For chain hoists without operating limit switch or with defective operating limit switch, the slipping clutch of the chain
hoist perfoms the function of the emergency limit stop device. This emergency limit stop device may only be ap‐
proached in exceptional cases, i.e. it must not be approached in normal operation. When the slipping clutch is
tripped, high additional loads are exerted on the chain.
Therefore the function "Operating limit switch for lifting" must be checked every day..
If the operating limit switch is defective, the hoist motor is switched off by the triggering of the electronic speed
monitoring device of the slipping clutch. The fact that the hoist unit is switched off in the highest hook position does
not indicate that the operating limit switch functions correctly. When switching off by the operating limit switch fails,
a warning is displayed, see ⇒ "Warning messages", Page 104.
Fig. 44 Buffer with limit switch not being actu‐
ated (A), buffer with limit switch being actuated
(B), defective buffer limit switch being actuated
(C).
Checking the operating limit switch for lifting: Lift the hook assembly or
bottom block up to approx. 10 cm below the highest hook position. Then
lift at creep speed up to the highest hook position until the chain hoist is
automatically switched off.
● 1/1 reeving:
After switching off the buffer or switch-off spring on the hook assembly
may be compressed only to a small extent.
● 2/1 reeving:
When a bottom block with internal switch-off springs is used, the upper
part may also be shifted onto the lower part only to a small extent so
that approx. 20 mm of the black part of the bottom block remain visible.
When a bottom block with external switch-off springs is used, the
springs may also be compressed only to a small extent when switching
off.
When the buffer or switch-off spring are excessively compressed, it may be assumed that the hoist motor is not
switched off by the operating limit switch but by the speed monitoring device of the slipping clutch. This may result
in broken chains when the end position is approached frequently.
Checking the operating limit switch for lowering
The function of the "Operating limit switch for lowering" must be checked at least once per year.
Proceed as follows:
● Remove chain collector box ⇒ "Dismantling the chain collector box", Page 77
● For further check procedure, proceed as described above under "Operating limit switch for lifting".
Optional geared limit switch
When the optional geared limit switch is used, the hoist unit must be switched off, before the bottom block or the
hook assembly touch the guide plate of the chain hoist. For checking the highest hook position must be approached
at high lifting speed (without load). After the hoist has been switched off, the minimum distance to the guide plate of
the chain hoist must be 20 mm.
8.5.4.2 Checking the operating limit switch actuator
The operating limit switch actuator must be checked for external damage, e.g. bent actuator plate.
78
21480244/181209
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