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)

Required Horsepower (HP):

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1. What is the Fire Pump Horsepower Formula?

The fire pump horsepower formula calculates the required power to move a specific volume of fluid against a given head pressure, accounting for the fluid's specific gravity and the pump's efficiency.

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 of the fluid (1 for water)
\( \eta \) — Pump efficiency as a decimal (0.0 to 1.0)
3960 — Conversion constant

Explanation: The equation converts the hydraulic power (flow × head × specific gravity) to mechanical horsepower, adjusted for pump efficiency.

3. Importance of Horsepower Calculation

Details: Proper horsepower calculation ensures the pump motor is correctly sized to handle the required flow and pressure without being oversized (wasting energy) or undersized (causing failure).

4. Using the Calculator

Tips:

For water systems, specific gravity is 1.0
Typical pump efficiencies range from 0.7 to 0.9 (70-90%)
Include safety factors in final motor selection
Account for worst-case scenario in flow and head requirements

5. Frequently Asked Questions (FAQ)

Q1: What is the 3960 constant in the formula?
A: It's the conversion factor that converts (GPM × feet × lb/gal) to horsepower (1 HP = 3960 (GPM·ft·lb)/min).

Q2: How do I determine pump efficiency?
A: Pump efficiency is typically provided by the manufacturer. For estimation, centrifugal pumps are often 70-85% efficient at their best efficiency point.

Q3: Should I add a safety factor to the calculated HP?
A: Yes, it's common practice to add 10-25% to the calculated HP to account for system losses and future demands.

Q4: What's the difference between hydraulic and brake horsepower?
A: Hydraulic HP is the theoretical power needed, while brake HP (calculated here) includes the pump's efficiency.

Q5: How does specific gravity affect the calculation?
A: Higher SG fluids require more power to pump - double the SG means double the HP requirement for the same flow and head.