The term drain-waste-vent, or DWV, when used in conjunction with describing plumbing systems is a system in which sewage and waste are removed from a building and gases are vented. Waste enters the DWV from plumbing fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, which is a dipped section of pipe that always contains water.
All plumbing fixtures must contain traps or risk gases backing up into the home or building. These traps connect all plumbing fixtures to common waste lines, which direct waste to what is called a soil stack. The waste is then removed from the building through a main drain and taken to a sewage line. From the sewage line, waste is then lead to a septic system or a public sewer, depending on the pluming system the home or building employs.
An important part of any plumbing system, the venting system pipes connect plumbing directly fixtures to the outdoors, often through the roof. Vents allow a release of sewer gases, they admit oxygen which allows sewage to begin to decompose, and prevent sewer gases from entering the building. With a few exceptions, every plumbing fixture is required by approved building codes to have an attached vent. Due to the unpleasant aroma coming issuing from these vents, they are sometimes called stink pipes.
DWV are powered by nothing more than gravity, and must maintain neutral air pressure in the drains to allow proper water flow drains and through waste pipes. Because gravity is the powering force of these plumbing systems, it is critical that all pipes have a downward slope throughout the system. In situations in which a downward slope cannot be created out of a building to the sewer, a collection pit and grinding lift 'sewage ejector' pump are necessary to deliver waste to the sewage system.
A sewer pipe maintains a neutral air pressure when compared to the surrounding atmosphere. When a column of waste water flows through a pipe, it naturally compresses the air already existing in the pipe, creating a positive pressure that must be released to prevent the air from pushing the waste back into the building. Conversely, as water passes through the pipe, air must also flow in behind the waste stream or suction will result, which will cause a siphoning of water from trap seals at plumbing fixtures. An empty trap can be a dangerous thing, as it can allow sewer gasses into a home or building.
Because the air pressure within sewage pipes is so essential, a manual valve housed in a valve box is always accessible to utility workers to ensure that air pressure, water, waste and sewage are always kept at safe levels to avoid catastrophic accidents, explosions and injuries.
Author Resource:
CP Test Services-VALVCO (http://www.cptest.com/) specialty is in the manufacturing of cathodic protection test stations, sewer cleanout caps and gas service curb and valve boxes . Art Gib is a freelance writer.Distributed by Content Crooner
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