Hydraulics

and the use of liquid pressure

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

Examples of the use of hydraulics

• Car brakes

• Car jacks

• Fork lift trucks

• Lifts

• bulldozers

• Television cameras

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

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

Using the formula P=F/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

Master PistonIs 5 cm2

10N

Slave piston

More questions on hydraulics

1. What will the force (F1) need to be to exert a pressure of 20 N/cm2 ?

2. 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

Master piston = 10cm2 Slave piston

= 100cm2

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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