Reference
Only
HOISTS
999 SERVICE/MAINTENANCE MANUAL
5-6
Published 05-16-17, Control # 233-03
BLOCK-UP LIMIT
A block-up limit control (also called anti-two-block device) is
a two-blocking prevention device which automatically stops
the load drum from hoisting and the boom from lowering
when a load is hoisted a predetermined distance.
Two-blocking is the unsafe condition in which the load block
or the weight ball contacts the sheave assembly from which
either is suspended.
Two-blocking can result in failure of sheaves and wire
rope, possibly causing load to fall.
The block-up limit controls consist of the following
components (see
):
•
Normally closed limit switch assembly fastened at any or
all of the following locations:
-
Lower boom point
-
Upper boom point
-
Fixed jib point (jib on boom or on luffing jib)
-
Luffing jib point
-
Luffing jib intermediate suspension
-
Universal anchor joint
•
Weight freely suspended by chain from each limit switch
actuating lever (weight encircles load line as shown in
•
Lift block fastened to load line or lift plates fastened to
load block (see
).
Operation
for component identification.
NOTE:
See wiring diagrams in Boom Wiring, Limits, and
Load Indicator Electrical Assembly drawing in 999
Operator Manual.
Block-Up Limit Control Deactivated
During normal operation, the weight overcomes the spring
force and rotates the actuating lever away from the limit
switch lever. This action allows the limit switch to close the
load drum
up
and boom/luffing jib
down
electric circuits.
Therefore, the load can be hoisted and the boom/luffing jib
can be lowered.
Block-Up Limit Control Activated
When the weight is lifted by the lift block or the lift plates,
spring force rotates the actuating lever against the limit
switch lever. This action causes the corresponding limit
switch to open the load drum
up
and boom/luffing jib
down
electric circuits.
The load drum and boom hoist pumps stroke to off. At the
same time, the load drum and boom/luffing jib parking brakes
apply to stop the load drum from hoisting and the boom/
luffing jib from lowering.
WARNING
Two-Blocking Hazard!
Block-up limit control is a protective device designed only
to assist operator in preventing a two-blocking condition;
any other use is neither intended nor approved.
Block-up limit control may not prevent two-blocking when
load is hoisted at maximum single line speed. Operator
must determine fastest line speed that allows block-up
limit control to function properly and thereafter not exceed
that line speed.
Содержание 999
Страница 1: ...R e f e r e n c e O n l y Service Maintenance Manual Manitowoc 999 ...
Страница 2: ...R e f e r e n c e O n l y ...
Страница 4: ...R e f e r e n c e O n l y THE ORIGINAL LANGUAGE OF THIS PUBLICATION IS ENGLISH ...
Страница 173: ...R e f e r e n c e O n l y Manitowoc Published 05 16 17 Control 233 03 4 19 999 SERVICE MAINTENANCE MANUAL BOOM 4 ...
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