Pump Horsepower (HP) Calculator

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 Pump Horsepower?

Pump horsepower (HP) is 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. It's a crucial parameter for selecting the right pump for an application.

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 dynamic head in feet
\( SG \) — Specific gravity of the fluid (1.0 for water)
\( \eta \) — Pump efficiency as a decimal (0-1)
3960 — Conversion factor to get horsepower

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

3. Importance of Pump Sizing

Details: Proper pump sizing ensures efficient operation, prevents motor overload, and extends equipment life. Undersized pumps can't meet demand, while oversized pumps waste energy and may cause cavitation.

4. Using the Calculator

Tips:

For water systems, use SG = 1.0
Typical pump efficiencies range from 0.7 to 0.9 (70-90%)
Include all head losses (static head + friction losses) in your head calculation
Always round up to the nearest standard motor size

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between brake horsepower and water horsepower?
A: Water horsepower is the theoretical power needed to move the fluid, while brake horsepower includes the pump's inefficiency (BHP = WHP/η).

Q2: How do I account for viscous fluids?
A: For viscous fluids (above 50 cP), you'll need viscosity correction factors not included in this basic calculation.

Q3: What's a typical pump efficiency?
A: Centrifugal pumps typically range from 50-85% efficiency, with larger pumps generally being more efficient.

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

Q5: How does altitude affect pump HP?
A: At higher altitudes, motors produce less power. You may need to derate the motor or select a larger size.