PUMPS AND THEIR VALUE TO MAN
181. "As difficult as for water to run up a hill!" Is there any one
who has not heard this saying? And yet most of us accept as a matter
of course the stream which gushes from our faucet, or give no thought
to the ingenuity which devised a means of forcing water upward through
pipes. Despite the fact that water flows naturally down hill, and not
up, we find it available in our homes and office buildings, in some of
which it ascends to the fiftieth floor; and we see great streams of it
directed upon the tops of burning buildings by firemen in the streets
below.
In the country, where there are no great central pumping stations,
water for the daily need must be raised from wells, and the supply of
each household is dependent upon the labor and foresight of its
members. The water may be brought to the surface either by laboriously
raising it, bucket by bucket, or by the less arduous method of
pumping. These are the only means possible; even the windmill does not
eliminate the necessity for the pump, but merely replaces the energy
used by man in working it.
In some parts of our country we have oil beds or wells. But if this
underground oil is to be of service to man, it must be brought to the
surface, and this is accomplished, as in the case of water, by the use
of pumps.
An old tin can or a sponge may serve to bale out water from a leaking
rowboat, but such a crude device would be absurd if employed on our
huge vessels of war and commerce. Here a rent in the ship's side would
mean inevitable loss were it not possible to rid the ship of the
inflowing water by the action of strong pumps.
Another and very different use to which pumps are put is seen in the
compression of gases. Air is forced into the tires of bicycles and
automobiles until they become sufficiently inflated to insure comfort
in riding. Some present-day systems of artificial refrigeration
(Section 93) could not exist without the aid of compressed gases.
Compressed air has played a very important role in mining, being sent
into poorly ventilated mines to improve the condition of the air, and
to supply to the miners the oxygen necessary for respiration. Divers
and men who work under water carry on their backs a tank of compressed
air, and take from it, at will, the amount required.
There are many forms of pumps, and they serve widely different
purposes, being essential to the operation of many industrial
undertakings. In the following Sections some of these forms will be
studied.
[Illustration: FIG. 131.--Carrying water home from the spring.]
182. The Air as Man's Servant. Long before man harnessed water for
turbines, or steam for engines, he made the air serve his purpose, and
by means of it raised water from hidden underground depths to the
surface of the earth; likewise, by means of it, he raised to his
dwelling on the hillside water from the stream in the valley below.
Those who live in cities where running water is always present in the
home cannot realize the hardship of the days when this "ready-made"
supply did not exist, but when man laboriously carried to his
dwelling, from distant spring and stream, the water necessary for the
daily need.
What are the characteristics of the air which have enabled man to
accomplish these feats? They are well known to us and may be briefly
stated as follows:--
(1) Air has weight, and 1 cubic foot of air, at atmospheric pressure,
weighs 1-1/4 ounces.
(2) The air around us presses with a force of about 15 pounds upon
every square inch of surface that it touches.
(3) Air is elastic; it can be compressed, as in the balloon or bicycle
tire, but it expands immediately when pressure is reduced. As it
expands and occupies more space, its pressure falls and it exerts less
force against the matter with which it comes in contact. If, for
example, 1 cubic foot of air is allowed to expand and occupy 2 cubic
feet of space, the pressure which it exerts is reduced one half. When
air is compressed, its pressure increases, and it exerts a greater
force against the matter with which it comes in contact. If 2 cubic
feet of air are compressed to 1 cubic foot, the pressure of the
compressed air is doubled. (See Section 89.)
[Illustration: FIG. 132.--The atmosphere pressing downward on _a_
pushes water after the rising piston _b_.]
183. The Common Pump or Lifting Pump. Place a tube containing a
close-fitting piston in a vessel of water, as shown in Figure 132.
Then raise the piston with the hand and notice that the water rises in
the piston tube. The rise of water in the piston tube is similar to
the raising of lemonade through a straw (Section 77). The atmosphere
presses with a force of 15 pounds upon every square inch of water in
the large vessel, and forces some of it into the space left vacant by
the retreating piston. The common pump works in a similar manner. It
consists of a piston or plunger which moves back and forth in an
air-tight cylinder, and contains an outward opening valve through
which water and air can pass. From the bottom of the cylinder a tube
runs down into the well or reservoir, and water from the well has
access to the cylinder through another outward-moving valve. In
practice the tube is known as the suction pipe, and its valve as the
suction valve.
In order to understand the action of a pump, we will suppose that no
water is in the pump, and we will pump until a stream issues from the
spout. The various stages are represented diagrammatically by Figure
133. In (1) the entire pump is empty of water but full of air at
atmospheric pressure, and both valves are closed. In (2) the plunger
is being raised and is lifting the column of air that rests on it. The
air and water in the inlet pipe, being thus partially relieved of
downward pressure, are pushed up by the atmospheric pressure on the
surface of the water in the well. When the piston moves downward as in
(3), the valve in the pipe closes by its own weight, and the air in
the cylinder escapes through the valve in the plunger. In (4) the
piston is again rising, repeating the process of (2). In (5) the
process of (3) is being repeated, but water instead of air is escaping
through the valve in the plunger. In (6) the process of (2) is being
repeated, but the water has reached the spout and is flowing out.
[Illustration: FIG. 133. Diagram of the process of pumping.]
After the pump is in condition (6), motion of the plunger is followed
by a more or less regular discharge of water through the spout, and
the quantity of water which gushes forth depends upon the speed with
which the piston is moved. A strong man giving quick strokes can
produce a large flow; a child, on the other hand, is able to produce
only a thin stream. Whoever pumps must exert sufficient force to lift
the water from the surface of the well to the spout exit. For this
reason the pump has received the name of _lifting pump_.
[Illustration: FIG. 134.--Force pump.]
184. The Force Pump. In the common pump, water cannot not be raised
higher than the spout. In many cases it is desirable to force water
considerably above the pump itself, as, for instance, in the fire
hose; under such circumstances a type of pump is employed which has
received the name of _force pump_. This differs but little from the
ordinary lift pump, as a reference to Figure 134 will show. Here both
valves are placed in the cylinder, and the piston is solid, but the
principle is the same as in the lifting pump.
An upward motion of the plunger allows water to enter the cylinder,
and the downward motion of the plunger drives water through _E_. (Is
this true for the lift pump as well?) Since only the downward motion
of the plunger forces water through _E_, the discharge is intermittent
and is therefore not practical for commercial purposes. In order to
convert this intermittent discharge into a steady stream, an air
chamber is installed near the discharge tube, as in Figure 135. The
water forced into the air chamber by the downward-moving piston
compresses the air and increases its pressure. The pressure of the
confined air reacts against the water and tends to drive it out of the
chamber. Hence, even when the plunger is moving upward, water is
forced through the pipe because of the pressure of the compressed
air. In this way a continuous flow is secured.
[Illustration: FIG 135.--The air chamber _A_ insures a continuous flow
of water.]
The height to which the water can be forced in the pipe depends upon
the size and construction of the pump and upon the force with which
the plunger can be moved. The larger the stream desired and the
greater the height to be reached, the stronger the force needed and
the more powerful the construction necessary.
The force pump gets its name from the fact that the moving piston
drives or forces the water through the discharge tube.
185. Irrigation and Drainage. History shows that the lifting pump
has been used by man since the fourth century before Christ; for many
present-day enterprises this ancient form of pump is inconvenient and
impracticable, and hence it has been replaced in many cases by more
modern types, such as rotary and centrifugal pumps (Fig. 136). In
these forms, rapidly rotating wheels lift the water and drive it
onward into a discharge pipe, from which it issues with great force.
There is neither piston nor valve in these pumps, and the quantity of
water raised and the force with which it is driven through the pipes
depends solely upon the size of the wheels and the speed with which
they rotate.
Irrigation, or the artificial watering of land, is of the greatest
importance in those parts of the world where the land is naturally too
dry for farming. In the United States, approximately two fifths of the
land area is so dry as to be worthless for agricultural purposes
unless artificially watered. In the West, several large irrigating
systems have been built by the federal government, and at present
about ten million acres of land have been converted from worthless
farms into fields rich in crops. Many irrigating systems use
centrifugal pumps to force water over long distances and to supply it
in quantities sufficient for vast agricultural needs. In many regions,
the success of a farm or ranch depends upon the irrigation furnished
in dry seasons, or upon man's ability to drive water from a region of
abundance to a remote region of scarcity.
[Illustration: FIG. 136.--Centrifugal pump with part of the casing]
cut away to show the wheel.
[Illustration: FIG. 137.--Agriculture made possible by irrigation.]
The draining of land is also a matter of considerable importance;
swamps and marshes which were at one time considered useless have been
drained and then reclaimed and converted into good farming land. The
surplus water is best removed by centrifugal pumps, since sand and
sticks which would clog the valves of an ordinary pump are passed
along without difficulty by the rotating wheel.
[Illustration: FIG. 138.--Rice for its growth needs periodical
flooding, and irrigation often supplies the necessary water.]
186. Camping.--Its Pleasures and its Dangers. The allurement of a
vacation camp in the heart of the woods is so great as to make many
campers ignore the vital importance of securing a safe water supply. A
river bank may be beautiful and teeming with diversions, but if the
river is used as a source of drinking water, the results will almost
always be fatal to some. The water can be boiled, it is true, but few
campers are willing to forage for the additional wood needed for this
apparently unnecessary requirement; then, too, boiled water does not
cool readily in summer, and hence is disagreeable for drinking
purposes.
The only safe course is to abandon the river as a source of drinking
water, and if a spring cannot be found, to drive a well. In many
regions, especially in the neighborhood of streams, water can be
found ten or fifteen feet below the surface. Water taken from such a
depth has filtered through a bed of soil, and is fairly safe for any
purpose. Of course the deeper the well, the safer will be the water.
With the use of such a pump as will be described, campers can, without
grave danger, throw dish water, etc., on the ground somewhat remote
from the camp; this may not injure their drinking water because the
liquids will slowly seep through the ground, and as they filter
downward will lose their dangerous matter. All the water which reaches
the well pipes will have filtered through the soil bed and therefore
will probably be safe.
But while the careless disposal of wastes may not spoil the drinking
water (in the well to be described), other laws of health demand a
thoughtful disposal of wastes. The malarial mosquito and the typhoid
fly flourish in unhygienic quarters, and the only way to guard against
their dangers is to allow them neither food nor breeding place.
The burning of garbage, the discharge of waters into cesspools, or, in
temporary camps, the discharge of wastes to distant points through the
agency of a cheap sewage pipe will insure safety to campers, will
lessen the trials of flies and mosquitoes, and will add but little to
the expense.
187. A Cheap Well for Campers. A two-inch galvanized iron pipe with
a strong, pointed end containing small perforations is driven into the
ground with a sledge hammer. After it has penetrated for a few feet,
another length is added and the whole is driven down, and this is
repeated until water is reached. A cheap pump is then attached to the
upper end of the drill pipe and serves to raise the water. During the
drilling, some soil particles get into the pipe through the
perforations, and these cloud the water at first; but after the pipe
has once been cleaned by the upward-moving water, the supply remains
clear. The flow from such a well is naturally small; first, because
water is not abundant near the surface of the earth, and second,
because cheap pumps are poorly constructed and cannot raise a large
amount. But the supply will usually be sufficient for the needs of
simple camp life, and many a small farm uses this form of well, not
only for household purposes, but for watering the cattle in winter.
If the cheapness of such pumps were known, their use would be more
general for temporary purposes. The cost of material need not exceed
$5 for a 10-foot well, and the driving of the pipe could be made as
much a part of the camping as the pitching of the tent itself. If the
camping site is abandoned at the close of the vacation, the pump can
be removed and kept over winter for use the following summer in
another place. In this way the actual cost of the water supply can be
reduced to scarcely more than $3, the removable pump being a permanent
possession. In rocky or mountain regions the driven well is not
practicable, because the driving point is blunted and broken by the
rock and cannot pierce the rocky beds of land.
[Illustration: FIG. 139--A driven well.]
[Illustration: FIG. 140.--Diagram showing how supplying a city with
good water lessens sickness and death. The lines _b_ show the relative
number of people who died of typhoid fever before the water was
filtered; the lines _a_ show the numbers who died after the water was
filtered. The figures are the number of typhoid deaths occurring
yearly out of 100,000 inhabitants.]
188. Our Summer Vacation. It has been asserted by some city health
officials that many cases of typhoid fever in cities can be traced to
the unsanitary conditions existing in summer resorts. The drinking
water of most cities is now under strict supervision, while that of
isolated farms, of small seaside resorts, and of scattered mountain
hotels is left to the care of individual proprietors, and in only too
many instances receives no attention whatever. The sewage disposal is
often inadequate and badly planned, and the water becomes dangerously
contaminated. A strong, healthy person, with plenty of outdoor
exercise and with hygienic habits, may be able to resist the disease
germs present in the poor water supply; more often the summer guests
carry back with them to their winter homes the germs of disease, and
these gain the upper hand under the altered conditions of city and
business life. It is not too much to say that every man and woman
should know the source of his summer table water and the method of
sewage disposal. If the conditions are unsanitary, they cannot be
remedied at once, but another resort can be found and personal danger
can be avoided. Public sentiment and the loss of trade will go far in
furthering an effort toward better sanitation.
In the driven well, water cannot reach the spout unless it has first
filtered through the soil to the depth of the driven pipe; after such
a journey it is fairly safe, unless very large quantities of sewage
are present; generally speaking, such a depth of soil is able to
filter satisfactorily the drainage of the limited number of people
which a driven well suffices to supply.
[Illustration: FIG. 141.--A deep well with the piston in the water.]
Abundant water is rarely reached at less than 75 feet, and it would
usually be impossible to drive a pipe to such a depth. When a large
quantity of water is desired, strong machines drill into the ground
and excavate an opening into which a wide pipe can be lowered. I
recently spent a summer in the Pocono Mountains and saw such a well
completed. The machine drilled to a depth of 250 feet before much
water was reached and to over 300 feet before a flow was obtained
sufficient to satisfy the owner. The water thus obtained was to be the
sole water supply of a hotel accommodating 150 persons; the proprietor
calculated that the requirements of his guests, for bath, toilet,
laundry, kitchen, etc., and the domestics employed to serve them,
together with the livery at their disposal, demanded a flow of 10
gallons per minute. The ground was full of rock and difficult to
penetrate, and it required 6 weeks of constant work for two skilled
men to drill the opening, lower the suction pipe, and install the
pump, the cost being approximately $700.
[Illustration: FIG. 142.--Showing how drinking water can be
contaminated from cesspool _(c)_ and wash water _(w)_.]
The water from such a well is safe and pure except under the
conditions represented in Figure 142. If sewage or slops be poured
upon the ground in the neighborhood of the well, the liquid will seep
through the ground and some may make its way into the pump before it
has been purified by the earth. The impure liquid will thus
contaminate the otherwise pure water and will render it decidedly
harmful. For absolute safety the sewage discharge should be at least
75 feet from the well, and in large hotels, where there is necessarily
a large quantity of sewage, the distance should be much greater. As
the sewage seeps through the ground it loses its impurities, but the
quantity of earth required to purify it depends upon its abundance; a
small depth of soil cannot take care of an indefinite amount of
sewage. Hence, the greater the number of people in a hotel, or the
more abundant the sewage, the greater should be the distance between
well and sewer.
By far the best way to avoid contamination is to see to it that the
sewage discharges into the ground _below_ the well; that is, to dig
the well in such a location that the sewage drainage will be away from
the well.
In cities and towns and large summer communities, the sewage of
individual buildings drains into common tanks erected at public
expense; the contents of these are discharged in turn into harbors and
streams, or are otherwise disposed of at great expense, although they
contain valuable substances. It has been estimated that the drainage
or sewage of England alone would be worth $ 80,000,000 a year if used
as fertilizer.
A few cities, such as Columbus and Cleveland, Ohio, realize the need
of utilizing this source of wealth, and by chemical means deodorize
their sewage and change it into substances useful for agricultural and
industrial purposes. There is still a great deal to be learned on this
subject, and it is possible that chemically treated sewage may be made
a source of income to a community rather than an expense.
189. Pumps which Compress Air. The pumps considered in the preceding
Sections have their widest application in agricultural districts,
where by means of them water is raised to the surface of the earth or
is pumped into elevated tanks. From a commercial and industrial
standpoint a most important class of pump is that known as the
compression type; in these, air or any other gas is compressed rather
than rarefied.
Air brakes and self-opening and self-closing doors on cars are
operated by means of compression pumps. The laying of bridge and pier
foundations, in fact all work which must be done under water, is
possible only through the agency of compression pumps. Those who have
visited mines, and have gone into the heart of the underground
labyrinth, know how difficult it is for fresh air to make its way to
the miners. Compression pumps have eliminated this difficulty, and
to-day fresh air is constantly pumped into the mines to supply the
laborers there. Agricultural methods also have been modified by the
compression pump. The spraying of trees (Fig. 143), formerly done
slowly and laboriously, is now a relatively simple matter.
[Illustration: FIG. 143.--Spraying trees by means of a compression
pump.]
190. The Bicycle Pump. The bicycle pump is the best known of all
compression pumps. Here, as in other pumps of its type, the valves
open inward rather than outward. When the piston is lowered,
compressed air is driven through the rubber tubing, pushes open an
inward-opening valve in the tire, and thus enters the tire. When the
piston is raised, the lower valve closes, the upper valve is opened
by atmospheric pressure, and air from outside enters the cylinder; the
next stroke of the piston drives a fresh supply of air into the tire,
which thus in time becomes inflated. In most cheap bicycle pumps, the
piston valve is replaced by a soft piece of leather so attached to the
piston that it allows air to slip around it and into the cylinder, but
prevents its escape from the cylinder (Fig. 144).
[Illustration: FIG. 144.--The bicycle foot pump.]
191. How a Man works under Water. Place one end of a piece of glass
tube in a vessel of water and notice that the water rises in the tube
(Fig. 145). Blow into the tube and see whether you can force the water
wholly or partially down the tube. If the tube is connected to a small
compression pump, sufficient air can be sent into the tube to cause
the water to sink and to keep the tube permanently clear of water.
This is, in brief, the principle employed for work under water. A
compression pump forces air through a tube into the chamber in which
men are to work (Fig. 146). The air thus furnished from above supplies
the workmen with oxygen, and by its pressure prevents water from
entering the chamber. When the task has been completed, the chamber is
raised and later lowered to a new position.
[Illustration: FIG. 145.--Water does not enter the tube as long as we
blow into it.]
Figure 147 shows men at work on a bridge foundation. Workmen, tools,
and supplies are lowered in baskets through a central tube _BC_
provided with an air chamber _L_, having air-tight gates at _A_ and
_A'_. The gate _A_ is opened and workmen enter the air chamber. The
gate _A_ is then closed and the gate _A'_ is opened slowly to give the
men time to get accustomed to the high pressure in _B_, and then the
men are lowered to the bottom. Excavated earth is removed in a similar
manner. Air is supplied through a tube _DD_. Such an arrangement for
work under water is called a caisson. It is held in position by a mass
of concrete _EE_.
[Illustration: FIG. 146--The principle of work under water.]
[Illustration: FIG. 147--Showing how men can work under water.]
In many cases men work in diving suits rather than in caissons; these
suits are made of rubber except for the head piece, which is of metal
provided with transparent eyepieces. Air is supplied through a
flexible tube by a compression pump. The diver sometimes carries on
his back a tank of compressed air, from which the air escapes through
a tube to the space between the body and the suit. When the air has
become foul, the diver opens a valve in his suit and allows it to pass
into the water, at the same time admitting a fresh supply from the
tank. The valve opens outward from the body, and hence will allow of
the exit of air but not of the entrance of water. When the diver
ceases work and desires to rise to the surface, he signals and is
drawn up by a rope attached to the suit.
192. Combination of Pumps. In many cases the combined use of both
exhaust and compression pumps is necessary to secure the desired
result; as, for example, in pneumatic dispatch tubes. These are
employed in the transportation of letters and small packages from
building to building or between parts of the same building. A pump
removes air from the part of the tube ahead of the package, and thus
reduces the resistance, while a compression pump forces air into the
tube behind the package and thus drives it forward with great speed.