Fire Fighting Pump Horsepower Calculator

Pump Horsepower Equation:

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

Flow Rate (Q):

GPM

Total Head (H):

feet

Specific Gravity (SG):

(1.0 for water)

Pump Efficiency (η):

decimal (0.1-1.0)

Required Horsepower (HP):

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1. What is Pump Horsepower Calculation?

The pump horsepower calculation determines the power required to move fluid through a system at a specified flow rate against a given head pressure. This is essential for selecting properly sized fire pumps that can meet system demands.

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 fluid (1.0 for water)
\( \eta \) — Pump efficiency (decimal between 0-1)
3960 — Conversion constant

Explanation: The equation accounts for the work needed to move fluid against gravity and system resistance, adjusted for the pump's mechanical efficiency.

3. Importance of Proper Pump Sizing

Details: Correct pump sizing ensures adequate fire protection while avoiding excessive energy consumption. Undersized pumps fail to meet demand, while oversized pumps waste energy and may cause system damage.

4. Using the Calculator

Tips: Enter flow rate in GPM, total head in feet, specific gravity (1.0 for water), and pump efficiency (typically 0.65-0.85 for centrifugal pumps). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is total head in pump calculations?
A: Total head is the sum of static head (vertical distance) and friction head (pressure loss due to pipe friction).

Q2: How do I determine pump efficiency?
A: Efficiency varies by pump type and size. Centrifugal pumps typically range from 65-85%. Consult manufacturer curves for specific pumps.

Q3: Should I add a safety factor to the calculation?
A: Yes, most applications add 10-20% safety factor to the calculated horsepower to account for system variations and future needs.

Q4: What's the difference between water and brake horsepower?
A: Water horsepower is the theoretical power needed to move the water. Brake horsepower includes pump inefficiencies and is what the motor must deliver.

Q5: How does specific gravity affect the calculation?
A: Heavier fluids (SG > 1) require more power to pump at the same flow rate and head compared to water.