Engineering
Pump Design Calculator
Estimate total dynamic head, selection head, hydraulic and electrical power, and NPSH margin for a steady incompressible water duty.
Combined friction and valve head (m)-
System total dynamic head (m)-
Pump selection head with margin (m)-
Hydraulic power delivered to liquid (kW)-
Required pump shaft power (kW)-
Estimated electrical input (kW)-
NPSH margin (m)-
NPSHA / NPSHR ratio-
Wire-to-water efficiency-
Decision view
Pump system curve, selected duty point, and NPSH reserve
Pump system curve, selected duty point, and NPSH reserveThe live operating point sits on a quadratic system curve while a separate NPSH rail protects suction performance.
Exact scenario comparisonDesign flow (m³/h) changes while all other entered assumptions remain constant.
| Design flow (m³/h) | Combined friction and valve head (m) | System total dynamic head (m) | Pump selection head with margin (m) | Hydraulic power delivered to liquid (kW) | Required pump shaft power (kW) | Estimated electrical input (kW) | NPSH margin (m) | NPSHA / NPSHR ratio | Wire-to-water efficiency |
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How to use Pump Design Calculator
- Enter the required duty flow and static elevation difference.
- Use losses calculated at that same flow.
- Enter manufacturer duty-point efficiency and NPSHR, then compare NPSHA.
Calculator guide
Understanding Pump Design Calculator
Pump selection begins with a hydraulic duty point, not a motor rating. This calculator assembles static lift, piping losses, valve allowance, efficiency, and suction margin without hiding which assumption drives power.
Detailed calculation process
Detailed pump duty and power calculation
The default duty is 90 m³/h through 24 m static head plus entered suction, discharge, and control-valve losses.
General formula: H_f=H_suction+H_discharge+H_valveH_T=H_static+H_fH_d=H_T(1+m)P_h=ρg(Q/3600)H_d/1000P_shaft=P_h/η_pP_e=P_shaft/η_mM_N=NPSHA-NPSHR Head terms can be added because each is energy per unit weight. Hydraulic power uses SI flow; equipment efficiencies increase required input.
What each symbol means
Worked substitution with the default inputs
The default selection point is 90 m³/h at 40.15 m, requiring about 13.72 kW electrical input with 2.6 m NPSH margin.
Worked situations
Practical examples
- The default piping and valve add 12.5 m to 24 m static head.
- A 10% margin produces 40.15 m selection head and about 13.72 kW electrical input.
Better inputs
Useful tips
- Plot several operating flows before selecting an impeller.
- Use fluid-specific density when it differs materially from water.
- Keep control-valve authority separate from arbitrary oversizing.
Before relying on the result
Limitations and common mistakes
- Water density and standard gravity are assumed.
- Losses are entered rather than recalculated from pipe geometry.
- No pump curve, viscosity correction, transient, minimum-flow, or motor service-factor check is included.
Reference
Key terms
- TDH
- Static head plus all modeled losses at the duty flow.
- NPSHA
- Suction head available above vapor pressure.
- Wire-to-water efficiency
- Pump efficiency multiplied by motor efficiency.
Important note
Confirm the final selection against the complete manufacturer curve, actual liquid properties, minimum continuous stable flow, runout power, NPSH policy, piping transients, and applicable design standards.
Frequently asked questions
Should the head margin also cover friction uncertainty?
Only when the entered margin is deliberately assigned to that uncertainty; do not double-count conservative losses.
Is a positive NPSH margin enough?
Manufacturer and project criteria may require a larger absolute or ratio margin.
Why use m³/h but power in kW?
The calculation converts flow to m³/s before applying ρgQH.