Figure 116 shows a gully used by Mr. Denton for many years, having advantages similar to the last. Finally Figs.
117 and 118 show gullies having removable sediment boxes. The gratings are made separate for convenience in casting and in lifting off. The boxes above the trap lessen evaporation in dry weather and can be removed and emptied into the scavenger's cart readily by one man.
The next figures show a number of disconnecting house traps described by Denton, all being more or less cesspools, with square top. Figure 123 is a horizontal house trap.
All should and will be done away with as fast as the people learn the value and economy of well ventilated sewers. The slide also gives a number of grease and sink traps.
Figure 121 is a species of grease traps having a catch-basin at the bottom. Fig. 122 is an earthenware sink trap Figure 124 is a rainwater pipe trap which, however, can not be depended upon unless means are provided for constantly renewing the water therein. Figure 125 is a running house trap with gully combined. A gully trap so used will always be sure of a seal while the house is occupied, because it takes the house waste and is not dependent upon rainy weather. Fig. 126 is another gully trap showing how it may be ventilated by a pipe rising along the outer wall of a house.
Fig. 127 shows a triple seal trap, used in England, and is introduced to show the madness to which main house trapping is sometimes carried. The water in this trap occupies two compartments separated from each other designed to prevent the one seal from polluting the other if the water in it should in any way become foul. The middle part of the trap receives the surface drainage, and also provides an escape for any sewer air which might be forced through the outer seal; all parts open directly into the outer air through gratings. The three dips are intended to afford extra security against the passage of sewer air. This trap is, of course, very objectionable on account of the great obstruction it offers to the passage of the drainage, and of its expense.
Self Cleansing Traps.
are those which are scoured throughout by the water which passes through them. They may be subdivided into (1) those which lose their water seal under the action of siphon-age or momentum, and (2) those which are capable of resisting such action.
(1) Siphonable Traps
Figures 128 to 134 represent different forms of siphonable traps. A very feeble suction is all that is necessary to break the seal of any of them. The modified forms possess no appreciable advantage over the common S trap of equal depth of seal in this respect.
Fig. 134 is an S trap with a small sediment chamber at its bottom. This chamber was introduced with the idea that it would give the trap greater resistance against siphonage. It has, however, no advantage whatever in this direction, since its enlargement is all below the seal proper.
Fig. 135 represents a complicated device for replenishing the seal exhausted by siphonage, evaporation or other cause. The device would evidently soon become inoperative, and is too expensive and delicate to deserve more than a passing notice. Fig. 133 shows the manner in which the ventilating opening of an S trap becomes clogged sometimes to a height of more than two feet from the mouth, and the same would result with the water supply pipe intended to refill the trap in Fig. 135 because it could evidently never be under water pressure.
Figures 136 and 137 are other illustrations of an excess of ill-directed zeal. The purpose is to refill on S trap automatically after siphonage, a small reservoir chamber being attached to the trap in such a manner as to deliver to it through atmospheric pressure a fresh supply of water whenever its level in the trap seal falls slightly below the normal. It works on the principle of the inverted bottle chicken feeder, and is itself replenished by a small feeder pipe operative when the supply cock of the fixture is opened for use. This complicated and costly device was conceived many years ago when the fear of sewer gas was at its greatest. It is true that the water pressure would be likely to keep the small openings in the reservoir chamber free from deposit and the trap well scoured out, but the trap might be siphoned while the fixture cock was not in use for a considerable length of time so that the entire device would serve only to inculcate a false sense of security, even though evaporation might not empty the supply vessel in a year.