Wet Well Sizing Guide
Why Wet Well Volume Matters
A wet well stores incoming liquid before pumps remove it. Good volume keeps pump starts within a safe range. It also prevents long retention, odor, turbulence, and excess sediment. The useful volume sits between pump start and pump stop levels. Total volume may include dead storage and freeboard. Designers should check both values because each serves a different purpose.
Hydraulic Inputs
The main inputs are geometry, liquid levels, inflow, pump capacity, and preferred starts per hour. A circular well uses diameter and water depth. A rectangular well uses length, width, and depth. A custom plan area works for irregular chambers. The calculator converts units before solving, so mixed output is easier to read. Use measured inside dimensions, not outside wall dimensions.
Pump Cycle Checks
Pump cycling depends on the usable storage and the net filling or emptying rate. During the off period, inflow fills the operating band. During the run period, the pump removes flow faster than liquid arrives. If pump capacity is less than inflow, the well cannot recover. The cycle time is the off time plus the run time. Starts per hour equal sixty divided by cycle minutes.
Detention And Operating Margin
Detention time estimates how long average inflow stays inside the selected volume. Long detention may create septicity in wastewater service. Very short detention can cause rapid starts and controls wear. The margin check compares calculated starts with the chosen limit. It also reports freeboard storage above the high level, if dimensions allow it. This helps review overflow risk.
Practical Use
This tool is intended for planning, comparison, and early design review. Final station sizing should follow local codes, pump manufacturer limits, float spacing rules, and hydraulic modeling. Always confirm emergency storage, standby power needs, and downstream restrictions. Check the result for realistic depths and velocities. A well sized only by storage may still perform poorly if inlet geometry causes air entrainment or solids buildup.
Record Keeping
Save each run with units, assumptions, and selected limits. Exported files support peer review and future comparisons. Keep notes on pump curves, alarm levels, and cleaning access. These records make revisions faster when inflow, equipment, or site conditions change later safely.