With Vent No. 2 open and stop-cock closed, it was not possible to remove any water from the S-trap, but with Vent No. 2 closed and stop-cock open, the seal of the trap was broken S-trap with vent shows the form of trap which the committee recommends.

Trap K was placed on Y-branch D to show back pressure, but Y-branch V, as well as Y-branch C was closed during experiments on syphonage.

Fig. 252. Worcester Trap Tests.

Fig. 252 shows the apparatus used in the Worcester experiments, and Fig. 253 is an illustration of some of the dangers incurred by the use of the trap vent-pipe.

Fig. 253. Trap Vent System in a Tall Building.

Fig. 253. Trap Vent System in a Tall Building.

The master plumbers of Worcester made some tests on the apparatus shown here. The S-trap shown on the highest branch was tested for siphonage, and its seal broken when ventilated through the 1 -inch vent next the soil pipe, the vent No. 2 being closed.

This cut (Fig. 253) was used to illustrate a paper on trap ventilation I read before the Boston Society of Architects in 1891. The top of the vent-pipe is shown clogged up by frost. One of the basin trap vents is trapped by a sag in the pipe, and the mouth of the sink trap-vent is clogged by grease.

In regard to the partial or total closure of the mouth of the "back vent" pipe by grease deposits, it is not even necessary that one should have had any experience in plumbing work at all to enable him to realize the importance of this item in condemnation of the back vent law. One would have to go back several eras beyond the dark ages to find any one who had not observed how melted grease congeals upon a cold surface and how tenaciously it adheres thereto. The first savage who knew enough to roast his meat over a fire and serve it on a stone was perfectly familiar with these properties of melted grease, and would not have to ask a "sanitary plumber" if it would deposit itself along the walls of a cold waste pipe under a kitchen sink. Let us reason at least as much as the primitive savage and find out why the framers of our plumbing laws ignore these simple lessons in physical science. Every plumber has seen vent pipes fouled by greasy deposits, which often completely close up its outlet and sometimes fill it solid full for several inches beyond its mouth.

It is sometimes urged that these deposits can, from time to time, be removed. Evidently. But in practice this simple remedy is oftener neglected than observed, partly because the inside of the vent pipe mouth is usually rather inconvenient of access; partly because whatever danger there may be from such deposits is seldom announced to the house owner until it is too late; and partly because, as a matter of fact, where a reasonably good form of trap is used, a clogged vent pipe is, like a dead Indian, a safer and better thing to have in the house than one which is free and fully equipped for business.

In any case, it is beginning to be understood by students of sanitary engineering who have as much as one eye open that a device intended for protection, which requires more watching than the thing it was designed to protect, affords but a false sense of security, and in this instance often leads to the use of traps which possess no power in themselves to withstand the action of siphonage when the vent pipe becomes inoperative. Therefore, when the public are compelled to back vent all the traps, they are obliged to incur also the expense of using antisiphon traps as well

Advocates of the back venting of traps will frankly admit that traps having large unscoured areas, often called "cesspool" traps, like the old fashioned D trap, or very large pot traps, are objectionable, especially under kitchen or pantry sinks on account of the accumulation of grease and dirt in these unscoured parts.

Now, the vent mouth opening, being entirely outside of the waterway of the trap, must receive even less scour than any part of the waterway of a cesspool trap. As a matter of fact, the mouth of the vent pipe will clog much more quickly than any part of a cesspool trap, because the warm, fatty vapors are drawn up into the vent pipe and there deposit and congeal more or less grease along its cool sides at varying distances above its mouth, thus adding to the deposits caused by splashing and liquid contact. In short, the mouth of the vent pipe forms an unscoured "pocket" far more dangerous than any of those other pockets now universally condemned, which constitute the one great characteristic feature of all "cesspool" traps.

Writers on plumbing who advocate "back venting" hold that the simple "S" trap, being self-scouring, is the best to use when protected from siphonage by back venting, and they are fond of illustrating this "excellent" combination by a diagram like our Fig. 254.

But these same writers are also fond of telling us that cesspool traps, like the old fashioned D traps, or like large "pot" and "bottle," and all "mechanical" seal traps, having large unscoured chambers in their waterway, are certain in time to become more or less clogged, especially under sinks, on account of these unscoured areas or "sediment pockets," and they explain correctly how they gradually become converted into "S" traps by illustrations like Figs. 255 and 256.

Trap Testing Apparatus 265

Fig. 254.

Trap Testing Apparatus 266

Fig. 255.

Trap Testing Apparatus 267

Fig. 256.

Trap Testing Apparatus 268

Fig. 257.

Trap Testing Apparatus 269