26
HYDRAULIC AND PNEUMATIC
ENGINEERING
Illustrate
this method of starting a large siphon with the
apparatus shown in Fig. 42. The tee at the top
is connected with the metal tank, which here represents
the small storage tank, the large pail represents
the hillside well, and the long arm of the
siphon represents the pipe to the house.
Open
the house faucet, then open the tee connection
to the storage tank. Does the water flow down
the long arm of the siphon? Now close the house
faucet and observe that the water runs down the
short branch into the pail. Now close the tee
connection and open the house faucet. Does the
siphon run?
Note: The
storage
tank needs to be filled only when the siphon
stops, which may be only once or twice a year.
OTHER
USES OF THE SIPHON
EXPERIMENT
No. 12
To
illustrate
other uses of the siphon.
You
can siphon cider, or other liquids, out of a barrel by means
of a
rubber tube, (1) Fig. 43.
Illustrate
this as in (2) Fig 43, where the bottle represents the barrel
and
the neck of the bottle the bung hole.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 27
You
can siphon water out of your boat when it is
out of the water, (1) Fig. 44, but not when it
is afloat.
Use a
tumbler to
represent your boat and show that you can
siphon water out of it when it is out of the
water, (2) Fig. 44; but that you siphon water
into the boat if it is afloat, (3) Fig. 44,
because the water outside the boat is higher
than that inside.
You
can
siphon sand, gravel, and mud with the water
when necessary. Illustrate this by siphoning
sand or mud with the water from one
tumbler to another, Fig. 45.
28
HYDRAULIC AND PNEUMATIC
ENGINEERING
VELOCITY
OF FLOW
EXPERIMENT
No. 13
To
show that
the velocity of the
water in a siphon is
greater, the greater the
distance,
between the water
levels about the two arms.
Arrange
the siphon with a
small difference in water level as shown in (1) Fig.
46 and allow the water to run for 15 seconds; then
arrange it with a greater difference as in (2)
Fig. 46 and again allow the water to run for 15
seconds.
Does more
water
flow in (2) than in (1), that is, is
the velocity greater the greater the difference
in water level?
OTHER
SIPHONS
EXPERIMENT No.
14
To make and
operate a double siphon and a three legged siphon.
Start
a double siphon, (1) Fig. 47. Raise the tumblers one at a
time,
then two at a time.
Does
the water always flow from the upper tumbler or tumblers to
the lower and does it always stop flowing when the water
levels are
the same?
Start a three
legged siphon, (2) Fig. 47 and repeat the above experiments.
Are the results the same?
HYDRAULIC
AND PNEUMATIC
ENGINEERING 29
HOW TO
START A SMALL SIPHON
EXPERIMENT
No. 15
To illustrate
two ways of starting a small siphon.
You
have been starting your small siphon by sucking
air out of the long arm. You can also start it
as shown in (1) Fig. 48. Fill the siphon with
water to force the air out, close the ends with
your fingers, invert the siphon, and when the
upper end is under water in the upper tumbler
remove both fingers, (2) Fig. 48.
Glass
siphons used to siphon acid have a starting
tube on the outside arm, (3) Fig. 48.
Illustrate
the use of this by siphoning water out of a bottle
with the siphon shown in (4) Fig. 48. Place the
upper end in the water, close the
lower end, suck out a little air, and open the
lower end.
Practice
until you can start the siphon without getting water
(representing the acid) on your fingers or
lips.
30
HYDRAULIC AND PNEUMATIC
ENGINEERING
AN
ENCLOSED FOUNTAIN
EXPERIMENT
No. 16
To make and
operate an enclosed fountain.
Arrange
the apparatus as shown in (1) Fig. 49; this is
really a siphon with a bottle at the top. Start
with 2 inches of water in the bottle, insert
the stopper with tubes, invert the whole
apparatus, and put the short arm in the
tank filled with water.
Does
the water run and is there a fountain in the
bottle?
Arrange the
apparatus as in (2) Fig. 49, lift the tank
until there is about 2 inches of water in the bottle,
then arrange as shown.
Is
there a fountain in the bottle? Repeat both of
these experiments but use instead of the
bottle, a wide glass tube closed at the top with
a solid rubber stopper, (1) Fig. 50.
Make
two fountains as shown in (2) Fig. 50, one
enclosed and one in the open.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 31
ATMOSPHERIC PRESSURE
You
have made a number of experiments with siphons and you have
learned
how they act under different circumstances; you will now make
some
experiments which will help you to understand "why" they act
as
they do.
Water moves
through a siphon because it is forced to do so by atmospheric
pressure. You will first make a number of experiments to
show that the atmosphere exerts pressure and then you will
show how
and why this atmospheric pressure forces water through a
siphon.
AIR HAS WEIGHT
If
you were asked the question "How much does air
weigh?", you would probably answer off hand,
"Air has no weight at all." Air, however, has
considerable weight and it would take a very
strong man indeed to carry a weight equal to that
of the air in a house of medium size.
You
cannot weigh air with the apparatus you have at
hand but this is how it is done. The apparatus
used is illustrated in part in Fig. 51. The air
is pumped out of the flask, by means of
an air pump (not shown). The flask is then balanced
exactly on the fine scales and air is admitted to the flask
again.
It is found that the flask weighs more when it is filled with
air
than when it is empty, and this proves that air has weight.
A
cubic foot of air, at the surface of the earth and at ordinary
temperatures
is found in this way to weigh about 1 1/4 oz. This is not
a great weight, but when you come to calculate the weight of
air in
a house of medium size you find that it amounts to a very
great deal,
for example, make the following calculation:
A
house with a flat roof is 40
feet long, by 30 feet wide, by 24 feet high; find the weight
of air in it, neglecting the space occupied by partitions,
furniture, etc.
32
HYDRAULIC AND PNEUMATIC ENGINEERING
The
house contains 40 x 30 x 24
28,800 cubic feet of air, and since each cubic foot of air
weighs 1
1/4 ozs. the
house contains 28,800 x 1 1/4 = 36,000 oz. of air, and since
there are
16 ozs. in 1 lb.
36000
the house contains
-------- = 2250 lbs. of air.
16
The house contains 2250
lbs.
of air or over a ton of air (1 ton = 2000 lbs).
This is a very astonishing fact, especially to those of us
who
have never thought of air as having any weight at all.
AIR EXERTS PRESSURE
You
have learned from your lessons in Physical Geography at school
that
we live at the bottom of an ocean of air the atmosphere which
is
many miles deep; and when you remember that a cubic foot of
air
weighs 1 1/4 ozs. - you are in a position to see that the
atmosphere
must
exert great pressure on everything at the earth's surface.
It
has been found by repeated experiments that the atmosphere
exerts
a pressure of 14.7 lbs. (nearly 15 lbs.) on each square inch
of
everything
at the earth's surface. This means, for example, that on every
square inch of our bodies the atmosphere exerts a pressure of
14.7
lbs. We might think that this would crush our bodies, until we
remember
that everything inside our bodies exerts the same pressure
outward,
our blood, the air in our lungs, etc.
A
pressure of 14.7 lbs per square inch is equal to the pressure
at a
depth of 34 feet under water, that is, if the air could be
removed from
the earth and be replaced by water, it would require a depth
of 34
feet of water all over the earth to produce a pressure equal
to that
produced
by the atmosphere, namely, 14.7 lbs. per square inch.
You
will now make experiments to show that the atmosphere exerts
pressure
EXPERIMENT
No. 17
To show that
the atmosphere exerts pressure.
Make
a U tube, Fig. 52, run water through the tube until all the
air
bubbles are gone, then empty out part of the water until the U
HYDRAULIC
AND PNEUMATIC ENGINEERING 33
is
a little more than half full. The water in the two arms is
then at the
same level.
Now
apply your
lips to the coupling on one arm, suck out the
air, and close the clip. Do you observe that,
when you suck out the air, the water in the open
arm descends while that in the other arm rises?
The explanation is as
follows. Everything on the earth is at the
bottom of an ocean of air many miles deep, and
since this air has weight it exerts pressure on
everything on the earth. Now when both arms of
the U tube are open, the water level is the
same in both and the pressure of the air on the
water surface in each is the same, namely, the pressure
of the atmosphere. When you remove the air from
the closed side, however, you remove the pressure
of the atmosphere from this side and the pressure
of the atmosphere in the open side forces the
water down on the open side and up the closed side.
This experiment shows you that the atmosphere
exerts pressure.
Repeat
and
make experiments of your own.
EXPERIMENT
No. 18
To
show that
the atmosphere will support a column of water.
Arrange
the apparatus as in (1) Fig. 53, fill the tube with water,
close
one end with a clip and hold both ends in the position
illustrated.
Does
the water remain in the tube? It remains because the pressure
of
the atmosphere downward on the water in the open tube supports
the
column of water in the long tube.
Turn
the open end sidewise and then downward. Does the water remain
in the tube? It remains because the atmosphere exerts pressure
sidewise and upward and supports the water.
34
HYDRAULIC AND PNEUMATIC
ENGINEERING
Arrange
the apparatus as shown in (2) Fig. 53. Place the lower end of
the tube in a tumbler of water, stand on a chair, and suck the
air out
of the tube, then close the upper end.
Does
the water remain? It remains because the pressure of the
atmosphere
downward on the water in the tumbler supports the water
in
the tube.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 35
Lift
the tube out of the tumbler, (3) Fig. 53, and the water will
remain
in the tube because it is supported by the upward pressure of
the
atmosphere. This is possible only with very narrow tubes. The
tube
you have used in these experiments is about 6 feet long and
you
have shown that the atmosphere will support a column of water
6
feet high. If you had a tube of sufficient length you could
show that
the
atmosphere will support a column of water 34 feet high, but no
more.
36
HYDRAULIC AND PNEUMATIC
ENGINEERING
EXPERIMENT
No. 19
To prove that
it is the pressure of the atmosphere which lifts the water.
Make
a U tube (1) Fig. 54, with four tubes on one side and two on
the
other, fill it half full of water so that the two tubes on the
short
side are quite full, then close the top of this
side with a coupling and clip. Now suck the air
out of the long side. Do you observe that the water does
not move?
It does not
move
because although you have decreased the air pressure
in the long side, the atmosphere cannot get at the water in
the
short side to force it down.
Open
the top and repeat the experiment. Does the water move?
To
show this in another way. Fill a bottle (2) with water, place
a glass
tube in it and suck the air out of the tube. You observe that
when you
remove the air pressure from the water in the tube, the
atmospheric
pressure
on the water in the bottle forces the water up into your
mouth.
Now
fill the bottle quite full to exclude the air, and close it
with a one
hole rubber stopper which has one glass tube stuck in the
under side
and another in the upper side, (3). Suck the air out of the
upper tube.
Do you find that the water does not rise?
It
does not rise because although you have decreased the air
pressure
in the upper tube, the atmosphere cannot get at the water in
the
bottle
to force it into your mouth.
You
have proved here that it is the pressure of the atmosphere
which
lifts the water.
EXPERIMENT
No. 20
To show in
other ways that the atmosphere exerts pressure downward and
upward.
Fill
the bottle
with water, close the top with the hand, invert the bottle in
a pail of water, and remove the hand under water, (1) Fig. 55.
The
downward pressure of the atmosphere on the water surface in
the pail supports the water in the bottle.
Repeat
with the tumbler and tube as shown in (2) and (3).
Fill
the bottle with water, cover with a piece of paper, hold the
paper
on with the hand, invert the bottle and remove the hand, (4).
The
paper is held on by the upward pressure of the atmosphere.
Repeat
this experiment with a tumbler and tube, (5) and (6).
HYDRAULIC
AND PNEUMATIC ENGINEERING 37
EXPERIMENT
No. 21
To illustrate
two simple uses of atmospheric pressure.
DRINKING SODA WATER
When
you drink soda water through a straw or glass tube, (1) Fig.
56, you
simply produce a vacuum in your mouth and it is the atmosphere
which
forces the soda water into your mouth.
Illustrate
this with the apparatus, (2) Fig. 56 in which the bottle
represents
your mouth. Suck air out of the bottle, close clip 1, and open
clip
2.
Does the atmosphere
force water into the bottle? It forces soda water
into your mouth in the same way.
38
HYDRAULIC AND PNEUMATIC
ENGINEERING
POULTRY DRINKING FOUNTAINS
Fill a
tumbler witn water, place two pieces of lead
pencil across the top, cover with a
saucer, and invert tumbler and saucer, (1) Fig.
57.
Repeat with the
glass
bottle, (2).
Does the
water
run out only until the edge of the tumbler or
bottle is covered?
To
imitate the poultry drinking the water, suck water
out of the saucer by means of a glass tube until
the water is below the edge of the tumbler.
Does
air enter and water run out only until the edge
is again covered?
The
atmosphere supports the water.
Note: The
atmosphere could support the water in a
fountain 34 feet high but no higher.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 39
THE SIPHON (Continued)
THE "WHY"
OF THE SIPHON
The
reason "why"
water flows through a siphon is as follows: Suppose,
for example, you have a siphon, Fig. 58, closed
at the top with a clip. The atmospheric pressure
on the water in the right hand tumbler supports
only 1 foot of water, while in the left hand
tumbler it supports two feet of water.
Now
the atmospheric pressure on each is equal to
the pressure of a column of water 34 feet high,
therefore at the top of the siphon the pressure at
the right of the clip is
34 - 1= 33 feet of
water;
at the left of
the
clip is
34 - 2 = 32
feet of
water.
The
pressure at the right is greater than that at
the left and if the clip is opened the water
flows from right to left, that is, from the
upper tumbler to the lower tumbler.
This
is the "why" of the siphon.
40
HYDRAULIC AND PNEUMATIC
ENGINEERING
PUMPS
EXPERIMENT
No. 22
To
illustrate
the action of a syringe.
The
simplest kind of pump is the syringe, (A) Fig. 59. When you
lift
the plunger, there is a vacant space or partial vacuum left
below
the
plunger and the atmospheric pressure on the water in the
tumbler lifts
water into the syringe.
Illustrate
this by means of the syringe,
(B)
Fig. 59. Soap the plunger to make it slippery,
fill the syringe, lift the nozzle end and
squirt the water out, (C) Fig. 59.
HYDRAULIC
AND PNEUMATIC ENGINEERING 41
WATER
GUN SHOOTING
GAME
No. 6
The
syringe makes a fine water gun. Use it as follows :
(1)
Put up a bent piece of cardboard as a target and try to hit it
from
various
distances, (A) Fig. 60.
(2) See
who
can send the stream to the greatest height.
(3)
See who can send the stream to the greatest distance.
BIG
GUN
BATTLE
GAME
No. 7
Each
player here puts up the same number of lead or paper soldiers
and
at a given signal each starts to knock down the enemy soldiers
with
his water gun which here represents a large caliber gun firing
shells,
(B), Fig. 60.
The
winner is
the one who first knocks down all the enemy soldiers.
42
HYDRAULIC AND PNEUMATIC ENGINEERING
MACHINE
GUN BATTLE
GAME
No. 8
Each
player is behind a barricade which represents a trench (A),
Fig.
61 and is armed with a syringe which here represents a machine
gun.
The rules about wounded and killed are the same as in Game No.
2. The winning side is the one which first kills all the
enemy.
THE
DIABLO WHISTLE
GAME
No. 9
The
apparatus, Fig. 61 B makes a most uncanny
whistle when you blow into it as illustrated
and move the plunger up and down.
The
game is: (1) to make the most diabolical sound
you can; (2) to play the eight notes of an
octave as well as you can; (3) to play a tune
if you can.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 43
THE LIFT PUMP
Common
pumps are of two kinds: lift pumps, Figs. 62,
63, which lift water only to the spout; and force
pumps, Fig. 65, which force the water to any height
above the spout. Both types of pumps have two
valves which open upward.
The
Lift Pump, Fig. 62, has one valve S at the bottom
of the barrel C and another V in the plunger P.
The atmospheric pressure lifts water from the
well into the pump through the suction pipe T.
The
way the lift pump lifts water is illustrated in
drawings 1 to 6, Fig. 63.
Before
the pump is started the condition is that shown in (1): both
valves
are closed and the water level in the suction pipe is the same
as
that in the well.
When
the
plunger is raised as in (2), the air in the barrel beneath the
plunger is given more room, it expands and its pressure on the
valve S
is decreased; the air in the suction pipe then lifts the valve
S and
part
44
HYDRAULIC AND PNEUMATIC
ENGINEERING
of
it expands into the barrel; this decreases the air pressure on
the
water
in the suction pipe, and the atmospheric pressure on the water
in
the well forces some water into the suction pipe.
When
the plunger is shoved down as in (3), valve S closes and the
air
in the barrel is forced up through the plunger valve V.
When
the plunger is raised again as in (4), the operations
explained in
(2) take place again, and the atmospheric pressure on the
water in the
well forces more water into the suction pipe and also into the
barrel.
When
the plunger is shoved down again as in (5), valve S closes
again
and all the air in the barrel, with part of the water, is
forced up
through
the plunger valve V.
When
the plunger is raised again as in (6), the water above the
plunger
is lifted to the spout and the atmospheric pressure on the
water
in the well forces more water into the suction pipe and
barrel.
After
this (5) and (6) are repeated as long as the plunger is
operated.
EXPERIMENT
No. 23
To
make and
operate a Lift Pump.
Arrange
the apparatus as shown in (1) Fig. 64. Soap the
plunger, place the lower end of the narrow tube
in a glass of water, and move the plunger up
and down slowly.
Do you
find that: on the up stroke of the plunger,
water moves up through the narrow tube and
lower valve into the pump barrel; and on the
down stroke, the water remains at the same
height because the lower valve closes, but as
the plunger moves down, the air and water pass
through the plunger valve? Do you notice that on
the succeeding up strokes, water rises and
flows over the top, and on succeeding down
strokes it moves through the plunger valve?
HYDRAULIC
AND PNEUMATIC
ENGINEERING 45
Attach
three or four narrow tubes below the pump barrel to make the
suction pipe longer, (2) Fig. 64, and repeat the experiment.
Attach
all the narrow tubes and the rubber tube to the pump barrel
and
repeat the experiment.
Do
you find that the atmospheric pressure on the water in the
tumbler
lifts the water into the pump barrel when you move the plunger
up?
The pressure of the
atmosphere is equal to the pressure of a column of
water 34 feet high and no more, therefore, a pump must be
placed at
a less height than 34 feet above the water it is pumping and
in
practice
the height is usually 25 feet or less.
THE FORCE PUMP
The
force pump, Fig. 65, has a valve A at the
bottom of the barrel, but the plunger V is
solid, the discharge pipe leaves the barrel
below the plunger, and the second valve B is
below an air chamber at one side; also the top
of the barrel is closed by an inverted U shaped
leather ring which surrounds the plunger and prevents
the water from escaping.
It
pumps water in exactly the same way as does the
lift pump.
The ball
valves
shown here have the advantage that they wear
evenly because they turn continuously. Both
lift pumps and force pumps can have either ball
valves or common flap valves.
The
air chamber protects the force pump from
excessive strain because the air compresses
under excessive pressure; it also tends to keep
a steady stream in the discharge pipe because
the compressed air continues to force the water
out of the air chamber while the plunger is making
the up stroke.
46
HYDRAULIC AND PNEUMATIC
ENGINEERING
EXPERIMENT
No. 24
To make and
operate a Force Pump.
Arrange
the apparatus as shown in (1), Fig. 66. Soap the plunger,
place
the suction pipe in a tumbler of water, pour a little water
above the
plunger to make sure it is air tight; and move the plunger up
and down.
Do you observe that on
the
up stroke water enters the barrel through the
valve, and that on the down stroke it is forced into the side
tube
through
its valve? If the valves are not quite air tight pour water
into both
tubes to cover them.
Make
an air chamber in the side tube by inserting a short narrow
glass
tube below the upper stopper, (2), Fig. 66.
Operate
the force pump.
Do you
observe that the air is slightly compressed in this chamber,
on
the down stroke of the plunger, and that this compressed air
keeps the
water flowing for a short time after the stroke is finished.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 47
Repeat
the experiment using short quick strokes of the plunger.
Do
you find that you can keep a fairly steady stream issuing from
the
nozzle?
Water can be
forced
to any height in the discharge pipe of a force pump
but the suction lift should not be more than about 25 feet,
that is
the pump plunger must be within 25 feet vertically of the
water it is
pumping.
EXPERIMENT
NO 25
To show how
water is pumped into an elevated
tank.
A
lift pump can be
used to pump water into an elevated tank only
if the top of the tank is not over 25 feet (34
feet theoretically) above the water in the well.
If the tank is higher than this, a force pump
must be used.
Illustrate
this use of a force pump by means of the
apparatus shown in Fig. 67. Pump water into the
tank and then draw off some through the faucet
below. This equipment represents a complete
water supply system.
FORCE
PUMP CONTEST
GAME
No. 10
The
game
here is to see who can force the water to the
greatest height and to the greatest distance.
Tie the stoppers in with cord and stretched
rubber bands. Use the apparatus shown in (2)
Fig. 66.
48
HYDRAULIC AND PNEUMATIC
ENGINEERING
HYDRAULIC APPLIANCES
The
hydraulic press (A), hydraulic elevator (B).
and hydraulic lift lock (C), Fig. 68, are each
operated by means of pressure exerted on water,
and in order to understand them you will
first illustrate Pascal's law which tells how pressure
is transmitted by water.
HYDRAULIC
AND PNEUMATIC
ENGINEERING 49
PASCAL'S LAW
Pascal's
Law is: Pressure exerted on a liquid is transmitted equally
and
undiminished in all directions.
This
law is usually illustrated by means of the apparatus shown in
(1)
Fig. 69. It is a syringe with a glass bulb which has five
nozzles of
the same size and in the same plane. When the
syringe, filled with water, is held with the
nozzles horizontal and the plunger is forced in, the streams
which issue from the nozzles are of exactly the same length.
This
shows that pressure exerted on water is transmitted equally in
all
directions.
This is very surprising because since the plunger exerts the
pressure in the direction of the front stream we might expect
this
stream
to be the longest: we find, however, that they all have the
same
length.
EXPERIMENT
No.
26
To show that
pressure on water is transmitted equally in all directions.
Use
the apparatus (2) Fig. 69. Fill the tube with water, insert
the
plunger,
hold the nozzles horizontal, and force the plunger
in steadily.
Are
the streams of equal length?
50
HYDRAULIC AND PNEUMATIC
ENGINEERING
Repeat
with the apparatus (3) Fig. 69.
With
(2) Fig. 69 you show that the pressure is transmitted equally
forward
and sidewise, and with (3) Fig. 69, that it is transmitted
equally in
both sidewise directions.
This
experiment shows that water transmits pressure equally in all
directions.
The experiments described below show that it transmits it
equally
and undiminished in
all directions.
The
two cylinders and connecting pipe, Fig. 70, are
filled with water and each cylinder is fitted
in with a water tight piston ; the area
of cross section of the small piston is
1 sq. in. and of the large piston, 100 sq. in.
If now a pressure of 1 Ib is exerted on the
small piston, it is found that this
pressure is transmitted equally and
undiminished by the water, and that therefore,
the upward pressure on the large piston is 1
lb. on each sq. in. or the total pressure
upward is 100 lbs. That is, 1 lb. on the small
piston supports 100 lbs. on the large piston.
This
is very surprising and it looks as if we were
getting something for nothing. This is not so,
however, because if the small piston is moved down
1 inch, the large piston moves up only 1/100 of
an inch. That is, "what is gained in force is lost
in distance moved."
The
hydrostatic bellows, Fig. 71, is an apparatus of
this kind and it illustrates Pascal's law beautifully.
It consists of two disks of wood connected by a
water-proof canvas cylinder to make a
collapsible drum. A small pipe passes through
the
lower disk and opens into the drum.
If
now the drum is filled with water and a man stands
on the upper disk, it is found that a very small
amount of water, AB, in the pipe will support his weight.
The
Science Notebook
