About Pump Sizing Calculator
The pump sizing calculator finds the total dynamic head, hydraulic power, and net positive suction head for a piping system per Hydraulic Institute and EN ISO 9906 methods. It is used by mechanical engineers to select pumps and motors, generate the system curve, and confirm that NPSH available exceeds NPSH required.
Enter the flow rate, static head, fluid, and each pipe segment with its length, diameter, and fitting losses. The tool returns the total dynamic head, the friction and velocity heads, the required shaft and motor power, the system curve, and the NPSH margin, all updating in real time.
How It Works
- Compute the flow velocity v = Q / A for each pipe segment and the Reynolds number to classify the flow regime.
- Find the Darcy friction factor (Swamee-Jain for turbulent flow, 64/Re for laminar) and the friction head hf = f * (L/D) * v^2 / (2g) plus fitting losses.
- Add static, friction, and velocity heads for the total dynamic head, then size the shaft and motor power from the hydraulic power and efficiencies.
- Evaluate NPSH available against an estimated NPSH required and build the system curve across the operating range.
Worked Example
Water at 20 deg C (density 998.2 kg/m3) flowing at 5 L/s through a 100 mm pipe has a velocity v = 0.005 / (pi*0.05^2) = 0.637 m/s and a velocity head hv = 0.637^2 / (2*9.81) = 0.021 m. Over 50 m with friction factor about 0.0195 and 5 fittings, the friction head is about 0.31 m, so the total dynamic head is 10 + 0.31 + 0.02 = 10.33 m above a 10 m static lift.
Formulas
- Pipe velocity
v = Q / (pi * (D/2)^2)- Reynolds number
Re = rho * v * D / mu- Darcy-Weisbach friction head
hf = f * (L/D) * v^2 / (2*g)- Total dynamic head
TDH = staticHead + frictionHead + velocityHead- Required shaft power
P = rho * g * Q * H / (eta_pump * eta_motor)- NPSH available
NPSHa = Patm/(rho*g) + h_suction - hf_suction - Pv/(rho*g)
Standards & References
- Hydraulic Institute
- EN ISO 9906
Frequently Asked Questions
What is total dynamic head?
Total dynamic head is the total energy a pump must add to the fluid, equal to the static head plus the friction head plus the velocity head. It is the head the pump must deliver at the design flow rate.
How is friction head calculated?
The tool uses the Darcy-Weisbach equation hf = f * (L/D) * v^2 / (2g) per segment, with the friction factor from the Swamee-Jain approximation for turbulent flow or 64/Re for laminar flow, plus minor losses from the sum of fitting K-values.
Why does NPSH matter?
NPSH available must exceed NPSH required or the pump will cavitate, damaging the impeller. The tool computes NPSH available from atmospheric pressure, suction head, suction friction, and vapour pressure, then compares it with an estimated NPSH required.
How is the motor power chosen?
The required shaft power P = rho * g * Q * H / (eta_pump * eta_motor) is rounded up to the next standard motor rating, giving a margin above the hydraulic duty at the design point.