MIL-HDBK-1005/9A
2.5.3.6
Wet Wells
a) Size. Wet wells should be as small as possible
for economic reasons and to prevent settling out of suspended
material. However, a wet well must be of adequate size to
contain the pumps (for submersible pumps) to provide adequate
depth for pump controls and to provide an adequate cycle time
between successive motor starts to prevent overheating of the
(1) Determine the length of cycle time by using
Equation 1:
EQUATION:
t = (V/D)[1/(1-Q/D) + (1/[Q/D])]
(1)
where
D = pump capacity, gpm (L/min)
V = wet well storage volume between high and low
levels, gallon (liter)
Q = inflow to wet well, gpm (L/min)
t = total time between successive pump starts, min.
When Q = 0.5 D, Equation 1 is reduced to t = 4V/D.
To obtain the minimum wet well volume required, use
Equation 2:
EQUATION:
V = tD/4 (2)
(2) Provide pump operating-cycle of at least 6
minutes for pump units less than 50 horsepower. Check with
motor manufacturer for recommended maximum number of cycles for
motor specified.
b) Bottom Slope.
Slope wet well bottom toward the
pump suction.
(1) Use slope of 1.75 vertical to 1 horizontal
(1.75:1).
(2) A minimum slope of 1:1 is permitted only where
special justification exists.
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