jcb JS70, Service Manual

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32 - 1
Section E Hydraulics
9803/6020
Section E
32 - 1
Issue 1
Control Valve
Control Valve Fault Finding
Control Valve in General
Symptoms Possible Causes Countermeasures
Spool sticking 1. Oil temperature is abnormally high. Remove the obstruction.
2. Hydraulic oil is dirty Replace the hydraulic oil and clean the
circuit at the same time.
3. Port connector is tightened Check the torque.
too much
4. Valve housing is deformed due to Loosen the installation bolt and check.
Installation
5. Pressure is too high Attach pressure gauge to pump port and
ram port and check the pressure.
6. Spool is bent Replace the valve assembly.
7. Return spring is damaged Replace the damaged parts.
8. Spring or cap is not on straight Loosen the cap and after aligning, tighten.
9. Temperature inside valve is not even. Warm up the circuit.
Spool does not stroke 1. Valve is clogged inside with dirt Remove the dirt (flushing).
Load cannot be maintained 1. Oil leakage from the ram Check the ram.
2. Oil is by-passing from the valve spool Replace the valve assembly.
3. Oil leakage from the port relief valve Remove the port relief from the housing
and clean the housing seat and relief
valve seat.
4. Oil leakage from the lock valve 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.
When the spool is selected from 1. Foreign matter in load check valve Disassemble the check valve and clean.
neutral to raise position, the load
falls.
2. Check valve poppet or seat Replace the poppet or lap the poppet and
damaged seat part.