DAF LF45, LF55 Series. Manual - part 445

©

 200436

2-1

Description of components

OPERATION OF BRAKE COMPONENTS

ΛΦ45/55 series

6

3

2. DESCRIPTION OF COMPONENTS

2.1 COMPRESSOR

The compressor is a 225-cm

3

 one-cylinder 

design with a water-cooled cylinder head. The 

compressor is mounted on the left side of the 

engine against the flywheel housing.

The compressor is driven by the camshaft gear 

via a gear wheel.

OPERATION OF BRAKE COMPONENTS

2-2

©

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Description of components

3

ΛΦ45/55 series

6

2.2 AIR SUPPLY UNIT

Purpose
The air supply unit is a combination of an air 

dryer, pressure regulator and four-circuit safety 

valve and has the following functions:

-

removing water, oil and other foreign matter 

from the air before it enters the brake 

system;

-

setting the system pressure by means of a 

built-in pressure regulator;

-

limiting the pressure build-up to a given 

value;

-

splitting the brake system into four circuits 

and, should one circuit fail, protecting the 

other circuits against running empty.

Air dryer function

Filling the system
The air supplied by the compressor reaches the 

air dryer via connecting point 1/12. In the filter 

element (1), the air passes through the coarse 

filter (2), which sieves out the oil and dirt particles.

In addition, the air condenses against the cool 

wall of the element. Subsequently, the air flows 

through filter grains (3), which extract the water 

vapour from the air. The air thus dried flows via a 

non-return valve (4) to connecting point 21.

R600359

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9

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7

11

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c

a

16

12

21

1/12

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3

4

2

1

18

17

14
13
15
19

©

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2-3

Description of components

OPERATION OF BRAKE COMPONENTS

ΛΦ45/55 series

6

3

Operation, pressure regulator
The pressure increase occurring during filling is 

returned to the built-in pressure regulator via 

bore 12.

When the pre-set cut-out pressure is reached, the 

control piston (13) is moved to the right against 

the pressure of spring 14. This releases bore 15 

in pin 16. The system pressure will enter space 

"a" above blow-off valve 8 via bore 17, opening 

the blow-off valve (8) against the pressure of the 

spring (18).

If the pressure in the brake system drops to the 

cut-in pressure due to air consumption, the 

control piston (13) will move to the left and shut 

bore 15 in pin 16. This bore, and therefore 

channel 17 and space a, will now be bled via 

bore 19. The blow-off valve (8) will close. The 

compressor will now again build up the pressure 

in the air system.

Regenerating
A regeneration tank is no longer necessary, 

because the air inside the circuits is used.

A built-in pneumatic time switch controls the 

regeneration process:

-

throttle 5 determines the amount of air;

-

throttle 6 determines the length of time.

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6.4

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6.2

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6.5
6.6
6.7

B

R600580

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OPERATION OF BRAKE COMPONENTS

2-4

©

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Description of components

3

ΛΦ45/55 series

6

Air is admitted to chamber "b" via throttle 6 and air 

is also admitted to chamber "c" via bore 7 in the 

piston (9). On cut-out by the pressure regulator, 

the blow-off valve (8) is opened and chamber "c" 

is bled via bore 7. The piston (9) is moved to the 

right against the pressure of spring 10 as a result 

of the difference in pressure between chambers 

"b" and "c". This releases the piston (9) from its 

seat (11) and air will flow in the opposite direction 

via throttle 5 from the system through the filter 

element. At the same time, pressure is reduced in 

chamber "b" via throttle 6. The piston (9) moves 

to the left until it abuts the seat (11). Regeneration 

is now complete.

Four-circuit safety valve operation
The air supply enters via connecting point 1. 

From there, the air flows to the built-in pressure 

relief valves of circuits 1, 2 and 4.

As soon as the valve of circuit 1 and/or circuit 2 

opens, the air will be able to flow through to 

circuit 3, the trailer brake and parking brake 

circuit. For reasons of safety, a built-in flowback 

function empties circuit 3 when the pressure in 

circuit 1 is too low. This is done to activate the 

emergency brake function.

R600475

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6.6
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R600476