4000 SRM 660 Operation
General
This section has the description, operation, and repair procedures for the masts used on this series of lift trucks:
Information on the lift cylinders, lowering control valves, carriage, and tilt cylinders is also described in this
section.
Description
The vertical frames of a mast are called weldments.
See Figure 10. Load rollers and bearing blocks are in-
stalled on the inner and outer weldments. The chan-
nels are the vertical parts of the weldments that have
the tracks for the load rollers and bearing blocks. The
load rollers and bearing blocks guide the weldments
as the mast lifts and lowers.
The mast can tilt forward and backward. Tilt cylin-
ders are installed between the frame of the lift truck
and the outer weldment. The pivot mounts are at the
bottom of the outer weldment and connect the mast
to the lift truck. During the tilt operation the mast
rotatesonthepivotpinsintheframe.
The mast has a carriage. The carriage is a separate
section that moves within the vertical channels of the
inner weldment on load rollers. The forks and fork
positioner cylinders are attached to the carriage.
Operation
The mast has an outer weldment and an inner weld-
ment. See Figure 1. The outer weldment is con-
nected to the lift truck by the pivot pins and the tilt
cylinders. The top of the outer weldment has two sets
of bearing blocks to control movement of the inner
weldment. The inner weldment has two load rollers
and a bearing block on each side. These parts travel
along the channels of the outer weldment and con-
trol the movement between the inner and outer weld-
ments.
The mast has two single-stage lift cylinders. The lift
cylinders are installed at the back of the mast. The
base of each lift cylinder is held to the mount plate at
the bottom of the outer weldment. The hydraulic fit-
ting and external lowering control valve for each lift
cylinder go through a hole in the mount plate. The
cylinder rod of each lift cylinder is held in position at
the top of the inner weldment.
Two lift chains control the movement of the carriage.
The chains are fastened to mounts near the top of
the outer weldment. The chains go up and over the
chain sheaves on the inner weldment and then con-
nect to the carriage. When a load on the carriage
is raised by the lift cylinders, the weight of the load
and carriage assembly is transferred from the car-
riagethroughthechainstotheouterweldment.
When the lift cylinders retract, the weight of the load,
the carriage, and inner weldment push the oil from
the lift cylinders. The oil flows from the lift cylin-
ders, through the lowering control valves, main con-
trol valve, and then to the hydraulic tank.
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