MIL-HDBK-1005/9A
b)
Example Calculation 2 - LET influent header
outlets:
The recommended equation for determining the number of
outlets on the distribution header is (first in English, then in
SI units):
No = 0.4085 Qmain/(Vo)(Do2)
EQUATION:
(14)
21.2 Qmain/(Vo)(Do2)
No =
where
No
= number of outlets on distribution header
Qmain = instantaneous flow rate from pierside
collection system pumping station, gpm (L/min)
Vo
= desired velocity of flow from distribution
header outlets, fps (m/s). Suggested value
0.5 fps (0.15 m/s)for first trial.
Do
= diameter of outlet openings in distribution
header, in. (mm)
Use standard flare diameter based on header diameter
for first trial.
In this example, Qmain is estimated from the average
daily flow using an assumed peaking factor of 3. In actual
design of a LET, Qmain would be available from the pierside
pumping station design or the actual pumps used in an existing
pierside pumping station. Qmain is determined by Equation 6.
For Example Calculation 1, LET daily discharge rate
from pierside of 70,000 gpd [264,970 L/d].
Assumptions
Qmain
= (70,000 gpd)(l day/1,44O min)(3) = 146 gpm
[(264,970 L/d)(1 day/1,440 min)(3)= 552 L/min
Vo
= 0.5 fps [0.1524 m/s]
Do
= 8 in. [203.2 mm]
135
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