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Mixer driver assembly shall include an electric motor connected to a gear
reduction unit whose output shaft is directly connected to the mixer
impeller shaft. Motor shall be constant speed, totally enclosed,
fan-cooled horizontal type, 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. Power transmission from motor to
impeller shaft shall be by means of a vertical or a right angle gear
reduction unit. Reduction ratio shall be such as to produce the proper
operating speed for the mixer. Gear reduction unit shall be designed to
withstand any loadings produced by thrust, out-of-balance, and vibration
resulting from operating conditions and shall operate from zero rpm to a
speed compatible with the impeller speed. All components shall be designed
to withstand continuously the full load motor wattage horsepower. Gearing
may be spur, helical, spiral, bevel, worm or a combination thereof. All
gears shall be wrought or alloy steel except that worm gears shall be
bronze. The gear teeth may be through-hardened, contour-induction-hardened,
nitrided, or carburized. Flame-hardened gears will not be acceptable. The
housing shall be of high quality, close-grained cast iron or fabricated
steel. A lubrication system shall be provided for the gears. Bearings may
be lubricated with oil or grease. Base plate or mounting lugs shall be of
steel or integrally cast with the gear reduction unit and shall be
furnished with leveling anchor bolts with lock nuts.
2.14.9.3
Impeller and Impeller Shaft Coupling
The gear reduction unit output shaft shall be connected to the flash mixer
impeller shaft by means of a rigid carbon steel coupling of the bolted
flange type. The coupling shall be located above the maximum liquid
operating level of the basin. All nuts, bolts and washers shall be made
from Type 316 stainless steel. The impeller shaft shall be of sufficient
diameter to withstand the loading imposed by the impeller, using a safety
factor of 1.5. The shaft shall be of solid steel construction, AISI Type
304 stainless steel. A key seat shall be provided to fit the key specified
for attachment of impeller; key seat shall conform to ASME B17.1 or ASME
B17.2 as appropriate. Impeller shall be fabricated from
corrosion-resisting material. The impeller shall be of a shape that will
effectively mix the raw sewage and sludge. Impeller shall be keyed and
bolted to the impeller shaft with Type 316 stainless steel bolts and shall
be readily adjustable on the shaft keyway and removable from the shaft.
2.14.10
Anchor and Connection Bolts
Nuts and washers shall be cadium-plated steel or stainless steel. Bolt
sizes and locations shall be as indicated on the manufacturer's certified
prints of the equipment furnished unless otherwise specified or indicated.
The manufacturer shall furnish templates to accurately position bolts in
multiple bolt installations. Aluminum shall be attached with stainless
steel machine bolts conforming to AISI type 302 or ASTM A 320/A 320M. Iron
or steel shall be attached with cadmium plated steel machine bolts
conforming to ASTM A 307.
SECTION 11375N
Page 80
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