Pump Motor Capacity Calculation

Pump Horsepower Formula:

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

Flow Rate (Q):

gpm

Head (H):

Specific Gravity (SG):

Efficiency (η):

decimal

Required Horsepower (HP):

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1. What is Pump Horsepower Calculation?

The pump horsepower calculation determines the required motor power to move fluid through a system based on flow rate, head pressure, fluid properties, and pump efficiency. This ensures proper pump selection and prevents under or over-sizing.

2. How Does the Calculator Work?

The calculator uses the standard pump horsepower formula:

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

Where:

\( HP \) — Horsepower (required motor power)
\( Q \) — Flow rate in gallons per minute (gpm)
\( H \) — Total head in feet (ft)
\( SG \) — Specific gravity of the fluid
\( 3960 \) — Conversion constant
\( \eta \) — Pump efficiency (decimal)

Explanation: The formula calculates the power needed to overcome friction losses, elevation changes, and pressure requirements while accounting for pump efficiency.

3. Importance of Pump Motor Sizing

Details: Proper pump motor sizing is critical for energy efficiency, system reliability, and preventing motor burnout. Undersized motors can overheat, while oversized motors waste energy and increase costs.

4. Using the Calculator

Tips: Enter flow rate in gpm, total head in feet, specific gravity (1.0 for water), and pump efficiency as a decimal (typically 0.65-0.85). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is specific gravity and when does it change?
A: Specific gravity is the ratio of fluid density to water density. It changes with temperature, concentration, and fluid type (chemicals, oils, etc.).

Q2: How do I determine pump efficiency?
A: Pump efficiency varies by type and size. Centrifugal pumps typically range from 60-85%. Check manufacturer specifications or use industry standards.

Q3: What is total head in pumping systems?
A: Total head includes static head (elevation difference), friction head (pipe losses), and pressure head (system pressure requirements).

Q4: Should I add a safety factor to the calculated horsepower?
A: Yes, typically add 10-20% safety factor to account for system variations, future demands, and motor service factor.

Q5: Can this calculator be used for all pump types?
A: This formula works best for centrifugal pumps. Positive displacement pumps may require different calculations due to their constant flow characteristics.