SERVICE REPAIR
S2.00XL S2.50XL S3.00XL Europe [A187]
1
INTRODUCTION
This section has the description and operation for the
HGF Hydraguide steering control unit made by Ross
Gear. The disassembly and assembly procedure is for
making repairs. A Troubleshooting chart is at the end of
the section.
DESCRIPTION
The steering control unit has two sections: a fluid con-
trol valve and a fluid metering section. The two sections
are connected hydraulically and mechanically inside of
the housing.
Control Valve Section
The open center control valve is a rotating valve plate.
The control valve controls the pressure and flow of the
hydraulic oil to the steering cylinder. The valve plate is
held in its center position by two sets of three coil
springs. When the valve plate is in the center position,
hydraulic oil flows from the hydraulic pump, through
the steering control unit, and returns to the hydraulic
tank. When the valve plate is moved from its center po-
sition by the steering wheel, a port is opened in the isola-
tor manifold and hydraulic pressure is sent to the meter-
ing section.
Metering Section
WARNING
The use of the steering control unit as a pump for
manual steering can damage the unit if the torque on
the steering wheel is greater than 170 N.m (125 lbf ft).
This damage will cause the complete loss of control of
the steering system.
The metering section has the following three functions:
• measures the hydraulic oil to the steering cylin-
der
• keeps a constant ratio of steering wheel turns to
the direction of the steered wheels
• operates as a pump for manual steering of the lift
truck if hydraulic pressure is not available from
the hydraulic pump
FIGURE 1. ROSS HGF STEERING CONTROL
UNIT
1. PORT COVER
2. PORT MANIFOLD
3. ISOLATOR MANIFOLD
4. METERING RING
5. ROTOR ASSEMBLY
6. UPPER COVER PLATE
7. DRIVE ASSEMBLY
8. VALVE SPRINGS
9. VALVE ASSEMBLY
10. DRIVE LINK
11. COMMUTATOR ASSEMBLY
12. DRIVE PLATE
13. THRUST BEARING
14. COVER AND TUBE ASSE