Manitowoc National Crane NBT40 Series Service Manual Download Page 75

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National Crane

Published 8-01-2017 Control # 287-11

4-1

NBT40 SERVICE MANUAL BOOM

MAINTENANCE

SECTION 4

BOOM MAINTENANCE

SECTION CONTENTS

Four Section Boom . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Five Section Boom . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

Boom Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21
5 Section Boom Disassembly . . . . . . . . . . . . . . . . . 4-21

Boom Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-41

Inner Side Pads. . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-41
Rear, Bottom Pads . . . . . . . . . . . . . . . . . . . . . . . . . .4-42

Multi-stage Extend Cylinder . . . . . . . . . . . . . . . . . . . .4-43

Cylinder Reassembly . . . . . . . . . . . . . . . . . . . . . . . .4-44

Jib Boom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-44

Jib Stowage Bracket Adjustment . . . . . . . . . . . . . . .4-44
Jib Jack Service and Maintenance . . . . . . . . . . . . . .4-47

FOUR SECTION BOOM

A two-stage, rod-fed, double-acting cylinder is attached to
and supports the 1st, 2nd and 3rd stage boom sections.

The 2/3/4 extend cables (Figure 4-1) 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 (Figure 4-1) 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 4-1) 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 4-1) 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 (Figure 4-1) retract cables 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 directly oppose the 2/3/4 extend cables to ensure that
the 3rd and 4th 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
s e ct i o n s w i l l n e e d t o b e a d j u s t e d t o u t i l i z i n g c a b l e
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.

Reference Only