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5-49
5
TROUBLESHOOTING
Symptoms
Major causes
Remedies
Spool’s neutral posi-
tion cannot be main-
tained (cylinder drops)
• 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 repair 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-
sure.
• Disassemble, overhaul or replace.
Load
cannot
be
moved (pressure can-
not be increased)
• 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-
sure.
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
Summary of Contents for TB 250
Page 1: ......
Page 3: ...1 1 SAFETY 1 Safety alert symbol 1 2 Safety precautions 1 3 Cautions when working 1 9...
Page 36: ...2 24 2 TIGHTENING TORQUE SERVICE DATA...
Page 38: ...2 26 2 HYDRAULIC CIRCUIT DIAGRAM SERVICE DATA Equipped with options 2 2...
Page 39: ...2 27 2 HYDRAULIC CIRCUIT DIAGRAM SERVICE DATA Equipped with angle blade and blade oat 1 2...
Page 40: ...2 28 2 HYDRAULIC CIRCUIT DIAGRAM SERVICE DATA Equipped with angle blade and blade oat 2 2...
Page 41: ...2 29 2 HYDRAULIC CIRCUIT DIAGRAM SERVICE DATA Equipped with high ow option 1 2...
Page 42: ...2 30 2 HYDRAULIC CIRCUIT DIAGRAM SERVICE DATA Equipped with high ow option 2 2...
Page 49: ......
Page 59: ...2 46 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 60: ...2 47 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 61: ...2 48 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 62: ...2 49 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 63: ...2 50 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 64: ...2 51 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 65: ...2 52 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 66: ...2 53 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 67: ...2 54 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 68: ...2 55 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 69: ...2 56 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 70: ...2 57 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
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Page 72: ...2 59 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 73: ...2 60 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA NAME STANDARD NO...
Page 74: ...2 61 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 75: ...2 62 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 76: ...2 63 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 77: ...2 64 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 78: ...2 65 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 79: ...2 66 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 80: ...2 67 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 81: ...2 68 2 WIRE HARNESS WIRING DIAGRAM SERVICE DATA...
Page 92: ...3 11 3 CONTROL VALVE FUNCTION...
Page 108: ...4 3 4 SERVICE STANDARDS DISASSEMBLY AND ASSEMBLY Clearance for pin and bushing...
Page 352: ...ENGINE 6 Machine model Mounted engine TB250 4TNV88...