uld break the seal of the trap under fixtures. The
pipe extending from top fixture connection, up to and through the
roof, is called the ventilation pipe. All vents that do not pass
directly through the roof terminate in this ventilation pipe.

To explain the use of vents, we might well start in the basement of
a dwelling house. Suppose there is a set of wash trays in the
laundry; the 2-inch trap of these trays should have a 1-1/4-inch
vent pipe leading from the crown of the trap up along side of the
stack. On the first floor a 1-1/4-inch pipe from the crown of the
kitchen sink trap will lead into it. Here the pipe should be
increased to 2 inches. On the second floor the 1-1/4-inch pipes
leading from the lavatory and bath traps come into it. The vent
stack now extends up into the attic and connects with the
ventilation pipe. In a general way, the above is an example of
venting. The old method of venting was very complicated and is
almost beyond describing with the pen.

[Illustration: FIG. 56.--Loop vent.]

In common use today, there are several kinds of venting, namely:
circuit and loop venting, crown venting, and continuous venting.
The _circuit venting_, Fig. 55, is used in connection with the
installation of closets. Take a row of toilets in which the waste
connection of each closet discharges into a Y-branch, and there
will be a series of Y-branches. One end of this series of branches
discharges into the main stack while the other end continues and
turns up at least to the height of the top of the closet and then
enters the main vent stack. When this main vent runs up along side
of the main stack and forces the vent pipe connected to the series
of Y-branches to travel back, it is called a loop vent. This type
of vent supplies air to the complete line of toilets and is very
efficient.

[Illustration: FIG. 57.--Continuous vent.]

[Illustration: FIG. 58.]

CONTINUOUS VENTING, Figs. 57 and 58, applies more to fixtures other
than toilets. A P-trap is used and enters a T in the stack. The
lower part of the T acts as and connects with the waste pipe while
the upper half is and connects with the vent pipe. A study of the
figures will aid the reader to understand thoroughly the above
explanations. In continuous venting the waste of the lowest fixture
is discharged into the vent pipe and extended to the main waste
stack where it is connected. This is done to allow any rust scales
that occasionally drop down the vent