Maeda MK0003, Service Manual, Page: 88 / 348

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6.4 FAILURE CAUSE AND COUNTERMEASURE
While each of the items indicated in the following table appears to be an independent problem, two or more of them
may occur concurrently.
Accordingly, employ such a method that the causes can be removed one by one.
Abnormal Phenomenon Cause Remedy
Oil leakage from a spool
seal area.
･
Sealing parts are scratched, or the seal lip
is worn out after serving for a long period
of time.
･ The sliding area of spool seal is scratched
from the outside (impact dent, scratch
blemish, etc.).
･
Mounting of the cover accommodating
sealing parts is strained.
･
The paint applied on the spool seal sliding
area is still sticking.
･ The tank circuit pressure has risen to
exceed the withstanding performance of
the sealing parts.
･
Replace with new ones.
･ Repair or replace the spool.
･
Correct it to the normal shape, while
checking the seal lip for its abrasion state.
･
Remove it by using diluent, or remove it
mechanically. Be cautious of possible
damage to the spool surface or seal lip.
･ Remove any object that increases the flow
resistance.
Spool sliding is not
smooth.
･ A foreign object is caught in the spool
sliding section.
･
Loss of oil film between the spool and
body due to an abnormal oil temperature
rise
･ Failure in lubrication due to degradation of
hydraulic oil
･
Abrasion of spool caused by a long time
use or uneven loading
･
The spool is bent by an external force.
･
Distortion of the whole valve body caused
by the stain on the mounting face.
･
Excessive tightening of valve mounting
bolts
･
Oil deposition inside each spring cover on
the spool operating side and on the other
side.
･ Overhaul the setup and repair or replace.
･
Take necessary measures to lower the oil
temperature. Also, if the relief valve is
operating frequently, check for the cause
and decrease the frequency.
･ Not only the oil replacement, but the
overhaul of the circuit may be required.
･
Check the spool diameter and determine if
it should be replaced.
･
Check the spool for its straightness and
other characteristics, and repair or replace
it as required.
･
Loosen the mounting bolts and check for
any cause of strain.
･
Re-tighten them with the specified torque.
･
Overhaul the setup and repair or replace
the seal.
Fails to travel (but
pressure rises).
･ The spool fails to perform the specified
stroke (6 mm).
･ The crawlers are overloaded.
･
The circuit is clogged with foreign objects
or piping is folded and bent.
･ Inspect the traveling lever link and repair
as required.
･ Check for any obstacle and clean it.
･
Check the piping for any bent or foreign
matter, and repair and clean as required.
The spool cannot be kept
at the neutral position.
･ The excessive gap between spool and
body causes an excessive leak.
･
The spool has not returned to the neutral
position correctly.
･ A foreign object is caught in the seat area
of port relief valve and anti-cavitation
valve, or the seat is damaged.
･ Replace the spool, or replace the valve
block assembly.
･
Manual operation: Inspect the traveling
lever link and repair as required.
･
Hydraulic operation: Check the pilot
pressure.
･ Overhaul the setup and repair or replace.
Fails to travel (and
pressure does not rise).
･
A foreign object is caught in the seat area
of relief valve, or the seat is damaged.
･
Loosening of relief valve adjusting screw
･
A foreign object is caught in the seat area
of port relief valve and anti-cavitation
valve, or the seat is damaged.
･ The spool fails to perform the specified
stroke (6 mm).
･ Oil flow rate from the pump is insufficient.
･
Overhaul the setup, check for foreign
matters, repair and clean or replace it.
･
Give an additional tightening to the
adjusting screw.
･
Overhaul the setup, check for foreign
matters, repair and clean or replace it.
･ Manual operation: Inspect the traveling
lever link and repair as required.
･ Hydraulic operation: Check the pilot
pressure.
･ Check the pump and repair it as required.