What Is the Centrifugal Pump Affinity Laws & Impeller Trim Calculator?
Pump affinity laws dictate that flow scales linearly with speed, head scales quadratically, and power scales with the cube of speed.
How Does the Centrifugal Pump Affinity Laws & Impeller Trim Calculator Work?
Applies geometric and kinematic similitude across operating points, assuming hydraulic efficiency remains nearly constant.
Centrifugal Pump Affinity Laws & Impeller Trim Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
rac{Q_2}{Q_1} = rac{N_2}{N_1} rac{D_2}{D_1}, quad rac{H_2}{H_1} = left( rac{N_2}{N_1} rac{D_2}{D_1}
ight)^2, quad rac{P_2}{P_1} = left( rac{N_2}{N_1} rac{D_2}{D_1}
ight)^3
Centrifugal pump affinity scaling laws for flow, head, and hydraulic power.
How to Use the Centrifugal Pump Affinity Laws & Impeller Trim Calculator
- Input baseline flow, head, power, RPM, and diameter, followed by new target speed and/or trimmed diameter.
Step-by-Step Example Calculation
VFD Speed Increase from 1450 to 1750 RPM
Input Values:
flow1M3Hr:120
head1M:45
power1Kw:18.5
speed1Rpm:1450
speed2Rpm:1750
diameter1Mm:220
diameter2Mm:220
Worked Steps: New flow Q2 = 144.8 m³/h, New head H2 = 65.6 m, New power P2 = 32.5 kW.
Understanding Your Result
Displays scaled flow in m³/h, new head in meters, new brake power in kW, and scaling ratio.
Factors That Affect the Result
- Trimming impellers by more than 15–20% creates internal clearance recirculation, degrading efficiency below affinity predictions.
When Should You Use This Calculator?
- Variable frequency drive energy savings analysis, impeller trimming for system balancing, and HVAC pump re-rating.
Assumptions & Limitations
- Applies to turbulent flow of low-viscosity fluids (water); viscous fluids require HI correction factors.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard Hydraulic Institute affinity law formulation.