Major Components of DWV Systems
Fixture drains connect fixtures to the buildings DWV piping system. Many fixtures have drains that strain the wastewater before it enters the drainage piping.
Examples of fixtures drain include baskets strainers for a kitchen sink, PO (pop up) plugs for lavatories, and other strainers for bidets and showers.
Traps are important components of the DWV piping systems. A trap is a fitting or device that provides a liquid seal of 2 to 4 inches.
While the seal prevents sewer gases from leaking back into the building, it does not affect the flow of sewage or wastewater through the drain.
The water seal protects people from airborne pathogens (germs), foul odors, and potentially explosive sewer gases.
Modern codes require every plumbing fixture to have a trap that protects the fixtures and users from the sanitary drain systems. Some fixtures, such as water closets and many urinals, have integral or built-in traps.
In order to function properly, a fixture trap must have the following features:
• It must flush completely.
• It must be self-cleaning.
• It must have a smooth interior waterway.
• It must be accessible for cleanout.
• It must have a vent system to protect it from siphonage, back pressure (backflow), wind, and aspiration.
• It must have an appropriate depth of the seal and must hold the appropriate amount of water.
Every trap requires a vent of some type. Vents are critical for plumbing fixtures to function correctly as part of the sanitary drainage systems.
Vents are installed to provide a free flow of air and to maintain equalized pressure throughout the drainage systems.
Venting prevents back pressure or siphonage from breaking the water trap seals that serve the fixture. All the vent pipes of a building create the vent system and are connected to the drain pipes. The system may include one or more pipes.
For vents to function properly, plumbers must size the vent correctly according to how many fixtures are connected, how much water discharges into the drain per minute, and the length of the vent pipe. If inadequately sized vents are installed, the plumbing system will not work properly.