rotation while the sheave is rising is governed by the
adjustable geared limit switch (1), which opens the
motor circuit when the sheave is fully up. An
adjustable torque limit switch (16), actuated by the
tripping plate washer (9), opens the motor circuit
when the sheave is fully lowered and further
provides overload protection for the unit. The
worm is normally held in position with a heavy
torque spring (13). If an obstruction under the
sheave prevents the sheave from lowering, the sleeve
cannot turn. Then the torque exerted by the worm
exceeds the normal torque, causing the worm to
slide along the wormshaft (12), pushing the tripping
plate washer (9), and opening the torque switch. A
handwheel (11) is provided for manual operation,
and a declutch lever (14) is provided to change from
motor to hand operation.
It is imperative that the deckedge operator know
whether the retractable sheave is in the UP position
during landing operations. During night operations,
visual sighting of the retractable sheave is
impossible.
An arresting gear SHEAVE-UP and BY-PASS
switch and indicator panel (fig. 3-26) is located aft
of the arresting gear deckedge control station to
indicate the status of the retractable sheave. The
panel is wired into the clear/foul deck light and will
prevent the arresting gear officer from giving a clear
deck signal if one or more of the retractable sheaves
is not in the fully up position.
If a retractable sheave cannot be raised, the
arresting gear officer directs that the affected deck
pendant be removed from the deck. A CLEAR
DECK signal can now be activated by closing the
respective by-pass switch and thus overriding the
shutdown arresting engine. The by-pass condition is
visually indicated by an amber warning light on the
by-pass switch and indicator panel. In addition, a
three-lamp, deckedge indicator panel with red,
amber, and green lenses, mounted aft of the
deckedge
control station,
will indicate the
retractable-sheave status. This panel will illuminate
red when any of the retractable sheaves are down
and green when all sheaves are up. In case one or
Figure 3-26.–Sheave-up and by-pass switch and indicator panel.
3-30
