Water Pump Sizing 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 for water)

Pump Efficiency (η):

decimal (0-1)

Required Pump Horsepower (HP):

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1. What is Pump Horsepower Calculation?

The pump horsepower calculation determines the power required to move a fluid at a specified flow rate 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 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 for water)
\( \eta \) — Pump efficiency (decimal, 0-1)
3960 — Conversion factor

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 Proper Pump Sizing

Details: Correct pump sizing ensures efficient operation, prevents energy waste, avoids cavitation, and extends equipment life. Undersized pumps won't meet demand while oversized pumps waste energy and may cause control problems.

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 all head losses (static, friction, pressure) in total head
Add 10-20% safety factor to the calculated HP

5. Frequently Asked Questions (FAQ)

Q1: What is total dynamic head?
A: The total resistance the pump must overcome, including static lift, friction losses, and pressure differences.

Q2: How do I determine pump efficiency?
A: Manufacturer curves typically provide efficiency data. For estimation, centrifugal pumps are often 70-85% efficient at their best efficiency point.

Q3: What's the difference between brake HP and water HP?
A: Water HP is the theoretical power needed to move the fluid. Brake HP (calculated here) includes pump inefficiencies and is what the motor must deliver.

Q4: When should I use specific gravity other than 1?
A: For fluids denser than water (SG > 1) like brine, or lighter than water (SG < 1) like gasoline.

Q5: How does viscosity affect pump sizing?
A: High viscosity fluids require more power and may need positive displacement pumps. This calculator is best for low-viscosity fluids like water.