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.
Fig. 60. - Cleanout on Trap Vent.
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 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 view, with the exception of the trap itself. This, as may well be supposed, is often a valuable feature. Generally when this style of vent is used, the material employed on both waste and vent is either brass or galvanized wrought iron, although lead may be used if for any reason it is found to be more desirable.
Fig. 61. - The Continuous Vent.
In a great deal of work on which the continuous vent is used, the cost of stock and labor involved is very much less than when the same work is installed according to the methods shown in the preceding chapter. This is particularly true of certain classes of large work. Fig. 62, for instance, shows the continuous vent principle applied to a line of fixtures, both front and end views being given. To this type of work the principle is particularly adaptable, and is being constantly employed to a greater extent. The method allows both horizontal main waste and main vent to be run back of partitions, concealed from view. Another material advantage of the continuous vent is the fact that the vent is taken off so far from the trap that the rate of evaporation is far less than under the conditions existing in work as ordinarily constructed. This is a more important feature than is generally acknowledged, for many traps, otherwise properly installed, fail because of the evil due to evaporation. In Fig. 63 is shown a vertical line of fixtures entering a waste stack, the traps being provided with continuous vents, and in Fig. 64 the same style of work in connection with a double line of fixtures on opposite sides of a partition. Double lines of fixtures are very often to be found on large work, such as apartment and office buildings, hotels, schools, factories, etc., and on such work as this there is no question whatever that the saving in labor and material is very great.
Fig. 62. - Continuous Venting for Line of Fixtures.
Figs. 63-66. - Examples of Continuous Venting.
In Fig. 65 is shown a water-closet vented from the vent hub of a vented T-Y, a method which is very acceptable. This particular vent is not generally spoken of as a continuous vent, but it actually is in principle, and is therefore considered in this chapter. Such work is very substantial, and particularly adapted to locations in which the plumbing is liable to rough usage, as, for instance, in factory work.
Fig. 67. - Continuous or Circuit Venting of Water-Closets,.
Fig. 66 shows the use of special patented fittings designed for vent work, the principle being very similar to that involved in the work of Fig. 65. In this connection it may be said that a great variety of vent fittings are now made, many of which will be noted in later illustrations, which are of very great value in the construction of continuous venting. Another modified form of continuous vent is to be seen in Fig. 67. This style of work, known as circuit venting, is applicable only to batteries of water-closets, but as it often happens that in the plumbing of hotels and other public buildings, extensive toilet rooms are located one above the other, the occasion often arises where the principle referred to may be put to good use. The illustration shows a line of water-closets on one floor only, but similar work on floors above or below would be put in in a like manner. The idea consists in the location at either end of the line of water-closets, of a vertical stack, one for soil and waste, and the other as a main vent. Each vertical line is carried through the roof, thus affording abundant circulation of air for each line of fixtures. Here again a great saving is made in labor and material over the separate vent method, in which a vent is taken from each lead bend. In the case of such work as that of Fig. 67, if fixtures other than water-closets waste into the horizontal soil pipe serving the water-closets, the vents from such fixtures may be run in the ordinary manner and connected into the vent stack.
It may be said that the continuous vent will prove a most valuable feature in the attainment of a perfect plumbing system, and that when its value becomes more thoroughly understood and appreciated, it is bound to be universally adopted. Indeed, it appears strange that it is not already put to more extensive use, as it certainly is a solution of some very serious problems.