Procedures For Ls Control Valve Troubleshooting - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service

(3) Procedures for LS Control Valve Troubleshooting

In the event of hydraulic trouble with the LS controller for KX080-3, complete the following basic check
items and check the manipulation of the hydraulic pilot system.
(1) Basic check items: Quantity of oil, quality of oil, filter clogging, oil leak, air suction, engine condi-
tions and the method of manipulating this machine
(2) Trouble with the hydraulic pilot system?
1) All the hydraulic pilot systems?
2) Certain hydraulic pilot system?
(3) Trouble with the actuator side?
If the check above detects no trouble, suspect the control valve or the pump.
With the following five items related to the control valve in mind, manipulate this machine or measure
the pressure to pinpoint defective portions.
The use of the five check items makes it relatively easy to pinpoint trouble in detail. Get to work on the
control valve first.
Basically, the control valve consists of the following parts. Trouble phenomena occur as shown below.
It is preferable that the following steps be performed to determine the cause of trouble.
1) Unload valve
Make a check if the unload pressure is not built up at the maximum rpm under no load with the valve
placed in the neutral position.
KX080-3: Max. engine KPM=27 kgf/cm
(Check the pump discharge quantity.)
2) Main relief valve
Make a check if the main relief pressure is not built up.
KX080-3: 285 kgf/cm
If any one actuator is relieved, the main relief pressure is built up.
(For the dozer UP only, however, there is a 135 k overload relief valve.)
3) Spool in the valve section
1. The spool must work at a full stroke under the secondary pressure of the pilot valve.
2. If the spool does not work at a full stroke even when the secondary pressure is the specified pres-
sure, suspect that the spool has got stuck.
3. If the cylinder speed does not increase even when the spool works at a full stroke, suspect that the
spool is misassembled.
4) High pressure selector valve
1. If the high pressure selector valve does not move normally due to a stick, its own high pressure
leaks from the valve, causing the PLS pressure to the compensation spool and the PLS pressure
to the LS regulator to decrease, respectively. As a result, tilting takes place so as to reduce the
pump discharge quantity, so that the actuator speed decreases.
2. Similar phenomena occur in the sections downstream from the section of the defective high pres-
sure selector valve.
3. The sections upstream from the section of the defective high pressure selector valve work nor-
mally.
4. If the section of the defective high pressure selector valve and the sections upstream from it are
manipulated at the same time, the PLS pressure to the pump acts on the upstream sections and
the pump is normally LS-controlled.
5. If the high pressure selector valve gets stuck, the same phenomena occur in both the A and B
ports.
2
(2.65 MPa, 384 psi)
2
Idle RPM=23 kgf/cm , 2.25 MPa, 327 psi
2
, 27.9 MPa, 4047 psi
IV-S-10
Hydraulic system