S
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9803/
3280
Issue
1
Priority Valve Operation 2
- Turning
As the steering unit
43
is operated, pressure is
applied to the spring end of the priority valve spool
2B
via sensing line
LS
from the steering unit.
This reduces the pressure differential across the
spool, causing it to move to the right under spring
force. This allows priority valve flow to the steering
unit which directs the flow to the power track rod
rams
40
and
41
untill the required steering lock is
reac hed . When t he st eering lo c k is held t he
pressure signal across the side port
LS
of the
st eering unit c eases, rest o ring t he p ressure
differential across spool
2B
. The spool moves back
to the left, allowing full pump flow to the loader
control valve
3
.
Because the pump output is always greater than
the flow required to operate the steering system,
flow to the loader valve is never completely cut off.
Maximum steering system pressure is controlled by
relief valve
43B
, located in the steering unit
43
.
Component Key:
LS
Load Sensing Port
P
From pump
T
To Loader Valve
2
Priority Valve
2A
Spring
2B
Spool
2C
Drilling
3
Loader Valve
40
Front Power Track Rod Ram
41
Rear Power Track Rod Ram
43
Steer Unit
43B
Relief Valve
5 -
3
5 -
3
Cir
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uit
D
e
sc
rip
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ns
S
e
c
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n H
S
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tio
n H