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How hydraulic systems work

Module by: Siyavula Uploaders. E-mail the author

TECHNOLOGY

Grade 9

HYDRAULIC AND PNEUMATIC SYSTEMS

Module 10

HOW HYDRAULIC SYSTEMS WORK

ACTIVITY 1:

To be able to describe how a hydraulic system works

[LO 1.3, 2.3]

Pneumatic and hydraulic systems are systems that exert control so that the input-output relationship changes in such a way that tasks can be done faster with less force.

There are two kinds of hydraulic systems:

An open hydraulic system contains a liquid that is placed under pressure, for example water and a garden hose with a pressure nozzle.The system can also contain water that flows in a pipe when there is a difference in pressure, between the two ends of the pipe. Just think of the great advantage this device offers to farmers.

A closed hydraulic system: This consists of a sealed unit containing two pistons that are connected to each other by means of a pipe or reservoir. An input force on the smaller piston is transmitted in all directions by the liquid and imparts an output force on the larger piston. Because the pressure is transmitted in all directions in the liquid, the larger piston can have a greater output because of its larger area. All hydraulic systems work according to this principle.

Figure 1
Figure 1 (Picture 1.png)

A syringe can also be used to illustrate the way in which a hydraulic system works.

Figure 2
Figure 2 (graphics1.png)

The piston on which the pressure is exerted, is called the master, or input, piston and the syringe that experiences the effect, is called the server, or output, piston.

In your own words, describe how a hydraulic system works. Also give two examples of hydraulic systems that are commonly used.

ACTIVITY 2:

To examine the transmission of pressure in a hydraulic system and to be able to describe it

[LO 1.3, 2.3]

You need the following items for this research:

2 x 10 mℓ plastic syringes marked A and B

1 x plastic tube

Connect the cylinders as indicated in the figure and fill the system with water.

Wet both ends of the plastic tube and fix it to the syringes as indicated in the drawing.

Figure 3
Figure 3 (graphics2.png)

1. Push the plunger of cylinder I in to a level of 2 cm deep. Make a note of your observation of the distance output in cylinder B.

2. Push the plunger of cylinder B in to a level of 2 cm deep. Make a note of the distance output in syringe A.

3. Has any mechanical advantage been observed?

4. Summary: The transmission of pressure in a hydraulic system.

ACTIVITY 3:

To examine the functioning of a pneumatic system and to compare it with that of a hydraulic system

[LO 1.3, 2.3]

Dry plastic syringes A and B and repeat the investigation done in Activity 2. This time draw up air into the cylinders instead of water.

1. What similarities exist between hydraulic and pneumatic systems?

2. What difference is there between the systems with regard to the effective transmission of the pressure?

ACTIVITY 4:

To examine the influence of the diameter of the piston disc on distance and power output and to be able to discuss it

[LO 1.3, 2.3]

You will need the following items for this investigation:

1 x 10 mℓ cylinder marked A

1 x 20 mℓ cylinder marked C

a tube

Connect the cylinders as indicated in the figure and fill the system with water.

Figure 4
Figure 4 (graphics3.png)

1. Push the plunger of cylinder A in so that it goes in 2 cm. Make a note of your observation of the distance output in cylinder C.

2. Push the plunger of cylinder C in so that it goes in 2 cm. Make a note of your observation of the distance output in syringe A.

3. What do you think will happen if the hydraulic system is replaced by a pneumatic system?

4. Replace the water with cooking oil and make a note of the difference / similarity in the functioning of the system.

5. Explain the advantages of using oil rather than water.

6. Summary of the results observed.

ACTIVITY 5:

To examine the connection between output distance, output force and diameter of the cylinder of hydraulic and pneumatic systems consisting of three cylinders

[LO 1.3, 2.3]

You need the following items to conduct this experiment:

1 x 20 mℓ syringe marked C

2 x 10 mℓ syringes marked A and B

3 x connecting tubes of the same size

1 x T connection

Fill syringe C with 10 mℓ water and fill both syringes A and B with 5 mℓ water.

Connect the syringes as indicated in the sketch.

Figure 5
Figure 5 (graphics4.png)

1. Press the plunger of syringe C in 2 cm and indicate the distance output of syringes A and B.

2. Write down your observation.

Summary of the findings of Activities 1 to 5

Assessment

Table 1
Learning outcomes(LOs)
 
LO 1
TECHNOLOGICAL PROCESSES AND SKILLSThe learner will be able to apply technological processes and skills ethically and responsibly using appropriate information and communication technology.
Assessment standards(ASs)
 
We know this when the learner:
investigates:1.1 identifies and explains a problem, need or opportunity from a real-life context, and investigates the context, the nature of the need, the environmental situation, and the people concerned;
1.2 analyses existing products relevant to an identified problem, need or opportunity based on:safety;fitness for purpose;cost;manufacturing method;
1.3 develops and performs practical testing proce­dures to determine or compare the suitability or fitness for purpose of relevant properties of materials, electrical or mechanical systems, structures, processes or finished products;
1.4 uses a variety of available technologies and methods to:locate (e.g. use library referencing system, database searches, indexes);collect (e.g. questionnaires, data collection forms, requests for information, information, searches, literature surveys);compare;sort;verify;evaluate (e.g. cross-checking different sources or resources);store information (e.g. filing systems, indexes);
designs:1.5 writes or communicates a short and clear statement or a design brief for the development of a product or system related to a context, problem, need or opportunity that has been identified by self;
1.6 lists product and design specifications and constraints for a solution based on all of the design key words listed below:purpose: function, what product will do;appearance and aesthetics: form, colour, shape, feel;
1.7 generates a range of possible solutions that are significantly different from each other, and that show clear links to the design brief and the specifications and constraints;
1.8 chooses possible solutions based on well-reasoned argument related to the specifications and personal options, develops a chosen idea using graphics;
makes:1.9 develops plans for making that include all of the following:resource lists;formal drawings showing dimensions or quantities;manufacturing sequence;
1.10 chooses and uses appropriate tools and materials to make designed products with precision and control by measuring, marking, cutting or separating, shaping or forming, joining or combining, and finishing a range of materials accurately and efficiently;
1.11 uses measuring and checking procedures while making to monitor quality and changes, and adapts designs in response to practical difficulties encountered when making products;
1.12 demonstrates knowledge and understanding of safe working practices and efficient use of safe working practices and efficient use of materials and tools.
LO 2
TECHNOLOGICAL KNOWLEDGE AND UNDERSTANDINGThe learner will be able to understand and apply relevant technological knowledge ethically and responsibly.
We know this when the learner:
systems and control:2.3 demonstrates knowledge and understanding of interacting mechanical systems and sub-systems by practical analysis and represents them using systems diagrams:gear systemsbelt drive or pulley systems with more than one stage;mechanical control mechanisms (e.g. ratchet and pawl, cleats);pneumatic or hydraulic systems that use restrictorsone-way valves;systems where mechanical, electrical, or pneumatic or hydraulic systems are combined.

Memorandum

ACTIVITY 1

A hydraulic system consists of two cylinders that are connected. Each cylinder contains a piston/plunger with a specific diameter and amount of liquid.

When the plunger is pushed in or drawn out, it causes a change in pressure that is propagated through the liquid. This pressure creates the mechanical force or kinetic advantage.

ACTIVTY 2

1. distance of delivery of piston B is 2 cm

2. the same/similar

3. no, the force/power is transferred with equal advantage (advantage =1)

4. The pressure in cylinder A is transferred to cylinder B.

ACTIVITY 3

1. The pressure is propagated from cylinder A to cylinder B.

2. The liquid/fluid propagates the pressure better than the air and offers greater resistance.

ACTIVITY 4

1. 1 cm

2. 4 cm

3. k will propagate less easily and the distance of delivery will not be exactly 1 and 4 cm respectively because air is compressible.

4. & 5. See synopsis

6. SYNOPSIS

With a piston that has a small diameter, the distance of delivery is great.

With a piston that has a greater diameter, the distance of delivery is small.

There will be better propagation of the pressure in the cylinder.

The density is greater and the force/power will therefore be propagated better than in water.

ACTIVITY 5

1. 2 cm at A and B respectively

2. The output of two 10-ml syringes each filled with 5 ml of water will be the same as the output of one 20-ml syringe containing 10 ml of water. The larger 20-ml syringe can control two 10-ml syringes if it contains twice (2 x 10 ml) the amount of water.

SYNOPSIS: ACTIVITY 1 – 5

A small force on a small piston/plunger produces a great force on a large piston/plunger.

A small piston/plunger will move over a large distance and a large piston/plunger over a small distance.

The larger piston/plunger is able to control a number of smaller pistons/plungers if its volume is equal to the sum of the volumes of the smaller pistons/plungers and the amount of water in the larger piston/plunger is equal to the combined volumes of the water in the smaller pistons/plungers.

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