*Figs 261 and 262 from "Safety in House Drainage," by W. E. Hoyt, C. E., in Pop. Science Monthly for July, 1888.
We see in Fig. 264 again some of the many ways in which the back vent pipe fails especially in the modern "skyscrapers." Clogging with grease is shown over the sink trap in the top story, which is now known to be so very common. At every quick bend under a long vertical run of iron vent pipe rust is certain to collect in large quantities as shown in the basement. A comparatively small amount of flaking-ofT of rust or sediment in such a place, especially with such tall stacks, may quickly destroy the efficiency of even the largest-sized vent pipes. Sagging, as shown higher up on the tenth story, is another frequent cause of failure.
Fig. 262. Complicated Plumbing in a New York Residence.
Water and sediment collect in the sagged portion, and failure is the result. Finally hoar frost and snow often close
Fig. 263. Apparatus for Trap Testing Used A3 the Museum of the upper opening of the pipe above the roof, producing again failure. When the main house trap is omitted frost cannot accumulate at the top of the main soil pipe because the warm air of the sewers will then constantly rise through the pipe and would melt any snow as fast as it could form. But the back vent pipe could not be so protected when it ascends independently through the roof. . The introduction of an intercepting trap at each building destroys the only practical and effective method now known of ventilating the sewers and rendering the air within them absolutely innocuous. Hence this trap becomes the sole creator of the nuisance it was designed to prevent.
Hygiene at Washington.
Figs.. 264 and 265. Two Diagrams comparing together the Complex and Simple Systems in a Modern Tall Office Building.
From the "Inland Architect and News Record" for Oct., 1905, article by J. P Putnam.
The chances of leakage in the back vent pipe are evidently increased in proportion to the increase of piping, and, what is more important still, no water flush passes through the vent pipes to announce to the eye the presence of leaks, and consequently the mischief may go on without the knowledge of the occupants.
It does not seem to occur to our lawmakers that a back vent pipe between thirty and forty stories high would have to be enlarged so much to offset friction as it climbed up from story to story that there would hardly be any room left in the upper stories for the occupants unless they planned to do their business inside the pipe itself. An enlargement such as is shown in our cut, which is simply taken from the sizes required in common practice, would be ridiculously inadequate. The modern skyscraper is performing at least one useful service in bringing the back vent law to a "Reductio ad absurdum." Thus it may be said that the rolling mill is cooperating with the microscope in revolutionizing the practice of sanitary engineering, since to the latter we owe the discoveries in bacteriology which have, almost within the last decade, sufficed to fundamentally alter our views as to the nature and proper treatment of sewage; and to the former the astonishing development of high building which is opening our eyes to the folly of over-complication.
Thus one evil involves another. Unnecessary complications exact others which are necessitated by them, and a departure from the all-important rule that "other things being equal the simplest is the best" is certain to result in an endless train of cares and troubles.
The next figures show the apparatus used by S. Stevens Hellyer of London* in 1882 for testing traps for siphon-age. Three slop sinks were fitted up with 1 ¼-inch cast lead traps, as shown in Fig. 267, and attached by 1¼-inch branches to the main vertical waste pipe, also 13/2-inch in diameter. A pailful of water thrown into the upper hopper siphoned ¾ of an inch out of each of the two lower traps. Another pailful unsealed them. When the air pipe at the top of the main waste pipe was stopped up this discharge of the top sink also siphoned its own trap.
Mr. Hellyer then ventilated each trap as shown by the dotted lines, and repeated the tests. This time scarcely a sixteenth of an inch appears to have been drawn out of the lower traps, although the water was vibrated in them.
With a trap at F at the bottom of the stack, back pressure was so great at the lower sink trap that it forced a spray of water 12 or 18 inches from the trap out into the sink.
Fig. 268 shows another arrangement used by Hellyer in his experiments. The perpendicular main waste pipe was here 2 inches in diameter and had three 2-inch branches, the upper for a bath, the middle for a slop-hopper and the lower for a wash basin. The middle branch had also several different sized traps on it.
When the traps were not ventilated each of them could be unsealed by the discharge of the bath tub. Indeed all four of the lower small traps were unsealed at once, but these ventilated the large trap on the middle branch and protected it partially. But it also lost an inch of its seal.
When the traps were ventilated, as shown by the dotted lines, only one trap lost any water. This was the trap U, which lost 1/8 of an inch.