Fire Pump Horsepower Calculator

Fire Pump Horsepower Formula:

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

Flow Rate (Q):

GPM

Head (H):

feet

Specific Gravity (SG):

(1 for water)

Efficiency (η):

decimal (0-1)

Pump Horsepower (HP):

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1. What is the Fire Pump Horsepower Formula?

The Fire Pump Horsepower formula calculates the required horsepower for a pump based on flow rate, total head, specific gravity of the fluid, and pump efficiency. It's essential for proper pump selection and system design in fire protection systems.

2. How Does the Calculator Work?

The calculator uses the standard pump horsepower equation:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total head in feet
\( SG \) — Specific gravity of the fluid (1.0 for water)
\( \eta \) — Pump efficiency as a decimal (0.0 to 1.0)
3960 — Conversion factor to convert to horsepower

Explanation: The formula accounts for the work needed to move a specific volume of fluid against a certain pressure head, adjusted for the fluid's density and the pump's efficiency.

3. Importance of Pump Horsepower Calculation

Details: Accurate horsepower calculation ensures proper pump selection, prevents underpowered or oversized pumps, and helps design efficient fire protection systems that meet NFPA requirements.

4. Using the Calculator

Tips: Enter flow rate in GPM, total head in feet, specific gravity (1.0 for water), and pump efficiency (typically 0.7-0.9 for centrifugal pumps). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is typical pump efficiency for fire pumps?
A: Centrifugal fire pumps typically have efficiencies between 70-85% (0.7-0.85). Always consult manufacturer data for specific pumps.

Q2: How does specific gravity affect horsepower?
A: Higher specific gravity fluids require more horsepower. For water (SG=1), it's the baseline. For other fluids, multiply by their SG.

Q3: What's included in "total head"?
A: Total head includes static head, friction losses, pressure requirements, and elevation differences in the system.

Q4: Should I add a safety factor to the calculated HP?
A: Yes, it's common practice to add 10-20% safety margin to account for system variations and future demands.

Q5: How does this relate to NFPA 20 requirements?
A: NFPA 20 requires pumps to be capable of delivering required flow and pressure. This calculation helps verify the power requirements meet those needs.