MIL-HDBK-1003/7
d) Select screen size and material to suit water conditions. Provide a
trash trench, backwash pump and dewatering bin for cleaning the screens. Trash cannot
be pumped back into water, but is disposed of either by incineration or in a landfill.
e) The flow area below the extreme low water level and the extreme high
water level determines the height of the traveling screen.
f) In the extreme case of large quantities of water plants and algae, it
may be necessary to back up the traveling screen with a fine stationary screen that can
be lifted out for cleaning.
Pumps. Each condenser circulating pump should be sized to serve half of a
12.5.5
condenser plus the water quantity required for turbine lubricating oil coolers,
generator air coolers, and closed cooling water system. Oversizing these pumps will
result in wasted power and in premature wear from operating continuously at pumping
heads less than the design point. Pump materials should be suitable for the water
conditions.
12.5.5.1 Vertical pumps. Use vertical pumps for large differences in extreme high and
low water levels and obtain manufacturers' recommendations on installation. Design the
suction chamber in accordance with Figures 43 through 46, because these pumps are very
sensitive to poor distribution of flow at suction bell entrances. Note that the
distance of the bell from the bottom of the well is critical.
Horizontal Pumps. Where economically justified, use horizontally split
12.5.5.2
centrifugal pumps in a dry well below extreme low water level to avoid the necessity of
foot valves and priming, as they are not as sensitive as vertical pumps to inlet flow
conditions. Where horizontal circulating pumps are located away from the intake
structure but above the suction flume, provide a means of priming the pumps.
12.5.5.3 Backwash Pump. The backwash pump for a traveling screen should be of the
horizontally split centrifugal type and should take its suction from the circulating
pump discharge. Where the intake structure and the circulating pump chamber are
separated, it will be necessary to install a vertical backwash pump in the traveling
screen well after the screen and to lengthen the intake structure accordingly.
A fire pump, where required, may be installed in the crossover well of the
intake structure.
Provide space for pump motor controllers, traveling screen, and backwash
pump on top of the structure.
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