| Avg inflow | Peak | Duty+Standby | Pipe | Static lift | TDH | Flow per pump | Motor rating |
|---|---|---|---|---|---|---|---|
| 60 m³/h | 2.5 | 2+1 | 150 m, 200 mm | 12 m | ~23 m | ~95 m³/h | ~11 kW |
| 35 L/s | 2.2 | 3+1 | 300 m, 300 mm | 18 m | ~30 m | ~92 L/s | ~60 kW |
| 800 gpm | 1.8 | 2+1 | 800 ft, 10 in | 40 ft | ~85 ft | ~720 gpm | ~30 hp |
| 120 m³/h | 3.0 | 3+1 | 250 m, 250 mm | 22 m | ~40 m | ~138 m³/h | ~40 kW |
| 18 L/s | 2.8 | 2+0 | 120 m, 160 mm | 10 m | ~18 m | ~28 L/s | ~9 kW |
- Design flow: Qdesign = Qavg × PF × (1 + I/I) × (1 + Reserve).
- Per-pump flow: Qpump = Qdesign / Nduty.
- Static head: Hstatic = Hsuction + Hdischarge.
- Pressure head: Hp = P / (ρg).
- Friction head (Hazen-Williams): Hf = 10.67 × L × Q1.852 / (C1.852 × D4.871).
- Minor losses: Hm = ΣK × v² / (2g), where v = Q/A.
- Total dynamic head: TDH = Hstatic + Hp + Hf + Hm.
- Hydraulic power: Phyd = ρgQ×TDH.
- Motor input: Pin = Phyd / (ηpump × ηmotor).
- Wet well cycling: Cycle = V/(Q−Qin) + V/Qin, so V = Cycle / (1/(Q−Qin) + 1/Qin).
- Enter average inflow and select the correct flow unit.
- Set peak factor, infiltration, and reserve allowances.
- Choose the number of duty pumps and standby pumps.
- Provide suction and discharge lifts, plus any residual pressure.
- Enter pipe length, diameter, roughness (C), and minor loss K.
- Set efficiencies and service factor to estimate motor rating.
- Optional: enable wet well sizing for cycling and diameter checks.
- Press Calculate, then export results as CSV or PDF.
A pump station is more than a single pump and a pipe. It is a controlled system that must meet peak demand, handle wet-weather variability, protect equipment from short cycling, and deliver reliable discharge conditions. This calculator helps you build a defendable first-pass sizing by converting planning assumptions into a design flow, total dynamic head (TDH), and an estimated motor rating per duty pump.
Start with the average inflow and apply a peak factor to represent diurnal demand or storm-driven surges. Add infiltration/inflow and reserve allowances when projects require contingency for unknowns, future growth, or conservative approvals. The calculator then divides the station design flow among the number of duty pumps, while allowing standby pumps to be specified for redundancy and maintainability.
Head requirements are assembled from practical components. Static head combines suction lift and discharge lift. If the discharge must maintain a minimum pressure, the pressure is converted to an equivalent head using H = P/(ρg). Pipe friction is estimated using the Hazen–Williams relationship for waterlike fluids in full pipes, and minor losses are calculated using the summed loss coefficient (ΣK) and the velocity head v²/(2g). The TDH output is the sum of static head, pressure head, friction head, and minor losses.
Power is calculated from hydraulic power ρgQH and then corrected for pump and motor efficiency. A service factor is applied to propose a practical motor rating that can tolerate typical operating variability. Use the pipe velocity output as a quick sanity check; unusually high velocity can increase losses, noise, and wear, while very low velocity may increase solids deposition in wastewater applications.
Worked example: Using an average inflow of 60 m³/h, a peak factor of 2.5, 10% infiltration, and 15% reserve, the station design flow is about 189.75 m³/h. With 2 duty pumps, each pump is sized near 94.88 m³/h. With 150 m of 200 mm pipe, C = 120, ΣK = 4.0, 12 m static lift, and 100 kPa residual pressure, the TDH is about 23 m and the recommended motor is about 11 kW per duty pump.
Treat these results as a sizing starting point. Final selection should confirm pump curves at the intended operating point, check NPSH available versus required, review solids handling and minimum submergence, confirm electrical starting constraints, and coordinate controls (VFD or on/off) with the wet well geometry.
1) What does “duty + standby” mean?
Duty pumps share the required flow during normal operation. Standby pumps provide redundancy for maintenance or failure, keeping the station operational when one unit is unavailable.
2) Which flow should I enter: average or peak?
Enter the average inflow and apply a peak factor. This keeps assumptions transparent and makes it easier to justify the final design flow during reviews.
3) When should I include infiltration/inflow and reserve?
Add them when the project requires contingency for wet weather, aging sewers, future connections, or conservative approvals. If you have measured peak wet-weather data, you may reduce allowances.
4) Is Hazen–Williams suitable for all fluids?
It is commonly used for waterlike fluids in full pipes under turbulent conditions. For viscous fluids, slurries, or unusual temperatures, a Darcy–Weisbach approach is typically more appropriate.
5) What is a reasonable pipe velocity?
Many systems target roughly 0.7–3.0 m/s depending on application and solids handling. Very high velocity raises losses and wear; very low velocity can cause sedimentation and odors.
6) How accurate is the motor rating output?
It is an estimate based on assumed efficiencies and a service factor. Final motor selection should be checked against manufacturer curves, voltage and starting limits, and any VFD control strategy.
7) Why enable the wet well sizing option?
It helps reduce short cycling by estimating drawdown volume and a circular wet well diameter for a chosen number of starts per hour and minimum run time. It supports controls and reliability planning.