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replacement split seal.  Slowly rotating shafts may be sealed with stacked rings
cut from commercial packing material pressed into the gland cavity.  The sealing
pressure is applied by a screw-advanced gland follower which can be tightened
periodically as required. Bumpers.  Bumpers are required on all crane structures or components that
come into contact with end stops.  The simplest and most widely used bumpers are
the coil spring and elastomeric types.  The elastomeric bumpers are standard
commercial items and are available in sizes and designs for every crane
application.  Coil spring bumpers were commonly used on older cranes, but are used
infrequently on the newer cranes.  With either type, the bumper must be sized so
that the permissible deceleration rate is not exceeded and the total kinetic
energy can be absorbed.
Hydraulic bumpers are used only for particularly sensitive applications.
Their deceleration rate can be set and readjusted very accurately.  They are
precision assemblies with hydraulic fluid and seals, which require more attention
and maintenance than the other types. End Stops.  Each crane bumper should have a matching end stop, sized to
absorb the maximum kinetic energy that may be developed by the striking bumper.
Overrunning crane bridge end stops should be installed on the runway girders;
overrunning trolley end stops on the bridge girder; and portal and container crane
end stops on the rail support structure.  End stops for underrunning crane
bridges, trolleys, and hoist/trolley units should be bolted to the girder web.
When two crane components or structures are on the same bridge, runway, or track
and are expected to contact each other during normal operations, one of them
should have solid stops in lieu of matching bumpers.
End stops which are used as integral "forks" or safety devices of track
interlocks (usually on underrunning cranes) normally are designed to contact the
wheel tread rather than the bumper.  The forks are pivoted to the
blocking position when its monorail track is not interlocked with another and
pivoted to the open position when the tracks are interlocked to permit the bridge
or trolley to transfer from one track to the other. Actuators.  Pneumatic, hydraulic, and electric (solenoid) actuators are
standard commercial assemblies used to operate mechanisms such as spud locks and
boom hoist pawls, monorail track interlocks, and twist locks on container crane
spreaders.  Each type is designed and constructed according to the applicable
industry standards.  The output motion of the actuator may be linear or
rotational.  Actuators operate or engage load bearing components of cranes but are
not themselves load bearing. Radius and Capacity Indicators.  All cranes with luffing booms are
equipped with a radius indicator.  Straight-line (fixed capacity) cranes have a
mechanical radius indicator composed of links or gears operated by the boom
position.  This mechanism may have a mechanical connection to the boom for
positive activation or a plain pendulum mounted near the foot of the boom within
sight of the operator.  Cranes with variable capacity ratings have the maximum
capacity indicated for each radius reading, usually in 5-foot increments.


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