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5
BOOM
TROUBLESHOOTING
2. Check the pilot valve
Disconnect the hose connecting the pilot valve and the
control valve (boom block) from the control valve. Fit
the pressure gauge to the hose just disconnected.
• Operate the lever (boom) and measure the pres-
sur
e.
• If the pressure is between 0 and 3.4 MPa depending
on the lever angle, the pilot valve is normal.
3. Check the spool operation
Disconnect the hose connecting the control valve
(boom block) and the boom cylinder from the cylinder.
Fit the pressure gauge to the discharge port on the
control valve.
• Operate the lever (boom) and measure the pres-
sur
e.
Supply pressure: 21.0 MPa
4. Test by replacing the port relief valve
Replace the port relief valve in question with a normal
port relief valve. If the boom cylinder operates with the
replacement valve, the port relief valve used on the
boom side is faulty.
Make sure to return the port relief valve to its regular
position after the above inspection.
5. Check the boom cylinder.
a. Disconnect the hose connecting the control valve
and the boom cylinder from the control valve side.
b. Connect the hose just disconnected to the arm or
bucket block.
c. Try to operate the boom cylinder. If the cylinder fails
to operate, the cylinder is faulty.
Before performing steps “a” through “c” above, fully
extend the bucket cylinder, completely retract the
arm cylinder and lower the bucket to the ground.
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