Hydraulics

1
Hydraulics

• and the use of liquid pressure

2
The important features of pressure in liquids

• Liquids will transmit pressure throughout the
  liquid, regardless of the shape of the container
• A force therefore can be applied wherever you
  want it
• The force can be multiplied according the the
  area of the pistons used to push down on the water

3
Examples of the use of hydraulics

• Car brakes
• Car jacks
• Fork lift trucks
• Lifts
• bulldozers
• Television cameras

4
How car brakes use hydraulics

• A small force on the brake pedal will act on a
  piston with a small area
• The small piston pushes against the brake fluid
• The pressure exerted is transmitted to all parts
  of the liquid
• The pressure acts against four bigger pistons
  with larger areas
• The large pistons will multiple the force and
  cause the brake pads to push against the wheels
• As pressure is transmitted equally throughout the
  liquid, each brake works evenly too

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Hydraulic brake

• The diagram shows a simple brake where a pedal
  will push down on the smaller master piston
• The force pushing down will put the liquid under
  pressure
• The pressure is transmitted through the liquid
  and against the slave piston
• The pressure causes the slave piston to exert a
  force where it is needed

6
Using the formula PF/A

• What is the pressure exerted on the liquid by the
  slave piston?
• Answer
• Pressure 10N / 5cm2
• 2 N/cm2
• Calculate the area of the slave piston that will
  lift a 100N load
• Answer
• Area force / pressure
• 100N / 2 N/cm2

10N
Slave piston
Master Piston Is 5 cm2
7
More questions on hydraulics
Master piston 10cm2
Slave piston 100cm2

• What will the force (F1) need to be to exert a
  pressure of 20 N/cm2 ?
• Calculate the weight (F2) that can be lifted by
  the slave piston.
• Answers 1. Force 20 N/cm2 x 10cm2 200N
• 2. Force 20 N/cm2 x 100cm3
  2000N

8
Summary of the principles of hydraulics

• Pressure is transmitted throughout a liquid
• A force may be applied anywhere to the liquid
• All hydraulic systems use a small master piston
  and a large slave piston
• A small force is used to create a very big force
• The small master piston is used to apply a force
• The slave piston is always bigger than the master
  piston
• The larger slave piston will multiply the
  original force put on the master piston

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