where eventual conversion to step aeration is
contemplated.
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The mechanical aerator shall be of the fixed type and shall include a drive
assembly, impeller shaft, impeller, and shroud, and may include a draft
tube. All accessories necessary for proper operation and to provide
necessary required oxygenation capacity, including flow straightening surge
rings or tank baffles, shall be provided.
2.8.3.1
Drive Assembly
Drive assembly shall include an electric motor, gear reduction unit,
bearings, and shall be fully enclosed for outdoor installation.
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NOTE: Insert electrical power characteristics.
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a.
Motor: Motor shall be constant speed, totally enclosed,
fan-cooled, horizontal type, with solid shaft, suitable for
outdoor service, and conforming to NEMA MG 1. The motor shall be
of adequate wattage horsepower to drive the equipment continuously
at the maximum load encountered under any operating condition
without overloading or exceeding the nameplate rating of the
motor. Motor shall be suitable for operation on [_____] volt,
[_____] phase, [_____] Hertz service. Motor shall be protected
against overload, low voltage, and unbalanced voltage. Vertical
motor shall be directly connected to the gear reduction unit or
else connected by a flexible coupling. Horizontal motor shall be
connected to the gear reduction unit by a flexible coupling only.
In lieu of a constant speed motor with a gear reduction unit, a
two-speed motor may be provided as a means of speed reduction.
b.
Gear Reduction Unit: The 2-speed gear reduction unit shall be of
the vertical gear motor type or the horizontal speed reducer type.
The minimum AGMA service factor when the unit is operating at full
load motor wattage horsepower, 24 hours a day continuous running
under moderate shock loads, shall be 1.5 for speed reducers and
2.0 for gear motors. It shall have a life expectancy of 100,000
hours with the probability of no more than 10 percent failures
prior to its expected life. The unit shall be designed to
withstand any loading produced by thrust, out-of-balance, and
vibration resulting from operating conditions. All components
shall be designed to withstand continuously the full load motor
wattage horsepower for the life expectancy specified, including
motor starting torques up to 250 percent of motor running torques.
Gearing may be spur, helical, spiral bevel, or a combination
thereof. If helical, the helical angle shall not exceed 0.314 rad
18 degrees. Worm gearing will not be acceptable. All gears shall
be AGMA Quality 10 or higher as outlined in AGMA 390.03A. All
gears shall be inspected in accordance with the best accepted
practice and shall be certified as to meeting the specified
quality. In establishing the capacity of the unit to transmit
power, the following AGMA standards for surface durability,
strength and materials shall govern: Spur gearing and helical
gearing: AGMA 908, AGMA 2001, AGMA 2004, AGMA 6010, and AGMA 6034
All gears shall be wrought or alloy steel.
The gear teeth may be
SECTION 11375N
Page 39
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