DAF LF45, LF55 Series. Manual — part 450

©

200436

2-21

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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©

200436

Description of components

3

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

©

200436

2-23

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

2-24

©

200436

Description of components

3

ΛΦ45/55 series

6

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