Doosan D20G, Service Manual

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Vehicle System Testing and Adjusting 36
Problem: The lift or tilt cylinders do not hold
their position with the valve control levers in
neutral position.
Probable Electric Cause
1. The valve spools do not hold their positions
because the springs for the valve spools are weak
or broken.
2. Control valve leakage caused by worn valve
spools or seals.
3. The check valves in the control valve are
defective.
4. Leakage of the cylinder lines or piston seals.
5. There is foreign material in the control valve.
Hydraulic Pump
Problem: Noise in the pump.
Probable Cause:
1. The oil level is low.
2. The oil is thick (viscosity too high) or seals.
3. The pump inlet line has a restriction in it.(strainer
plugged).
4. Worn parts in the pump.
5. Oil is dirty.
6. Air leaks into the inlet line
Problem: The oil temperature is too high.
Probable Cause:
1. The oil level is low.
2. There is a restriction in an oil passage.
3. The relief valve setting is too low.
4. The oil is too thin.
5. There is air leakage in the system.
6. The pump has too much wear.
7. The system operates at too high a pressure.
a. Relief valve setting too high.
b. Attachment components cause a restriction
during movement.
c. Restrictions in flow control valve, load check
valve and in oil lines.
8. Severe hydraulic usage.
Problem: Leakage on the shaft seal.
Probable Cause:
1. The shaft seal is worn.
2. There is a broken gasket behind the seal..
3. The inner parts of the pump body are worn.
4. Operation with too low oil level in tank causes
suction on the seal.
5. Seal cut on shoulder of pump or keyway during
installation.
6. Seal lips are dry and hardened from heat.
Problem: There is failure of the pump to deliver
fluid.
Probable Cause:
1. Low level of the oil in the tank.
2. There is a restriction in the pump inlet line.
3. There is air leakage in the pump inlet line.
4. The viscosity of the oil is wrong.
5. The pump has too much wear.
6. Failure of the pump shaft or coupling.
7. The bolts of the pump do not have the correct
torque.
8. Filter by-pass not working or installed backwards.