The Science Notebook
Gilbert Hydraulics - Part 2

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NOTE:  This book was published in 1920, and while many of the experiments and activitied here may be safely done as written, a few of them may not be considered particularly safe today.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.

 Pages 26-50

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 with 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.


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