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Secondary cir-
cuil,
pressurel
ess
Secondary ci
rc
u
it,
high
pressure
Prim
ary
circui
t,
pressureless
Fig. 5-37.
Brake application with
leaka
ge in
the primary circuit
VOLVC
103 186
The hydraulic pressure
between
the
pistons can then
rise
and apply
the brakes in
the primary circuit. If
leakage
occurs in the
primary circuit, the primary
piston
is
moved
and
the brakes
are app
li
ed
until
the
primary
piston
makes
contact with the secondary
piston. Both pistons
are then pressed inwards,
the
pressure in front of the
secondary
plun
ger rises and
the
brakes in
th
e secondary circuit are app
li
ed
(Fig.
5-37).
WARNIN'
G VALVE
A warning valve
is
connected between the brake
lines
from the master
cylinder
and the branch
pres-
sure for both brake
circuits.
Its function is to warn
the
driver when the pressure difference between the
5
:
18
14 13 12
11
10
9
8
Fig. 5-38. Warning
valve
l.
Electrical connection
2. Switch washer
3. Switch
hou sing
4.
Guide pin
5. Connection, rear
wheel
brakes
6. Connection, master
cylinder
7.
End piece
8. Sealing washer
9. Sprir,g
10.
Connection, front
wheel
brakes
11. Thrust
washer
12.
O-ring
13.
Piston
14. Housing
VO LVO
102454
Fig. 5-39.
Normal
position
VOLVO
IC2J
).J
two brake circuits exceeds about
10 kg/cm
2
(1
42
Ib/sq.in. ). The
valve
construction
is
shown
in
Fig. 5-38
and
it operates
as follows:
If
there is no
fa
ult
in
the circuits and
the brakes
are
applied, the hydraulic
pressure on
the pistons is
large
ly
the
same
on both
sides (Fig
.
5-39). But
shou ld,
for
examp le,
the pressure in the
seco
ndary
circ
uit
be
somewhat
high
er
th
an
in
the
primary
circuit,
this will
try to displace
th
e
pistons to the
right in
the figure.
This lifts
the thrust
washer
(11)
and
the
pressure
of
the
spring
(9)
counteracts
the
displacement.
It is only when the
pressure
in the
secondary circuit
first
exceeds
that in the
primary circuit
by
about
10 kg/cm
2
(142
Ib/sq.in.
)
that the
pistons are
pushed
so
far
to the right that the quide pin (4)
can
be pres-
sed
downwards.
When this happens, the
switch
washer (2) reaches
the
housing (3)
and current
is
cut
in (Fig.
5-40).
The guide
pin
is prevented from return
-
ing to its normal position until the fault has been
rectified
and
the warning
switch
(3) removed.
Fig. 5-40.
Warning position
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