Case Study: Poor Manipulation And Abnormal Operation - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service
c. Case - Study : Poor Manipulation and Abnormal Operation
Problems
1 The engine stalls at the 1) The control pin has got stuck.
rated rpm when a load
(traveling, etc.) is
2) There is a control pressure leak due to wear in the control pin (large diameter
imposed.
pin).
3) The control spool of the horsepower control valve has got stuck.
4) The horsepower control valve is set improperly.
2 The response of the work 1) The orifice in the pump is clogged with dirt.
machine is abnormally
2) The unload valve orifice is clogged with dirt.
slow. (Especially, at low
3) The PLS line orifice is clogged with dirt.
temperatures)
3 An abnormal sound is 1) Air bleeding hose is kept open.
heard from the pump.
2) The quantity of working fluid is smaller than the required quantity.
3) The working fluid viscosity is improper.
4) Air is sucked through the suction hose or pipes.
5) There are contaminants or pieces of metal.
4 Loud noise is heard from 1) The delivery hose touches something and rattles.
around the control unit.
2) The relief valve makes squeaking noises.
5 The boom is not raised There is a possibility that the arm compensation spool has got stuck on the open
when horizontal work is side.
done through simulta- (Principle)
neous manipulation of the When the boom is manipulated, the arm compensation spool works in the direction
boom and the arm at idle where it is closed, since the operating pressure for raising the boom is high. How-
or low rpm. ever, the pressure compensation is not made due to a stick and the pump flow is
directed to the arm crowd side under light load. As a result, the pressure for raising
the boom is not built up.
6 The spontaneous boom 1) Failure of the seal in the cylinder
fall amount is large.
2) Failure of the boom overload relief valve
3) Failure of the load check valve
4) Failure of the holding valve seat
7 The swivel does not stop. The makeup poppet has got stuck. It is clogged with dirt.
The swivel main spool has got stuck.
The relief valve of the swivel motor is clogged with dirt.
Fig. 14 Horse power control setting
Probable causes
Fig. 15 LS control valve
IV-S-6
Remedies Ref.Fig.
1) Eliminate the cause of the stick completely or Fig.13
replace the pin assembly.
2) If the control pressure leak is caused by wear,
replace the pump assembly.
3) If the horsepower control valve is set improperly,
reset it.
For the resetting of the horsepower control valve, Fig.14
refer to the P-Q characteristic diagram.
1) Disassemble and clean.
1) Disassemble and clean.
1) Disassemble and clean.
1) Bleed the air from the pump and plug the hose.
1) Check the quantity of working fluid and replenish.
1) Use the recommended working fluid.
1) Check and retighten the hose and pipe. Bleed
them.
1) Overhaul and clean the pump. Replace the pump
assembly if necessary.
1) Reinstall the hose. Prevent the hose from touch-
ing.
1) Check the relief pressure. Disassemble and clean
the relief valve. Replace the relief valve assembly if
necessary.
1) Eliminate the cause of a compensation spool stick Fig.11
completely.
2) Replace the arm section assembly of the control
valve.
1) Replace the seal.
1) Disassemble and clean the relief valve.
1) Check the load check valve.
1) Disassemble and clean the fall prevention valve.
Disassemble and clean the poppet.
Disassemble and clean the control valve swivel por-
tion.
Disassemble and clean the relief valve.
Fig. 12 High pressure selection valve
Overload relief
valve
Main spool
Pressure
compensation
spool
Load check
Hydraulic system
Overload relief
valve
High pressure
selection valve
Backet(Boom) section