Doosan D20G, Service Manual

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Vehicle System Testing and Adjusting 32
Testing and Adjusting
Troubleshooting
Troubleshooting can be difficult. A list of possible
problems and corrections are on the pages that
follow.
This list of problems and corrections will only give an
indication of where a problem can be and what
repairs are needed. Normally, more or other repair
work is needed beyond the recommendations on the
list. Remember that a problem is not necessarily
caused only by one part, but by the relation of one
part with other parts. This list can not give all
possible problems and corrections. The serviceman
must find the problem and its source, then make the
necessary repairs.
Tools Needed
Fittings Group 1
The Fitting Group is used to make the pressure tests
of the hydraulic system. Before any test is made,
visually inspect the complete hydraulic system for
leakage of oil and for parts that have damage.
WARNING
To prevent personal injury when testing and
adjusting the hydraulic system, move the
machine to a smooth horizontal location and
lower the mast and carriage to the ground. If the
mast and carriage can not be on the ground,
make sure they are blocked correctly to keep
them from a fall that is not expected. Move away
from machines and personnel that are at work.
There must be only one operator. Keep all other
personnel away from the machine, or where the
operator can see the other personnel.
Before any hydraulic pressure plug, line or
component is removed, make sure all hydraulic
pressure is released.
Visual Checks
A visual inspection of the hydraulic system and its
components is the first step when a diagnosis of a
problem is made. Lower the carriage to the floor and
follow these inspections;
1. Measure the oil level. Look for air bubbles in the
oil tank..
2. Remove the filter element and look for particles
removed from the oil by the filter element. A
magnet will separate ferrous particles from
nonferrous particles (piston rings, O-ring seals,
etc.).
3. Check all oil lines and connections for damage or
leaks.
4. Check all the lift chains and the mast and carriage
welds for wear or damage.
Performance Tests
The performance tests can be used to find leakage
in the system. They can also be used to find a bad
valve or pump. The speed of rod movement when
the cylinders move can be used to check the
condition of the cylinders and the pump.
Lift, lower, tilt forward and tilt back the forks several
times.
1. Watch the cylinders as they are extended and
retracted. Movement must be smooth and regular.
2. Listen for noise from the pump.
3. Listen for the sound of the relief valve. It must not
open except when the cylinders are fully extended
or retracted without load on forks.
Hydraulic Oil Temperature (Too Hot)
When the temperature of the hydraulic oil gets over
98.8° C (210° F), polyurethane seals in the system
start to fail. High oil temperature causes seal failure
to become more rapid. There are many reasons why
the temperature of the oil will get this hot.
1. Hydraulic pump is badly worn.
2. Heavy hydraulic loads that cause the relief valve
to open.