How The Lift Truck Works - UniCarriers FRSB14-8 Operation & Maintenance Manual

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HOW TRUCK BALANCE IS MAINTAINED HOW TRUCK BALANCE IS MAINTAINED
Load's center of gravity Load's center of gravity
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
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KNOW THE CENTER OF GRAVITY OF KNOW THE CENTER OF GRAVITY OF
YOUR LOAD YOUR LOAD
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

HOW THE LIFT TRUCK WORKS?

HOW THE LIFT TRUCK WORKS?
Trailing Trailing
wheel wheel
Truck's center of gravity Truck's center of gravity
Fulcrum Fulcrum
fully retracted. fully retracted.
Load's center Load's center
of gravity of gravity
Distance Distance
Weight x distance = Weight x distance =
A A moment (constant) moment (constant)
l l
l l
o o
w w
a a
b b
l l
e e
Basic load center Basic load center
l l
o o
d d a a
( (
k k
g g Load center (from fork root) mm Load center (from fork root) mm
) )
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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
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Acceleration, deceleration Acceleration, deceleration
• •
Loading Loading or or unloading unloading
• •
Surface condition Surface condition
• •
Tilt Tilt angle of angle of the forks the forks
• •
Type Type of of attachment used attachment used
• •
Tire Tire material material
• •
Center of load Center of load
Combined Combined
center of center of
gravity gravity
Truck's center Truck's center
of gravity of gravity
Combined center Combined center
of gravity of gravity
Center of the truck Center of the truck
Center of load Center of load
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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.
1-15 1-15
of the of the load load
and turning and turning radius radius
height height
and gradient and gradient of the of the road road
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
Rear view of the truck with load Rear view of the truck with load