U20-3, U25-3 WSM Hydraulic system (Service section)
IV-S-77
[3] Trouble shooting
It is not easy to pinpoint trouble spots. The table below lists some typical problems, their possible causes
and corrections. Before starting repair jobs, refer to the table below.
A machine trouble is not necessarily caused by just one part, but by come different parts combined. It
should be noted that the corrections listed below might not be enough and additional measures might be
needed.
This chart does not cover all possible causes and corrections. Whenever necessary, it is therefore
essential for the repair supervisor to look further into the problem and cause in question.
Problem Causes Corrections
Secondary pressure failure to rise (1) Primary pressure too low.
(2) Secondary-pressure spring (241)
broken or worn out.
(3) Too large a gap between the spool
(201) and casing (101).
(4) Steering wheel too loose.
(1) Ensure the specified primary
pressure.
(2) Replace the spring with new one.
(3) Replace the remotely operated valve
with new one.
(4) Disassemble and reassemble the
related section. Or replace the
steering wheel as required.
Secondary pressure unstable (1) Sliding parts stuck.
(2) Tank line pressure fluctuating too
much.
(3) Air sucked in the piping.
(1) Correct the stuck spot.
(2) Return the oil direct to the oil tank.
(3) Operate the machine to let out the
air.
Secondary pressure too high (1) Tank line pressure too high.
(2) Sliding parts stuck.
(1) Correct the stuck spot.
(2) Return the oil direct to the oil tank.
Photo 7-37 Photo 7-38
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