Group 34, Uprights
34-1-2 • Upright Specifications and Description SM 765, Nov ’06
• Lift chain tension should be checked every 50-250
hours or monthly.
• Upright and carriage roller checks should be per-
formed every 50-250 hours or monthly.
• Roller patterns should be checked every 6 months
or after 1000 hours of service.
• Racking and drift tests should be performed every
50~250 hours or monthly.
• The complete extended inspection should be per-
formed at least every year or 2000 hours of opera-
tion.
Description
The upright assembly includes the lift chains, lift cylin-
ders, carriage, forks, and mast or rail sets. Each of the
components can be serviced using the tests, checks,
adjustments, and removal and replacement procedures in
the following Sections.
The upright uses the hydraulic cylinders and chain sets to
lift the carriage and rail sets. On standard, two-stage
uprights, the lift cylinders lift the carriage with chains and
directly lift the inner rail set. On triple-stage uprights, the
primary (free-lift) cylinder lifts the carriage by chains.
When the primary cylinder reaches its maximum exten-
sion, fluid is diverted to the secondary lift cylinders,
which lift the inner rails using a second set of chains and
lift the intermediate rails by direct lift.
On Hi-Lo uprights, the primary(free-lift) cylinder lifts the
carriage by chanis. The secondary cylinders directly lift
the inner rail set by rod. Hi-Lo uprights not used second
set of chain for secondary cyliner.
Friction and play between the nesting rails is controlled by
roller sets mounted on the rails and carriage. When rails or
rollers become worn, the gap between the rollers and rails
becomes larger, creating more play in lifting and lowering
operations. The rail web to roller side clearances can be
reduced by shimming the rollers to close the gap between
the roller and rails. The gap between the rail flange and
roller bearing surface can be reduced by the use of over-
size rollers on a one-time basis.
Forks use a hanger design for mounting on the carriage.
Auxiliary attachments may be added to the upright for
specialized handling operations. The hydraulic circuit is
modified with a hose adapter kit and an auxiliary section
is added to the main hydraulic valve to operate the attach-
ment.
The lift and secondary cylinders on standard uprights and
triple-stage uprights (TSUs) are piston type cylinders. The
primary cylinder on TSUs and HILO are piston-type cyl-
inder. See the chart under “Specifications” to determine
the type of cylinder used on the upright you are servicing.
Piston-type cylinders contain a by-pass check valve in the
piston that allows air and fluid that have accumulated in
the rod end of the cylinder to return to the system. The
check valve can be removed and cleaned if indicated by
troubleshooting. A non-serviceable check-ball-type cush-
ioning function is built into ram and piston cylinders for
smooth staging during the lowering cycle. The primary
cylinder on TSUs incorporates cushioning on the lift
cycle. A velocity fuse in the hydraulic port of the lift cyl-
inders (secondary cylinders on TSUs) prevents the mast
from falling rapidly in case of sudden fluid pressure loss
due to line breaks or other malfunction of the hydraulic
circuit.
As the cushion system is added to lift cylinder of standard
upright and the 1st cylinder of TSU, the speed will get
slow for a moment before the fork touches the ground. It
is helpful to protect the ground.
As explained in more detail in Group 30, the main pump
sends fluid to the main hydraulic control valve, which
contains spools that route fluid to the lift cylinders and tilt
cylinders. The valve assembly also contains a counter-
balance valve that prevents upright tilt when the truck is
not operating.
Fluid flow rates for lift functions are factory set and not
adjustable. Flow rates for tilt and auxiliary functions are
controlled by adjustments on the main hydraulic valve. A
non-adjustable “load-lowering” flow valve mounted on
the upright limits upright lowering speed.
Groups 29 and 30 contain general hydraulic information
including upright hydraulic functions. Other hydraulic
checks for the upright appear in “Troubleshooting,” Sec-
tion 2.
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