DAF LF45, LF55 Series. Manual - part 450

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Description of components

OPERATION OF BRAKE COMPONENTS

ΛΦ45/55 series

6

3

2.12 EMERGENCY FILLING/TEST CONNECTION

In various places in the brake system there are 

test connections for carrying out inspections and 

adjustments. A pipe leads from point 24 of the air 

dryer to the rear left of the cab. There is a test 

connection here that can be used as an 

emergency/tyre filling connection.

Note:

With a leaf-spring front axle this test connection is 

on point 11 of the air dryer.

If a pipe is connected to the test connection, 

screwing in the union will lift the spring-loaded 

valve (A) from its seat, opening the supply. If the 

union is removed, the valve is pushed onto its 

seat by spring B, closing the supply.

A

B

R600495

OPERATION OF BRAKE COMPONENTS

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Description of components

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ΛΦ45/55 series

6

2.13 BRAKE CYLINDER

Purpose
The purpose of the brake cylinder is to apply the 

brake shoes or pads to the brake drum/disc.

Operation
When the foot brake valve is operated, 

compressed air is admitted at the pressure side 

of the diaphragm (1). The diaphragm (1) and 

push rod (2) are pushed outwards against the 

pressure of the spring. As a result, the brake 

shoes are forced against the brake drum via a 

lever mechanism. The air on the other side of the 

diaphragm can escape via bleed holes and the 

clearance around the push rod.

When the brakes are released, the coil spring (3) 

will force the push rod and the diaphragm back to 

their initial position.

When the brakes are released, the brake cylinder 

will always draw in outside air on the non-

pressure side. When the brakes are released the 

push rod should return fully to its initial position. 

The actuating pressure should not exceed 

0.5 bar.

R600505

2

1

3

R600506

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Description of components

OPERATION OF BRAKE COMPONENTS

ΛΦ45/55 series

6

3

2.14 PARKING BRAKE VALVE

PARKING BRAKE VALVE WITH TRAILER 
VEHICLE CONNECTION
Purpose
The parking brake valve enables simultaneous, 

controlled operation of both the parking brake 

system of the prime mover and the trailer brakes.

Operation
The parking brake valve has 3 positions:

-

driving

-

parking

-

test

Driving
With the handle in the driving position, there is a 

through-connection in the valve of the supply 

pressure (connecting point 1) to the connecting 

points for the spring-brake cylinders (21) and the 

trailer (22). The bleed vent is now closed.

The output pressure at connection points 21 and 

22 is now approx. 8 bar (see graph).

3

21

1

22

2
3

5

4

6

8

7

9

10

R600397

1

21

22

OPERATION OF BRAKE COMPONENTS

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Description of components

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ΛΦ45/55 series

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Emergency braking
If the handle is pulled a little backwards against 

the spring pressure, tappet 3 will move 

downwards via the eccentric (2). The space at 

connecting point 21 can now be bled and as a 

result the pressure at connecting point 21 will 

drop. Via the bore in valve 10 the pressure at 

connection point 22 will also drop. Spring 4 forces 

piston 5 down until valve 6 comes into contact 

with the seal collar of tappet 3. A state of 

equilibrium has now been achieved.

When the handle is moved against stop 7, the 

bleed vent will remain open, so that the spring 

brakes and the trailer brakes will be applied to 

their maximum (max. emergency-brake position).

Parking
When the handle is pulled past stop 7, it is locked 

in position.

Connection points 21 and 22 will remain 

pressureless, so that the spring brakes and the 

trailer brakes are still applied to their maximum.

Test
When the handle is moved beyond the parking 

position, cam 8 will move tappet 9 downwards, 

causing the bore in valve 10 to be closed and this 

valve to be lifted from its seat.

The supply pressure can now be passed to 

connection point 22 via a bore in piston 5. As a 

result, the trailer brakes will be released. 

Connection point 21 remains bled, so that the 

spring brakes keep the parking brake applied.

The combination is now braked only by the force 

exerted by the spring-brake cylinders on the 

tractor. It can now be checked whether the 

combination remains motionless when the trailer 

vehicle brakes are not applied. When the handle 

is released, it will automatically return to the 

parking position.

Releasing the brakes
When the handle is once again moved fully 

forwards, tappet 3 will move upwards, seat 

against valve 6 and push it from its seat in piston 

5. As a result, the pressure can reach connection 

points 21 and 22.

3

21

1

22

2
3

5

4

6

8

7

9

10

R600397

1

21

22

3

21

1

22

R600399