1. What is a Pump Motor Selection Calculation?

Definition: This calculator determines the required horsepower for a pump motor based on flow rate, total head, fluid density, and pump efficiency.

Purpose: It helps engineers and technicians properly size pump motors for various fluid transfer applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( HP \) — Horsepower required
• \( Q \) — Flow rate (gallons per minute)
• \( H \) — Total head (feet)
• \( \rho \) — Fluid density (pounds per gallon)
• \( \eta \) — Pump efficiency factor (0-1)

Explanation: The formula calculates the power needed to move a specific fluid volume against a given head pressure, adjusted for pump efficiency.

3. Importance of Proper Pump Sizing

Details: Correct motor sizing ensures efficient operation, prevents underpowering (which can cause failure) and overpowering (which wastes energy).

4. Using the Calculator

Tips: Enter the flow rate in GPM, total head in feet, fluid density (default 8.34 lb/gal for water), and efficiency factor (default 0.85). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is total head?
A: Total head is the vertical distance the fluid must be pumped plus friction losses in the piping system.

Q2: Why is efficiency important?
A: Pump efficiency accounts for energy losses in the system. Typical centrifugal pumps have 70-90% efficiency.

Q3: What density should I use for other fluids?
A: For fluids other than water, use their specific weight in lb/gal (e.g., gasoline ≈ 6.0 lb/gal, seawater ≈ 8.6 lb/gal).

Q4: Should I round up the calculated HP?
A: Yes, always select the next standard motor size above your calculated value to ensure adequate power.

Q5: What's the 3960 constant?
A: This converts units to horsepower (1 HP = 550 ft-lb/sec) and accounts for gallons to cubic feet conversion.