rotating cutting teeth shall be evenly spaced around the entire outer
perimeter of the rotating drum. As the drum rotates, the cutting teeth
shall pass through a stationary comb section and cut against it. The
cutting and screening mechanism shall cut or shred all sewage solid,
including sticks, rags, and stringy materials, without removing them from
the sewage flow, without clogging the screen, and without binding, jamming,
or stalling the moving parts. The comminutor shall be readily removable
from its housing without disturbing plant operation. The rotating drum and
the support casting shall be of high-quality close-grained cast iron or
cast aluminum of adequate strength and rigidity to withstand all loads
imposed in them from the operation of the comminutor and drive assembly.
Cast iron shall meet the requirements of ASTM A 48M ASTM A 48, Class 30,
minimum. Aluminum shall be a heat-treated aluminum alloy. Casing may be
composed of one or more parts. The comminutor shall reduce the solids in
sewage to a size that will pass through 6 mm 1/4 inch slots in the rotating
drum. The comminutor shall operate automatically and continuously, it
shall be designed to pass a minimum flow of [_____] L/s GPD, an average
flow of [_____] L/s GPD, and maximum flow of [_____] L/s GPD, and shall be
capable of satisfactory operation at zero flow conditions. Comminutor
shall be designed for free discharge where the discharge is located above
the liquid level in the aeration tank or controlled discharge when the drum
is partially submerged.
3.7.2.1
Comminutor Drive
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NOTE: Insert electrical power characteristics.
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Comminutor shall be driven by an electric motor, constant speed, totally
enclosed, horizontal or vertical type, suitable for outdoor service, and
conforming to NEMA MG 1. The motor shall be of adequate attage orsepower
to drive the comminutor 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 rotating element shall be by means of a vertical or a right
angle gear reduction unit provided as an integral part of the motor.
Reduction ratio shall be such as to produce the proper operating speed for
the comminutor mechanism. The 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 drum shaft 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. The comminutor electric circuitry shall
include an automatic overload type reversing device with momentary time
delay to prevent jamming or damage to the unit should an exceptionally hard
object be encountered in the sewage. The gear motor shall be mounted on
the comminutor in a close coupled arrangement.
SECTION 11375N
Page 113
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