OO-C-2821
permit routine maintenance and quick removal. A large heater, used as a
combination heater and defroster, is acceptable. There shall be a powered
window wiper, with control within operator's reach. When specified (see 6.2),
there shall be a catwalk around the revolving upperstructure.
3.7.2 Gantry. A gantry, A-frame, or mast, of sufficient strength to
withstand stresses induced by lifting the boom from the ground to operating
position, shall be furnished. The gantry, A-frame, or mast shall be of the
foldable, retractable, or lowering type without requiring the use of an outside
power source, in order to reduce traveling or transport cube. The gantry crane
shall be capable of lifting the maximum length of boom and jib as required.
3.7.3 Turntable.
3.7.3.1 Supporting rollers. The revolving upperstructure shall be supported
by large, fixed rollers, rollers in pairs on tandem bogies, a live ball, or by a
roller ring. The rollers shall be heat-treated steel and shall be accurately
machined. Fixed rollers or rollers in pairs on tandem bogies shall be fitted
with antifriction bearings or replaceable bronze bushings, and shall be provided
with lubrication means. The balls or rollers shall be accessible and
removable.
3.7.3.2 Hook rollers. Where the holddown function is performed by hook
rollers, the rollers may be of the dual-purpose type in which one set of rollers
performs both the supporting and holddown functions, or may be of the holddown
type only. Hook rollers may operate singly or in pairs on tandem bogies and
shall be provided with grease fittings. When required by design, hook rollers
shall be provided with vertical or horizontal adjustment.
3.7.4 Swing brake. A swing brake capable of holding the upperstructure in
any desired position shall be provided. The swing brake control shall be
located within reach of the operator while the operator is seated.
3.7.5 Swing controls. The rotation of the rotating frame shall be
controlled through a hydraulic valving mechanism or through friction,
hydrostatic or electromagnetic type clutches designed for fast cycling, craning
and other operations. The hydraulic valving or clutch shall be capable of
transmitting power exceeding that of the crane rated lifting loads or of the
maximum governed engine torque. The operating temperature of the swing clutches
shall not exceed the maximum temperature recommended by the clutch" lining
manfacturer. Clutches or hydraulic valving shall be controlled by either
mechanical linkage, air, a manual effort applied through hydraulic linkage or by
full-power hydraulics.
3.7.6 Drums. Pitch diameter of the drum or drum laggings shall be not less
than 18 times the diameter of the largest rope used thereon. The drums shall
have sufficient rope capacity to accommodate the specified rope lengths (see
3.12.2). Primary and secondary load hoist drums shall be provided. Power at
the load hoist drum shall be not less than that required to meet lifting
capacities specified at recommended reeving with rope of the length specified in
3.12.2 installed. Load brakes shall be capable of holding or smoothly lowering
rated loads on recommended reeving, when properly adjusted. The brakes shall be
capable of being locked in a set position. Drum clutches shall be capable of
withstanding high-speed, continuous operation, as encountered in normal
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