Q.. Write short notes for requirements of brake


Brake Fluid

In a hydraulic braking system, to transmit the braking
force from the brake pedal to the brake drum, the liquid used is
called brake fluid.


1.Brake fluid should be chemically inert.
2.Unaffected by high or low temperatures.
3.Should not affect the metallic and rubber parts in the
braking system.
4.Provide lubrication for the master cylinder and wheel
cylinder pistons.
5.Mineral oil should not be used as a brake fluid as it
causes rubber parts to swell and disintegrate resulting
in faulty braking action and complete failure of the

Q28. Write short notes on pneumatic brakes.


Pneumatic Brakes

The brakes in which the braking medium is air are called
pneumatic brakes i.e., air is used to apply braking force to the
brake shoes. Hence they are also called air brakes. The air
may be either compressed above atmospheric pressure, at
atmospheric pressure i.e., 1.0332 kgF/cm2 or at vacuum i.e.,
below atmospheric pressure. The application occurs due to
pre-differences. An air brake system includes air compressor
unit, water and oil separator, air receiver, brake cambers or
diaphragm unit, brake valve, piping and pipe unions,
unloaded valve with a governor, air pressure gauge, safety
valve and stop light switch.

To maintain the air pressure in the tanks, the air
compressor which is a small air pump is used. Atmospheric air
enters into the compressor via an air filter. Compressor
activated by the engine, forces the air at a pressure through
water and oil separator to air receiver. The pressure gauge
indicates the air pressure in the receiver. The receiver contains
enough compressed air for several braking operations. For
maintaining adequate braking force at all times even when the
engine is not running, an air-reservoir tank is also necessary.
From the receiver, air is supplied to the brake valve. The brake
valves prevent the pressure of air to the brake chambers, when
the brake is not depressed hence no braking effect.
But when the pedal is depressed, the position of the
brake valves changes and compressed air is admitted into the
wheel brake chambers. In the chambers, air acts upon flexible
diaphragm, moves them and pushes out the rods connected
with the levers of the brakes gear cams. When the cam turns.

shoes are separated, thus braking occurs.

Pneumatic brakes are used in trucks, buses and
other HCVS, Tata LPT 1612.


Pneumatic brakes utilize air as the braking medium
instead of using mechanical components, brake oil. An air
operated braking system is employed in medium and heavy
trucks because,

1.The required braking force can be developed with a
very small effort applied by the driver to the brake
2.Compressed air can also be used to inflate the tyres to
drive the windshield wiper, to actuate the steering
gear booster, to open and close the doors in the buses.
and to operate pressure horns etc.
3.This is the most convenient and dependable device
for braking full-trailers and semi-trailers.
4.It is more powerful than the mechanical and hydraulic
5. Components of it can be located conveniently any
where on the chassis. Therefore the chassis design is


Q.. Write short notes on vacuum brakes.


Vacuum Brakes

The braking medium in these brakes is vacuum i.e., the
air medium pressure is below atmospheric pressure. The
vacuum brakes operate due to the difference in atmospheric
pressure and vacuum. Vacuum brakes are used in Bedford
trucks. Here is a schematic arrangement of a purely vacuum

In this system, vacuum is applied on one side of a
large piston, through a vacuum reservoir. The other side of
the piston is exposed to the atmospheric pressure. The vacuum
pressure is less than atmospheric pressure and hence the
difference in pressure on two sides of the piston causes it to
move within a cylinder. An air breather port is provided in the
cylinder, through which the atmospheric air escapes out.
Purely vacuum unit is not used but used in combination with
other types of brakes. It can be used with a mechanical or
hydraulic brake system and is universally adopted in power

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