One of the evil effects of the complication of piping due to the trap vent law is that it renders the plumbing more difficult to arrange, repair, and understand. The proper placing of the vent-pipes often requires considerably more skill on the part of the workmen than is expected of or found in them. The result is a very frequent misplacement of the pipes, which sometimes remains undiscovered by the plumber, and even by the owner, until made known by foul odors or more serious evils. Figs. 289 to 293 illustrate the manner in which this complication leads to trouble. The vents in these cases were all put according to the letter of the plumbing law, and seem at first sight to be correctly placed, but upon closer examination it will be discovered that they are not only themselves utterly valueless as ventilators, but that they destroy the value of all the traps. They form by their peculiar combinations open passageways for the entrance of sewer-air from the soil-pipe into the house. The errors appear to have been brought, after the completion of the work, to the attention of the board of health.
These first five drawings are from the "Sanitary Engineer." The arrows show the manner in which the sewerair may find its entrance by circuitous route into the dwelling. In Fig. 289 three fixtures are trapped and vented. The wastepipe of the wash-basin enters that of the bath-tub inside of the bath-tub trap. Had it entered beyond the trap, the difficulty would have been avoided. But inasmuch as it is not unusual, where no vent-pipes are used, to enter short branches on the house side of the trap, the error is not an unnatural one for the plumber to make. It is one which is not easily detected at a glance, and which might never be observed by the house-owner or anyone who was not an expert. The warmth of the air in the house and the draught of the fire-places would often be sufficient to create a reverse current in the vent-pipe, and produce the movement shown by the arrows. It will be observed that the bath-tub trap is vented on both sides. The effect of this is to increase the destructive action of the ventilating current on the water seal of the trap. An S-trap, having the usual depth of seal of 1½ in. or 1¾ in., would lose this seal in a few hours if the current were rapid, or within two or three days with an ordinary current. The water closet trap being, as shown, larger than the others, a current might easily be formed over the bath trap simultaneously on both sides of the trap.
Figs. 291, 292, 293 give similar examples. In all cases the mistake lays in entering the waste of one fixture on the wrong side of the trap of another. In each illustration one of the traps will be found to have a double action exercising against its water seal.
As here arranged, we have excellent conditions for producing self-siphonage of the wash-basin trap. When a basin having an outlet as large as the one shown is discharged by lifting the plug it will fill its waste pipe "full-bore," and the contents of the basin up to its overflow opening will fill the pipe full as far as to the horizontal runs of the pipe. This long arm of the siphon will at once pull over the water in the short arm as soon as the basin is empty, and the suction on the trap will continue until the water column has traversed the entire length of the branch waste, thus giving the siphoning action ample time to suck out any water that may trickle down into the trap from the basin after the discharge. This action will be the more positive the longer the branch waste and the greater its pitch, attaining its maximum with the perpendicular position of the waste pipe.
Fig. 294 exhibits still more forcibly the absurd confusion this system leads us to when we attempt to carry it out completely in its logical consequences. We have here the vent and waste pipes for three simple fixtures, which are taken with some modification from a house in New York, where they have been exhibited with pride by their perpetrators. These fixtures and arrangements are repeated on each of several stories. We have shown only the waste and vent pipes. When to these, we imagine, are added the necessary hot and cold water supply and service pipes, we can form a pleasant idea of the condition of things our "branch-waste" ventilating engineers are bringing us to. The fixtures have the double vent, recommended by some of our sanitary engineers and plumbers. The upper vent enters a flue or pipe heated by an interior steam-pipe, as shown, and is called the overflow and local vent pipe. None of the shallow traps used could withstand the action of these strong air-currents more than a few days or even hours. In consequence of this, house-owners often close up the overflow openings of wash-basins and bath-tubs with putty or corks in the hopes of rendering themselves secure against the odors resulting from evaporated trap seals. And this closure of the air supply to traps through overflow passages greatly increases the danger of trap siphonage, as we shall hereafter show.
Observe the complication of the plumbing involved by the use of these wriggling, interwining ventpipes, which, like venomous snakes, literally crawl about, ready to poison as well as puzzle and alarm the unhappy houseowner or plumber who unskillfully handles them, with the noxious vapors which they are designed to carry off in their bodies. In the economy of nature the serpent is found to have certain useful purposes, but the trap-vent has none, and should suffer the serpent's curse and be crushed out of existence as soon as possible.
One of Boston's leading plumbers said to me one day: "We know perfectly well that the 'back-vent' law is an imposition upon the public, but the law was brought about by the influence of the early sanitary engineers and the sanitary engineers must, therefore, be the ones to get it taken off again." But the plumbers are doing better than this remark implied, for many of them are co-operating with the sanitary engineers in their efforts to have this burden removed.
The public are becoming so much alarmed at this increasing complication that they are reducing the conveniences of plumbing in their buildings to the smallest amount possible, where its comforts might otherwise be enjoyed in perfect safety. It is throwing an undeserved distrust upon the whole system of water-carriage.
Past Experiments on Siphonage Made by Hellyer, Waring, Philbric, Bowditch, and Others.
The experiments on the effects of siphonage made and published in this country and in Europe before those I have already described, were made chiefly with pan and hopper closets, and in such a manner as to produce a much feebler siphoning action than is obtained by the use of valve or plunger closets. A pan-closet produces a very slight siphoning action, and this closet is comparatively seldom used to-day, although it is by no means extinct. Valve and plunger closets are fast giving way to the improved forms of hopper closets, but there are, nevertheless, thousands still in use in all parts of the country.
Even when the bowl of a pan-closet is filled to the brim and emptied, as in the experiments of Col. Waring for the National Board of Health, by means of a plug, the obstructions to the downfall of the water offered by the sides of the receiver and the inertia of the water standing in the trap, prevent a disturbance at all comparable with that caused by the discharge of powerful flushing closets. The value of a closet as a flushing-tank for the drain pipes is almost exactly proportional to its siphoning power. The investigations of Col. Waring are valuable particularly in showing the siphoning power on branch wastes of the discharge of bath-tubs into the main soil pipes, an arrangement extremely common, and in establishing the utmost limit of the siphoning power of the pan-closet, the one then most widely known and used. With the basin filled to the brim and suddenly discharged, the siphonage produced immediately broke the seal of unvented S-traps, but could not unseal a vented S.
In the experiments of Bowditch and Philbrick a short hopper closet, the next in general use at that time, was employed, and, to secure as useful results as possible, the closet was charged with water from a two-gallon pail, in the manner usually done when it is used as a slop-hopper. Such a use of the short hopper forms a far severer test than its ordinary flushing, though not severer than may often be produced with the powerful flushing of modern fixtures. More powerful siphoning action is often produced in practice in houses than was given by these tests, and the deductions based upon them which gave rise to the trap-vent law in many cities must be radically changed. For they showed that an S-trap, ventilated as they did it, and subjected to this strain, was secure, whereas a heavier strain or a different method of venting may break its seal as I have described.
The experiments of Hellyer in England form a better basis for plumbing legislation, inasmuch as his tests were made with those water-closets and other fixtures in common use in England which produce a much severer effect.