SPECIFICATIONS

Vehicle Systems Systems Operation
Full Free Triple Lift Mast
Full Free Triple Lift Mast
(Typical Example)
(3) Primary lift cylinder. (4) Crosshead. (5) Intermediate mast.
(6) Inner mast.
On trucks equipped with a Full Free Lift or Full Free
Triple Lift Mast, the carriage can move the full length
of inner mast (6) before any increase in height of the
inner mast. This is possible because primary lift
cylinder (3) moves the carriage only.
The carriage is lifted when the lift control lever is
pulled back. Oil under pressure flows from the con-
trol valve into the base of primary lift cylinder (3) and
secondary lift cylinders (7). Since the primary lift
cylinder has the larger diameter for the oil to work
against, the primary lift cylinder moves up first. The
carriage moves up with the primary lift cylinder, with
the assistance of crosshead (4) and the lift chains,
until the carriage reaches the top of inner mast (6).
From the start of the lift cycle until the carriage
reaches the top of the inner mast, the mast is in its
free lift period. During this lift cycle, the carriage
moves up at a 2 to 1 ratio with the rod movement of
primary lift cylinder (3).
Full Free Triple Lift Mast At Free Lift
(Typical Example)
(3) Primary lift cylinder.
When the movement of the primary cylinder is com-
pleted, pressure oil then works against the pistons in
secondary cylinders (7). The movement of secondary
cylinders (7) starts the movement of the inner mast
on the Full Free Lift models or intermediate mast (5)
and inner mast (6) on the Full Free Triple lift models.
The inner mast moves at a 2 to 1 ratio and the inter-
mediate mast moves at a 1 to 1 ratio with the rods of
secondary cylinders (7) until they reach the top of
their travel.
At this position, the pressure relief valve in the con-
trol valve will open if the lift control lever is held back
and release the extra pressure until the lift control
lever is released. The oil flows through the relief
valve and the control valve and then into the
hydraulic tank. The carriage will be stationary at this
full height until the lift control lever is moved to the
lowered position.
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5
3
4
3
6
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