Takeuchi TL150, Workshop Manual

Page: 201 / 312

IV-55
HYDRAULIC UNITS
CONTROL VALVE
Symptom Probable Causes Remedy
Can
·
t be held in the
spool neutral position
(cylinder drops).
• Could be mistaken for a great amount of
leakage in the cylinder.
• The gap between the spool and body is
large, so the amount of oil leaking from
the spool is great.
• Spool won
·
t return completely to the
neutral position.
• Foreign matter is biting into the port
relief valve seat or the anti-cavitation
valve seat and oil is bypassing. Or a seat
is damaged.
• Check if it isn
·
t just the cylinder
·
s natu-
ral drop when the cylinder is held. If the
problem is in the cylinder, disassemble
and repair it.
• Replace the spool or replace the valve
block assembly.
• Manually Operated :
Check if there is something interfering
with the link mechanism.
Pilot Operated:
Check the pilot pressure.
• Disassemble and check, then overhaul
or replace.
The load won
·
t move.
(Pressure won
·
t in-
crease.)
• Foreign matter is biting into the relief
valve seat and oil is bypassing. Or the
seat is damaged.
• The relief valve
·
s adjustment screw is
loose.
• Foreign matter is biting into the port
relief valve seat or the anti-cavitation
valve seat and oil is bypassing. Or a seat
is damaged.
• Spool stroke is not the specified stroke.
• Pump is damaged and no oil is dis-
charged.
• Disassemble and check, then overhaul
or replace.
• Try tightening the adjustment screw. If
it is loose, correct the setting and tighten
the lock nut securely.
• Disassemble and check, then overhaul
or replace.
• Manually Operated:
Check if there is something interfering
with the link mechanism. Check if a pin
or a pin hole in the link connection is
worn.
Pilot Operated:
Check the pilot pressure.
• Check if the pump is abnormal or not.
If the pump is bad, replace it. Check if
the cause of the abnormality is air being
sucked in, deterioration of hydraulic oil
or shafts not centered, etc.
Load doesn
·
t move.
(Pressure rises.)
• The load is too heavy.
• Mechanical resistance of connecting
parts is great regardless of the hydraulic
pressure in the operating unit.
• A large piece of foreign matter is trapped
in the circuit or a pipe is bent, causing
great resistance.
• Spool stroke is not the specified stroke.
• Compare with an object of the specified
weight.
• Check and replenish hydraulic oil, etc.,
modify or repair.
• Find the affected place and repair it.
• Check if there is something interfering
with the link mechanism. Check if a pin
or a pin hole in the link connection is
worn or not.