Kubota KX080-3 Workshop Manual page 412

WSM KX080-3 Service
a. Case - Study : Abnormal speed
Problems Probable causes
5 The speed of a certain 1) Swing: The swing pilot valve malfunctions.
actuator is too low. 2) Dozer: The dozer pilot valve malfunctions.
3) Service port: The service port solenoid valve malfunctions. 1) Check the solenoid valve.
4) Hydraulic pilot system: Poor operation of the rele-
vant pilot valve
5) Actuator in the cylinder system: An internal leak is
increased due to breakage in the cylinder packing.
6) Poor operation of the spool in the control valve
section
7) A leak from the overload relief valve or improper
pressure
8) Misassembling of the main C/V spool
The max speed of the actuator depends on the
machined opening in the spool. If the spool is misas-
sembled, therefore, the max speed may not be
achieved.
9) Misassembling of the compensation spool
10) Misassembling of the high pressure selector valve.
11) Compensation spool stick
If the compensation spool does not open, the
required quantity of fluid does not flow to the actuator
and the necessary speed is not achieved.
12) High pressure selector valve is sticking.
All of downstream sections pressure became low.
6 The speed of the arm This problem arises when the pilot valve types are
crowd and boom lower- confused.
ing section is too low.
7 The speed of a certain 1) The high pressure selector valve has got stuck.
C/V section and its A high pressure selector valve stick causes a leak of
downstream actuator high pressure and the PLS pressure does not
is too low. increase. As a result, the pump swash plate does not
tilt correctly.
8 The traveling speed 1) Improper setting of the horsepower control valve
only is too low. 2) Travel independence valve spool sticks.
9 The speed on the arm 1) Stick of the pump LS regulator spool
or bucket crowd side The PLS pressure is low when the load pressure on
decreases occasion- the crowd side is low. The force that pushes the LS
ally. regulator spool is therefore weak, so that the tilting of
(Especially, in the the pump swash plate delays momentarily.
engine's low-range or However, the PLS is sufficiently high at high load
midrange) pressure and the spool shifts normally.
10 The traveling speed When the load pressure increases, the system
decreases when the enters the horsepower control area, causing the
front system is pump discharge quantity to decrease.
relieved during travel- In the relief mode, the pump discharge quantity
ing. decreases to approximately 40 liters/min.
11 The port A or B speed 1) The control spool has got stuck on one side.
in a certain hydraulic
pilot section is too low.
2) The relevant spool of the pilot valve has got stuck. 1) Disassemble and service the pilot valve. Eliminate the cause
Remedies
1) Check the function of pilot valve.
1) Check the function of pilot valve.
1) Measure the pilot secondary pressure. Disassemble and
check the pilot valve.
1) Disassemble the cylinder and replace the seal.
1) Disassemble and check the control valve.
1) Disassemble, clean and adjust the relief valve or replace it.
1) If the spool or the spring is misassembled, replace it with a
normal part.
1) Eliminate the cause of the stick completely or replace the
entire assembly.
1) Check the corresponding high pressure selector valve.
1) Replace it with a normal pilot valve.
1) Eliminate the cause of the stick completely or replace the
valve assembly if necessary.
1) Readjust the horsepower control valve.
At a low temperature, the effect of pressure loss increases,
causing the traveling second gear to slow down occasionally.
Warm up the traveling motor up to 50°C or so and make a
retest.
1) Disassemble and clean the spool to eliminate the cause of
the hitch.
Replace the regulator valve assembly if necessary.
1) This action is normal, since the horsepower control is exer-
cised.
1) Disassemble and service the control valve. Eliminate the
cause of the stick. Replace the valve assembly if necessary.
of the stick. Replace the assembly if necessary.
IV-S-4
Fig. 4 Relief valve layout
Ref.Fig.
b
3
a
4
a
a 1
3
b
6
b
4
b
1
b
5
b
1
Fig.3
Fig.1
Fig.1
Fig.1
b
1
Fig.12
Fig.14
Fig.13
Fig. 6 Pilot filter
Fig.10
Fig.8, 9
Hydraulic system
b
2
a
2
b
1
b
5
Fig. 7 Change valve
Fig. 8 Pilot valve at neutral
Spring seat
Pilot spring
Return spring
Spool