MIL-PRF-52470A (AT)
3.3.2 Mounting platform. The mounting platform shall be of a size to support all the
operating machinery and the operator. An expandable metal or raised pattern deck plate not less
than 0.3 centimeter (cm) (1/8 inch (in.)) thick shall cover the operator's working area of the top
surface of the platform. The deck plate shall be painted with a nonskid, abrasive-type, deck point.
The platform shall extend and retract not less than a distance of 1.2 meter (m) (4 feet (ft.)).
3.3.3 Crown block. The derrick shall be fitted with a crown block assembly. Sheaves
shall be furnished with provisions for preventing the wire rope from jumping off the sheaves
grooves and shall be equipped with self-lubricating antifriction bearings. An eve-type anchor shall
be attached to the underside of the crown block.
3.3.4 Derrick. The derrick shall be constructed of an electrically welded steel tubing
frame consisting of four legs reinforced with diagonal and cross members. The derrick shall be
rated by its manufacturer to sustain a gross axial capacity of 27 200 kilogram (kg)
(60 000 pounds (lb.)) and shall be of sufficient height to accommodate 9 m (30 ft.) long sections
of casing. The derrick shall be equipped with kelly holders to attach the kelly bar to the derrick
for transit. The derrick shall be raised and lowered hydraulically by two cylinders not less than
15 cm (6 in.) in diameter. Each cylinder shall be provided with one or more pilot-operated check
valves.
3.3.5 Kelly. The kelly shall be of the telescoping type of not less than 13.3 cm (5.25 in.)
square or 15.2 cm (6 in.) in diameter. The inner kelly shall have an individual hoist operated by a
hand lever and controlled by a brake foot pedal. A lock or brake shall be incorporated to prevent
the outer and inner kelly bars from telescoping when maximum down pressure is applied to the
auger bit at any point during the digging operation to the full length of the extended kelly. An
instrument shall be furnished to determine the position of the kelly from vertical to 45° in
increments of not more than 5° and shall be visible to the operators when seated in the operator's
seat.
3.3.6 Rotary table. The rotary table shall transfer the rotation from the power source to
the kelly bar. The rotary table shall be furnished with a replaceable kelly bushing or rollers. The
rotary table shall have not less than six rotary speeds forward and one or more reverse speeds.
The maximum torque available at the kelly shall not be less than 19 800 Newton·meter (N·m)
(175 000 inch·pounds (in·lb)) at 25 revolutions per minute (rpm) of the kelly bar. The highest
rotary speed imparted to the kelly shall not be less than 120 rpm.
3.3.7 Power feed and retracting mechanism. The power feed and retracting mechanism
shall provide pressure to the kelly to increase or decrease the pressure on the auger bit. The
power feed shall impart a maximum travel speed to the kelly of not less than 50 m (165 ft.) per
minute in both up and down directions. Means shall be provided for applying not less than
13 600 kg (30 000 lb.) down pressure along the entire travel of the kelly without regard to the
position of the kelly.
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