, not only to
meet present demands, but also such increased demand as
may arise in the more immediate future. Where large works
are being constructed 50 years is not an unreasonable length
of time to look forward to, and as a minimum the probable
increase in 30 years should be provided for. Many towns
have been recently subject to immense inconvenience and
anxiety on account of this neglect, or from underestimating
the growth of the population and the consequent increased
demand for water.

The conditions which affect the decision as to the size of
settling and service reservoirs are of a different character, but
probably the most important is the effect of storage. This
varies somewhat with the character of the water ; speaking
generally, the purer the water the less the liability to change.
In natural reservoirs, or lakes, water is less prone to be
infested by organisms, which affect the odour and taste, than
in artificially- constructed reservoirs. Pure surface water
contains too little organic matter to favour the growth of
these algae and fungi, and the effect of storage is beneficial
rather than otherwise ; yet cases are recorded where very pure
waters have developed an objectionable odour and taste.



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THE STORAGE OF WATER 363

These growths are usually found to occur in reservoirs storing
water collected from gathering grounds which are in [>art
cultivated. The small amount of manurial matter, or the
products of its oxidation taken up by the water, supplies
constituents necessary to the growth and multiplication of
these low forms of life. Peaty water tends to lose its
colour if long stored, probably from the action of light, but
the observers for the Massachusetts ltoard of Health, who
have very fully studied the effect of storage, found that 1 2
months' exposure was necessary to completely bleach such
water. They found that surface waters, by storing, suffered
no change in the amount of ammonia and nitrates present, but
in other waters the nitrates were slightly reduced. Investi-
gating waters taken from various depths from a deep but
small lake, they concluded that vertical circulation took place
during the winter months, but that during the summer this
was in abeyance, and that the water at the bottom of the lake
remained stagnant. When the air is colder than the water,
the surface of the latter will cool, becoming at the same time
denser and tending to sink ; when the air is warmer than
the water, or the latter is exposed to the direct action of the
sun's rays, the surface will become heated, and, decreasing in
density, will retain its position. This, of course, applies to
water stored in large or small reservoirs, provided the water
is exposed to the air. The result of the stagnation is probably
very slight in waters of great hygienic purity, but in waters
containing organic matter the free oxygen disappears, the
water deteriorates, free ammonia increasing in amount,
especially at depths below 20 feet, and at such times samples
of water from near the top and near the bottom may yield
very different results upon analysis.

Ground water when stored in open reservoirs is said to
"deteriorate at all seasons of the year." The albumenoid
ammonia, or rather the organic matter yielding ammonia
upon distillation with alkaline permanganate, increases, and
in spring and summer the free ammonia becomes excessive,



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364 WATER SUPPLIES

and at the same time nitrates are reduced. The micro-
organisms, which in the water at its source are few in number,
increase rapidly, so that they may even be in excess of those
found in much more impure waters. The same water when
kept in covered tanks is said to suffer but an inappreciable
change ; this is attributed to the absence of light and the
difficulty of access of air -conveyed microbes. I have fre-
quently observed, however, that the waters taken from a
whole series of wells over a definite area yielded much better
results both chemically and bacteriologically when examined
in winter than when collected in summer. In small open
tanks through which water is constantly passing, the water
undergoes, as a rule, but little change, but numerous instances
are recorded of the rapid and persistent growth of organisms
even in service tanks. This is almost certainly prevented by
thoroughly cleansing and covering the tanks. One organism,
however, grows better in the dark than in the light, the
" Crenothrix," and occasionally gives rise to trouble by im-
parting a nauseous odour and taste to the water. As this
fungus requires for its growth both protoxide of iron and
organic matter, a water in which it can flourish is not desirable
for a domestic supply.



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