MIL-HDBK-1003/7
Intake Structures. The intake structure, usually made of concrete, shall
12.5
contain stationary and mechanical traveling screens that are used to remove debris from
the cooling water before entering the pumps.
Location. Locate the intake structure as close to the water source as
12.5.1
possible in order to limit the hydraulic losses to the pump suction and to eliminate the
possibility of a sand silt buildup in the wells of the structure. Connect the structure
with the power plant through suitable pipes or reinforced concrete flumes or tunnels.
The intake structure shall be provided with access roads and power wiring.
Arrangement. Provide at least two parallel sets of wells in the structure to
12.5.2
permit alternate operation when one set is being cleaned. Each set shall contain an
entry well, with a trash rack in front and a sluice gate (or stop logs) at its outlet; a
screen well, with a traveling water screen; and a crossover well with sluice gates to
permit closing off the screen well and directing the water flow from either set of wells
to a selected pump flume or pump well.
The pump chamber may be combined with the intake structure when the power
plant is some distance away or they may be separated by flume or pipe when they are
close by and the pumps are installed near the condensers. In the combination intake
structure and pump chamber, vertical centrifugal pumps are usually installed above a wet
well, whereas horizontal centrifugal pumps may be installed in a dry well below low
water level. A determination of extreme low and high water levels of the water source
must be made.
Trash Racks. Inlet ports to the entry wells should be covered with trash
12.5.3
racks as a rough screen for such items as logs, sticks, leaves, and ice. They should be
designed to pass maximum velocities of 2 feet per second at extreme low water levels and
arranged for manual raking from the outside.
12.5.4
Traveling Water Screen
a) Use screen approach water velocities of 0.5 to 0.75 feet per second to
avoid entrapment of fish.
b) The maximum water velocity through the net screen area when passing the
circulating pump capacity should not exceed 2.5 feet per second at extreme low water
level. The net screen area is one-half of the waterway area, after deducting for the
screen frame and boot interference. Manufacturers will guarantee a maximum 2 feet head
loss under the above conditions.
c) One or two speed drives are available, the higher speed for intermittent
operation when debris is light and the lower speed for continuous operation when the
debris is heavy.
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