VENTING THE WASTE SYSTEM
The waste system is vented to allow free air circulation within the system, to reduce the pressure on trap seals, and to remove foul gas odors caused by sewerage. Venting must tie into the stack. The method used to vent the waste system depends on where the fixtures are to be located and how they are grouped. This learning event describes three methods-unit venting, wet venting, and circuit venting. This learning event also describes water seals and cleanout fittings.
Unit venting allows two similar fixtures to use the same stack fitting. The waste drains of the two fixtures must be at the same height from the floor.
Wet venting allows the drain line of one fixture to serve also as a vent line for another fixture. The size of the wet vent depends on the distance between trap outlets.
Circuit venting can be used when two or more fixtures, such as lavatories, are installed in a row. The circuit vent is connected to the waste drain line between the last two fixtures in the row. Then the circuit vent is connected to the main vent.
A water seal stops sewer gases from coming into the building. It is a column of water in a fixture trap. The column is maintained by the atmospheric pressure from the venting (14.7 pounds per square inch, at sea level).
Water seal for water closets. Water closets have built-in traps that provide a visible water seal.
Water seal for other fixtures. Other fixtures require a P-trap to provide a water seal. The P-trap seal is a column of water (about 2 inches) between the trap's crown weir and the trap's top dip.
A cleanout is a fitting with a removable plug that is placed in a roughed-in waste system to help clear any stoppage in waste drain lines. Cleanouts are placed at the connection between the building sewer line and drain line, at the base of a vertical stack, and at all places where pipe direction changes 90 degrees.
Cleanout for a building sewer line. This cleanout can be just outside or inside the building. It must be 2 or more inches above the ground or the building floor.
Cleanout at the base of vertical stack. This cleanout must be 6 inches or more above the floor.
Cleanout for a 90-degree change-of-pipe direction. This cleanout is installed to clear any possible stoppage caused by the 90-degree turn in the line.
|David L. Heiserman, Editor||
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Revised: June 06, 2015