Size a sewage pump or ejector pit: pump capacity, wet well working volume from the cycle time, force main velocity, total head and pump power.
The working volume between pump-on and pump-off levels is smallest, and the pump starts most often, when the inflow is exactly half the pump rate. With 6 starts per hour (10-minute cycle) and a 4 L/s pump, V = 600 s × 4 ÷ 4 = 600 L. In a duplex station the pumps alternate, so each one starts half as often.
Keep at least 0.6 m/s (2 ft/s), and preferably about 1 m/s, so solids do not settle; above 2.5–3 m/s friction and surge become excessive. Building codes also set a minimum discharge size (often 2 inch) and require pumps that pass solids (often 2 inch spheres). Check surge with the Water Hammer Calculator and gravity drains with the Drainage Slope Calculator.
Working volume V = T × Q ÷ 4, where T is the minimum cycle time in minutes (60 ÷ allowed starts per hour) and Q the pump rate. Add volume below the pump-off level for submergence and above the alarm level for emergency storage.
At least 0.6 m/s (2 ft/s) to keep solids in suspension, with about 1 m/s preferred, and normally below 2.5–3 m/s.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
No comments yet. Be the first to add one.