It is a fact that after being in use for a length of time, a large majority of vents connected as in Fig. 41 become almost, if not entirely closed with grease, lint, etc., and in that condition of course become inoperative. Many expedients have been tried in the manufacture of traps to overcome this difficulty, but with little apparent success. Some few plumbing ordinances call for the location of a cleanout on each trap vent, but this is by no means a solution of the difficulty, for the seat of the trouble is always hidden from view, and that a stoppage of the vent exists is almost never known. In addition, the average owner or tenant knows so little concerning these matters that he cannot be depended upon to clear the vent at proper intervals, and in most cases not at all. The knowledge of the great extent of this evil is one of the chief reasons for the great activity in the search for a nonsiphonaole trap, such a device naturally not requiring the vent, and therefore being free from this trouble.
Certain cities have even gone so far as to adopt the nonsiphon-able traps now on the market, allowing their installation without venting, preferring to take chances with the so-called nonsiphon-able trap rather than with the ordinary trap and its attendant closed vent. There is a form of venting known as continuous venting, or venting, in the rough, which may be said to be free from the stoppage evil, and the subject is of such importance that the following chapter will be devoted to its consideration. A stoppage of the trap vent is to be considered more dangerous than a stoppage of the waste, as the latter quickly makes itself known by the setting back of the waste into the fixture, while the former is seldom known unless the work is taken apart.
Little has so far been said concerning the vent and waste connections of drum traps, and a consideration of the subject will be of value. A great majority of drum traps installed are probably connected as shown in Fig. 45. The chief argument against this style of work is that if the trap screw gasket does not happen to be tight, there is direct communication with the drainage system or the sewer and the house. Such conditions would also arise while the cover was removed during the cleaning of the trap. This trouble may be avoided by a connection such as in Fig. 46. The chief objection to the connections of Fig. 40, however, is the fact that there is of necessity a greater length of pipe in which waste may stand and possibly cause the fouling of the outlet. On the whole, however, Fig. 46 represents a very satisfactory arrangement. The connections of Fig. 47 also prevent the escape of gases when the trap screw is off or not tight, but the objectionable feature in allowing the outlet pipe to project into the trap is that it presents an obstruction in the body of the trap, and around it filth may collect, making the stoppage of the trap more probable. The vent connection, however, is good, and more free of the danger of stoppage than most of the other connections shown. This fact applies also to Fig. 49.
The method of taking the vent connection off the trap-screw cover, as in Fig. 48, is quite a common one, and not to be recommended, as each time the trap is to be cleaned it is necessary to twist the vent pipe back out of the way. The connections shown in Fig. 49 are in many respects very good. The cleanout cover being submerged, any leakage is at once apparent, but with the cleanout in this position, it is impossible to prevent the escape of gases when the cover is removed. Many other forms of connection showing modifications and combinations of those illustrated might be given.
In providing a supply of air to the trap vent, one of three courses may be followed. If there are no fixtures above, it may be entered into the soil or waste vent at any point below the roof; it may be carried directly through the roof; or it may be carried into a line of main vent,"as shown in Figs. 45 to 49. The only objection to entering the trap vent directly into the soil or waste vent when there are no fixtures above, is that unless the fixture is on the top floor, other fixtures may be located above at some future time. The carrying of the trap vent directly through the roof not only makes an extra roof connection necessary, with considerable extra expense, but as such a pipe is somewhat apart from the main system, the air in it is colder and the circulation of air therefore less satisfactory. The most approved method, then, is to connect the trap vent into a main line of vent, illustrations of which will be seen later. A very important point in the running of trap vents as well as main vents, is that they shall pitch upward at every point. A considerable amount of condensation and scale forms in the vent pipes, and if there is no pitch on the pipes these accumulations cannot find their way back into the trap, where they may flow out through the waste. The size of the trap vent should generally be the same as that of the trap to which it is connected.
Figs. 45 - 49. - Waste and Vent Connections of Drum Traps.
Fig. 50. - Venting of Water-Closets.
The important exception to this rule is the vent from the water-closet. The, waste from the water-closet is 4 inches in diameter, but experience shows that a 2-inch vent is sufficiently large.
Fig. 50 shows the correct and the wrong method of venting the water-closet. When properly installed, a 2-inch vent is taken from the top of the horizontal part of the lead bend carried above the fixture and entered into the main vent. It is considered poor practice to connect this vent on the vertical arm of the bend, as paper and other substances are liable to collect about the entrance and finally close it. Its location on the horizontal arm of the bend is comparatively free from this difficulty. Another very good method, the principle of which is similar, is the connection of the vent to the vent hub of a vented T-Y fitting, into which the lead bend is calked. This method will be illustrated later. The incorrect method, shown in Fig. 50, consists of the connection of the vent to the vent horn of the water-closet, a method which is now prohibited by nearly all plumbing ordinances. The objection to such a method is that any blow which the fixture may receive, or the settling of floors, will break off the vent horn, for the reason that the vent pipe is usually too rigid to take up any movement of the closet. The water-closet is naturally the fixture most difficult to siphon, inasmuch as it is more difficult to form a vacuum in a 4-inch pipe than in pipes of smaller diameter. Therefore, it is not necessary to vent this fixture under certain circumstances, for instance, when it is located close to the stack on the top floor. In this location, with no fixtures above it to produce siphonic conditions, there is nothing to be gained in venting. The vents from a number of fixtures may be connected into one line, and this line connected into the main vent, such a method often being more advisable for many reasons than the running of each trap vent separately into the main. When so installed, however, as the several vents enter the branch to the main vent, the size of the branch vent should be increased, as shown in Fig. 51. In the case of a small number of fixtures, however, such as to be found in the bath room, the 2-inch vent to the water-closet need not be increased in size after receiving the vents of the other fixtures, as it is of sufficient size to provide air to the several fixtures.
Fig. 51. - Connection of Branch Vents.