Centrifugal Pump Selection Calculator

Pump Power Equation:

\[ HP = \frac{Q \times H \times SG}{3960 \times \eta} \]

Flow Rate (Q):

GPM

Head (H):

Specific Gravity (SG):

Efficiency (η):

(0-1)

Pump Horsepower (HP):

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1. What is the Centrifugal Pump Power Equation?

The pump power equation calculates the required horsepower for a centrifugal pump based on flow rate, head, fluid specific gravity, and pump efficiency. It's essential for proper pump selection and system design.

2. How Does the Calculator Work?

The calculator uses the pump power equation:

\[ HP = \frac{Q \times H \times SG}{3960 \times \eta} \]

Where:

\( Q \) — Flow rate (gallons per minute, GPM)
\( H \) — Total dynamic head (feet, ft)
\( SG \) — Specific gravity of the fluid (dimensionless)
\( \eta \) — Pump efficiency (decimal, 0-1)
3960 — Conversion factor (ft·lb/min per HP)

Explanation: The equation calculates the power required to move a fluid at a given flow rate against a specific head, accounting for fluid density and pump efficiency.

3. Importance of Pump Power Calculation

Details: Proper pump sizing is critical for energy efficiency, system reliability, and avoiding cavitation. Undersized pumps won't meet system requirements, while oversized pumps waste energy and may cause operational issues.

4. Using the Calculator

Tips:

Flow rate should be in GPM (gallons per minute)
Head should include all static and dynamic components (suction + discharge)
Specific gravity is 1.0 for water at 60°F
Typical pump efficiency ranges from 0.5 to 0.85 (50% to 85%)

5. Frequently Asked Questions (FAQ)

Q1: What is total dynamic head?
A: The total equivalent height that a fluid is to be pumped, accounting for static lift, friction losses, and pressure differences.

Q2: How do I account for viscous fluids?
A: For viscous fluids, you may need to apply correction factors to both the flow rate and head, or use specialized pump selection software.

Q3: What's a typical pump efficiency?
A: Centrifugal pumps typically range from 50-85% efficiency, with higher efficiencies for larger pumps operating near their best efficiency point (BEP).

Q4: Should I add a safety factor?
A: It's common practice to add 10-20% to the calculated HP to account for system uncertainties and future expansion.

Q5: How does this relate to motor sizing?
A: The motor should be sized for the calculated HP plus any service factors required by the application (typically 1.1-1.25 times the pump HP).