removable or so arranged as to allow access to the equipment for
maintenance. If equipment is housed in a lockable enclosure, this shall be
sufficient protection and no additional guards are necessary.
2.4
SEWAGE SHREDDER
**************************************************************************
NOTE: Retain "aeration" for extended aeration type
plants. Retain "contact" for contact stabilization
type plants.
**************************************************************************
A sewage shredder shall be provided in the influent line immediately
upstream of the [aeration] [contact] zone.
2.4.1
Performance and Design Requirements
The sewage shredder shall be capable of cutting all sewage solids including
sticks, rags, and stringy material without clogging the screen or binding,
jamming or stalling the moving parts under normal load conditions. The
unit shall be designed to clear jams by repeatedly reversing and
restarting. The shredder shall be designed to operate continuously and
shall have a hydraulic capacity at least equal to the treatment plant peak
flow rate.
2.4.2
Screening and Cutting Mechanism
**************************************************************************
NOTE: Alternate shredder (comminutor) design
utilizes two vertical cutter shafts with hardened
4130 steel alloy cutters of 42 to 48 Rc hardness.
**************************************************************************
Screen configuration shall be such that all wastewater must pass through it
before entering the treatment plant. Screen bars shall be spaced not
greater than 6 mm 1/4 inch apart. Cutters shall be constructed of tool
steel with a surface hardness of at least 35 on Rockwell C scale. Cutters
shall be removable to facilitate replacement.
2.4.3
Motor and Mounting
The drive motor shall be in accordance with NEMA MG 1 and shall be suitable
for outdoor service in a high moisture atmosphere. Motor shall be suitable
for [_____] volts ac [3] [_____] phase, 60 Hz power supply and shall be
equipped with a thermal overload protector with manual reset. The motor
shall be direct-coupled to a gear reducer unit which shall be coupled to
the cutting mechanism. The shredder shall be mounted on a suitable cast
[iron] [or] [aluminum] support.
2.4.4
Controls
A control unit shall conform to NEMA ICS 1 and shall be provided for
operation of the shredder. The control unit shall contain a
hand-off-automatic selector switch; forward start, stop, and reverse start
pushbuttons for manual operation; automatic controls; dual magnetic
starters, one forward and one reverse; and other equipment required for
proper operation. If a jam occurs when in the automatic mode of operation,
the automatic controls shall alternately reverse and restart the shredder
until the jam is cleared or the thermal overload in the motor is tripped.
SECTION 11390
Page 16
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