gear box is not of self locking type.
5.4
Limit Switches
5.4.1 General
The limit switches, after being tripped, shall
automatically reset themselves within a reasonable
distance travelled in opposite direction, This does
not prevent the use of changeover type limit switches
where resetting is achieved by striker when moving
inopposite direction. They maybe mechanically driven
from the shaft.
5.4.2
Hoist Limit Switch
5.4.2.1
It is a device provided to.cut off the current,
stop the motion of hoist mechanism and to apply
the brake when the gate has reached a predetermined
level. Rotary type double acting limit switch shall
be provided.
5.4.2.2 Limit switches for intermediate positions of
travel, if required, shall also be provided.
5.4.3 Limit switches shall be weather-proof type.
Adequate adjustment shall also be provided to
compensate for rope elongation.
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GATE POSITION INDICATOR
6.1
The gate position indicators shall invariably
be provided with each hoist unless otherwise
specified by the purchaser.
6.2 The indicator dial shall be made from non-
rustingmetal or~namelled plate or thick plastic sheet.
It shall generally-be of circular shape. If agreed to,
other shapes may also be adopted.
6.3 The markings on dial in the operating range
may preferably be kept at reading of 1/20th of metre.
The metre markings shall be very bold. The words
‘closed’, ‘open’ or ‘fully raised’.shall also be engraved
or permanently marked.
-6.4 ‘The dial shall be located at a convenient place
from where it maybe easily seen by the gate operator.
6.5 The indicator point shall be made of non-rusting
metal. Electroplated indicator pointer can also b-e
provided, if mutually agreed to. Digital type indicator
may also be used.
6.6
Control Equipment
6.6.1
The hoist mechanism shall be complete with
one local control panel with push buttons, The control
panel shall be totally enclosed with 1P54 protection.
The.push buttons shall be suitably labelled as ‘Raise’,
‘Stop’ and ‘Lower’.
6.6.2 Lamps to indicate the condition of the control
IS 6938:2005
circuits and direction of motion maybe provided.
6.6.3 For emergencygate hoist requiring crack opening,
one additional push button of momentary contact
type, labelled ‘Crack’ shall be provided along with
the indicating lamp showing ‘Gate cracked open’.
6.6.3.1 Crack operation push button shall have
suitable limit switch/timer control to limit the initial
operation time of motor crack opening as per
recommendations of the manufacturer of the motor
for utilizing torque higher than that referred for
normal operation.
6.6.4 The hoist shall be-provided with all the necessary
relays, starter, heaters, if required, fises, limit switches
and indicating lights complete with suitable wiring
so that all the functions are carried out smoothly.
6.6.5 Remote control equipment, ifrequirecf, shall be
provided to enable the operation of gates from
regulation roam. Gate position indicator, alarms,
suitable interlocks with local control panel, shall be
provided in regulation room, ifrequired. Fibre optical/
conventional cables may be used for communication
link.
“6.6.6 All the controls shall be so interlocked that the
proper functioning of individual parts for the purpose
is ensured.
6.6.7 Alternative source of electrical supply+nay be
provided by the purchaser for important projects, if
considered necessary.
6.6.8 Protection for rope overload and slack rope may
be provided at the discretion of the designer.
6.7
Manual Operation for EleetricallyOperated Hoists
6.7.1
The manual operation shall be provided, if
required for emergency operation in.theevent of electric
supply failure.
6.7.2 Electrical interlocks shall be provided to prevent
operation by electrical power when the manual drive
is engaged.
6.7.3 The manual operation should be designed
in such a manner that the continuous effort per
man does not exceed a crank force of 100 N with
400 mm of crank radius at a continuous rating of
24 rev/rein. The maximum number of persons may
be restricted to 4.
6.7.4 Manual operation shall be provided with
ratchet and pawl arrangement so that the gates do
not fall of their own weight during manual operation.
6.8 If desired by the purchaser, only manual operation
may be provided for small capacity hoists.
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