Control Valve Component Troubleshooting; Control Valve In General Troubleshooting - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service
f. Control valve component troubleshooting
--Control valve in general--
Failure symptom
1. Spool will not stroke. (Machine will
not pick up speed.)
2. Load cannot be held.
3. Load drops when the spool is
switched from neutral to high position.
Suspected causes
1. Oil temperature is raised abnor-
mally.
2. Contamination of hydraulic oil.
3. Over-tightening of the piping port
joint.
4. Valve housing is distorted after
mounting.
5. Pressure is too high.
6. Spool is bent.
7. Return spring is damaged.
8. Spring or cap is displaced.
9. Temperature distribution in the
valve is not uniform.
10. Valve is clogged with dust.
11. Pilot pressure is insufficient.
12. Compensation spool is seized.
1. Oil leaks from the cylinder.
2. Oil bypasses from the spool.
3. Oil leaks from the overload relief
valve.
4. Oil leaks from the holding valve.
1. Load check valve is clogged with
dust.
2. Poppet or seat of the check valve is
damaged.
IV-S-16
Hydraulic system
Remady
Remove something which hampers oil
flow in the piping system.
Replace hydraulic oil, and clean the
circuit at the same time.
Check the tightening torque.
Loosen the set bolt and check the
housing for distortion.
Set a pressure gauge between the
pump port and the cylinder port, and
check the pressure.
Replace the valve assembly.
Replace the damaged spring.
Loosen the cap to make centering and
then tighten.
Warm up the whole circuit.
Remove (Brush off) dust.
Check the pressure of the pilot valve
and pilot relief valve.
Replace the compensation spool or
section assembly.
Check the cylinder seal.
Check the spool for any defect.
Clean the valve housing seat and
relief valve seat.
Disassemble the anti-drift valve, and
clean the seats of parts. If seat is dam-
aged, replace the poppet, or lap the
poppet and seat.
If any abnormality exists at the spool
of holding valve, replace both the
spool and sleeve, which are fitted in
mutually.
Disassemble the check valve and
clean it.
Replace the poppet, or lap the poppet
and seat.