Vehicle Systems
Testing and Adjusting
44
WARNING
First of all, the needle valve in control valve as
seen in a picture below should be loosened with
about half counterclockwise turn, which makes
it possible to lower the mast or carriage safely
when lift spool is shifted for lowering. After
absolutely lowering the mast or carriage to the
ground and a start key off, the possible causes
will be inspected. If mast or carriage won’t lower
by loosening a needle valve, its cause would be
a mechanical problem or a hydraulic problem
rather than an electrical problem. After the
related problems are completely fixed, the
needle valve should be re-tightened in a
clockwise turn. If not so, the safety lift lock
doesn’t properly work.
Probable Electric Cause
1.
Not to supply the electric power to solenoid valve
in lift section of control valve.
2.
A broken solenoid valve in lift section of control
valve
Probable Hydraulic Cause
1.
Lift poppet (lift lock) damaged and contaminated
Probable Mechanical Cause
1.
Lift cylinder damaged or bent.
2.
Load roller defective (bearing) or not adjusted
Problem: Safety lift lock doesn’t work
Safety lift lock function: Once the operator leaves a
seat more than 3 seconds or a start key is off, the lift
cylinder doesn’t lower, even though lift spool is
pulled for lowering. If the operator is seated on a key
on, immediately the lowering will normally work.
Probable Electric Cause
1.
The electric switch (on-off) below a seat damaged
2.
The electric parts (relay and controller) related to
a solenoid valve in lift section of control valve
damaged
Probable Hydraulic Cause
1.
Lift poppet (lift lock) damaged and contaminated.
2.
Needle valve is loosened.
Problem: The lift or tilt cylinders do not hold
their position with the valve control levers in
neutral position.
Probable 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.
3.
The load check valves in the control valve are bad.
4.
Leakage of the cylinder lines or piston seals.
5.
There is foreign material in the control valve.
Hydraulic Gear Pump
Problem: Noise in the pump.
Probable Cause:
1.
The oil level is low.
2.
The oil is thick (viscosity too high).
3.
The pump inlet line has a restriction in it.
4.
Worn parts in the pump.
5.
Oil is dirty.
6.
Air leaks into the inlet line.
