Design & SizingQuestion 26 of 110
A sewage sump receiving a peak inflow of 45 gpm is served by a pump that discharges 90 gpm when running. If useful storage between pump-on and pump-off is 30 gallons, how long does one pump-down cycle (running time) last during peak inflow?
a.30 s
b.40 s
c.60 s
d.90 s
Explanation
While running, the net removal rate is pump output minus inflow = 90 - 45 = 45 gpm. Draw-down time = storage / net rate = 30 / 45 = 0.667 min = 40 s. Sizing sump volume this way limits motor starts per hour to protect the pump; too small a volume causes short-cycling.
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