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. A
lubrication system shall be provided for the gears. Bath
lubrication systems requiring oil seals for containment or
lubrication systems which rely upon an oil circulating pump shall
include a proven reliable means to stop the drive motor in the
event of insufficient lubrication. Pressure indicating devices
influenced by oil sludge and changes in oil viscosity will not be
acceptable. Bearings may be lubricated with oil or grease.
c.
Bearings shall have a minimum rated life expectancy (L-10) of
100,000 hours based on ABMA SBRB Standards when operating
continuously at the rated full-load motor wattage horsepower and
speed under the specified loading conditions. Internal bearings
may be either oil or grease lubricated. All grease lubrication
pressure lines shall be fed from fittings accessibly located above
the platform supporting the mechanism. Underwater bearings will
not be acceptable.
d.
Base plate or mounting lugs shall be either constructed of steel
or shall be integrally cast with the gear reduction unit and shall
be furnished with not less than three leveling anchor bolts with
lock nuts.
2.8.3.2
Impeller Shaft
The 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
removable from the speed reducer by means of a bolted coupling. The shaft
shall be of solid steel construction conforming to ASTM A 108 or steel pipe
conforming to ASTM A 53.
2.8.3.3
Impeller
The impeller shall be of fabricated structural steel, Type 304, stainless
steel, or of glass fiber reinforced polyester plastic laminate. The
aeration blades shall be designed to achieve the maximum aeration and
pumping effect. The impeller shall be bolted to the impeller shaft with
Type 316 stainless steel bolts and shall be readily removable from the
shaft.
2.8.3.4
Shroud
The aerator shall be equipped with a shroud designed to prevent the mixed
liquor from splashing and spraying the underside of the supporting
platform, walkway, railings, and walls of the aeration tank. The shape of
the shroud shall be circular and extend beyond the diameter of the
impeller. The shroud shall either be attached to the impeller and rotate
with it or be mounted in a stationary position above it supported from the
platform. The shroud may be in more than one section and shall permit easy
removal from the aerator. If the shroud rotates with the impeller, it
shall be dynamically and statically balanced to prevent any out-of-balance
loading on the driving unit. The size, shape and location of the shroud
shall not reduce the required certified oxygenation capacity of the
aerator. The aerator with shroud in place shall operate without excessive
spraying. The shroud shall prevent splashing at the selected speed and at
any submergence of the impeller within the specified operating liquid
levels of the aeration tank. Shroud shall have adequate cross-section to
SECTION 11375N
Page 40
Previous Page
