Fundamentals Of Ls Pump Troubleshooting (Defective Portions And Symptoms) - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service

2) Fundamentals of LS Pump Troubleshooting (Defective Portions and Symptoms)

Failure symtom
Portion contributable to the failure of
pump swash plate control
1. Increased pressure leak due to wear
in the control pin A (small diameter pin)
2. Increased pressure leak due to wear
in the control pin B (large diameter pin)
3. Stick of the horsepower control feed-
back pin
4. Stick of the con- The passage Pc
trol spool of the pressure
horsepower con- gets stuck on the
trol valve tank side.
Stick in the posi-
tion
passage Pc pres-
sure
open to the P pres-
sure.
5. Stick of the LS Stick in the posi-
regulator spool tion where the Pc
passage
dumped.
Stick in the posi-
tion
passage
blocked.
The speed of the work machines is
low, since the required flow is not
discharged from the pump.
(LS control failure)
The swash plate tilting power is weak
and the required flow is not discharged,
since the pressure that acts on the con-
trol pin A (small diameter pin) leaks.
(The speed decreases especially in the
arm rake-up mode at low rpm.)
The LS control is disturbed, since the
power to return the swash plate to a
small tilting angle is weak.
The pump discharge quantity is slightly
larger than usual.
A pin stick causes the control spring to
push in the control spool all the time, to
lead the pressure of the control pin B to
the tank.
When PPS < PLS + FLS, the tilting
angle of the pump swash plate is maxi-
mized.
When PPS > PLS + FLS, the LS flow
control is exercised up to the pin stick
position.
In the area of PPS < PLS + FLS, the
always pump swash plate is always forced to be
held at the maximum tilting angle.
looks like a fixed capacity pump of
approx. 72LPM
In the area of PPS > PLS + FLS, the
flow is LS-controlled.
The high pressure that has acted on the
where the control pin is not released, since the
control pressure of the control pin is not
is always linked to the tank in the control spool
section. As a result, the pump swash
plate tilts in the direction that decreases
the discharge quantity. The work speed
decreases. Running in the standby flow
state. It works like a fixed capacity pump
in the standby state.
The tilting angle of the pump swash
plate is maximized and the pump works
is like a conventional variable capacity
pump.
The extra flows through the unload
valve.
The LS regulator-based LS control is
disabled.
All the work speed decreases, since the
where the swash plate is held in the standby flow
Pc is position. The LS control is disabled.
Pump performance
It
IV-S-13
Hydraulic system
The engine stalls in certain condi-
tions. (Horsepower control failure)
The engine does not stall.
The engine is apt to stall, since the con-
trol power to move the swash plate to a
small tilting angle is weak even when
the load pressure is increased.
The horsepower control is disturbed.
The engine stalls when a load that
decreases the swash plate
beyond the pin stick position is imposed,
since the horsepower control is dis-
abled.
The engine stalls if the load pressure
increases in excess of the control horse-
power.
In the LS control area, the flow is con-
trolled with the LS regulator and the nor-
mal flow is obtained.
The engine does not stall, since it is
fixed in the standby flow position when
the PPS pressure from the LS spool acts
on the control pin. It goes into the
standby state.
The pump works like a conventional
variable capacity pump and the engine
does not stall.
The engine does not stall, since the
pump swash plate is always controlled
to a small tilting angle.
tilting