Troubleshooting; Control Valve: Overall - Doosan DX140R Shop Manual

TROUBLESHOOTING

Control Valve: overall

Problem
Spool does not stroke.
Cannot maintain load.
When the spool is moved
from neutral to higher
position, load carrying
capacity is reduced.
Main Control Valve
Possible Cause
Oil temperature is too high.
Hydraulic oil is contaminated.
Piping port joint is loose.
Valve housing is torted after
installation.
Pressure is too high.
Spool is bent.
Return spring is damaged.
Spring or cap is separated.
Temperature distribution in valve is
not uniform.
Dust in valve.
Insufficient pilot pressure
Cylinder oil leak.
Oil is bypassed in spool.
Oil leak at overload relief valve oil.
Oil leak at anti-drift valve.
Dust in load check valve.
Poppet or seat of valve is
scratched.
Remedy
Remove obstructions in the piping line,
which may resist oil flow.
Replace hydraulic oil, wash circuit.
Check torque.
Check by unscrewing joint bolts.
Install pressure gauge to check pressure
at pump and cylinder port.
Replace with valve assembly.
Replace damaged part.
Unscrew cap to fix, and tighten it.
Warm up the whole circuit.
Remove dust.
Check pilot valve and pilot relief pressure.
Check cylinder seal.
Check if spool is scratched.
Wash valve housing seat and relief valve
seat.
Disassemble anti-drift valve, wash all the
seats clean.
If seat is scratched, replace the poppet, or
lap the poppet and seat.
If the anti-drift valve spool has a problem,
spool and sleeve must be replaced
together (they are match-finished).
Disassemble and wash check valve.
Replace poppet or lap poppet and seat.
SP001029
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