allows the two vertical lines to be run very close together. In Fig.
59, at B, is shown a wrong method of connecting the main vent
into a trap vent, instead of re-entering the main stack. The same
connection may perhaps be seen more clearly in Fig. 56.

When the lower end of the main vent stack is reduced to re-
ceive a trap vent, as in Fig. 56, there is abundant opportunity for
the collection of scale, rust, and condensation in the heel of the
reducing elbow, and no opportunity whatever for it to be washed

away as in the correct method. The latter connection is the more
rigid of the two also. For these reasons the connection of Fig. 57
is the one now generally called for by the best plumbing ordi-

nances.

Fig. 59 shows the various connections on the vent system, with various common fittings in use.

In Fig. 55 also are shown main vent connections, and a special

FIG. 59.-Vent System, Showing Main and Trap Vents, Use of Fittings, etc.

form of vent fitting, which is not only excellent in principle, but allows the work to be installed very compactly.

A few words should be said concerning the material used on the vent system. For main vent lines cast iron or galvanized wrought iron pipe is used, and for trap vents either brass, lead, or galvanized wrought iron, the latter being the most extensively used in both cases.

CHAPTER VIII

CONTINUOUS VENTING

As seen in the preceding chapter, the great obstacle to the operation of the trap vent is the collection of grease, etc., about the vent opening into the trap, in such quantity as to completely close the opening. If the vent should be disconnected from the trap it would be found that in a vast number of cases the opening is completely closed, and the vent entirely useless, which condition generally renders the trap easily subject to siphonage. As already stated, numerous mechanical devices have been tried in the attempt

to regulate this difficulty, but all without avail. Even the use of the cleanout on the trap vent, as seen in Fig. 60, does not constitute a solution of the difficulty, although in some cities it is required. The trouble seems to be too deep-seated to be remedied by superficial means. In order to solve the difficulty, a different principle

should be applied, and it would seem that in the continuous vent a very satisfactory solution has been found. There may be places where it is difficult to apply this method, but in general it may be successfully done.

In Fig. 61 are shown two examples of the application of the continuous vent to both the S and the drum trap.

This vent system is, by the way, sometimes called "venting in the rough." The principle involved in the continuous vent is readily seen. It consists essentially in the use of a fitting of the

FIG. 61.-The Continuous Vent.

T-Y style, in such a manner that the vent may be taken from the top of it, and the waste from the bottom. This form of installation necessitates the use of the half-S trap, and prohibits the use of other forms of S trap, with the exception of the running S trap. It hardly need be stated that the opportunity of closing the vent opening is far less in this form of venting than in the method of the preceding chapter, which is in common use. This opening is not only further from the trap, and therefore more free from the splashing of the waste as it enters the trap, but the use of the T-Y fitting also tends to make the accumulation of grease about the opening more difficult. Another advantage gained in the use of the continuous vent is that no part of the work need be exposed to