ENGINEERING – PUMP & TURBINE CALCULATOR
Pump Similarity Laws
A precise tool.
What is the Pump Similarity Laws & How does it work?
Pump affinity (or similarity) laws describe how the performance of a centrifugal pump changes when its rotational speed is altered while the impeller geometry remains constant.
The three core relationships are:
\frac{Q_2}{Q_1}=\frac{N_2}{N_1},\quad \frac{H_2}{H_1}=\left(\frac{N_2}{N_1}\right)^2,\quad \frac{P_2}{P_1}=\left(\frac{N_2}{N_1}\right)^3
Q = flow rate, H = head, P = power, N = rotational speed
By applying these ratios, engineers can predict new operating points, select appropriate motors, and evaluate energy consumption without costly physical testing.
Parameters
Result
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Frequently Asked Questions
How does changing the rotational speed of a pump affect its flow rate?
The flow rate increases proportionally to the increase in rotational speed.
What happens to the head when the pump’s rotational speed is doubled?
The head increases by a factor of four when the rotational speed is doubled.
How does power consumption change with an increase in pump speed?
Power consumption increases cubically with an increase in rotational speed.
Can you explain the relationship between flow rate and head in a centrifugal pump?
Flow rate is directly proportional to rotational speed, while head is proportional to the square of rotational speed.
What are the implications of using these laws for pump selection?
These laws help engineers predict pump performance and select appropriate models based on desired operating conditions.
How do I calculate the new head when the pump’s speed is reduced by 50%?
The new head will be one-fourth of the original head when the speed is halved.
What factors should be considered when applying similarity laws to real-world pumps?
Viscosity, fluid density, and impeller geometry can affect the accuracy of these calculations in practical applications.
Results are for informational purposes only and do not constitute professional advice.