Well Pump Horsepower Calculator by Size

Pump Horsepower Formula:

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

Flow Rate (Q):

GPM

Total Head (H):

feet

Specific Gravity (SG):

(water = 1.0)

Pump Efficiency (η):

decimal (0-1)

Required Horsepower (HP):

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1. What is Pump Horsepower?

Pump horsepower (HP) is the power required to move a specific volume of fluid against a given head (pressure) at a certain efficiency. Properly sizing a pump ensures it can meet system requirements without being oversized (wasting energy) or undersized (failing to meet demand).

2. How Does the Calculator Work?

The calculator uses the standard pump horsepower formula:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total head in feet
\( SG \) — Specific gravity of fluid (water = 1.0)
\( \eta \) — Pump efficiency (0-1, typically 0.7-0.9)
3960 — Conversion constant (foot-pounds per minute per horsepower)

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

3. Importance of Proper Pump Sizing

Details: Correct pump sizing is critical for energy efficiency, system reliability, and longevity. Oversized pumps waste energy and can cause cavitation, while undersized pumps fail to meet demand and may overheat.

4. Using the Calculator

Tips:

Measure flow rate (GPM) based on your water demand
Calculate total head (vertical lift + friction losses)
Use SG=1.0 for water, higher for denser fluids
Typical pump efficiency ranges from 70-90% (0.7-0.9)

5. Frequently Asked Questions (FAQ)

Q1: How do I determine total head?
A: Total head = static head (vertical distance) + friction head (pipe resistance). Friction depends on pipe size, length, and material.

Q2: What's a typical efficiency for well pumps?
A: Submersible pumps typically range 70-85% efficiency, while jet pumps are usually 50-70% efficient.

Q3: Should I round up the HP result?
A: Yes, select the next standard motor size (e.g., if calculation gives 1.4 HP, use 1.5 HP motor).

Q4: How does specific gravity affect HP?
A: Higher SG fluids require more power. For brine (SG=1.2), HP is 20% higher than for water.

Q5: What about motor service factor?
A: Many pumps have a 1.0-1.15 service factor, allowing temporary operation above nameplate HP.