Traps are commonly installed on fixtures, such
as lavatories, sinks, and urinals. At times, the
P-trap may also be suitable in shower baths and
other installations that do not require wasting of
large amounts of water.
A VENT (pipe) allows gases in the sewage
drainage system to discharge to the outside. It also
allows sufficient air to enter, reducing the air
turbulence in the system. Without a vent, once
the water is discharged from the fixture, the
moving waste tends to siphon the water from the
other fixture traps as it goes through the pipes.
This means that the vent piping must serve the
various fixtures, as well as the rest of the sewage
drainage system. The vent from a fixture or group
of fixtures ties in with the main vent. A MAIN
VENT is the principal artery of the venting system
to which vent branches maybe connected and run
undiminished in size as directly as possible from
the building drain to the open air above (fig. 8-19).
The MAIN SOIL AND WASTE VENT or
VENT STACK, installed in a vertical position,
refers to the portion of the stack that extends
above the highest fixture branch, through the
roof, and to the exterior of the building.
Various types of vents are used in the ventila-
tion of fixtures. The selection of a particular type
depends largely on the manner in which the
plumbing fixtures are to be located and grouped.
An INDIVIDUAL VENT, also known as a
BACK VENT, connects the main vent with the
individual trap underneath or behind a fixture.
This method of venting is shown in figure 8-19.
Figure 8-19.-Typical stack and vent installation.