99903514: TELESCOPIC CRANE: 1-12 SECTION 1: OPERATION
1-9: ANTI TWO BLOCKING SYSTEM
“Two-Blocking” is the condition in which the
lower load block or hook assembly comes in
contact with the upper load block or boom point
sheave assembly. This can cause winch cable
and sheave damage.
WARNING
ANY ANTI TWO BLOCKING SYSTEM CONSISTS OF
A SERIES OF MECHANICAL COMPONENTS AND
CANNOT BE 100% FAILSAFE.
An anti two-blocking system can help prevent
cable damage by sensing the position of the
winch cable end attachments with respect to
the sheave case and shutting down the func-
tions that cause two blocking.
IMT telescopic cranes have two types of anti
two-blocking systems; a rod and weight system
and a switch activation mechanism.
The crane operator should check the anti two-
block system daily as follows:
1. Examine flexible rod and weight / switch
activation mechanism to insure free unre-
stricted mechanical operation
2. Examine cord for damage, cuts or breaks.
Grasp cord and pull to check operation of cord
reel. The cord should retract on reel when
released.
3. Start vehicle, engage PTO and slowly winch
the loadline up until anti two-block weight /
switch activation mechanism comes in contact
with the hook end of the loadline cable. At the
moment the weight is fully supported, the winch
up function should become non-functioning.
Slowly increase truck engine speed while
simultaneously actuating the winch up function.
The winch should not function. If operation
other than as described occurs, stop immedi-
ately and investigate. Failure to do so will risk
damage to the cable or the crane.
If all is well at this point, actuate the boom
extend function slowly, and gradually increase to
full actuation. Once again the function should
be non-existent with no tightening of the winch
cable. If operation other than described occurs,
stop immediately and reverse the function.
The final check involves actuating both the
winch up and extend functions together and
checking for proper operation of the anti two
blocking circuit. Once again, start slowly and
stop if it appears the cable is being tensioned.
If the anti two block function appears to be
functioning normally, winch the cable down until
the sensing weight swings free or thw switch
activation mechanism returns to the normal
position.
WINCH CABLE
MICRO SWITCH
SWITCH ACTIVATION
MECHANISM
ELECTRICAL CABLE TO
CRANE ELECTRIC SYSTEM
CRANE EXTENSION
BOOM
SNATCH BLOCK
LOAD HOOK
Figure A-13: Anti Two-
Blocking System - Low
Profile Boom Tip Cranes
20030115
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