6.1.1 Gravity Drainage Explained

Key Concepts

• Gravity Drainage System
• Slope and Fall
• Ventilation
• Traps and P-Traps
• Materials and Fittings

Gravity Drainage System

Gravity drainage is a plumbing system that relies on the force of gravity to move wastewater from fixtures to the sewer or septic system. This system is designed to ensure that water flows smoothly and efficiently without the need for pumps.

Slope and Fall

The slope, or fall, of the drainage pipes is crucial for effective gravity drainage. A proper slope ensures that wastewater flows downhill, preventing clogs and ensuring continuous movement. The standard slope for drainage pipes is typically 1/4 inch per foot of pipe length.

Ventilation

Ventilation in a gravity drainage system is essential to prevent negative pressure and maintain proper air flow. Proper ventilation allows air to enter the system, equalizing pressure and preventing traps from siphoning. Common ventilation methods include vent stacks and roof vents.

Traps and P-Traps

Traps, particularly P-traps, are U-shaped pipes located under fixtures like sinks and showers. They hold a small amount of water to create a seal that prevents sewer gases from entering the living space. P-traps are crucial for maintaining hygiene and preventing odors.

Materials and Fittings

The materials used in gravity drainage systems must be durable and resistant to corrosion. Common materials include PVC (Polyvinyl Chloride), ABS (Acrylonitrile Butadiene Styrene), and cast iron. Proper fittings, such as couplings, elbows, and tees, are essential for connecting pipes and ensuring a leak-free system.

Examples and Analogies

Think of a gravity drainage system as a "water slide" in a theme park. Just as the slide's slope ensures smooth and continuous movement of riders, the slope of drainage pipes ensures continuous flow of wastewater. Ventilation can be compared to the air vents in a car, ensuring proper airflow and preventing pressure buildup.

P-traps are like "water dams" under sinks, holding water to block harmful gases, similar to how a dam holds back water in a river. The materials and fittings used in gravity drainage are like the sturdy materials used to build a bridge, ensuring durability and reliability.