The drum trap for general fixture use is 4 in. in diameter, and into it are wiped the inlet and outlet waste pipes. The trap, then, represents an enlargement in the waste from a pipe of 1 1/4, 1 1/2, or 2-in. diameter to 4 in., and under this condition it cannot be expected that the drum trap will possess the scouring qualities to be found in the S-trap. The drum trap, however, certainly possesses one very strong point. While the S-trap is the trap most easily siphoned, the drum trap is one of the most difficult to siphon. In fact, under any ordinary working conditions the drum trap is practically non-siphon-able. Special tests of great severity have shown that at least a part of its seal may be siphoned, but these tests subject the trap to conditions far more severe than they encounter when installed on the plumbing system. The strong point of the drum trap is that, unlike the S-trap, it holds a large body of water, and when subjected to siphonic influence, such action takes place through a passage of the same diameter as the waste pipe, allowing the remaining body of water to fall back and form the seal.
Plate XII. Connections For Drum Traps-Practical Requirements Of Venting
Conmections for Drum Traps
While acknowledging that the drum trap is far less subject to siphonage than the S-trap, it should be vented, in order that every possible precaution may be taken to eliminate this danger and to give the entire system the benefits to be derived from thorough Ventilation.
It would seem a poor policy to maintain a radical stand against the use or in favor of either the S- or the drum trap. A better course is to select the form of trap to be used after considering the nature of the fixture which it is to serve, and the special conditions under which the plumbing system acts.
For instance, in country districts, where venting is not always used, it would appear to be good practice to make free use of the drum trap. Wherever the continuous vent can be applied to the trap, however, the use of the S-trap will give excellent results.
The drum trap is of special value in serving the bath tub, as it may be easily cleaned, and very often a better pitch can be secured for the outlet pipe than in the use of the S-trap. It is also well adapted to the laundry tubs, as it will easily receive the inlets from the several compartments, and may be placed in a more advantageous position than the S-trap, often avoiding a long line of horizontal waste extending from the farthest section to the S-trap. The drum trap is often used to serve two or more fixtures, but this is a practice which should not be followed, as each fixture should have its own separate trap.
Connections to the drum trap may be made in a great variety of ways, several of the more common connections being shown in Plate 12.
The connections of Fig. A are no doubt the most common, but the trap so installed is open to an evil which is not often considered. The trap screw is made tight by means of a rubber or leather gasket, and unless this joint is perfectly tight, direct communication with the sewer will exist. It is almost impossible to open this clean-out after the gasket has been in use for some time without destroying it, and a defective joint is very liable to be left. There are a number of ways in which this danger may be avoided. Fig. G shows a method of using the drum trap so that any defect in the cleanout gasket will at once be made apparent by leakage from the trap. The cleanout may be placed at the bottom or on the side, as shown by dotted lines. In either case it is not only submerged, but allows the trap to be cleaned to better advantage. Many ordinances now require the cleanouts of fixture traps to be submerged.
Fig. B shows a trap which is well guarded, having its outlet submerged, in which case, when the trap screw is removed, there is no direct communication.
This method of connection, however, is open to a serious objection. By taking the outlet from the bottom of the trap, where the heavy parts of the sewage collect, and thereby making the outlet pipe form the trap, there is much greater liability of stoppage.
In Fig. C the outlet ends inside the trap, dipping down into the seal, and thereby preventing direct communication with the sewer when the trap screw is removed. Although gaining this point, the part of the outlet inside the trap forms an obstruction, and there is opportunity for the collection of grease, etc., around it. The interior of the trap should always be free from any obstruction.
Fig. D shows a trap in which the vent is connected through the cleanout cover. Many ordinances prohibit a vent connection of this kind on the ground that no vent connection should be made by means of a union and gasket.
There is still another objection to this form of vent connection.
All traps sooner or later have to be opened and cleaned out, and in this case to remove the cleanout the vent must be bent around out of the way, which is not only an annoyance but harmful to the vent.
In Figs. E and F the outlet pipe is shown dipping down to the bottom of the trap. This is done to prevent direct communication when the cleanout cover is removed, but is a bad practice, for two reasons. In the first place, it takes up space in the trap, and forms an obstruction around which collections of foul matter may form. In the second place, either of these two forms of trap is very much more liable to siphonage than would be the traps in Figs. A and B, for the inlet and outlet openings are close enough together to practically form an S-trap, which is very susceptible to siphonage.
Fig. H shows a trap which is compact in the manner in which its connections are made, but which has the same fault that is found in Figs. C, E, and F.
This trap will siphon more readily than when connected as in Figs. A and B.
Fig. K shows a trap provided with a continuous vent, that is, a connection so made that the vent may be taken off the waste fitting. As stated in connection with S-traps, this method is an excellent one.
It is taken up thoroughly under Plates 26, 27, and 28.
In the case of Fig. K, the fault is the same as in Fig. A, that is, there will be direct communication with the sewer whenever the cover is removed. The same trap reversed, however, so that its cleanout is submerged, overcomes this objection.
Therefore, in summing up, it would seem that the trap shown in Fig. G, connected like that shown in Fig. K, would present the drum trap under the most favorable conditions possible.