How to Calculate Pump Power
What is Pump Power?
Pump power requirement is calculated from flow, head, and efficiency. Proper sizing prevents under-pumping and excessive energy waste.
Formula
Calculate: P = (Q × H × ρ × g) / η
- P
- (GPM × Total Head) / (3960 × Efficiency) — (GPM × Total Head) / (3960 × Efficiency)
- Q
- Q value — Variable used in the calculation
- H
- H value — Variable used in the calculation
Step-by-Step Guide
- 1Calculate: P = (Q × H × ρ × g) / η
- 2Or: P = (GPM × Total Head) / (3960 × Efficiency)
- 3Account for motor losses beyond pump efficiency
Worked Examples
Input
Q = 0.05 m³/s, H = 20 m, ρ = 1000 kg/m³, η = 0.75
Result
P ≈ 13 kW required
Select larger motor for margin
Common Mistakes to Avoid
- ✕Under-estimating system friction loss
- ✕Over-sizing pump (operates inefficiently at partial load)
Frequently Asked Questions
Why does head matter more than volume?
Quadratic relationship with head; doubling head doubles power. Efficiency varies with duty point.
How do you select pump size?
Choose pump with duty point (Q, H) near best efficiency point for long equipment life.
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