15 - 10
Hydraulic System
- Variable Flow
Fault Finding Contents
Page No.
Introduction 15 - 10
High or low system pressure 15 - 10
Pump stays at high pressure 15 - 10
Pressure or flow obtained at one port only 15 - 10
No pressure or flow at either port 15 - 10
High work port leakage 15 - 10
Leaks between sections 15 - 11
Sticking spool 15 - 11
Detent will not hold 15 - 11
Electrical detent will not hold 15 - 11
Poor performance, slow operating speed and/or
low maximum stall speed 15 - 11
Introduction
This section details the possible faults that may be found
with the loader and backhoe valve blocks. The faults listed
only appertain to valve blocks fitted on variable flow
hydraulic machine systems (Rexroth valves).
1 Before you begin fault finding, read the Safety
information at the beginning of this manual.
2 Make simple checks before say, stripping a major
component.
3 Make sure that the hydraulic fluid is at correct working
temperature (50 °C, 122 °F).
4 What ever the fault, check the condition of the
hydraulic fluid. Drain and replace if necessary.
5 Make any relevant electrical checks before moving on
to the hydraulics.
6 Be sure to remove ALL contamination and if possible
identify its origin. It may be part of a component from
elsewhere in the circuit.
7 Replace any seals such as 'O' rings before re-
assembling hydraulic components.
Section E
Hydraulics
9803/3280
Section E
15 - 10
Issue 1
Fault Finding
PROBLEM: High or Low system pressure.
POSSIBLE CAUSE: 1) Wrong pressure and/or flow regulator valve settings. 2) Loss of pilot signal due to shuttle
failure.
CORRECTIVE ACTION: 1) Readjust regulator valves. 2) Operate individual services to determine which shuttle is at fault,
refer to Service Procedures, Variable Flow Pumps, Shuttle Valve Signal Network -
Testing.
PROBLEM: Pump stays at high pressure.
POSSIBLE CAUSE: 1) Sticking main spool. 2) Sticking compensator spool.
CORRECTIVE ACTION: 1) See ‘Sticking Spool’ guide. 2) Remove & clean compensator spool.
PROBLEM: Can only obtain pressure or flow at one port.
POSSIBLE CAUSE: 1) Dirt in primary shuttle or damaged o-ring.
CORRECTIVE ACTION: 1) Remove & clean shuttle, inspect o-ring and replace if required.
PROBLEM: No pressure or flow at either port.
POSSIBLE CAUSE: 1) Dirt in secondary shuttle.
CORRECTIVE ACTION: 1) Shift one spool at a time with blocked ports until faulty section found, remove shuttle and
clean, inspect o-ring and replace if required.
PROBLEM: High work port leakage.
POSSIBLE CAUSE: 1) Spool not centred. 2) Dirt in port relief valve.
CORRECTIVE ACTION: 1) Check centring springs. 2) Remove & clean relief valve.
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