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 ap p ert ain t o valve b loc ks fit t ed on variab le flow
hydraulic machine systems (Rexroth valves).
1
B ef o re yo u b eg in f ault f ind ing , read t he Saf et y
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 t he f ault , c hec k t he c o nd it io n o f t he
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
Rep lac e any seals suc h as ' O' ring s b ef o re re-
assembling hydraulic components.
Section E
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.
