TCM FB10-7, Service Manual

Page: 121 / 175

7. HYDRAULIC SYSTEM
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7.1.4 LIFT CYLINDER
The two lift cylinders of single-acting type are located on the outer mast frame. Each lift cylinder,
consists of cylinder body, rod, piston, and cylinder cap.
The piston fastened to the rod with a snap ring is provided with a wear ring and packing on its
circumference.
At this lower part of the cylinder body provided is a cut-off valve which works as a safety device
when the high-pressure hose connecting the right and left lift cylinders is broken.
The bushing and oil seal pressed into the cylinder cap serve to support the rod and protect the inside
of the cylinder from dust.
■
Cut-off valve operation
The oil from the cylinder flows back to the tank
via the piston holes
A
and
B
. In this step, if the
flow rate passing through the holes are within a range
of the flow rate which can be controlled by the flow
regulator, the pressure difference between the front
and rear of the piston is less than the spring force so
that the piston does not move.
If the hose is ruptured and the oil passing through
the holes
A
and
B
exceeds the flow to be controlled,
the pressure difference between the front and rear
of the piston becomes larger than the spring force,
moving the piston to the right.
The piston is thereby in firm contact the section
C
of the case so that the oil in the cylinder does not
flow out, stopping the fork go down.
Fig. 7.6
In Below Control Flow Rate
Fig. 7.7 In Over Control Flow Rate
CASE
PISTON
SPRING