1. What is a Fire Pump Size Calculator?

Definition: This calculator determines the required flow rate (in gallons per minute) for a fire pump based on horsepower, efficiency, total head, and fluid density.

Purpose: It helps fire protection engineers and designers properly size fire pumps for building protection systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The formula calculates how much water the pump can move based on its power, efficiency, and the resistance (head) it must overcome.

3. Importance of Proper Fire Pump Sizing

Details: Correct pump sizing ensures adequate water supply for fire suppression systems, meeting NFPA requirements and building safety standards.

4. Using the Calculator

Tips: Enter the pump horsepower, efficiency (default 0.75), total head in feet, and fluid density (default 8.34 lb/gal for water). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the constant 3960 in the formula?
A: This is a conversion factor that relates horsepower, flow rate, head, and specific gravity in consistent units.

Q2: What's a typical pump efficiency value?
A: Most fire pumps have efficiencies between 70-85% (0.7-0.85), with 0.75 being a common default.

Q3: How do I determine total dynamic head?
A: Total head includes static head (vertical distance), friction losses, and pressure requirements at the discharge point.

Q4: When would fluid density change?
A: Density changes if using additives (like foam concentrates) or pumping fluids other than water at standard temperature.

Q5: Does this account for NFPA requirements?
A: This calculates theoretical flow. Always verify against NFPA 20 standards for fire pump installations.