Pump Horsepower Calculator

Pump Horsepower Formula:

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

Flow Rate (Q):

GPM

Head (H):

Specific Gravity (SG):

(1 for water)

Efficiency (η):

decimal (0-1)

Pump Horsepower (HP):

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1. What is Pump Horsepower?

Pump horsepower (HP) is the power required to move a fluid at a specified flow rate against a specified head, accounting for the fluid's specific gravity and the pump's efficiency. It's a crucial parameter in pump selection and system design.

2. How Does the Calculator Work?

The calculator uses the pump horsepower formula:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total dynamic head in feet (ft)
\( SG \) — Specific gravity of the fluid (dimensionless)
\( \eta \) — Pump efficiency as a decimal (0-1)
3960 — Conversion factor to horsepower

Explanation: The formula calculates the theoretical power required to move the fluid, then divides by the pump's efficiency to get actual required horsepower.

3. Importance of Pump Horsepower Calculation

Details: Proper horsepower calculation ensures correct pump selection, prevents underpowering or overpowering, and helps design efficient systems that minimize energy costs.

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., 85% = 0.85). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between brake horsepower and water horsepower?
A: Water horsepower is the theoretical power needed to move the fluid, while brake horsepower includes the pump's inefficiency (water HP ÷ efficiency).

Q2: How do I estimate pump efficiency?
A: Typical centrifugal pump efficiencies range from 50-85%. Smaller pumps tend to have lower efficiency. Consult manufacturer curves for exact values.

Q3: What if my fluid isn't water?
A: Use the specific gravity of your fluid (ratio of its density to water's density). For example, seawater is about 1.03.

Q4: Why is the conversion factor 3960?
A: It comes from (8.33 lb/gal × 60 min/hr) / (550 ft-lb/sec-HP), combining unit conversions and the definition of horsepower.

Q5: Should I add a safety factor?
A: Yes, it's common to add 10-20% to the calculated horsepower to account for system variations and future needs.