7 - 2
Loader Valve - Variable Flow
Priority Inlet Section Operation
The priority inlet section houses the steering priority valve
and a relief valve assembly. Operation is as follows:
Steering
When the steering wheel is turned, a priority pressure
demand signal is sent from the hydraulic steer unit and
received at the priority inlet section (port
PRLS
). The signal
oil flows through port
A
into chamber
C
via gallery
B
.
The combined force of spring
D
and signal oil pressure
moves spool
E
up. The position of the spool now allows oil
from the pump inlet port
P
to flow out to the hydraulic steer
unit via priority work port
PR
.
It must be noted that relief valve assembly
J
is redundant.
This relief valve is part of the inlet section, however the
hydraulic steer unit also houses a steer system relief valve.
To ensure the relief valve in the hydraulic steer unit controls
the steer system pressure, valve
J
is set abnormally high
(172 bar; 2500 lb/in
2
).
Component Key:
P
Pump Inlet
T
Tank
LS
Load sense port (to pump)
PRLS
Priority Load Sense Port (from steer unit)
PR
Priority Work Port (to steer unit)
Section E
9803/3280
Section E
7 - 2
Issue 1
Circuit Descriptions
LS
T
P
PRLS
PR
EXHAUST
PUMP
LOAD SENSE
A
B
D
C
E
J
PR
PR
P
PRLS
LS
T
A273940
A273930