BOOM MAINTENANCE NBT40 SERVICE MANUAL
4-20 Published 8-01-2017 Control # 287-11
FIVE SECTION BOOM
A two-stage, rod fed, double-acting cylinder is attached to
and supports the 1st, 2nd and 3rd stage boom sections.
The 3/4/5 extend cables (Figure 4-6) attach to the base of
the 3rd stage boom, are reeved around sheaves at the tip of
the 4th stage boom and attach to the base and support the
5th stage boom.
The 5/4/3 retract cables (Figure 4-6) are attached to the
base of the 5th stage boom, are reeved around sheaves at
the base of the 4th stage boom and attach to the tip of the 3rd
stage boom.
The 2/3/4 extend cables (Figure 4-6) attach to the base of
the 2nd stage boom, are reeved around sheaves at the tip of
the 3rd stage cylinder and attach to the base and support the
4th stage boom. The 4/3/2 retract cables are attached to the
base of the 4th stage boom, are reeved around sheaves at
the base of the 3rd stage boom and attach to the tip of the
2nd stage boom.
The 1/2/3 extend cables (Figure 4-6) attach to the base of
the 1st stage boom, are reeved around sheaves at the tip of
the 2nd stage boom and attach to the base of the 3rd stage
boom.
The 3/2/1 retract cables (Figure 4-6) attach to the base of the
3rd stage boom, are reeved around sheaves at the base of
the 2nd stage boom and attach to the tip of the 1st stage
boom.
The 3/2/1 retract cables (Figure 4-6) directly oppose the 1/2/
3 extend cables to ensure that the 2nd and 3rd stage booms
extend and retract equally at all times.
The 4/3/2 retract cables (Figure 4-6) directly oppose the 2/3/
4 extend cables to ensure that the 3rd and 4th stage booms
extend and retract equally at all times.
The 5/4/3 retract cables (Figure 4-6) directly oppose the 3/4/
5 extend cables to ensure that the 4th and 5th stage booms
extend and retract equally at all times.
A boom assembly is considered properly timed when
telescoping sections extend equally relative to each other
and bottom out simultaneously at full retraction and do not
spring back out after retract pressure is returned to neutral.
Hydraulic extend cylinder construction will dictate which
extendable section will be the driver that the other extend
sections will need to be adjusted to utilizing cable
adjustment.
A single stage cylinder will control first extendable section.
A dual stage cylinder will control second extendable section.
Timing sequence of cables will depend on number of
sections and the extend cylinder construction.
Design intent of the cable tensioning is to balance the
preload of extend and retract cables for each extendable
section. In addition, sequencing of the sections during
retraction requires retract cables of every section to be
indexed relative to each other.
1/2/3 EXTEND 2/3/4 EXTEND 3/4/5 EXTEND
5/4/3 RETRACT4/3/2 RETRACT3/2/1 RETRACT
1ST STAGE 2ND STAGE 3RD STAGE 4TH STAGE
5TH
STAGE
FIGURE 4-6
Reference Only
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