The subject of traps is a fundamental one, inasmuch as upon the proper operation of the trap depends the operation of the entire plumbing system, from a sanitary standpoint.
Defined, the trap is a vessel holding a quantity of water, whose purpose is the prevention of the passage of gases and odors from the sewer or cesspool, and from the plumbing system itself, into the house.
In order to protect the house from such danger, a trap is required not only under each plumbing fixture, but also on each floor drain, cellar drain, rain leader, etc.
The use of traps under the various fixtures, and their connections, is to be seen in Fig. 26. The subject of venting, which is so closely associated with trap work, will be considered in another chapter.
It may be said that all traps used in plumbing construction are based upon one or the other of two fundamental types. These are shown in Fig. 27, the two types being known as the S trap and the drum trap. These two forms of trap are more commonly used than any others, and concerning their comparative excellence there has long been much debate. By many the S trap is considered the best form of trap, inasmuch as it is self-scouring and therefore more easily kept from becoming foul. The chief argument against the S trap is the fact that it may easily lose its seal by siphonage, such action resulting in establishing direct communication between the sewer and the interior of the house. The characteristics of the S and drum traps are exactly opposite; where one is weak the other is strong. The drum trap holds a large body of water, a large part of which is inactive. Therefore it is not to be expected that this form of trap will be so free of filth as the S trap; in fact its opponents claim that the drum trap is in the nature of a small cesspool. On the other hand, the drum trap is far less liable to siphonage than the S trap, a 4-inch drum trap being found by test to be practically nonsiphonable under conditions generally existing in the plumbing system.
Fig. 27. - Fundamental Types of Traps.
In the use of these two forms of traps a neutral position would appear to be more logical than the radical position so generally maintained by the plumbing fraternity, there being places where either one will certainly do better work than the other. For instance, when vented and used in connection with such fixtures as lavatories, also in the construction of water-closets, main traps, etc., the S trap is the better and more convenient form to use, for while holding the advantage of being self-cleansing, its size in many of these instances, and the size of its connecting pipes, eliminates almost entirely the danger of siphonage. Many times it is essential that to insure perfect work, the delivery from the trap should be as rapid as possible, and it can readily be seen that delivery from the S trap more nearly satisfies such requirement than the delivery from the drum trap. On the other hand, the drum trap is especially well adapted to use beneath floors, for instance, in bath-tub work, Fig. 28 showing such a connection.
Fig. 28. - Use of Drum Trap under Floors.
As a rule, the waste pipe from such a fixture as the bath tub has none too much fall, particularly when the trap is at some distance from it. Under such conditions a better pitch can be secured in the use of the drum trap, and in addition, the cleaning facilities are much better in the case of the drum trap. Another point which recommends the drum trap is its great depth of seal, this being an important feature of the trap, particularly if attached to a fixture not often in use, for with a shallow seal evaporation soon breaks it.
Although not considered the best practice, it often happens that two or more fixtures enter the same trap, as for instance, bath and lavatory, or sink and laundry tubs, and when so installed the drum trap is almost a necessity, as its construction allows several waste pipes to enter it at different points at the bottom, while a pipe of larger size from the top forms the outlet.
From these two traps scores of other traps have sprung into existence. In the illustrations shown in Fig. 29 will be found various forms of these traps now in common use. There are traps which have valves of one kind or another. In general these valves are very simple, consisting usually of a ball resting against a seat, the ball being displaced when waste enters the trap, and reseating itself after the waste stops running. In these traps, which also have the ordinary water seal, dependence is made for addi-tional protection upon this valve or mechanical seal as it is called. When new, such a trap may do good work, but the trap soon becomes foul, and the valve likewise, in which condition it not only fails to perform its work, but becomes actually an obstruction around which substances may collect and eventually form a complete stoppage of the trap. Most plumbing ordinances now prohibit the use of this class of traps. There is another class of traps having one or more partitions within the body of the trap. Such traps usually have the advantage of being compact, convenient for use in many places, and make a neat appearance. However, when such internal partitions project above the water line in the trap, danger is always present, from the fact that sand holes or other imperfections may exist, under which condition direct communication with the sewer is established. A particularly bad feature of such partitions is that serious flaws may exist, and remain undetected, for whatever leakage may come from them shows only inside the trap, never outside. If it could be detected from the outside the faulty trap might be replaced, thus obviating the continuance of the resulting danger for an indefinite length of time. Many ordinances now discriminate against this form of trap.
Fig. 29. - Various Patented Traps in More or Less Common Use.