921E 7A
CONTENT
Page
PUMP INSTALLATION 2
SIMPLIFIED CIRCUIT 3
EUROPEAN STEERING HYDRAULIC CIRCUIT 4
STEERING COMBINATION VALVE 5
LOCATION OF STEERING COMPONANTS 6
PRESSURE CHECK AND ADJUSTMENT 7
CYLINDER 8
1
7A - 921E
STEERING PUMP AND PRIORITY VALVE ILLUSTRATION
2nd Pump
1st Pump
1. RETURN TO TANK 6. TO LOADER VALVE
2. STEERING LOAD SENSE 7. BOLT
3. PILOT PRESSURE TUBE 8. MOUNTING BOLTS
4. PILOT PRESSURE TUBE 9. PRIORITY VALVE
5. TO STEERING CONTROL VALVE
2
921E 7A -
SIMPLIFIED STEERING CIRCUIT
Steering
Loader valve
valve
Steering
Priority Valves
st pump nd pump
3
7A -
HYDRAULIC STEERING CIRCUIT
T
R
8 to 0 b
5
P
LS
L
SLS ST
0 b T
7
.
To loader valve
LS CF
. b
LS EF CF
. 0
.8
0. b
T
0 b
G1
TP5 b
G2
TP
0 b
TP
TP
B B
8 DECREASE DECREASE
Diminution Diminution
M
cc
INCREASE
INCREASE
9
Augmentatio
Augmentation
n
A0V0 - 85 cc A0V0 - 85 cc
L1 cutoff 80b cutoff 80b
L2 delta P 8 to b S S delta P 7 to 0 b L4 L3
0 5
4
921E 7A -
STEERING PRIORITY COMBINATION VALVE (30)
EF CF
A1 A2
TP5
P1
LS
C
B D1 D2
LS AUX LS1 LS2 TP1 P2
Priority valve (A1):
The cartridge (A1) provides priority flow in the steering unit, while allowing excess flow to be used for loader
functions. With port P1 providing inlet flow, port (CF) will deliver the required priority flow regardless of load sense
pressure (LS). Excess flow exits at (EF) to supply the loader valve if it is used.
Priority valve (A2):
The cartridge (A2) provides priority flow in the steering unit, while allowing excess flow to be used for loader
functions. With port P2 providing inlet flow, port (CF) will deliver the required priority flow regardless of load sense
pressure (LS). Excess flow exits at (EF) to supply the loader valve if it is used.
Relief valve (B):
The relielf valve (B) blocks flow from (LS) to tank port (DR) until sufficient pressure (207 b) is present at (LS) to for-
ce the spring-opposed poppet from its seat. When the steering cylinders reach the end of their travel the pressure
increases on the steering valve (23) and in the LS line. As the oil flows to the reservoir, the LS pressure cannot
continue to rise. The pressure on the non-spring side of the spools (A1) & (A2) can then overcomes the force of
the spring + the LS pressure. The spool (A1) & (A2) shift shutting off the oil flow to the steering system (CF) and
the pump flow is sent to the loader valve port (EF) if it is used.
Shuttle valve (C):
The shuttle valve (C) allows flow from the higher pressure of (LS) port and (LS AUX) port to (LS1) and (LS2) pump
ports.
Directional valve (D):
The directional valve (D1) & (D2) are a spring-biased blocking valve which will shift to allow full flow from (P1) or
(P2) to (T) only when pressure at (P1) or (P2) exceeds the cumulative pressure of (LS1) (or (LS2) plus the bias
spring pressure value. This to limit the maximum value of the differential pressure (40b) between pump outlets and
LS pressure.
5
7A - 921E
LOCATION OF STEERING COMPONANTS
TP1
TP5
PRIORITY VALVE 30
27a
26
TP5
STEERING UNIT 24 EMERGENCY STEERING VALVE 27
25 Back pressure valve (8 to 10 bar) 25
26 Steering pressure switch
27a Steering LS line isolation solenoid
TP1 2nd pump pressure test point
TP5 1st pump pressure test point
6
921E 7A -
PRESSURE SETTING TEST
NOTE: The1st pump differential pressure must be properly adjusted before doing this test. Refer to Section 8 tes-
ting and adjusting the differential pressure of the 1st pump.
1 Connect a 350 bar pressure gauge to the test port (TP5).
2 Make sure that the temperature of the hydraulic oil is at least 54 °C.
3 Start the engine and operate the machine at full throttle.
4 With the articulation lock still in place, turn and hold the steering wheel for a hard right turn.
5 Continue holding the steering wheel, and read the pressure gauge.
6 The pressure gauge must indicate 239 to 243 bar (3465 to 3525 psi). If the pressure is not
correct, adjust the steering relief valve (B).
PRESSURE SETTING ADJUSTMENT
1 Turn the adjusting screw (B) clockwise to increase the pressure setting. Turn the adjusting screw (B) counter
clockwise to decrease the pressure setting.
2 Repeat pressure test procedure.
3 If necessary, adjust the limit valve (B) again until within the specified range.
4 Stop the engine before removing the pressure gauge.
Tools required : 1/4 in male key and 3/4 in spanner
TP5
7
7A - 921E
STEERING CYLINDERS (23)
1. LOCK SCREW
2. GLAND
3. BACKUP RING
4. O-RING
5. WIPER
6. WIDE SEAL
7. NARROW SEAL
8. BUSHING
9. PISTON ROD
10. CAST IRON RING
11. LOADER RING
12. PISTON SEAL
13. WEAR RING
14. PISTON
15. CAP SCREW WITH WASHER
16. SNAP RING
17. SELF-ALIGNING BUSHING
18. TUBE
The cylinders are hydraulically cushioned when the machine is fully 40° steered to reduce jarring.
The piston gets an orifice to reduce the flow of oil comming out the outlet port.
