5-49
5
TROUBLESHOOTING
Symptoms Major causes Remedies
Spool’s neutral posi-
tion
cannot be main-
tained (cylinder dr
ops)
• There are cases of a large oil leak inside the
cylinder
• Since the clearance between the spool and
the body is too large, oil is leaking from the
clearance
•
Spool is not completely back in the neutral
position
•
Foreign matter is caught in the seat of the
port relief valve or of the anti-cavitation valve,
and thus the oil is bypassing the section. Or,
the seat is damaged
•
Check if the cylinder drops spontaneously
when it is held. If the cylinder is faulty, disas-
semble and r
epair it.
• Replace the spool and the valve block as-
sembly.
•
Manual: Check if the link mechanism is inter-
fering with others.
Hydraulic operation: Check the pilot pres-
sur
e.
• Disassemble, overhaul or replace.
Load cannot be
moved (pressure can-
not be incr
eased)
• Foreign matter is caught in the seat of the
port relief valve, and thus the oil is bypassing
the section. Or, the seat is damaged
• Adjuster screw on the relief valve is loose
• Foreign matter is caught in the seat of the
port relief valve or of the anti-cavitation valve,
and thus the oil is bypassing the section. Or
the seat is damaged
•
Spool stroke is out-of-spec
• Oil supply from the pump is insufficient, be-
cause the pump is damaged
•
Disassemble, overhaul or replace.
• Screw in the adjuster screw. If loose, set the
adjustment again and fasten with a lock nut.
• Disassemble, overhaul or replace.
• Manual: Check if the link mechanism is inter-
fering
with others. Check if the pin or pin hole
on the linking section is worn out.
• Hydraulic operation: Check the pilot pres-
sur
e.
Check for any abnormality in the pump.
If the pump is faulty, replace it and find the
cause of the abnormality (e.g., faulty air suck-
ing or oil degradation).
Load
cannot be
moved (pressure is
being increased)
• Overloading
• Mechanical resistance of related parts/de-
vices
(unrelated to the hydraulic pressure of
the hydraulic oil) is large
•
Large resistance is generated, because the
circuit is clogged with large foreign matter or
the piping is bent
•
Spool stroke is out-of-spec
• Compare with a one with standard load.
• Check and add oil, modify or repair the parts/
devices.
•
Repair if the location of clogging or bent is
known.
•
Check if the link mechanism is interfering
with others and if the pin or pin hole on the
linking section is worn out.
When the arm float
is operated, the float
function fails.
•
Foreign matter is caught in the pilot valve or
the valve is stuck
•
The pilot spool is stuck
• Overloaded
• Floating is impossible due to low Pp port
pressure
• Solenoid wire is broken
• Disassemble and clean. If the damage is
large, replace the pilot valve.
• Control of the hydraulic oil contamination
• Remove the overloading
• Measure the Pp pressure.
• Replace the solenoid.
CONTROL VALVE
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