Hydraulic System Troubleshooting; Case Study: Abnormal Speed - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service
A.Troubleshooting
a. Case - Study : Abnormal speed
Problems Probable causes
1 The speed of all 1) The engine rpm is low.
actuators is low.
2) The quantity of working fluid in the hydraulic oil tank is too
small. The oil quality is poor.
3) The suction line (suction filter) is clogged.
4) The control differential pressure of the LS regulator is too low.
The locknut of the differential pressure control spring in the LS
regulator is loosened or maladjusted.
(If the speed of all actuators is too high, suspect that the control
differential pressure is too high.)
5) Gear pump volumetric efficiency is too low, so that LS control
pressure difference is not enough.
6) Leak from the PLS signal circuit (abnormal conditions of the
PLS signal circuit in the control valve)
7) Insufficient pressure due to defects in the unload valve seat
8) Insufficient pressure due to defects in the main relief valve
seat
9) Shut-off valve of inlet section is loosened, so that main pump
pressure got down to tank.
10) Defects or wear in the pump-mounting coupling
11) Breakage or wear in the pump drive shaft
12) Seizure, breakage or wear in the pump internal parts
2 The speed of all 1) The pilot filter is clogged.
the actuators in
2) Dust caught in the changeover valve or wear has caused the
the hydraulic
pilot primary pressure to drop.
pilot system is
3) Pilot primary relief valve is misadjusted.
too low.
4) Insufficient discharge quantity of the pilot pump
3 All the speeds 1) The screen built in the pilot valve on the R or L side is
on the R or L clogged.
side in the pilot
2) The pilot primary line on the R or L side is defective or the pilot
manipulation
valve is defective.
system are too
low or the
manipulation is
poor.
4 The speed of a 1) The control spool has got stuck in the neutral position.
certain hydraulic
pilot section is
2) The relevant spool of the pilot valve has got stuck.
too low.
(In both the A and B ports, a stick is rare.)
3) The pilot secondary pressure is too low.
Remedies
1) Adjust the accelerator cable or link.
2) Check the engine systems (fuel system, compression system).
1) Replenish or replace the working fluid.
1) Check the suction line. Replace the suction filter.
1) Actually measure the front unit or the swivel speed and make an
adjustment so as to bring the setting of the spring within specifications.
In the figure, tightening the setscrew increases the actuator speed and
loosening the setscrew decreases the speed.
1) Check gear pump delivery pressure and volumetric efficiency. Renew
gear pump.
1) Check the hose connections for leak. Disassemble and check the
PLS signal circuit in the control valve.
1) Measure the unload pressure. Disassemble and clean the unload
valve seat.
1) Measure and readjust the main relief pressure. Disassemble and
clean the relief valve seat.
1) Check shut-off valve and retighten.
1) Repair or replace the pump coupling.
1) Replace the shaft.
1) Repair or replace the pump.
1) Clean the pilot filter. Replace the filter if necessary.
1) Disassemble and clean the changeover valve and adjust the pilot
relief pressure.
1) Check the pressure and readjust it with shim.
1) Test the pilot pump performance. Replace the pump if it is defective.
1) Disassemble and clean the screen.
1) Check the defective pilot valve primary line. Replace the pilot valve
assembly if necessary.
1) Disassemble and service the pilot valve. Eliminate the cause of the
stick. Replace the assembly if necessary.
1) Measure the pilot secondary pressure. Adjust the pressure using a
shim.
1) Check the pilot spool for abnormal wear. Replace the valve assembly
if necessary.
Fig.1 Main relief valve
Ref.Fig.
Sleeve "E"
Fig.15
Chamber "D"
Main poppet
Fig.2
Fig. 2 Unload valve
Fig.1
LS
sensing
Fig.6
Pp
3
Fig.7
Fig.8, 9
Arm regeneration orifice
Fig. 3 Overload relief valve
Fig.10
Fig.8, 9
IV-S-3
Hydraulic system
Pilot poppet
LS main
relief valve
Unload valve
Unload valve and LS main relief valve