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NOTE: Delete reference to comminutor when not
required for plant. For plants of 1.09 L/s 25,000
GPD capacity and below, the comminutor and bar
screen unit may be omitted, and in lieu thereof, a
screening basket provided in the aeration tank. For
installations in which all sewage has passed through
a comminutor and bar screen upstream of the plant, a
comminutor and bar screen unit need not be provided
as a part of the plant equipment.
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NOTE: Delete reference to sludge collector drive
motor for extended aeration type below 6.60 L/s
150,000 GPD capacity. For plants below 0.66 L/s
15,000 GPD capacity, hopper bottom only should be
specified for settling tanks. For plants above 4.38
L/s 100,000 GPD capacity, mechanical sludge
collectors only should be used in settling tanks.
For plants between 0.66 and 4.38 L/s 15,000 and
100,000 GPD capacity, either hopper bottom or
mechanical sludge collector should be allowed as a
Contractor's option. However, of the various types
of mechanical sludge collectors, rotating sludge
collectors appear to be available for plants of 1.31
L/s 30,000 GPD and above; chain-and-flight, 1.75 L/s
40,000 GPD and above; traveling reciprocating type,
0.66 L/s 15,000 GPD and above.
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Magnetic starters shall be provided for each blower motor, [(each)
mechanical aerator motor,] [comminutor motor,] and froth control system
pump motor, [sludge collector drive motor (when used)]. Magnetic starters
shall have ambient compensated, bi-metallic overload heaters in each phase
line. Reset buttons for magnetic starters shall be mounted on enclosure
doors. Contactors shall be provided for [chlorinator housing heater]
[hypochlorinator housing heating device].
2.13.6
Selector Switches, Pushbuttons, and Pilot Lights
Selector switches, pushbuttons, and pilot lights shall be mounted on the
outside of the enclosure. One Hand-Off-Automatic (H-O-A) selector switch
shall be provided for each motor starter. One selector switch shall be
provided for changing lead blower in the lead-standby system. Selector
switches shall be heavy-duty oil-tight type. Push buttons shall be
provided for manual (Hand) operation of motors. Pilot lights shall be
provided for each H-O-A selector switch: red to indicated motor is running
and amber to indicate automatic operation. Connections to the selector
switch shall be such that only the normal automatic regulating control
devices will be by-passed when the switch is in the "Hand" position. All
safety control devices such as motor overload protection devices shall be
connected in the motor control circuit in both the "Hand" and "Automatic"
positions.
2.13.7
Circuit Controls
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SECTION 11375N
Page 74
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