💧 Centrifugal Pump Formulas Explained – Efficiency, Head, NPSH, and More
Centrifugal pumps are the most widely used pumps in industries such as water supply, chemical processing, HVAC, oil & gas, and power plants. To design, operate, and maintain these pumps effectively, engineers rely on a set of standard formulas that describe pump efficiency, head, power, and flow relationships.
This blog provides a comprehensive guide to centrifugal pump formulas to help professionals and students understand pump performance calculations.
Pump Efficiency to KW or KW to Pump Efficiency
Power at the Pump shaft KW = flowrate(Q) x Head(H) x Specific Gravity (SG)/367 x Efficiency of Pump
Where:
- Q = Flowrate (m³/hr)
- H = Head (m)
- SG = Specific Gravity of fluid
- η = Pump efficiency
- This formula helps convert pump efficiency to KW or vice versa, ensuring proper motor sizing
Head to Pressure or Pressure to Head conversion:
Head (H) = 10.2 x Pressure (P)/Specific Gravity (SG)
Where:
- H = Head (m)
- P = Pressure (kg/cm²)
- SG = Specific Gravity
- This conversion is essential when designing systems that specify either pressure or head requirements
NPSH available at pump suction = NPSH available
= 10.2x (Suction Pressure – Vapor pressure)/Specific Gravity(SG)
Motor input current to Power or Motor power to current
Power(P) KW = square root of 3 x Voltage(V) x Current((I) x Power factor(PF) x Efficiency /1000
Mass Flow to Volumetric Flow or Volumetric flow to Mass flow
= Flowrate(Q) = Mass flowrate(M) / Specific Gravity(SG
Specific speed is a unit less an index used to predict desired pump performance and the general shape of a pumps impeller. It is the speed of a geometrically similar pump which would deliver unit quantity (1 M3/sec) against a unit Head (1 Mtr).
Specific Speed = Ns = RPM(N) x Square root of Flowrate(Q)/Head(H)¾
For multi stage pump, Head per stage = Total Head/ Nos of stage
For double suction impeller pump flow, Q = half of total flow Q/2
🔹 Key Takeaways
- Centrifugal pump formulas cover efficiency, head, NPSH, motor power, flow conversions, and specific speed.
- These calculations are essential for pump design, selection, and troubleshooting.
- Proper application ensures energy efficiency, reliability, and longer equipment life.
