Pump Motor Size Calculator

Pump Motor Size Formula:

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

Flow Rate (Q):

gpm

Head (H):

feet

Specific Gravity (SG):

unitless

Efficiency (η):

decimal

Horsepower (HP):

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1. What is the Pump Motor Size Calculation?

The pump motor size calculation determines the required horsepower for a pump based on flow rate, head, specific gravity, and pump efficiency. Proper sizing ensures the pump operates efficiently without being underpowered or overpowered.

2. How Does the Calculator Work?

The calculator uses the pump motor size 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
\( SG \) — Specific gravity of the fluid (unitless)
\( \eta \) — Pump efficiency (decimal)
3960 — Conversion constant

Explanation: The formula calculates the theoretical horsepower required to move a fluid at a given flow rate against a specific head, adjusted for fluid density and pump efficiency.

3. Importance of Pump Motor Sizing

Details: Proper pump motor sizing is essential for energy efficiency, system reliability, and preventing premature motor failure. Oversized motors waste energy and increase costs, while undersized motors may fail to meet system requirements.

4. Using the Calculator

Tips: Enter flow rate in gpm, head in feet, specific gravity (1.0 for water), and pump efficiency as a decimal (e.g., 0.8 for 80% efficiency). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is specific gravity?
A: Specific gravity is the ratio of the density of a substance to the density of water. Water has a specific gravity of 1.0.

Q2: How do I determine pump efficiency?
A: Pump efficiency is typically provided by the manufacturer and varies by pump type and operating conditions. Common values range from 0.5 to 0.85.

Q3: Should I add a safety factor to the calculated HP?
A: Yes, it's common practice to add a 10-20% safety factor to account for system losses and future demands.

Q4: What if my fluid has high viscosity?
A: This calculation is best for water-like fluids. For high viscosity fluids, additional corrections are needed.

Q5: Can this formula be used for all pump types?
A: This formula provides a general estimate for centrifugal pumps. Positive displacement pumps require different calculations.