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HYDRAU LIC FOOTBRAKE SYSTEM
DESCRI PTION
MASTER CYLI N DER
The master cylinder
is
of the tandem type.
Its
co
n-
struction
is
shown in
Fig.
5-33 and
its
function
is as
follows
:
Fig.
5-33.
Master cylinder
l.
Equalizing
hole
17. Stop
screw
2. Overflow
hole
18. Seal
3.
Washer
19. Piston
sea
l
4. Pisfon
sea
I
20. Connec
lion
for
5.
Washer
primary circuit
6. Pisfon sea
I
21. Piston
sea
l
7.
Washer
22. Secondary piston
8.
Circlip
23. Washer
9.
Pri mary piston
24. Piston seal
10.
Washer
25. Connection for
11
.
Piston seal
secondary
circuil
12. Washer
26
.
Cylinder
13. Thrusf washer
27.
Spring
14.
Spring
28. Thrust washer
15.
Screw
29. Washer
16. Spring retainer
2
Secondary cir-
cuil, pressureless
YSWP
Fig.
5-34.
Rest position
and
2.
Connec1ion for brake fluid container
-
-
Secondary
c
ir-
cuit,
pressureless
Seco
ndary
circuit,
high
pressure
-
-
Primary circuit,
pressureless
Primary circuit,
high
pressure
Fig. 5-35.
Normal brak", applicat ion
V
O LVO
103184
When
th
e
system
is
at
rest
(Fig
.
5-34), the pistons are
kepi' pressed back by the force of
the
springs.
When
the
pistons are
in this
position,
the
co
nn ections
be-
tween
the
brake fluid container and wheel brake
units
are open. At the moment braking takes place, the
primary piston (to the right) is pressed
in
by the
piston rod. This closes the
connection
between the
container and the wheel brake unit and the pressure
in front of the piston
rises. This
pressure
influences
the
se::ondary piston
so
that it also is
moved
to the
left.
The
same
over-pressure arises in front of both pistons
(Fig. 5-35),
the
brake fluid is forced out into the
respective brake
line
and all the wheel
·
brakes are
applied, providing the
system
is
functioning
properly.
If a
leakage
has occurred in the secondary circuit,
no
hydraulic
counterpressure
builds
up
in front of the
secondary
piston. Instead, this piston is moved in-
wards when the brakes are appl:ied until
it
is stopped
by the end of the cylinder (Fig. 5-36).
Secondary
cir-
•
cuit pressureless
Fig.
5-36.
Brake application with
leakage
in
the
secondary
circuit
VOLVO
103185
5:
17
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