Pump Horsepower Calculation Formula

Pump Horsepower Formula:

\[ HP = \frac{GPM \times Head\ (ft) \times SG}{3960 \times Eff} \]

Flow Rate (GPM):

GPM

Head:

feet

Specific Gravity (SG):

(unitless)

Efficiency:

fraction

Pump Horsepower (HP):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Pump Horsepower?

Pump horsepower is the power required to drive a pump, calculated based on flow rate, head, fluid properties, and pump efficiency. It determines the motor size needed for proper pump operation.

2. How Does the Calculator Work?

The calculator uses the pump horsepower formula:

\[ HP = \frac{GPM \times Head\ (ft) \times SG}{3960 \times Eff} \]

Where:

\( HP \) — Pump horsepower
\( GPM \) — Flow rate in gallons per minute
\( Head \) — Total dynamic head in feet
\( SG \) — Specific gravity of the fluid
\( Eff \) — Pump efficiency as a fraction (0.0 to 1.0)
\( 3960 \) — Conversion constant

Explanation: This formula calculates the theoretical horsepower required to pump a fluid, accounting for flow rate, pressure head, fluid density, and mechanical efficiency.

3. Importance of Pump Horsepower Calculation

Details: Accurate horsepower calculation is crucial for proper pump selection, motor sizing, energy efficiency optimization, and preventing equipment failure due to under or over-sizing.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What is the significance of the 3960 constant?
A: The constant 3960 converts the units from (GPM × ft-lb/min) to horsepower, where 1 HP = 33,000 ft-lb/min and 33,000/8.34 ≈ 3960.

Q2: How do I determine pump efficiency?
A: Pump efficiency varies by type and size. Typical efficiencies range from 50-85% for centrifugal pumps. Check manufacturer curves for specific values.

Q3: What is specific gravity and why is it important?
A: Specific gravity is the ratio of fluid density to water density. It affects the power required - denser fluids require more power to pump.

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

Q5: What's the difference between hydraulic HP and brake HP?
A: This formula calculates hydraulic HP. Brake HP includes mechanical losses and is calculated as Hydraulic HP divided by pump efficiency.