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Fig. 6-36.
Servo
pump
a lte
r
w hen
th
e
rotor ro tates. W hen a
coupl
e
of
vanes
are mo
ved
from the suction side to the press ure
side,
the area
between them
and
the
sucked-
in oi
l
increases
to
start
with. When
the co
nnection with t
he suction
side has bee
n passed,
a
link-up w it
h
t he press ure side
is then
atta ined instead.
Sin
ce t he
space
betwee
n
the
va nes
cont
racts a
t th
e same
tim e, th
e press ure
will
rise
a
nd oil will.
be
forced out into the delivery line
.
Due
to the fact that there are two inlet and two
outlelt channels, the pump has double
capacity.
CONTROL
VALVE
The pump housing contains
.a
controi valve which
regulates partly the oil flow and partly the maximum
pressure
.
When the pump starts functioning, the valve (5, Fig.
6-37) maintains the valve
·
pressed to the Teft of the
spring (7).
The oil
suppl'
i ed by the pump passes
through the delivery channel (3) via the check valve
3
6: 22
Fig. 6-37.
ControI
valve,
normal position
l
.
Delivery line
5.
Controi valve
2.
Check valve
6.
Safet)' val ve
3.
Del ivery ch a n ne I
7.
Spring
4.
Return channel
8. Link channel
VO LVO
102 U 7
Fig. 6-38.
ControI
valve,
maximum pressure
(2)
out
into the de livery line
(1)
and
from
there
to t
he
steering box. The space to
the
right of the controi
va lve is linked-up
with the delivery
line (1
)
by
means
of the lin k
channe
l (8)
and
has, therefore,
the same
press ure.
The check
valve 's
(2)
funct
io
n
is
to
ens
ure that
th
e
pres-
sure on
the left-
hand side of the
contro
i
va lve p iston
is higher t
han
that in
the
lin
e and a lso
to the rig ht
of t
he piston.
W hen the
spri
ng press ure
is
overcome,
t he p
iston
is, therefore,
d isp
laced
to the
rig
ht. And
w he
n
t he
speed
is s uff icie
ntly hi
g
h in
re
lation to
the
counte
rpress
ure, th
e
pi ston
has be
en di spl
a ce
d so
mu ch that th
e s urp lus
oil
ca
n flow
back!
to th
e
inl
e
t
sid
e
of the pump,
see
Fig. 6-37. Since th
e
pump should
deliver a quantity smalle
r
than the maximum capacity,
this valve adjustment can be called normal.
Should the pump flow through the outlet be
stopped!
for example, because the front wheel turning is block
-
ed, the pressure in the delivery line (1), will rise and
the pressure difference between both ends of the
controi valve wiH be
equaliz
ed. This will cause the
spring to be moved to the left, the connection with
the return channel to be closed and the pressure to
rise even more. At about 75 kg/cm
2
(1066 Ib/sq .in.) the
spring pressure on the safety valve (6) is overcome,
that is, the inner part of the controi valve, and oil
can then pass out to the return channel (4), see Fig.
6-38.
The pressure on the right-hand side of the piston will
then drop and the entire controi valve will be tyloved
to the right so that the connection with the return
channel
opens.
When the pressure drops to its normal
value, the safety valve closes and the controi valve
returns to its normal position
.
Oil
co,nta
i ner
The oil container is placed in the engine compartment
where it is easily
accessible.
It is provided with a
filter, from the centre of which oil is sucked to the
pump. By means of the by-pass valves, oil can flow
past the filter should it become blocked. The oil level
can be seen against the level line after removing the
cap.
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