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HOW THE LIFT TRUCK WORKS?
HOW THE LIFT TRUCK WORKS?
1-15
1-15
■
■
HOW TRUCK BALANCE IS MAINTAINED
HOW TRUCK BALANCE IS MAINTAINED
Truck’s center of gravity
Truck’s center of gravity
Trailing
Trailing
wheel
wheel
Load’s center of gravity
Load’s center of gravity
Fulcrum
Fulcrum
Reach trucks have load handling equipment,
Reach trucks have load handling equipment,
including a mast assembly, which travels back and
including a mast assembly, which travels back and
forth along the outriggers. The trailing wheels of the
forth along the outriggers. The trailing wheels of the
truck work as a fulcrum to achieve balance between
truck work as a fulcrum to achieve balance between
the truck's center of gravity and the load's center of
the truck's center of gravity and the load's center of
gravity. The relationship between the locations of
gravity. The relationship between the locations of
those two centers of gravity is vitally important for
those two centers of gravity is vitally important for
safety. The stability of the reach truck is maintained
safety. The stability of the reach truck is maintained
best when the mast assembly is
best when the mast assembly is
fully retracted.
fully retracted.
■
■
KNOW THE CENTER OF GRAVITY OF
KNOW THE CENTER OF GRAVITY OF
YOUR LOAD
YOUR LOAD
Load center (from fork root) mm
Load center (from fork root) mm
Load’s center
Load’s center
of gravity
of gravity
Distance
Distance
A
A
l
l
l
l
o
o
w
w
a
a
b
b
l
l
e
e
l
l
o
o
a
a
d
d
(
(
k
k
g
g
)
)
Weight x distance =
Weight x distance =
moment (constant)
moment (constant)
Basic load center
Basic load center
Materials of various shapes such as boxes or at or
Materials of various shapes such as boxes or at or
cylindrical items may be loaded on the lift truck. In
cylindrical items may be loaded on the lift truck. In
order to accurately judge the stability of the truck,
order to accurately judge the stability of the truck,
it is vitally important for the operator to know the
it is vitally important for the operator to know the
location of the center of gravity for each type of load.
location of the center of gravity for each type of load.
■
■
HOW THE CENTER OF GRAVITY SHIFTS
HOW THE CENTER OF GRAVITY SHIFTS
The stability of the lift truck is determined by the
The stability of the lift truck is determined by the
combined center of gravity, which is the product of
combined center of gravity, which is the product of
the centers of gravity of the truck and the load.
the centers of gravity of the truck and the load.
When the truck is empty, this point is the same as
When the truck is empty, this point is the same as
the center of gravity for the truck, and when it is
the center of gravity for the truck, and when it is
loaded it shifts according to the center of gravity
loaded it shifts according to the center of gravity
of the load. Since the center of gravity of the load
of the load. Since the center of gravity of the load
changes whenever the mast assembly is advanced
changes whenever the mast assembly is advanced
or retracted along the outriggers or the forks are
or retracted along the outriggers or the forks are
raised or lowered, the combined center of gravity
raised or lowered, the combined center of gravity
also changes. The center of gravity is also governed
also changes. The center of gravity is also governed
by the following factors:
by the following factors:
•
•
Size, weight
Size, weight
and shape
and shape
of the
of the
load
load
•
•
Acceleration, deceleration
Acceleration, deceleration
and turning
and turning
radius
radius
•
•
Loading
Loading
or
or
unloading
unloading
height
height
•
•
Surface condition
Surface condition
and gradient
and gradient
of the
of the
road
road
•
•
Tilt
Tilt
angle of
angle of
the forks
the forks
•
•
Type
Type
of
of
attachment used
attachment used
•
•
Tire
Tire
material
material
Rear view of the truck with load
Rear view of the truck with load
The higher
The higher
the load, the
the load, the
higher the
higher the
combined
combined
center of
center of
gravity
gravity
Combined
Combined
center of gravity
center of gravity
with truck tilted
with truck tilted
Center of load
Center of load
Combined
Combined
center of
center of
gravity
gravity
Truck’s center
Truck’s center
of gravity
of gravity
Center of load
Center of load
Combined center
Combined center
of gravity
of gravity
Center of the truck
Center of the truck
■
■
THE TRUCK TIPS WHEN THE CENTER
THE TRUCK TIPS WHEN THE CENTER
OF GRAVITY IS OUTSIDE THE
OF GRAVITY IS OUTSIDE THE
STABILITY TRIANGLE
STABILITY TRIANGLE
For a reach truck to remain stable, the combined
For a reach truck to remain stable, the combined
center of gravity must be inside the triangle formed
center of gravity must be inside the triangle formed
by the ground contact points of the left and right
by the ground contact points of the left and right
trailing wheels and the ground contact point of the
trailing wheels and the ground contact point of the
drive wheel. This is called the stability triangle.
drive wheel. This is called the stability triangle.
If the combined center of gravity moves back further
If the combined center of gravity moves back further
than the trailing wheels, the truck will tip over
than the trailing wheels, the truck will tip over
backward with the trailing wheels as the fulcrum. If
backward with the trailing wheels as the fulcrum. If
the combined center of gravity moves outside the
the combined center of gravity moves outside the
stability triangle to the left or the right, the truck will
stability triangle to the left or the right, the truck will
fall over to that side.
fall over to that side.
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Summary of Contents for FRSB14-8
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