Sanitary Drainage Systems Overview

Study Notes

Sanitary Drainage Systems

The primary purpose of a sanitary drainage system is to remove wastewater from plumbing fixtures and equipment to a designated disposal point.
A sanitary drainage system usually consists of various components including:
- Horizontal branches that connect fixtures to the vertical stack.
- Vertical stacks that carry the wastewater.
- A building drain inside the structure.
- A building sewer that extends from the building to the disposal point.
The system is designed to efficiently remove wastewater, considering factors like:
- The smallest possible pipe size to avoid clogging.
- Rapid removal to prevent solid waste buildup and excessive pressure.
- Minimizing noise generation.
The design incorporates vents and venting systems, which are explained in detail in Chapter 3 of the handbook.
Flow within stacks:
- A stack is a vertical pipe carrying discharge from fixtures like toilets, urinals, or other equipment.
- Water enters the stack from the drain through fittings like tee-wye or sanitary tee.
- The entry of water into the stack accelerates downwards under gravity, creating a sheet of water around the wall of the stack.
- This allows air to flow freely within the center of the pipe.
Stack capacities:
- Research conducted by Wyly and Eaton at the National Bureau of Standards determined the flow capacity of stacks based on different pipe sizes and rates of flow, providing valuable data for drainage system design.
Water flow in branches:
- Water flowing from the branch into the stack either mixes with the existing flow or deflects it.
- Deflection requires significant hydrostatic pressure in the branch to overcome the momentum of the downward flowing stream in the stack.