3.2.4
Supernatant Transfer
When a pump is used for supernatant transfer from the aerobic digester tank
to the aeration tank, the pump shall be an airlift pump as specified in
paragraph entitled "Sludge Transfer Pump(s)," except that it shall be 50 mm
2 inch size. A shear gate or other positive means of flow regulation shall
be provided. All necessary piping shall be provided. Materials for piping
and valves shall be as specified in paragraph entitled "Piping."
3.3
AIR BLOWER ASSEMBLY
Air blower assembly shall include air blower, blower driver, V-belt drive
(for positive displacement blower), housing and accessories.
3.3.1
Air Blower
Air blower shall have the capacity to produce the plant air requirement at
the necessary operating pressure including allowance for pressure drop in
air piping, fittings, and accessories. Operating speed and size of blower
driver shall be commensurate with capacity of blower. Not less than two
blowers shall be provided. When two blowers are provided, each should have
the capacity to provide the total plant air requirement. When more than
two blowers are provided, they shall be in such capacities as to produce
the total plant air requirement with the single largest air blower out of
service. The air blower shall be the rotary positive displacement,
single-stage centrifugal or multi-stage centrifugal type. Means shall be
provided for adjusting the output of the blower. The blower shall be
equipped with heavy-duty anti-friction bearings. Impeller(s), except when
cast integrally with the shaft, shall be made of close-grained cast iron
conforming to Class 35 of ASTM A 48M ASTM A 48, ductile iron conforming to
ASTM A 395M ASTM A 395 or ASTM A 536or welded alloy steel conforming to
ASTM A 331. Impeller(s) shall have strong internal ribbing, shall be
machined on exterior surfaces, and shall be dynamically balanced. Shaft(s)
shall be machined and, except when cast integrally with the impeller, shall
be made of steel conforming to ASTM A 108. When shaft and impeller are cast
integrally, the casting shall be of ductile iron conforming to ASTM A 536.
When shaft and impeller are cast separate pieces, impeller shall be either
press fitted onto the shaft and held by means of a Woodruff key and lock
nut, or the impeller shall be mounted on the shaft with a reverse threaded
connection. The casing shall be cast iron conforming to ASTM A 48M ASTM A 48,
Class 30. The rotary displacement type blower shall have two timing gears
machined from heat-treated steel to synchronize the impellers accurately to
maintain maximum rotational efficiency. The following AGMA standards for
surface durability, strength and materials for spur gearing and helical
gearing, as applicable, shall govern:
Spur gearing and helical gearing:
AGMA 390.03A, AGMA 908, AGMA 2001, AGMA
2004, and AGMA 6010
Gears shall be enclosed in an oil-tight housing and shall be lubricated by
a splash oiling system from oil contained in the gear housing or pressure
lubricated with integrally driven oil system. Blower shall be equipped
with a Kingsbury type thrust bearing on the drive shaft so that thrust from
the driver will not be transmitted to the blower impellers. The blower
shall have an operating sound pressure level not to exceed 90-decibels over
a frequency range of 37.5 to 9,600 cycles per second measured at 1.5 m 5
feet from the unit. The manufacturer shall provide any silencing on the
blower needed to meet this requirement.
SECTION 11375N
Page 102
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