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 Fire Pump Horsepower?

Fire pump horsepower is the power required to move water through a fire protection system at a specified flow rate and pressure. It accounts for the pump's efficiency and the fluid's specific gravity.

2. How Does the Calculator Work?

The calculator uses the fire 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 (1.0 for water)
\( \eta \) — Pump efficiency (decimal 0-1)
3960 — Conversion factor (ft-lb/min per HP)

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

3. Importance of Pump Horsepower Calculation

Details: Proper horsepower calculation ensures the pump can deliver required flow and pressure while preventing motor overload. It's critical for fire protection system design and pump selection.

4. Using the Calculator

Tips:

Flow rate should be the system demand in GPM
Head includes friction loss and elevation change
Typical efficiency for centrifugal pumps: 70-85% (0.7-0.85)
For water, specific gravity remains 1.0

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between brake horsepower and water horsepower?
A: Water horsepower is theoretical power needed to move the water. Brake horsepower (calculated here) includes pump efficiency and is what the motor must deliver.

Q2: How do I account for motor efficiency?
A: Motor efficiency is separate from pump efficiency. Divide the calculated HP by motor efficiency to get required input power.

Q3: What's a typical efficiency value for fire pumps?
A: Most centrifugal fire pumps operate at 70-85% efficiency when operating near their best efficiency point (BEP).

Q4: How does specific gravity affect the calculation?
A: Higher SG fluids require more power. For water-based systems, SG is 1.0. For foam concentrate systems, use the actual SG of the fluid.

Q5: Should I add a safety factor to the calculated HP?
A: NFPA 20 recommends selecting a pump driver rated at least 10% above the calculated brake horsepower.