1. What is a Gravity Drain Flow Rate Calculator?

Definition: This calculator estimates the flow rate (in gallons per minute) for a gravity-fed drainage system based on the head height and pipe cross-sectional area.

Purpose: It helps engineers, plumbers, and designers determine the expected flow rate for gravity drainage systems.

2. How Does the Calculator Work?

The calculator uses two fundamental formulas:

Where:

• \( V \) — Velocity of flow (ft/s)
• \( Q \) — Flow rate (gallons per minute)
• \( g \) — Acceleration due to gravity (32.174 ft/s²)
• \( h \) — Head height (ft)
• \( A \) — Cross-sectional area of pipe (ft²)

Explanation: The first formula calculates the theoretical velocity of water under gravity, while the second converts this to flow rate in GPM.

3. Importance of Flow Rate Calculation

Details: Proper flow rate estimation ensures adequate drainage capacity, prevents system overload, and helps in selecting appropriate pipe sizes.

4. Using the Calculator

Tips: Enter the head height (vertical drop), pipe cross-sectional area, and gravity constant (default 32.174 ft/s²). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the 448.83 conversion factor?
A: This converts cubic feet per second to gallons per minute (1 ft³/s = 448.83 GPM).

Q2: Is this the actual flow rate I'll get?
A: This is theoretical maximum; actual rates will be lower due to friction losses and other factors.

Q3: How do I find pipe cross-sectional area?
A: For circular pipes: \( A = \pi \times r^2 \) where r is radius in feet.

Q4: What's typical head height for residential drains?
A: Typically 1/4" per foot (0.25%) slope, but varies by code and application.

Q5: Does this account for pipe friction?
A: No, this is ideal flow. For real-world applications, consider using Hazen-Williams equation.