9
9
4
4
Hydraulic
Hydraulic System
System
As high-pressure oil from the main oil pump flows through the priority valve, it is
As high-pressure oil from the main oil pump flows through the priority valve, it is divided between
divided between
two circuits. One circuit runs via
two circuits. One circuit runs via the multi-way valve. High-pressure oil from this multi-way valve is
the multi-way valve. High-pressure oil from this multi-way valve is
routed to the lift cylinder or tilt cylinder. When the slide valves of both the lift and tilt cylinders are
routed to the lift cylinder or tilt cylinder. When the slide valves of both the lift and tilt cylinders are
in the neutral position, no oil is supplied by the priority valve. When the lift slide valve is pulled,
in the neutral position, no oil is supplied by the priority valve. When the lift slide valve is pulled,
the high-pressure oil flows under the lift cylinder piston and pushes the piston rod upward. When
the high-pressure oil flows under the lift cylinder piston and pushes the piston rod upward. When
the lift slide valve is pushed, the bottom of the lift cylinder piston is changed to the low pressure
the lift slide valve is pushed, the bottom of the lift cylinder piston is changed to the low pressure
and relies on its own weight and the load weight to make the piston rod drop. At this point, oil
and relies on its own weight and the load weight to make the piston rod drop. At this point, oil
flowing out of the lift cylinder and through the one-way speed limiting valve controls the lowering
flowing out of the lift cylinder and through the one-way speed limiting valve controls the lowering
speed, and oil is not supplied by the priority valve. When the tilt slide valve is operated,
speed, and oil is not supplied by the priority valve. When the tilt slide valve is operated,
high-pressure oil flows into a chamber of the tilt cylinder and the other side is changed to the low
high-pressure oil flows into a chamber of the tilt cylinder and the other side is changed to the low
pressure, thereby causing the mast to tilt forward or backward. The other circuit runs via the
pressure, thereby causing the mast to tilt forward or backward. The other circuit runs via the
steering gear
steering gear, which is
, which is prioritised to ensure operation of the
prioritised to ensure operation of the steering system.
steering system.
Main oil pump
Main oil pump
Fault
Fault
Possible
Possible cause
cause
Corrective
Corrective measure
measure
Oil pump not
Oil pump not
pumping out
pumping out
oil
oil
Low
Low oil
oil tank
tank level
level
T
Top
op up
up to
to specified
specified oil
oil level
level
Clogged suction pipe or filter
Clogged suction pipe or filter
Flush oil circuit and oil tank. Change
Flush oil circuit and oil tank. Change
hydraulic oil if dirty
hydraulic oil if dirty
Oil pump
Oil pump
delivers oil at
delivers oil at
low pressure
low pressure
Worn
Worn bearing;
bearing; damaged
damaged ring,
ring, O-ring
O-ring
Replace
Replace defective
defective parts
parts
Misadjusted
Misadjusted safety
safety valve
valve
Raise
Raise the
the pressure
pressure with
with a
a pressure
pressure gauge
gauge
Air in the oil pump
Air in the oil pump
Tighten loose connectors on the suction
Tighten loose connectors on the suction
side
side
Add hydraulic oil to the tank
Add hydraulic oil to the tank
Check pump oil seals
Check pump oil seals
Wait for bubbles in oil tank to disappear
Wait for bubbles in oil tank to disappear
before using pump
before using pump
Oil pump
Oil pump
noisy
noisy
Cavitation
generated
by
kinked
Cavitation
generated
by
kinked
suction-side hose or clogged filter
suction-side hose or clogged filter
Adjust or replace hose and clean filter
Adjust or replace hose and clean filter
Air
Air
entering
entering
from
from
loosened
loosened
suction-side connectors
suction-side connectors
Re-tighten every connector
Re-tighten every connector
Cavitation caused by high viscosity of
Cavitation caused by high viscosity of
hydraulic oil
hydraulic oil
Replace with new hydraulic oil of viscosity
Replace with new hydraulic oil of viscosity
suitable for the oil pump operating speed
suitable for the oil pump operating speed
Only work when oil temperature is normal
Only work when oil temperature is normal
Air bubbles in hydraulic oil
Air bubbles in hydraulic oil
Check cause of bubbles, then take
Check cause of bubbles, then take
appropriate steps
appropriate steps
Oil pump
Oil pump
leaks oil
leaks oil
Damaged pump oil seal, damaged
Damaged pump oil seal, damaged
O-ring or sliding surfaces of oil pump
O-ring or sliding surfaces of oil pump
worn
worn
Replace defective parts
Replace defective parts
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