Pump Motor Sizing Calculator

Pump Motor Sizing Formula:

\[ Power = \frac{Flow\ Rate \times Head \times Specific\ Gravity}{3960 \times Efficiency} \]

Flow Rate:

GPM

Head:

feet

Specific Gravity:

dimensionless

Efficiency:

decimal (0-1)

Required Power:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Pump Motor Sizing Formula?

The pump motor sizing formula calculates the required horsepower for a pump based on flow rate, head pressure, fluid specific gravity, and pump efficiency. It helps engineers select appropriately sized motors for pumping applications.

2. How Does the Calculator Work?

The calculator uses the pump sizing equation:

\[ Power = \frac{Flow\ Rate \times Head \times Specific\ Gravity}{3960 \times Efficiency} \]

Where:

\( Flow\ Rate \) — Gallons per minute (GPM)
\( Head \) — Total dynamic head in feet
\( Specific\ Gravity \) — Ratio of fluid density to water density (1.0 for water)
\( Efficiency \) — Pump efficiency as decimal (0.0-1.0)
\( 3960 \) — Conversion factor (foot-pounds per minute per horsepower)

Explanation: The formula converts the hydraulic power required to move the fluid into mechanical power required by the motor, accounting for pump efficiency.

3. Importance of Proper Pump Sizing

Details: Correct pump motor sizing ensures energy efficiency, prevents motor overload, extends equipment life, and maintains optimal system performance. Oversizing wastes energy while undersizing causes premature failure.

4. Using the Calculator

Tips: Enter flow rate in GPM, head in feet, specific gravity (1.0 for water), and pump efficiency as decimal (e.g., 0.85 for 85%). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is typical pump efficiency?
A: Centrifugal pumps typically range from 50-85% efficiency, with higher efficiency in larger, well-designed pumps.

Q2: How do I account for motor efficiency?
A: The calculated power is brake horsepower (BHP). Divide by motor efficiency to get input power requirements.

Q3: What safety factor should I add?
A: Common practice adds 10-25% to calculated power for safety margin and future capacity.

Q4: How does viscosity affect the calculation?
A: High viscosity fluids require special considerations as they reduce pump efficiency and increase power requirements.

Q5: Can I use this for positive displacement pumps?
A: This formula is primarily for centrifugal pumps. Positive displacement pumps require different calculations.