Fig. 55. - Circuit vent.
Vents are the most important pipes in the plumbing system. Modern plumbing successfully attempts to make living in crowded and thickly populated districts, as well as in isolated buildings, free from all unpleasant odors and annoyances. This could not be accomplished without the use of vents. Vents relieve all pressure in the system by furnishing an outlet for the air that is displaced by the waste discharged from the fixtures. Another of its functions is to supply air when syphonic action starts, thereby stopping the action that would 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.
Fig. 56. - Loop vent.
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 11⁄4-inch vent pipe leading from the crown of the trap up along side of the stack. On the first floor a 11⁄4-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 11⁄4-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.
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.
Fig. 57. - Continuous vent.
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 pipe, and render it unfit to perform its duty, to be washed away into the sewer.
Crown venting, Fig. 59, is as its name implies, a vent that is taken from the crown of the trap, thence into the main vent.
Each one of these methods of venting is used and considered good practice, provided it is properly installed and correctly connected with the use of proper fittings.
Fig. 59. - Crown venting.