Calculate Pump Horsepower from Flow and Head Diagram

Pump Horsepower Formula:

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

Flow Rate (Q):

GPM

Head (H):

Specific Gravity (SG):

dimensionless

Efficiency (η):

decimal (0-1)

Pump Horsepower (HP):

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1. What is Pump Horsepower?

Pump horsepower is the power required to move a fluid at a specified flow rate against a specified head, accounting for the fluid's specific gravity and the pump's efficiency. It's a crucial parameter in pump selection and system design.

2. How Does the Calculator Work?

The calculator uses the pump horsepower formula:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total dynamic head in feet (ft)
\( SG \) — Specific gravity of the fluid (dimensionless)
\( \eta \) — Pump efficiency (decimal between 0 and 1)
3960 — Conversion factor (foot-pounds per minute per horsepower)

Explanation: The equation calculates the power needed to move a given flow rate against a specified head, adjusted for fluid density and pump efficiency.

3. Importance of Pump Horsepower Calculation

Details: Accurate horsepower calculation ensures proper pump selection, prevents motor overload, and helps design efficient pumping systems. It's essential for energy consumption estimation and system optimization.

4. Using the Calculator

Tips: Enter flow rate in GPM, 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'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 (water HP = brake HP × efficiency).

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: What if my fluid isn't water?
A: Use the specific gravity of your fluid (ratio of its density to water's density). For example, seawater is about 1.03.

Q4: Why is the conversion factor 3960?
A: It comes from unit conversions: 1 HP = 550 ft-lb/s = 33,000 ft-lb/min, and water weighs 8.34 lb/gal (33,000/8.34 ≈ 3960).

Q5: How does head relate to pressure?
A: Head (ft) = Pressure (psi) × 2.31 / SG. The calculator uses head because it's independent of fluid density.