General
This manual contains the description and repair
procedures for the two stage mast and its
components on the A238 and B238 truck series. The
components of the mast include the inner and outer
mast, the tilt and lift cylinders, the carriage, and
the forks.
Description And Operation
MAST SYSTEM
The function of the mast assembly is to lift a load
vertically. It consists of an outer mast, inner mast
and a carriage. The outer mast is attached to the
truck frame. Inside the channels of the outer mast,
the inner mast moves up and down on rollers. Inside
the channels of the inner mast, the carriage moves
up and down on rollers. The carriage carries the lift
forks or an attachment.
The vertical movement of the inner mast and
carriage is provided by two lift cylinders and lift
chains. Forward and backward tilting of the mast
are provided by the tilt cylinders. Different carriage
options exist for side shifting, fork positioning or for
attachments.
The masts for H16XM-9, H18XM-7.5 (H360-36HD)
and H16XM-12, H18XM-9 (H360-48HD) trucks are
similar. The difference is in the dimensions of their
components. See Figure 1.
TILTING
The mast pivots on pins which are clamped to the
frame in the mast mounts. Friction is reduced by
bushings which are pressed into the mast hangers.
The mast tilts forward or backward by extending or
retracting the tilt cylinders. The maximum tilt
angle is determined by the end stroke position of the
tilt cylinders. The length of the two tilt cylinders
must be adjusted to prevent that the tilt cylinders
twist the mast in the maximum back tilted position.
The hydraulic pressure in the tilt cylinders is
determined by the combined weight of the mast
assembly and the load, and by the horizontal
distance between the mast pins and the combined
point of gravity of mast and load.
Figure 1. Two-Stage Mast
4000 SRM 1664
General
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