Here are step-by-step worked examples covering key centrifugal pump calculations, including:
Pump Power (P)
Head (H)
Flow Rate (Q)
Specific Speed (Nₛ)
NPSH (Net Positive Suction Head)
Problem:
Calculate the power required for a pump delivering 50 m³/h of water at 30 m head, assuming 80% efficiency.
Solution:
Use the pump power formula:
P=ηρ⋅g⋅Q⋅H
Where:
ρ (water density) = 1000 kg/m³
g (gravity) = 9.81 m/s²
Q (flow rate) = 50 m³/h = 0.0139 m³/s
H (head) = 30 m
η (efficiency) = 0.8
Calculation:
P=0.81000⋅9.81⋅0.0139⋅30=5116 W=∗∗5.12kW∗∗
Conclusion: The pump requires ~5.1 kW of power.
Problem:
A pump draws water from a 3 m deep well and discharges it to an open tank 25 m above. Friction losses are 2 m. Calculate the total dynamic head (TDH).
Solution:
TDH=Hstatic+Hfriction+Hvelocity
Hstatic=25 m (discharge)+3 m (suction)=28 m
Hfriction=2 m
Hvelocity (negligible for most cases)
TDH=28+2=∗∗30 m∗∗
Conclusion: The pump must overcome 30 m total head.
Problem:
A pump curve shows:
At 2500 RPM, H = 40 m when Q = 0.02 m³/s.
If speed reduces to 2000 RPM, what’s the new Q and H?
Solution:
Use Affinity Laws:
Q2Q1=N2N1,H2H1=(N2N1)2
New speed ratio: 25002000=0.8
New flow: Q2=0.02×0.8=∗∗0.016m3/s∗∗
New head: H2=40×(0.8)2=∗∗25.6m∗∗
Conclusion: At 2000 RPM, Q = 16 L/s, H = 25.6 m.
Problem:
A pump runs at 2900 RPM, delivers 100 m³/h at 50 m head. Find its specific speed (Nₛ).
Solution:
Ns=H3/4NQ
N=2900 RPM
Q=100 m³/h=0.0278 m³/s
H=50 m
Ns=503/42900×0.0278=18.82900×0.167=∗∗25.7∗∗
Conclusion:
Ns=25.7 → Radial-flow impeller (typical for high-head pumps).
Problem:
A pump takes water from a 2 m deep tank (atmospheric pressure = 101.3 kPa). Pipe friction loss is 0.5 m, and vapor pressure is 2.34 kPa (at 20°C). Find NPSHₐ.
Solution:
NPSHa=ρgPatm−Pvap+Hstatic−Hfriction
Patm=101.3 kPa=101300 Pa
Pvap=2.34 kPa=2340 Pa
Hstatic=2 m
Hfriction=0.5 m
NPSHa=1000×9.81101300−2340+2−0.5=10.1+2−0.5=∗∗11.6m∗∗
Conclusion: The system provides 11.6 m NPSHₐ.
Parameter | Formula |
---|---|
Pump Power (P) | P=ηρgQH |
Total Head (TDH) | TDH=Hstatic+Hfriction |
Affinity Laws | Q2Q1=N2N1,H2H1=(N2N1)2 |
Specific Speed (Nₛ) | Ns=H3/4NQ |
NPSH Available | NPSHa=ρgPatm−Pvap+Hs−Hf |
Would you like help with real-world system design or CFD validation? Let me know your requirements!
The above content is compiled and published by Zhilong Drum Pump supplier, please specify, to buy oil drum pump, electric drum pump, high viscosity electric drum pump, fuel drum pump, food grade drum pump and so on, please contact us.