Water Pump Size Calculator

Pump Power Equation:

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

Flow Rate (Q):

GPM

Head (H):

feet

Specific Gravity (SG):

(1 for water)

Pump Efficiency (η):

decimal (0-1)

Pump Horsepower (HP):

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1. What is the Pump Power Equation?

The pump power equation calculates the required horsepower for a water pump based on flow rate, head pressure, fluid properties, and pump efficiency. It's essential for selecting properly sized pumps in water systems.

2. How Does the Calculator Work?

The calculator uses the pump power equation:

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

Where:

\( HP \) — Pump horsepower
\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total head in feet
\( SG \) — Specific gravity of fluid (1.0 for water)
\( \eta \) — Pump efficiency (typically 0.6-0.9)
3960 — Conversion factor (foot-pounds per minute per horsepower)

Explanation: The equation calculates the power needed to move a specific volume of fluid against a given pressure head, accounting for pump efficiency.

3. Importance of Proper Pump Sizing

Details: Correct pump sizing ensures efficient operation, prevents energy waste, reduces wear, and extends equipment life. Oversized pumps can cause cavitation and excessive energy use, while undersized pumps won't meet system demands.

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 total head in pump calculations?
A: Total head is the sum of static head (vertical distance), friction head (pipe resistance), and pressure head (system pressure).

Q2: How do I determine pump efficiency?
A: Pump efficiency varies by type and size. Centrifugal pumps typically range from 60-90%. Check manufacturer specifications for exact values.

Q3: What's the difference between water horsepower and brake horsepower?
A: Water HP is the theoretical power needed to move water, while brake HP includes pump inefficiencies (what the motor must actually deliver).

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

Q5: Can this be used for other liquids besides water?
A: Yes, by adjusting the specific gravity for the fluid being pumped (e.g., 0.8 for gasoline, 1.03 for seawater).