INTRODUCTION

Ever since the invention of the wheel, if there

has been "go" there has been a need for "whoa."

As the level of technology of human

transportation has increased, the mechanical

devices used to slow down and stop vehicles has

also become more complex. In this report I will

discuss the history

of vehicularbraking technology and possible

future developments. 

Before there was a "horse-less carriage," wagons,

and other animal drawn vehicles relied on the

animal’s power to both accelerate and decelerate

the vehicle. Eventually there was the development

of supplemental braking systems consisting of a

hand lever to push a wooden friction pad directly

against the metal tread of the wheels. In wet

1

conditions these crude brakes would lose any

effectiveness. 

The early years of automotive development were an

interesting time for the designing engineers, "a

period of innovation when there was no

established practice and virtually all ideas were

new ones and worth trying. Quite rapidly,

however, the design of many components stabilized

in concept and so it was with brakes; the

majority of vehicles soon adopted drum brakes,

each consisting of two shoes which could be

expanded inside a drum." 

In this chaotic era is the first record of

the disk brake. Dr. F.W. Lanchester patented a

design for a disk brake in 1902 in England. It

was incorporated into the Lanchester car produced2

between 1906 through 1914. These early disk

brakes were not as effective at stopping as the

contemporary drum brakes of that time and were

soon forgotten. Another important development

occurred in the 1920’s when drum brakes were used

at all four wheels instead of a single brake to

halt only the back axle and wheels such as on the

Ford model T. The disk brake was again utilized

during World War II in the landing gear of

aircraft. The aircraft disk brake system was

adapted for use in automotive applications, first

in racing in 1952, then in production automobiles

in 1956. United States auto manufacturers did not

start to incorporate disk brakes in lower priced

non-high-performance cars until the late 1960’s. 

3

HOW BRAKES WORK

We all know that pushing down on the brake pedal

slows a car to a stop. But how does this happen?

How does your car transmit the force from your

leg to its wheels? How does it multiply the force

so that it is enough to stop something as big as

a car?

BRAKE BASICS

When you depress your brake pedal, your car

transmits the force from your foot to its brakes

through a fluid. Since the actual brakes require

a much greater force than you could apply with

your leg, your car must also multiply the force

of your foot. It does this in two ways: 

• Mechanical advantage (leverage) 

• Hydraulic force multiplication 

The brakes transmit the force to the tires using

friction, and the tires transmit that force to 4

the road using friction also. Before we begin our

discussion on the components of the brake system,

let's cover these thre

e

principles: 

Leverage 

5

Hydraulics 

Friction 

System operation[

In a hydraulic brake system, when the brake pedal

is pressed, a pushrod exerts force on the

piston(s) in the master cylinder, causing fluid

from the brake fluid reservoir to flow into a

pressure chamber through a compensating port.

This results in an increase in the pressure of

the entire hydraulic system. This forces fluid

through the hydraulic lines toward one or more

calipers where it acts upon one or two caliper

pistons sealed by one or more seated O-rings

which prevent the escape of any fluid from around

the piston.

The brake caliper pistons then apply force to the

brake pads, which pushes them against the

spinning rotor, and the friction between the pads

and the rotor causes a braking torque to be

6

generated, slowing the vehicle. Heat generated by

this friction is either dissipated through vents

and channels in the rotor or conducted through

the pads, which are made of specialized heat-

tolerant materials such as kevlar or sintered

glass.

Subsequent release of the brake pedal/lever

allows spring(s) to return the master piston(s)

back into position. This relieves the hydraulic

pressure on the caliper, allowing the brake

piston in the caliper assembly to slide back into

its housing and the brake pads to release the

rotor.

The hydraulic braking system is designed as a

closed system: unless there is a leak in the

system, none of the brake fluid enters or leaves

it, nor does the fluid get consumed through use.

An example of a hydraulic brake system[

Hydraulic brakes transfer energy to stop an 7

object, normally a rotating axle. In a very

simple brake system, with just two cylinders and

a disc brake, the cylinders could be connected

via tubes, with a piston inside the cylinders.

The cylinders and tubes are filled with

incompressible oil. The two cylinders have the

same volume, but different diameters, and thus

different cross-section areas. The one with the

smallest diameter is called the master cylinder.

The spinning disc brake will be placed down

at[clarification needed] the piston with the larger cross-

section. Suppose the diameter of the master

cylinder is half the diameter of the slave

cylinder, so the master cylinder has a cross-

section four times smaller. Now, if the piston in

the master cylinder is pushed down 40 mm, with

10 newtons (N) of force, the slave piston will

then move 10 mm, with a force of 40 N.

This force can be further increased by inserting

8

a lever connected between the master piston, a

pedal, and a pivot point. If the distance from

the pedal to the pivot is three times the

distance from the pivot to the connected piston,

then it multiplies the pedal force by a factor of

3, when pushing down on the pedal. Now, if we

push the pedal 120 mm down, with 10 N of force, a

force of 30 N will then be applied to the master

piston, and the slave piston will move the brake

pad by 10 mm, with a force of 120 N.

Component specifics[

(For typical light duty automotive braking

systems)

The brake pedal is a simple lever. One end is

attached to the framework of the vehicle, a

pushrod extends from a point along its length,

and the foot pad is at the other end of the

lever. The rod either extends to the master

cylinder (manual brakes) or to the vacuum booster

9

(power brakes).

In a four-wheel car, the FMVSS Standard 105,

1976; requires the master cylinder is divided

internally into two sections, each of which

pressurizes a separate hydraulic circuit. Each

section supplies pressure to one circuit.

Passenger vehicles typically have either a

front/rear split brake system or a diagonal split

brake system (the master cylinder in a motorcycle

or scooter may only pressurize a single unit,

which will be the front brake).

A front/rear split system uses one master

cylinder section to pressurize the front caliper

pistons and the other section to pressurize the

rear caliper pistons. A split circuit braking

system is now required by law in most countries

for safety reasons; if one circuit fails, the

other circuit can stop the vehicle.

Diagonal split systems were used initially

10

on American Motors automobiles in the 1967

production year. The right front and left rear

are served by one actuating piston while the left

front and the right rear are served, exclusively,

by a second actuating piston (both pistons

pressurize their respective coupled lines from a

single foot pedal). If either circuit fails, the

other, with at least one front wheel braking (the

front brakes provide most of the speed reduction)

remains intact to stop the mechanically-damaged

vehicle. Just before 1970, diagonally split

systems had become universal for automobiles sold

in the United States. This system was developed

with front wheel drive cars suspension design to

maintain better control and stability during a

system failure.

The diameter and length of the master cylinder

has a significant effect on the performance of

the brake system. A larger diameter master

11

cylinder delivers more hydraulic fluid to the

caliper pistons, yet requires more brake pedal

force and less brake pedal stroke to achieve a

given deceleration. A smaller diameter master

cylinder has the opposite effect.

A master cylinder may also use differing

diameters between the two sections to allow for

increased fluid volume to one set of caliper

pistons or the other.

Power brakes[

12

The vacuum booster or vacuum servo is used in

most modern hydraulic brake systems which contain

four wheels. The vacuum booster is attached

between the master cylinder and the brake pedal

and multiplies the braking force applied by the

driver. These units consist of a hollow housing

with a movable rubber diaphragm across the

center, creating two chambers. When attached to

the low-pressure portion of the throttle body or

intake manifold of the engine, the pressure in

both chambers of the unit is lowered. The

equilibrium created by the low pressure in both

chambers keeps the diaphragm from moving until

the brake pedal is depressed. A return spring

keeps the diaphragm in the starting position

until the brake pedal is applied. When the brake

pedal is applied, the movement opens an air valve

which lets in atmospheric pressure air to one

chamber of the booster. Since the pressure

13

becomes higher in one chamber, the diaphragm

moves toward the lower pressure chamber with a

force created by the area of the diaphragm and

the differential pressure. This force, in

addition to the driver's foot force, pushes on

the master cylinder piston. A relatively small

diameter booster unit is required; for a very

conservative 50% manifold vacuum, an assisting

force of about 1500 N (200n) is produced by a

20 cm diaphragm with an area of 0.03 square

meters. The diaphragm will stop moving when the

forces on both sides of the chamber reach

equilibrium. This can be caused by either the air

valve closing (due to the pedal apply stopping)

or if "run out" is reached. Run out occurs when

the pressure in one chamber reaches atmospheric

pressure and no additional force can be generated

by the now stagnant differential pressure. After

the run out point is reached, only the driver's

14

foot force can be used to further apply the

master cylinder piston.

The fluid pressure from the master cylinder

travels through a pair of steel brake tubes to

a pressure differential valve, sometimes referred

to as a "brake failure valve", which performs two

functions: it equalizes pressure between the two

systems, and it provides a warning if one system

loses pressure. The pressure differential valve

has two chambers (to which the hydraulic lines

attach) with a piston between them. When the

pressure in either line is balanced, the piston

does not move. If the pressure on one side is

lost, the pressure from the other side moves the

piston. When the piston makes contact with a

simple electrical probe in the center of the

unit, a circuit is completed, and the operator is

warned of a failure in the brake system.

From the pressure differential valve, brake

15

tubing carries the pressure to the brake units at

the wheels. Since the wheels do not maintain a

fixed relation to the automobile, it is necessary

to use hydraulic brake hose from the end of the

steel line at the vehicle frame to the caliper at

the wheel. Allowing steel brake tubing to flex

invites metal fatigue and, ultimately, brake

failure. A common upgrade is to replace the

standard rubber hoses with a set which are

externally reinforced with braided stainless-

steel wires; these have negligible expansion

under pressure and can give a firmer feel to the

brake pedal with less pedal travel for a given

braking effort.

Special considerations[

Air brake systems are bulky, and require air

compressors and reservoir tanks. Hydraulic

systems are smaller and less expensive.

Hydraulic fluid must be non-compressible.

16

Unlike air brakes, where a valve is opened and

air flows into the lines and brake chambers until

the pressure rises sufficiently, hydraulic

systems rely on a single stroke of a piston to

force fluid through the system. If any vapor is

introduced into the system it will compress, and

the pressure may not rise sufficiently to actuate

the brakes.

Hydraulic braking systems are sometimes subjected

to high temperatures during operation, such as

when descending steep grades. For this reason,

hydraulic fluid must resist vaporization at high

temperatures.

Water vaporizes easily with heat and can corrode

the metal parts of the system. If it gets into

the brake lines, it can degrade brake performance

dramatically. This is why light oils are often

used as hydraulic fluids. Oil displaces water,

protects plastic parts against corrosion, and can

17

tolerate much higher temperatures before

vaporizing.

"Brake fade" is a condition caused by overheating

in which braking effectiveness reduces, and may

be lost. It may occur for many reasons. The pads

which engage the rotating part may become

overheated and "glaze over", becoming so smooth

and hard that they cannot grip sufficiently to

slow the vehicle. Also, vaporization of the

hydraulic fluid under temperature extremes or

thermal distortion may cause the linings to

change their shape and engage less surface area

of the rotating part. Thermal distortion may also

cause permanent changes in the shape of the metal

components, resulting in a reduction in braking

capability that requires replacement of the

affected parts

18

LEVERAGE

The pedal is designed in such a way that it can

multiply the force from your leg several times

before any force is even transmitted to the brake

fluid. 

In the figure above, a force F is being applied

to the left end of the lever. The left end of the

lever is twice as long (2X) as the right end (X).

Therefore, on the right end of the lever a force

of 2F is available, but it acts through half of

the distance (Y) that the left end moves (2Y).

Changing the relative lengths of the left and

right ends of the lever changes the multipliers. 

HYDRAULIC SYSTEMS

The basic idea behind any hydraulic system is 19

very simple: Force applied at one point is

transmitted to another point using an

incompressible fluid, almost always an oil of

some sort. Most brake systems also multiply the

force in the process 

FRICTION

Friction is a measure of how hard it is to slide

one object over another. Take a look at the

figure below. Both of the blocks are made from

the same material, but one is heavier. I think we

all know which one will be harder for the

bulldozer to push. 

Friction force versus weight

To understand why this is, let's take a close

look at one of the blocks and the table: 

Even though the blocks look smooth to the naked

eye, they are actually quite rough at the 20

microscopic level. When you set the block down on

the table, the little peaks and valleys get

squished together, and some of them may actually

weld together. The weight of the heavier block

causes it to squish together more, so it is even

harder to slide. 

Different materials have different microscopic

structures; for instance, it is harder to slide

rubber against rubber than it is to slide steel

against steel. 

The type of material determines the coefficient

of friction, the ratio of the force required to

slide the block to the block's weight. If the

coefficient were 1.0 in our example, then it

would take 100 pounds of force to slide the 100-

pound (45 kg) block, or 400 pounds (180 kg) of

force to slide the 400-pound block. If the

coefficient were 0.1, then it would take 10

pounds of force to slide to the 100-pound block

or 40 pounds of force to slide the 400-pound 21

block. 

So the amount of force it takes to move a given

block is proportional to that block's weight. The

more weight, the more force required. This

concept applies for devices like brakes and

clutches, where a pad is pressed against a

spinning disc. The more force that presses on the

pad, the greater the stopping force. 

A SIMPLE BRAKE SYSTEM

The distance from the pedal to the pivot is four

times the distance from the cylinder to the

pivot, so the force at the pedal will be

increased by a factor of four before it is

transmitted to the cylinder. 

The diameter of the brake cylinder is three times

the diameter of the pedal cylinder. This further

multiplies the force by nine. All together, this

system increases the force of your foot by a

factor of 36. If you put 10 pounds of force on 22

the pedal, 360 pounds (162 kg) will be generated

at the wheel squeezing the brake pads. 

There are a couple of problems with this simple

system. What if we have a leak? If it is a slow

leak, eventually there will not be enough fluid

left to fill the brake cylinder, and the brakes

will not function. If it is a major leak, then

the first time you apply the brakes all of the

fluid will squirt out the leak and you will have

complete brake failure. 

TYPES OF BRAKES

1. DRUM BRAKES

2. DISC BRAKES (CALLIPER BRAKES)

DRUM BRAKES 

The drum brake has two brake shoes and a piston.

When you hit the brake pedal, the piston pushes

the brake shoes against the drum This is where it23

gets a little more complicated. as the brake

shoes contact the drum, there is a kind of

wedging action, which has the effect of pressing

the shoes into the drum with more force. The

extra braking force provided by the wedging

action allows drum brakes to use a smaller piston

than disc brakes. But, because of the wedging

action, the shoes must be pulled away from the

drum when the brakes are released. This is the

reason for some of the springs. Other springs

help hold the brake shoes in place and return the

adjuster arm after it actuates. 

DISK BRAKE BASICS:-

The disk brake has a metal disk instead of a

drum. It has a flat shoe, or pad, located on each

side of the disk. To slow or stop the car, these

two flat shoes are forced tightly against the

rotating disk, or rotor. Fluid pressure from the 24

master cylinder forces the pistons to move in.

This action pushes the friction pads of the shoes

tightly against the disk. The friction between

the shoes and the disk slows and stops the disk.

ADVANTAGES OF DISC BRAKES OVER DRUM BRAKES

As with almost any artifact of technology, drum

brakes and disk brakes both have advantages and

disadvantages. Drum brakes still have the edge in

cheaper cost and lower complexity. This is why

most cars built today use disk brakes in front

but drum brakes in the back wheels, four wheel

disks being an extra cost option or shouted as a

high performance feature. Since the weight shift

of a decelerating car puts most of the load on

the front wheels, the usage of disk brakes on

only the front wheels is accepted manufacturing

practice. 

Drum brakes had another advantage compared to

early disk brake systems. The geometry of the 25

brake shoes inside the drums can be designed for

a mechanical self-boosting action. The rotation

of the brake drum will push a leading shoe brake

pad into pressing harder against the drum. Early

disk brake systems required an outside mechanical

brake booster such as a vacuum assist or

hydraulic pump to generate the pressure for

primitive friction materials to apply the

necessary braking force. 

All friction braking technology uses the process

of converting the kinetic energy of a vehicle’s

forward motion into thermal energy: heat. The

enemy of all braking systems is excessive heat.

Drums are inferior to disks in dissipating

excessive heat:

"The common automotive drum brake consists

essentially of two shoes which may be expanded

against the inner cylindrical surface of a drum.

The greater part of heat generated when a brake

is applied has to pass through the drum to its 26

outer surface in order to be dissipated to

atmosphere, and at the same time (the drum is)

subject to quite severe stresses due to the

distortion induced by the opposed shoes acting

inside the open ended drum.

The conventional disk brake, on the other hand,

consists essentially of a flat disk on either

side of which are friction pads; equal and

opposite forces may be applied to these pads to

press their working surfaces into contact with

the braking path of the disks. The heat produced

by the conversion of energy is dissipated

directly from the surfaces at which it is

generated and the deflection of the braking path

of the disk is very small so that the stressing

of the material is not so severe as with the

drum." 

The result of overheated brakes is brake 27

fade...the same amount of force at the pedal no

longer provides the same amount of stopping

power. The high heat decreases the relative

coefficient of friction between the friction

material and the drum or disk. Drum brakes also

suffer another setback when overheating: The

inside radii of the drum expands, the brake shoe

outside radii no longer matches, and the actual

contact surface is decreased. 

Another advantage of disk brakes over drum brakes

is that of weight. There are two different areas

where minimizing weight is important. The first

is unsprung weight. This is the total amount of

weight of all the moving components of a car

between the road and the suspension mounting

points on the car’s frame. 

Auto designs have gone to such lengths to reduce

unsprung weight that some, such as the E-type

Jaguar, moved the rear brakes inboard, next to 28

the differential, connected to the drive shafts

instead of on the rear wheel hubs. The second

"weighty" factor is more of an issue on

motorcycles: gyroscopic weight. The heavier the

wheel unit, the more gyroscopic resistance to

changing direction. Thus the bike’s steering

would be higher effort with heavier drum brakes

than with lighter disks. Modern race car disk

brakes have hollow internal vents, cross drilling

and other weight saving and cooling features. 

Most early brake drums and disks were made out of

cast iron. Current OEM motorcycle disk brakes are

usually stainless steel for corrosion resistance,

but after-market racing component brake disks are

still made from cast iron for the improved

friction qualities. Other exotic materials have

been used in racing applications. Carbon fiber

composite disks gripped by carbon fiber pads were

common in formula one motorcycles and cars in the

early 1990’s, but were outlawed by the respective29

racing sanctioning organizations due to sometimes

spectacular failure. The carbon/carbon brakes

also only worked properly at the very high

temperatures of racing conditions and would not

get hot enough to work in street applications.

A recent Ducati concept show bike uses brake

disks of silesium, developed by the Russian

aerospace industry(3), which claim to have the

friction coefficient of cast iron with the light

weight of carbon fiber. 

Another area of development of the disk brake is

the architecture of the brake caliper. Early

designs had a rigidly mounted caliper gripping

with opposed hydraulic pistons pushing the brake

pads against a disk mounted securely to the wheel

hub. Later developments included a single piston

caliper floating on slider pins. This system had

improved, more even pad wear. Most modern

automobiles and my 1982 Kawasaki motorcycle uses

this type caliper. Current design paradigm for 30

motorcycle brakes have up to six pistons, opposed

to grip both sides of a thin, large radius disk

that is "floating" on pins to provide a small

amount of lateral movement; two disks per front

wheel. 

Improvements in control have been made available

with the application of Anti-Lock Brake

technology. Wheel sensors convey rotation speed

of each wheel to a computer that senses when any

of them are locked up or in a skid, and modulates

individual wheel brake hydraulic pressure to

avoid wheel skidding and loss of vehicular

control. 

The use of exotic materials for additional weight

savings would be likely for the future of motor

vehicle braking. Disks mounted to the wheel’s rim

gripped by an internally located caliper is not

necessarily a new design (Porsche, 1963) (4) but

could be a futuristic looking option for

motorcycle wheels. Electric vehicles of the 31

future will likely utilize regenerative braking,

the electric motors become generators to convert

kinetic energy back to electricity to recharge

the batteries. As production vehicles become

increasingly quicker, the need for "whoa" will

always accompany the "go." 

TYPES OF DISK BRAKES

The three types of disk brakes are:-

1. FLOATING CALIPER DISK BRAKES

2. FIXED CALIPER DISK BRAKES

3. SLIDING CALIPER DISK CALIPER

MAIN PARTS:

32

The main components of a disc brake are: 

• The brake pads 

• The caliper, which contains a piston 

• The rotor, which is mounted to the hub 

BRAKE PAD

CALIPER AND ROTOR

WORKING OF DISC BRAKES

FLOATING-CALIPER DISK BRAKES

The caliper is the part that holds the break

shoes on each side of the disk. In the floating-

caliper brake, two steel guide pins are threaded

into the steering-knuckle adapter. The caliper 33

floats on four rubber bushings which fit on the

inner and outer ends of the two guide pins. The

bushings allow the caliper to swing in or out

slightly when the brakes are applied 

When the brakes are applied, the brake fluid

flows to the cylinder in the caliper and pushes

the piston out. The piston then forces the shoe

against the disk. At the same time, the pressure

in the cylinder causes the caliper to pivot

inward. This movement brings the other shoe into

tight contact with the disk. As a result, the two

shoes “pinch” the disk tightly to produce the

braking action 

STAGES OF WORKING

.34

FIXED-CALIPER DISK BRAKE

This brake usually has four pistons, two on each

side of the disk. The reason for the name fixed-

caliper is that the caliper is bolted solidly to

the steering knuckle. When the brakes are

applied, the caliper cannot move. The four

pistons are forced out of their caliper bores to

push the inner and outer brake shoes in against

the disk. Some brakes of this type have used only

two pistons, one on each side of the disk

SLIDING-CALIPER DISK BRAKE

The sliding-caliper disk brake is similar to the

floating-caliper disk brake. The difference is

that sliding-caliper is suspended from rubber

bushings on bolts. This permits the caliper to 35

slide on the bolts when the brakes are applied. 

Proper function of the brake depends on (1) the

rotor must be straight and smooth, (2) the

caliper mechanism must be properly aligned with

the rotor, (3) the pads must be positioned

correctly, (4) there must be enough "pad" left,

and (5) the lever mechanism must push the pads

tightly against the rotor, with "lever" to spare.

Most modern cars have disc brakes on the front

wheels, and some have disc brakes on all four

wheels. This is the part of the brake system that

does the actual work of stopping the car

The most common type of disc brake on modern cars

is the single-piston floating caliper. In this

article, we will learn all about this type of

disc brake design

SELF ADJUSTMENT OF DISK BRAKES:

Disk brakes are self adjusting. Each piston has a

seal on it to prevent fluid leakage. When the 36

brakes are applied, the piston moves toward the

disk. This distorts the piston seal. When the

brakes are released, the seal relaxes and returns

to its original position. This pulls the piston

away from the disk. As the brakes linings wear,

the piston over travels and takes a new position

in relation to the seal. This action provides

self adjustment of disk brakes.

EMERGENCY BRAKES

In cars with disc brakes on all four wheels, an

emergency brake has to be actuated by a separate

mechanism than the primary brakes in case of a

total primary brake failure. Most cars use a

cable to actuate the emergency brake. 

Some cars with four-wheel disc brakes have a 37

separate drum brake integrated into the hub of

the rear wheels. This drum brake is only for the

emergency brake system, and it is actuated only

by the cable; it has no hydraulics. 

DISK BRAKE VENTS

A moving car has a certain amount of kinetic

energy, and the brakes have to remove this energy

from the car in order to stop it. How do the

brakes do this? Each time you stop your car, your

brakes convert the kinetic energy to heat

generated by the friction between the pads and

the disc. Most car disc brakes are vented. 

Vented disc brakes have a set of vanes, between

the two sides of the disc, that pumps air through

the disc to provide cooling. 

WHY DISK BRAKES?

Why disk brakes in a truck or bus that travels 38

in excess of 65 mph? 

Improved road handling, higher engine ratings and

torque, reduced drag and rolling resistance

resulting in faster acceleration and higher

average speeds 

Higher vehicle speeds with full loads 

Higher traffic density, greater chances of

emergency braking 

Extremely high kinetic energy needed to brake on

wet roads, high front axle loads effecting

vehicle directional stability 

The power and behavior of drum brakes cannot be

improved 

Disk brakes provide optimum braking while 39

retaining directional stability

Why are disk brakes more efficient? 

Flat brake disk (axial brake) under high pressure

versus round brake drum (radial brake) during

braking 

Full friction surface of the brake pad on the

plane brake disk 

No loss of brake power due to overheating or

partial contact from brake drum parts expansion 

Disk brakes can withstand higher loads and its

efficiency is maintained considerably longer even

under the highest stresses 

Higher residual brake force after repeating

braking 40

Brake disks can withstand extremely high

temperatures 

Full contact of brake pads achieve maximum

effect 

No vitrification of brake pads. Dangerous fading

or slipping is almost completely eliminated 

Why do disk brakes have a better braking

behavior? 

Driver friendly braking behavior. Sensitive

braking in all situations and better 

Sensitive brake application and better brake

feeling 

41

Uniform braking from small fluctuations in brake

forces 

Retardation values retained even under heavy

stresses 

Minimal "pulling to one side" due to uneven brake

forces 

Disk brake axial arrangement permits a simple and

compact design 

Linear characteristics lead to an even

progression of brake force 

Basic design principle makes for higher

efficiency 

Low hysteresis is particularly suitable to ABS

control cycles

42

Why are disk brakes more economical? 

Clear economic benefits due to long service life

and reduced maintenance downtime 

Long service life of disks and pads versus drum

brakes 

Shorter service downtime due to quick pad

changes 

Good access for visual brake components checks 

Maintenance free brake components 

Optimized installation space in the wheel rim

resulting in the largest possible brake disks and

pads 

Optimized cooling resulting from open sliding

caliper design with internally ventilated brake

discs 

Even and safe brake pad wear resulting from 43

simple pad guide with level braking faces 

Why do disk brakes have higher safety

reserves? 

Minimal braking effect from high temperatures and

extreme driving requirements 

Minimal heat fading 

No brake disk distortion from extreme heat due to

internal ventilation 

with directional stability and large power

reserve under high stress 

The decisive safety aspects of the disk brake

design are shorter braking distances 

High power and safety reserves for emergencies 

Constant braking power under high stresses 

Shortened braking distance under emergency 44

braking with considerably improved directional

stability 

LIMITATIONS

BRAKING SYSTEMS FAILS IF THERE IS LEAKAGE IN

THE BRAKE LINES

THE BRAKE SHOES ARE LIABLE TO GET RUINED IF THE

BRAKE FLUID LEAKES OUT

TESTING OF DISK BRAKES

The individual components are subjected to

extensive test on the test bed. The optimum

arrangement of components on the axle beam, 45

operational reliability and convincing

performance are requirements that must be met

prior series production. 

Today, all MAN city, inter-city buses and coaches

utilize the MAN disk brake system on all wheels

with ABS. The disk brake system is used with and

without retarders

Brake performance is tested on the test track and

in racing to ensure their practice. Only after

these extensive tests can the disk brake be

cleared for production .

The brake disks are subjected to the highest

stresses from contact pressure. The broad brake

disks with radial cavities made of heat resistant

special gray cast iron, are still operational in

temperatures in excess of 1380 degrees F 46

DISK BRAKES IN PRACTICE... 

All friction brakes (drum and disk) have wear

parts and are unsuitable for continuous braking,

i.e. on long down hill runs 

Disk brakes are no substitute for an engine brake

or retarder. Economic driving with sensible use

of the engine brake or retarder optimizes the

service life of pads and disks that are equal to

those in comparable drum brakes 

Economic use of technology means driving and

braking with anticipation and economic thinking.

Disk brakes offers safety in any situation

47

CONCLUSION

Many trucks and buses are equipped with air

actuated sliding caliper disk brakes 

The high contact forces are transmitted

mechanically via needle mounted actuating device

Depending on size the actuating pressure is

transmitted evenly to the brake pads via one or

two plungers

The easy action, fully sealed guides between the

axially moving sliding caliper and fixed brake

anchor plate are maintenance free. Integrated

automatic adjustment with wear display. There are

no brake shafts, external levers or cylinder

brackets, as the brake cylinders are directly

attached.

The high efficiency of 95% is achieved by only a 48

few moving parts and low friction bearings

Asbestos free brake pads 19 to 23 mm thick,

depending on version extremely heat resistant

brake disks (34 to 45 mm) made of special gray

cast iron with internal ventilation 

The brake disks are 330 to 432 mm in diameter andHydraulic fluids

Hydraulic fluids, also called hydraulic liquids,

are the medium by which power is transferred

in hydraulic machinery. Common hydraulic fluids

are based on mineral oil or water.[1] Examples of

equipment that might use hydraulic fluids

49

include excavators and backhoes, hydraulic

brakes, power

steering systems, transmissions, garbage

trucks, aircraft flight control systems, lifts,

and industrial machinery.

Hydraulic systems like the ones mentioned above

will work most efficiently if the hydraulic

fluid used has zero compressibility.

Functions and properties

The primary function of a hydraulic fluid is to

convey power. In use, however, there are other

important functions of hydraulic fluid such as

protection of the hydraulic machine components.

The table below lists the major functions of a

hydraulic fluid and the properties of a fluid

that affect its ability to perform that

function:[2]

Function Property

50

Medium for power

transfer and

control

Non compressible (high

bulk modulus)

Fast air release

Low foaming tendency

Low volatility

Medium for heat

transfer

Good thermal capacity and

conductivity

Sealing Medium

Adequate viscosity and vis

cosity index

Shear stability

Lubricant Viscosity for film

maintenance

Low temperature fluidity

Thermal and oxidative

stability

Hydrolytic stability /

water tolerance

Cleanliness and

51

filterability

Demulsibility

Antiwear characteristics

Corrosion control

Pump efficiency

Proper viscosity to

minimize internal leakage

High viscosity index

Special function

Fire resistance

Friction modifications

Radiation resistance

Environmental

impact

Low toxicity when new or

decomposed

Biodegradability

Functioning life Material compatibility

Composition[edit]

Base stock[edit]

The original hydraulic fluid, dating back to the

time of ancient Egypt, was water. Beginning in

52

the 1920s, mineral oil began to be used more

than water as a base stock due to its

inherentlubrication properties and ability to be

used at temperatures above the boiling point of

water. Today most hydraulic fluids are based on

mineral oil base stocks.

Natural oils such as rapeseed (also

called canola oil) are used as base stocks for

fluids where biodegradability and renewable

sources are considered important.

Other base stocks are used for specialty

applications, such as for fire

resistance and extreme temperature applications.

Some examples

include: glycol, esters, organophosphate

ester,polyalphaolefin, propylene glycol,

and silicone oils.

Other components

53

Hydraulic fluids can contain a wide range of

chemical compounds, including: oils, butanol,

esters (e.g. phthalates, like DEHP,

and adipates, like bis(2-ethylhexyl)

adipate), polyalkylene

glycols(PAG), organophosphate (e.g. tributylphos

phate), silicones, alkylated aromatic

hydrocarbons, polyalphaolefins (PAO)

(e.g. polyisobutenes), corrosion

inhibitors (incl acid scavengers), anti-

erosionadditives, etc.

Biodegradable hydraulic fluids

Environmentally sensitive applications

(e.g. farm tractors and marine dredging) may

benefit from using biodegradable hydraulic

fluids based upon rapeseed (Canola) vegetable

oil when there is the risk of an oil spill from

a ruptured oil line. Typically these oils are

available as ISO 32, ISO 46, and ISO 68

54

specification oils. ASTM standards ASTM-D-6006,

Guide for Assessing Biodegradability of

Hydraulic Fluids and ASTM-D-6046, Standard

Classification of Hydraulic Fluids for

Environmental Impact are relevant.

Brake fluid

Brake fluid is a subtype of hydraulic fluid with

high boiling point, both when new (specified by

the equilibrium boiling point) and after

absorption of water vapor (specified by wet

boiling point). Under the heat of braking, both

free water and water vapor in a braking system

can boil into a compressible vapor, resulting in

brake failure. Glycol-ether based fluids

are hygroscopic, and absorbed moisture will

greatly reduce the boiling point over time.

Silicone based fluids are not hygroscopic.

Safety

55

Because industrial hydraulic systems operate at

hundreds to thousands of PSI and temperatures

reaching hundreds of degrees Celsius, severe

injuries and death can result from component

failures and care must always be taken when

performing maintenance on hydraulic systems.

Fire resistance is a property available with

specialized fluids.

Trade names]

Some of the trade names for hydraulic fluids

include Arnica, Tellus, Durad, Fyrquel, Houghto-

Safe, Hydraunycoil, Lubritherm Enviro-Safe,

Pydraul, Quintolubric, Reofos, Reolube,Valvoline

Ultramax and Skydrol.

Aircraft hydraulic systems

As aircraft performance increased in mid-20th

century, the amount of force required to operate

mechanical flight controls became excessive, and

56

hydraulic systems were introduced to reduce

pilot effort. The hydraulic actuators are

controlled by valves; these in turn are operated

directly by input from the aircrew (hydro-

mechanical) or by computers obeying control laws

(fly by wire). See flight controls.

Hydraulic power is used for other purposes. It

can be stored in accumulators to start an

auxiliary power unit (APU) for self-starting the

aircraft's main engines. Many aircraft equipped

with the M61family of cannon use hydraulic power

to drive the gun system, permitting reliable

high rates of fire.

The hydraulic power itself comes from pumps

driven by the engines directly, or by

electrically driven pumps. In modern commercial

aircraft these are electrically driven pumps;

should all the engines fail in flight the pilot

will deploy a propeller-driven electric

57

generator called a Ram Air Turbine (RAT) which

is concealed under the fuselage.[3] This provides

electrical power for the hydraulic pumps and

control systems as power is no longer available

from the engines. In that system and others

electric pumps can provide both redundancy and

the means of operating hydraulic systems without

the engines operating, which can be very useful

during maintenance.

Specifications

Aircraft hydraulic fluids fall under various

specifications:

Common petroleum-based:

Mil-H-5606: Mineral base, flammable, fairly

low flashpoint, usable from −65 °F (−54 °C) to

275 °F (135 °C), red color

Mil-H-83282: Synthetic hydrocarbon base,

higher flashpoint, self-extinguishing,

58

backward compatible to -5606, red color, rated

to −40 °F (−40 °C) degrees.

Mil-H-87257: A development of -83282 fluid to

improve its low temperature viscosity.

Phosphate-ester based:

US/NATO Military Specification - MIL-H-8446

Boeing Seattle - BMS3-11

Boeing Long Beach - DMS2014

Boeing Long Island - CDS5478

Lockheed - LAC C-34-1224

Airbus Industrie - NSA307110

British Aerospace - BAC M.333.B

Bombardier - BAMS 564-003

SAE - Ac974

SAE - AS1241

Contamination[

Special, stringent care is required when

handling aircraft hydraulic fluid as it is

critical to flight safety that it stay free from59

contamination. It is also necessary to strictly

adhere to authorized references when servicing

or repairing any aircraft system. Samples from

aircraft hydraulic systems are taken during

heavy aircraft maintenance checks (primarily C

and D checks) to check contamination.

Hydraulic systems have reservoirs which can

usually be accessed by removing a cap from the

top of the brake lever. This reservoir and

bladder is an important feature of the system

because when the brake fluid heats up it expands

and needs somewhere to go. The reservoir acts as

a release for the excess fluid to prevent it

from splitting a cable.

Bleeding: This is a process to allow the trapped

air to escape from brake cables and callipers.

If you have air in the system it will result in

a much slower braking response as air can be

easily compressed whereas brake fluid can't.

60

Take care to keep all parts of the system clean,

especially the reservoir and the pads. Take off

the wheels being careful not to damage the discs

as they pass through the calliper. Remove the

brake pads and replace them with either

cardboard/wood spacer or some old pads. The bike

should be positioned so that the cable is

continually facing uphill between the calliper

and the reservoir. The top surface of the

reservoir should be parallel to a flat ground

(if not adjust the brake levers). Take the bleed

pipe and attach it to the bleed nipple on the

calliper. Use the elastic band to attach the

plastic bag to the other end of the pipe. Make

sure you wipe any dirt away from the brake lever

and around the reservoir. Unscrew the reservoir

tank cap and remove the cover and bladder. Fill

the reservoir tank to the top with the correct

brake fluid. Unscrew the bleed nipple with one

turn. Repeatedly pump the brake lever. The fluid61

in the tank will bubble and the level will

probably drop. Make sure the reservoir is topped

up as the level drops. Tap the cable to dislodge

any trapped air. Fluid will eventually start to

come out of the bleed nipple - close the nipple.

When you test the brakes they should eventually

become firm when applied. If not, open the bleed

nipple and continue. When firm, hold the brake

lever and keep the pressure applied. Use the

wrench to loosen the bleed nipple, opening and

closing in the space of a second whilst looking

at the fluid passing through the bleed pipe.

This should expel any remaining air bubbles. Let

go of the brake lever and top up the reservoir.

Pump the lever once again until firm. Top up the

reservoir. The system should now be free of air.

Replace the bladder and reservoir cap. Be ready

to wipe any overflowing fluid from the lever -

this is normal. Screw the cap on securely. Take

off the bleed pipe from the nipple and wipe any 62

fluid off the calliper. Replace the pads and

wheels. Finally check the brakes work.

Replacing Brake Fluid: Carry out all the steps

mentioned above but leave the nipple open when

pumping the levers, and keep topping up the

reservoir. Eventually the new fluid will replace

the older fluid.

That's it, your brakes should now be air free

and fully topped up with new fluid.

Pascal's Principle and Hydraulics

SUBJECT: Physics

TOPIC: Hydraulics

DESCRIPTION: A set of mathematics problems

dealing with hydraulics. 

CONTRIBUTED BY: Carol Hodanbosi 

EDITED BY: Jonathan G. Fairman - August 1996

63

Hydraulic systems use a incompressible fluid,

such as oil or water, to transmit forces from

one location to another within the fluid. Most

aircraft use hydraulics in the braking systems

and landing gear. Pneumatic systems use

compressible fluid, such as air, in their

operation. Some aircraft utilize pneumatic

systems for their brakes, landing gear and

movement of flaps.

Pascal's law states that when there is an

increase in pressure at any point in a confined

fluid, there is an equal increase at every other

point in the container.

A container, as shown below, contains a fluid.

There is an increase in pressure as the length

of the column of liquid increases, due to the

increased mass of the fluid above.64

For example, in the figure below, P3 would be

the highest value of the three pressure

readings, because it has the highest level of

fluid above it.

If the above container had an increase in

overall pressure, that same added pressure would

affect each of the gauges (and the liquid

throughout) the same. For example P1, P2, P3

were originally 1, 3, 5 units of pressure, and 5

units of pressure were added to the system, the

new readings would be 6, 8, and 10.

Applied to a more complex system below, such as

a hydraulic car lift, Pascal's law allows forces65

to be multiplied. The cylinder on the left shows

a cross-section area of 1 square inch, while the

cylinder on the right shows a cross-section area

of 10 square inches. The cylinder on the left

has a weight (force) on 1 pound acting downward

on the piston, which lowers the fluid 10 inches.

As a result of this force, the piston on the

right lifts a 10 pound weight a distance of 1

inch.

The 1 pound load on the 1 square inch area

causes an increase in pressure on the fluid in

the system. This pressure is distributed equally

throughout and acts on every square inch of the

10 square inch area of the large piston. As a

result, the larger piston lifts up a 10 pound

weight. The larger the cross-section area of the

second piston, the larger the mechanical

advantage, and the more weight it lifts.

66

The formulas that relate to this are shown

below:

P1 = P2 (since the pressures are equal

throughout).

Since pressure equals force per unit area, then

it follows that

F1/A1 = F2/A2

It can be shown by substitution that the values

shown above are correct,

67

1 pound / 1 square inches = 10 pounds / 10 square

inches

Because the volume of fluid pushed down on the

left side equals the volume of fluid that is

lifted up on the right side, the following

formula is also true.

V1 = V2

by substitution,

A1 D1 = A2 D2

A = cross sectional area

D = the distance moved

or

A1/A2= D2/D1

This system can be thought of as a simple

machine (lever), since force is multiplied.The

68

mechanical advantage can be found by rearranging

terms in the above equation to

Mechanical Advantage(IMA) = D1/D2 = A2/A1

For the sample problem above, the IMA would be

10:1 (10 inches/ 1 inch or 10 square inches / 1

square inch).

Given these simple formulas, try to answer the

questions below.

Bernoulli's principle

This article is about Bernoulli's principle and Bernoulli's equation

in fluid dynamics. For Bernoulli's theorem in probability, see law

of large numbers. For an unrelated topic in ordinary differential

equations, see Bernoulli differential equation.

69

A flow of air into a venturi meter. The kinetic

energy increases at the expense of the fluid

pressure, as shown by the difference in height

of the two columns of water.

In fluid dynamics, Bernoulli's principle states

that for an inviscid flow, an increase in the

speed of the fluid occurs simultaneously with a

decrease inpressure or a decrease in

the fluid's potential energy.[1][2] The principle

is named after Daniel Bernoulli who published it

in his book Hydrodynamica in 1738.[3]

Bernoulli's principle can be applied to various

types of fluid flow, resulting in what is

loosely denoted as Bernoulli's equation. In

fact, there are different forms of the Bernoulli

equation for different types of flow. The simple

form of Bernoulli's principle is valid

for incompressible flows (e.g.

70

most liquid flows) and also for compressible

flows (e.g. gases) moving at low Mach

numbers (usually less than 0.3). More advanced

forms may in some cases be applied to

compressible flows at higher Mach

numbers (see the derivations of the Bernoulli

equation).

Bernoulli's principle can be derived from the

principle of conservation of energy. This states

that, in a steady flow, the sum of all forms of

mechanical energy in a fluid along

a streamline is the same at all points on that

streamline. This requires that the sum of

kinetic energy and potential energy remain

constant. Thus an increase in the speed of the

fluid occurs proportionately with an increase in

both its dynamic pressure and kinetic energy,

and a decrease in its static

pressure and potential energy. If the fluid is

71

flowing out of a reservoir, the sum of all forms

of energy is the same on all streamlines because

in a reservoir the energy per unit volume (the

sum of pressure and gravitational potential ρ g h)

is the same everywhere.[4]

Bernoulli's principle can also be derived

directly from Newton's 2nd law. If a small

volume of fluid is flowing horizontally from a

region of high pressure to a region of low

pressure, then there is more pressure behind

than in front. This gives a net force on the

volume, accelerating it along the streamline.[5][6]

[7]

Fluid particles are subject only to pressure and

their own weight. If a fluid is flowing

horizontally and along a section of a

streamline, where the speed increases it can

only be because the fluid on that section has

moved from a region of higher pressure to a

72

region of lower pressure; and if its speed

decreases, it can only be because it has moved

from a region of lower pressure to a region of

higher pressure. Consequently, within a fluid

flowing horizontally, the highest speed occurs

where the pressure is lowest, and the lowest

speed occurs where the pressure is highest.

Contents

Incompressible flow equation[

In most flows of liquids, and of gases at

low Mach number, the density of a fluid parcel

can be considered to be constant, regardless of

pressure variations in the flow. Therefore, the

fluid can be considered to be incompressible and

these flows are called incompressible flow.

Bernoulli performed his experiments on liquids,

so his equation in its original form is valid

only for incompressible flow. A common form of

73

Bernoulli's equation, valid at

any arbitrary point along a streamline, is:

(

A

)

where:

 is the fluid flow speed at a point on a

streamline,

 is the acceleration due to gravity,

 is the elevation of the point above a

reference plane, with the positive z-

direction pointing upward – so in the

direction opposite to the gravitational

acceleration,

 is the pressure at the chosen point, and

 is the density of the fluid at all points

in the fluid.

74

For conservative force fields,

Bernoulli's equation can be

generalized as:[8]

where Ψ is the force potential at

the point considered on the

streamline. E.g. for the Earth's

gravity Ψ = gz.

The following two assumptions must

be met for this Bernoulli equation

to apply:[8]

the flow must be incompressible

– even though pressure varies,

the density must remain constant

along a streamline;

friction by viscous forces has

to be negligible. In long lines

mechanical energy dissipation as

75

heat will occur. This loss can

be estimated e.g. using Darcy–

Weisbach equation.

By multiplying with the fluid

density  , equation (A) can be

rewritten as:

or:

where:

 is dynamic pressure,

 is the piezometric

head or hydraulic head (the sum of the

elevation z and the pressure head)[9][10] and

 is the total pressure (the sum of

the static pressure p and dynamic

pressure q).[11]

The constant in the

Bernoulli equation can 76

be normalised. A common

approach is in terms

of total head or energy

head H:

The above equations suggest there is

a flow speed at which pressure is

zero, and at even higher speeds the

pressure is negative. Most often,

gases and liquids are not capable of

negative absolute pressure, or even

zero pressure, so clearly Bernoulli's

equation ceases to be valid before

zero pressure is reached. In liquids

– when the pressure becomes too low

– cavitation occurs. The above

equations use a linear relationship

between flow speed squared and

pressure. At higher flow speeds in

77

gases, or for sound waves in liquid,

the changes in mass density become

significant so that the assumption of

constant density is invalid.

Incompressible flow equation[edit]

In most flows of liquids, and of gases at

low Mach number, the density of a fluid parcel

can be considered to be constant, regardless of

pressure variations in the flow. Therefore, the

fluid can be considered to be incompressible and

these flows are called incompressible flow.

Bernoulli performed his experiments on liquids,

so his equation in its original form is valid

only for incompressible flow. A common form of

Bernoulli's equation, valid at

any arbitrary point along a streamline, is:

(

A

)

78

where:

 is the fluid flow speed at a point on a

streamline,

 is the acceleration due to gravity,

 is the elevation of the point above a

reference plane, with the positive z-

direction pointing upward – so in the

direction opposite to the gravitational

acceleration,

 is the pressure at the chosen point, and

 is the density of the fluid at all points

in the fluid.

For conservative force fields,

Bernoulli's equation can be

generalized as:[8]

where Ψ is the force potential at

the point considered on the

79

streamline. E.g. for the Earth's

gravity Ψ = gz.

The following two assumptions must

be met for this Bernoulli equation

to apply:[8]

the flow must be incompressible

– even though pressure varies,

the density must remain constant

along a streamline;

friction by viscous forces has

to be negligible. In long lines

mechanical energy dissipation as

heat will occur. This loss can

be estimated e.g. using Darcy–

Weisbach equation.

By multiplying with the fluid

density  , equation (A) can be

rewritten as:

80

or:

where:

 is dynamic pressure,

 is the piezometric

head or hydraulic head (the sum of the

elevation z and the pressure head)[9][10] and

 is the total pressure (the sum of

the static pressure p and dynamic

pressure q).[11]

The constant in the

Bernoulli equation can

be normalised. A common

approach is in terms

of total head or energy

head H:

81

The above equations suggest there is

a flow speed at which pressure is

zero, and at even higher speeds the

pressure is negative. Most often,

gases and liquids are not capable of

negative absolute pressure, or even

zero pressure, so clearly Bernoulli's

equation ceases to be valid before

zero pressure is reached. In liquids

– when the pressure becomes too low

– cavitation occurs. The above

equations use a linear relationship

between flow speed squared and

pressure. At higher flow speeds in

gases, or for sound waves in liquid,

the changes in mass density become

significant so that the assumption of

constant density is invalid.

Simplified form[

82

In many applications of Bernoulli's equation,

the change in the ρ g z term along the streamline

is so small compared with the other terms that

it can be ignored. For example, in the case of

aircraft in flight, the change in height z along

a streamline is so small the ρ g z term can be

omitted. This allows the above equation to be

presented in the following simplified form:

where p0 is called 'total pressure', and q is

'dynamic pressure'.[12] Many authors refer to

the pressure p as static pressure to

distinguish it from total

pressure p0 and dynamic pressure q.

InAerodynamics, L.J. Clancy writes: "To

distinguish it from the total and dynamic

pressures, the actual pressure of the fluid,

which is associated not with its motion but

with its state, is often referred to as the

static pressure, but where the term pressure 83

alone is used it refers to this static

pressure."[13]

The simplified form of Bernoulli's equation

can be summarized in the following memorable

word equation:

static pressure + dynamic pressure = total pressure[13]

Every point in a steadily flowing fluid,

regardless of the fluid speed at that point,

has its own unique static pressure p and

dynamic pressure q. Their sum p + q is

defined to be the total pressurep0. The

significance of Bernoulli's principle can

now be summarized as total pressure is constant along

a streamline.

If the fluid flow is irrational, the total

pressure on every streamline is the same and

Bernoulli's principle can be summarized

as total pressure is constant everywhere in the fluid flow.[14] It is reasonable to assume that

84

irrotational flow exists in any situation

where a large body of fluid is flowing past

a solid body. Examples are aircraft in

flight, and ships moving in open bodies of

water. However, it is important to remember

that Bernoulli's principle does not apply in

the boundary layer or in fluid flow through

long pipes.

If the fluid flow at some point along a stream line is brought to rest, this point is called a stagnation point, and at this point the total pressure is equal to the stagnation pressure. Pressure appllied in a confined liquid is transmitted uniformly in all direction through out the liquid.

..to those who dontt undrstand the word ‘confined liquid’, take out a dictionary & applyits meaning in the context of this principle. Basically in B.M it means..”cecair yang berada dalam bekas tertutup”.

So if the liquid is trapped in a container and pressure is applied, according to the principle;this pressure will be transmitted equally in all

85

direction.

If u watch above diagram..according to pascal principle, all the water that moves out from theholes received the same pressure.

Applications of Pascal’s Principle in Everyday LifeA hydraulic system is a device in which a small applied force can give rise to a larger force.The principle in the hydraulic system is widely used in jacks, vehicle brake systems, hydraulic presses and heavy machinery.

Hyraulic JacksHydraulic jacks are used to lift a heavy load such as when changing a car tyre. When the handle is pressed down, a valve closes and the small piston forces hydraulic fluid through another valve to the larger cylinder. The

86

pressure transmitted results in a large force onthe load.

When the handle is raised, valve B closes and hydraulic fluid flows from the buffer tank through valve A into the small cylinder. The handle is moved up and down repeatedly until theload is sufficiently lifted up.The large piston can be lowered at the end by opening the release valve to allow all the hydraulic fluid to flow back into the buffer tank.

Hydraulic Brakes

Hydraulic brakes are used in cars, lorries and motorcycles.

In a hydraulic brake system, a liquid, known as

87

brake fluid,is used to transmit pressure from the brake pedal to all the wheels of the vehicle.When the brake pedal is pressed, the piston of the control cylinder applies a pressure on the brake fluid and this pressure is transmitted, via a system of pipes, to each cylinder at the wheels.

The cylinder at the wheels cause a pair of pistons to push a pair of friction pads to pressagainst the surface of the brake discs or brake drums. The frictional forces between these brakecomponents cause the vehicle to slow down and stop.

When the brake pedal is released, a spring restores the brake discs to their original positions.

References[edit]

1. Jump up^ Csere, Csaba (January 1988), "10Best Engineering Breakthroughs", Car and Driver 33 (7): 61

2. Nice, Karim. "How Brakes Work". How StuffWorks. Retrieved 18 June 2010.

88

3. "Hydraulic Brakes". Integrated Publishing. Retrieved 18 June 2010.

89