Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Explain the components of a wastewater drainage system.
• Differentiate between types of fixture traps and their uses.
• Explain the purpose of vent pipes in a drainage system.
• Sketch a basic drainage system for a single-story building.
• Identify common drainage problems and how to prevent them.

Lesson summary

This week, we delve into the critical aspects of drainage, plumbing, and sanitation in buildings. In South Africa, access to clean water and effective sanitation systems are fundamental rights enshrined in our constitution.

However, many communities still face challenges related to inadequate infrastructure, leading to health risks and environmental degradation. Understanding these systems is crucial for civil technologists to design, build, and maintain buildings that promote public health and environmental sustainability. Poor drainage can lead to flooding, structural damage to buildings, and the spread of diseases. Faulty plumbing can result in water wastage and contamination.

Lesson notes

2. 1.

Wastewater Drainage Systems: An Overview A wastewater drainage system removes used water and sewage from buildings to a municipal sewer or septic tank. The system comprises various components, each playing a vital role in efficient and hygienic waste disposal. The fundamental principle is gravity – wastewater flows downhill through a network of pipes. 2.

2. Components of a Wastewater Drainage System Fixtures: These are the appliances that discharge wastewater (e.g., sinks, toilets, showers, washing machines).

Fixture Drains: The pipes connecting fixtures to the main drainage system.

Fixture Traps: These are critical components located under each fixture.

Drain Pipes (Horizontal and Vertical): The pipes that carry wastewater horizontally and vertically throughout the building. These include branch drains, main drains (also called soil or waste stacks), and the building drain.

Vent Pipes: These pipes allow air into the drainage system to prevent siphoning of water from fixture traps.

Cleanouts: Access points in the drainage system for clearing blockages.

Building Drain: The lowest horizontal drain pipe that receives all drainage from soil, waste, and other drainage pipes inside the walls of the building and conveys it to the building sewer.

Building Sewer: The pipe extending from the end of the building drain and conveying the sewage to a public sewer, private sewer, individual sewage disposal system (septic tank). 2.

3. Fixture Traps: The Key to Preventing Sewer Gases A fixture trap is a U-shaped (or similar shape) fitting installed in the drain line of each plumbing fixture. Its primary function is to retain a small amount of water (the trap seal) to prevent sewer gases from entering the building. Sewer gases contain harmful and unpleasant substances like methane, hydrogen sulfide, and ammonia. These gases pose health risks and create foul odors.

P-Trap: The most common type, shaped like a "P" laid on its side. It's universally used under sinks and washbasins.

S-Trap: Similar to a P-trap but with a longer, more pronounced curve. S-traps are generally prohibited by most modern building codes (including SANS 10400-P) because they are highly susceptible to self-siphoning.* This means the entire water seal can be sucked out due to pressure changes in the drain line, leaving the trap ineffective.

Drum Trap: A cylindrical trap, often used for bathtubs and showers in older buildings. Drum traps have a larger water seal capacity but are prone to clogging and are difficult to clean. Drum traps are also generally prohibited by most modern building codes (including SANS 10400-P).* Bottle Trap: A compact trap often used in contemporary basin installations. 2.

4. Vent Pipes: Maintaining Pressure and Preventing Siphoning Vent pipes are essential for maintaining atmospheric pressure within the drainage system. Without proper venting, the flow of wastewater can create a vacuum (negative pressure) that siphons water from fixture traps, breaking the seal and allowing sewer gases to enter the building.

Purpose of Venting: Prevent Trap Siphoning: Vent pipes provide air to equalize pressure in the drain line, preventing the vacuum that causes siphoning.

Promote Efficient Drainage: By allowing air into the system, venting ensures smooth and consistent wastewater flow.

Protect the Trap Seal: A properly vented system ensures the water seal in the trap remains intact, preventing sewer gas entry.

Types of Venting Systems: Individual Vent: A vent pipe connected directly to the fixture drain, extending upwards and connecting to the main vent stack.

Common Vent (Dual Vent): A single vent pipe serving two adjacent fixtures.

Circuit Vent: A vent pipe that serves a group of fixtures, typically in a row (e.g., multiple sinks in a commercial kitchen).

Wet Vent: A section of drain pipe that also serves as a vent. Wet venting is permitted in certain situations but requires careful design to ensure adequate venting.

Stack Vent: The extension of a soil or waste stack above the highest fixture connection, serving as the main vent for the system.

Air Admittance Valve (AAV): A one-way valve that allows air into the drain line to prevent siphoning but does not allow sewer gases to escape. AAVs are permitted in some situations as a supplemental vent, but they are generally not a substitute for proper venting to the outside.* SANS 10400-P provides guidance on their correct usage. 2.

5. SANS 10400-P (Drainage) This South African National Standard provides requirements for the design, installation, and testing of drainage systems in buildings. Adherence to SANS 10400-P is mandatory for ensuring safe and effective drainage systems. The standard covers various aspects, including pipe sizing, materials, venting requirements, and inspection procedures. Always refer to the latest version of SANS 10400-P for the most up-to-date information. 2.

6. Worked Examples Example 1: Calculating the required fall for a horizontal drain pipe.