Main Control Valve - jcb JS300 Service Manual

Symptoms
Spool sticking
Spool does not stroke
Load cannot be maintained
When the spool is selected
from neutral to raise position,
the load falls.
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Main Control Valve

Table 2.
Possible Causes
1. Oil temperature is abnormally high.
2. Hydraulic oil is dirty
3. Port connector is tightened too much
4. Valve housing is deformed due to
Installation
5. Pressure is too high
6. Spool is bent
7. Return spring is damaged
8. Spring or cap is not on straight
9. Temperature inside valve is not even.
1. Valve is clogged inside with dirt
1. Oil leakage from the ram
2. Oil is by-passing from the valve spool
3. Oil leakage from the port relief valve
4. Oil leakage from the lock valve
1. Foreign matter in load check valve
2. Check valve poppet or seat damaged
9813/5100-1
Section E - Hydraulics
Hydraulic System Fault Finding
Main Control Valve
Countermeasures
Remove the obstruction.
Replace the hydraulic oil and clean the
circuit at the same time.
Check the torque.
Loosen the installation bolt and check.
Attach pressure gauge to pump port and
ram port and check the pressure.
Replace the valve assembly.
Replace the damaged parts.
Loosen the cap and after aligning, tighten.
Warm up the circuit.
Remove the dirt (flushing).
Check the ram.
Replace the valve assembly.
Remove the port relief from the housing
and clean the housing seat and relief valve
seat.
Disassemble the lock valve and clean the
poppet seat and sleeve, plug seat. If the
seat is damaged, replace the poppet, or lap
the poppet and seat.
Disassemble the check valve and clean.
Replace the poppet or lap the poppet and
seat part.
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