5 - 621F

5 - STEERING

CONTENT

Page

DATA 2

GENERAL DESCRIPTION 3

STANDARD STEERING HYDRAULIC CIRCUIT 4

621F SECONDARY STEERING HYDRAULIC CIRCUIT

521F SECONDARY STEERING HYDRAULIC CIRCUIT

ELECTRICAL CONTROL OF AUXILIARY CIRCUIT 8

STEERING PRESSURE CHECK 10

1
5 - STEERING 5 - 621F

DATA

521F 621F

3 Pump displacement 134 l/min (35.4 gpm) 171l/min (45 gpm)

8 Steering relief valve (included in the loader valve) 239-243 bar (3465 - 3525 psi)
9 Steering and loader LS pressure test point
15 Steering cylinders
16 Steering control valve
17 Back pressure valve 8 - 10 bar
42 Flow divider for auxiliary steering with 240 bar relief valve
43 Auxiliairy pump 11 cm3 11 cm3
44 Steering pressure switch 2.4 bar 2.4 bar

STANDARD STEERING CIRCUIT

Working of the priority valve

The steering priority valve is an infinite positioning valve located in the inlet of the control valve (8). It ensures that
the closed centered steering system receives oil, before sending steering pump oil to the loader control valve.
Oil enters the inlet port (a) of the priority valve from the piston pump, through the inlet of the loader valve. The
priority spool is spring-loaded (h) and blocks off the loader valve port (c). The oil flows around the priority valve
spool (f), then out of the steering control port (b) and on to the steering control valve (16). Excess pump flow
causes the pressure to build up through the balance orifice (g) on the non-spring side of the priority spool (f ).
This causes the priority spool (f) to start shifting, allowing the extra pump flow to be sent out through port (c) and
on to the loader valve while still meeting the steering flow demand. When the steering system is being used, it
needs more oil, and a pilot signal is sent back through the steering signal port (d) to the spring end of the priority
spool (f). When the priority valve senses the steering demand, the signal oil pressure on the spring end (h) of the
priority spool (f), in addition to the spring force, starts to shift the spool. This action restricts oil flow to the loader
valves. So the piston pump supplies more oil to the steering circuit.

Relief of the steering pressure

When the steering cylinders reach the end of their travel, the pressure increases on the steering relief valve (e)
that is tied into the steering signal line. The steering relief valve is adjustable. The steering relief valve poppet
opens and sends the pilot oil back to the reservoir. As the oil flows to the reservoir, the pilot pressure on the
spring side of the priority spool (f) can not continue to rise. The pressure on the non-spring side of the spool conti-
nues to build through the balance orifice (g). The pressure on the non-spring side of the spool can then overcome
the spring tension and the pressure on the spring side of the priority spool. The spool shifts, shutting off the oil
flow to the steering system (b) and the pump flow is sent to the loader control valve (c).

2
5- 621F 5 - STEERING

5- 621F STANDARD STEERING CIRCUIT

0.7
5
7

6

0.8

9 4b h

a
0.6
c

g
3 cutoff 80b
delta P b f
X B
Bypass 3.4b
Switch .7b

DECREASE
Diminution

INCREASE
4
Augmentation

A0V0DFR 
L L1
90 cc S

3
5 - STEERING 5- 621F

621F STEERING HYDRAULIC CIRCUIT WITH AUXILIARY PUMP 44

42

42 J F

43 6

0.7 5
7

ST

T 40 b H 10
0.3
J
0
F
60 bar
0.3 l
P 0.7mm
0.3
G
.4 b
SW

4 K CF LS
44
>

0.8
9 4b

0.6

X B

3
Delta P b
Bypass 3.4b
Switch .7b

Cutoff 80b
DECREASE
Diminution

43 INCREASE
 Augmentation

M 4
cc
A0V0DFR
L L1
90 cc S

4
5- 621F 5 - STEERING

621F SECONDARY STEERING COMBINATION VALVE (42 ) (For ECC regulation)

Hydraulic Description
When the secondary steering pump (43) is electricaly activated, oil flows from the pump (43) to the piloted direc-
tional cartrige (F); with the spool in it’s closed position oil flows through a one way check (G) and on to the supply
port of the steering control valve. There is a check valve (K) located in the block to prevent the secondary steering
pump oil from entering the main control valve (9).

Steering not in use with pump (43) energized

With the steering control valve (16) in the neutral position, no pressure comes from the load sense line and the
spool (F) is operated. The flow of pump (43) enters the block in (P) port and flows past the spool (F), letting secon-
dary steering pump oil flow to tank port (T).

Steering in use with pump (43) energized

When the steering wheel is turned, the load sense pressure (SLS) built up and the spool (F) comes back to closed
position. The oil of the pump (43) flows through the check valve (G) and supplies the steering unit (16) by port
(ST).

Relief pressure :
The relief valve (H) limits the over pressure of the SLS line to get maximum pressure (240 b) at pump (43).
Solenoid valve:
When the pump is energized the solenoid (J) is energized too, to depressurize the normal LS line of the steering
loader pump (3), this to avoid pump flow. Solenoid valve ON the load sense line of the steering orbitrol is totally
disconnected from the normal LS line .

SLS T
H

.03
J

LS

G
.03

K
ST

SW
.4 bar steering
pressure switch
Manocontact de
direction de secours
CF

5
5 - STEERING 5- 621F
521F STEERING HYDRAULIC CIRCUIT WITH AUXILIARY PUMP (For ECC regulation)

) (
0.7
5
7

6
0
60 bar
0.3 l .4 b

0.7mm
44

44a

4a

0.8

9 4b

8 0.6

cutoff 80b
delta P b
destroke 59b Bypass 3.4b
Switch .7b

4
40b
4

43
cc M A0V07
7cc 
3

10
44

44a
42
42a

6
5- 621F 5 - STEERING

521F EMERGENCY STEERING FLOW DIVIDER

a: Relief valve 240b

EF To tank
CF Steering orbitrol EF CF
P Pump delivery
T Tank
LS From steering orbitrol

LS

T
P

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5 - STEERING 5- 621F

ELECTRICAL DESCRIPTION
Power is provided to the secondary steering module from the accessory relay fuse ECA F17 to terminal (7) of the
module, from the fuse ECA F4 to terminal (1) of the module and fromthe fuse PRM A F2 to terminal (3). When the
operator starts the engine, hydraulic pressure builds up in the secondary steering switch above 2.4 bar (35 PSI)
and supplies a ground to terminal (9) of the module. Terminal (4) of the module is connected to the rear chassis
ground stud. Terminal (11) and (12) of the module is connected to the rear engine block ground stud.

If the machine loses steering pressure below 2.4 bar the pressure switch moves to the normally closed position,
and supplies terminal (8) of the secondary steering module a ground. Also tee’s off (spl-SEC STR) and supplies a
ground to the instrument cluster, to light the indicator on theAIC that tells the operator that the secondary steering
has been activated. At this time the secondary steering module will send power out terminal (2), to energize the
secondary steering motor. and the solenoid valve.

NOTE: The motor will run until the key is turned off.

Operation Test

While steering the machine at low idle, if the operator turns OFF the key switch and quickly turns it back to the ON
position, the secondary steering motor will turn on and the steering wheel can be turned back and forth to steer the
machine. The key switch must be turned to the on position before the pressure switch activates.

NOTE: To exit the test mode turn the key switch to the off position.

12 Electrical motor
13 Electronic seconday steering module
42 Secondary steering valve
43 Secondary steering pump
44 Secondary steering pressure switch 2.4b

621E 13

12

13

42

44
43

42

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5- 621F 5 - STEERING

EMERGENCY STEERING

SECONDARY STEERING MODULE

SECONDARY STEERING IGNITION  9R Or - .0

SECOND. STEER. MOTOR CONTROL  51 W -1.0
TO FUSE F4 ECA sheet 9 BATTERY
+
TO FUSE  PRM A LS SIGNAL
SECOND. STEER. MODULE B+ 3 9S Or - .0 sheet 9
SOLENOID
SECOND. STEER. CHASSIS GROUND 4 0 Bk - .0
NONE 5
NONE 6
TO FUSE F7
SECONDARY STEERING ACCESSORY 7 9M Or - .0 ECA sheet 9
SECOND. STEER. LOW PRES. SIGNAL 8 35 Y - .0
SECOND. STEER. HIGH PRES. SIGNAL 9
NONE 0
51 W - 1.0
.4 bar M
STEERING
SECOND. STEER. SIGNAL GROUND  PRESSURE SECONDARY
SECOND. STEER. SIGNAL GROUND  SWITCH STEERING
To AIC 2 PUMP/
ENGINE STOPPED 0 Bk - .0 0 Bk - .0 terminal  MOTOR

IGNITION KEY OFF

SECONDARY STEERING MODULE

SECONDARY STEERING IGNITION  9R Or - .0 TO FUSE F4 ECA sheet 9 + BATTERY

SECOND. STEER. MOTOR CONTROL  51 W -1.0 +
TO FUSE  PRM A LS SIGNAL
SECOND. STEER. MODULE B+ 3 9S Or - .0 sheet 9 + SOLENOID
SECOND. STEER. CHASSIS GROUND 4 0 Bk - .0
NONE 5
NONE 6
TO FUSE F7
SECONDARY STEERING ACCESSORY 7 9M Or - .0 ECA sheet 9 +
SECOND. STEER. LOW PRES. SIGNAL 8 35 Y - .0
SECOND. STEER. HIGH PRES. SIGNAL 9
NONE 0
51 W - 1.0
STEERING
.4 bar M
SECOND. STEER. SIGNAL GROUND  PRESSURE SECONDARY
SECOND. STEER. SIGNAL GROUND 
SWITCH STEERING
to AIC 2 PUMP/
ENGINE RUNNING 0 Bk - .0 terminal  MOTOR
0 Bk - .0
NORMAL STEERING
PRESSURE > .4b

SECONDARY STEERING MODULE

SECONDARY STEERING IGNITION  9R Or - .0 TO FUSE F4 ECA sheet 9 BATTERY

SECOND. STEER. MOTOR CONTROL  51 W -1.0 +
SECOND. STEER. MODULE B+ 3 9S Or - .0
TO FUSE  PRM A LS SIGNAL
sheet 9 SOLENOID
SECOND. STEER. CHASSIS GROUND 4 0 Bk - .0
NONE 5
NONE
SECONDARY STEERING ACCESSORY 7
6
TO FUSE F7 +
9M Or - .0 ECA sheet 9
SECOND. STEER. LOW PRES. SIGNAL 8 35 Y - .0
SECOND. STEER. HIGH PRES. SIGNAL 9
NONE 0
51 W - 1.0
STEERING
.4 bar M
SECOND. STEER. SIGNAL GROUND  PRESSURE SECONDARY
SECOND. STEER. SIGNAL GROUND 
SWITCH STEERING
to AIC 2 PUMP/
EMERGENCY PUMP ON 0 Bk - .0 terminal  MOTOR
0 Bk - .0

STEERING PRESSURE < 2.4b

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5 - STEERING 5- 621F

PRESSURE SETTING TEST

NOTE: The pump differential pressure must be properly adjusted before doing this test. Refer to Section 8 testing
and adjusting the differential pressure of the pump.

1 Connect a 350 bar pressure gauge to the test port (TP1).

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.

11

10