Under the subject of venting, taken up under Plate II, it was seen that the trap seal may be lost by siphonage, the latter action following the formation in the drainage system of a vacuum or partial vacuum. Some of the ways in which this vacuum may be formed in the drainage system that is not provided with a system of trap vents, are considered in the following.

Siphonage of a trap may be caused by the outflow of the waste from its own fixture, the momentum of which is sometimes sufficient to suck out a large part of the seal. When two fixture wastes branch into the same pipe, the passage of the waste from one fixture may fill the pipe sufficiently to produce a vacuum behind the column of waste, and thus siphon out the seal of the other trap.

A fixture having a long line of horizontal waste is often endangered by a partial temporary stoppage in the horizontal part of the waste. When this stoppage is relieved, the waste filling the pipe may flow off so strongly as to produce a vacuum behind it and cause siphonage. This is true even of the water closet. The passage of a heavy volume of waste down a vertical stack may produce a partial vacuum at the entrance into the stack of another fixture, causing the trap of the latter to lose its seal. Fixtures at the foot of a stack are more open to the danger of trap siphonage than those nearer the top of the stack. As the lower floors are reached, more waste fills the stack than at points farther up, and as this heavy volume of waste strikes the horizontal line it is naturally impeded, and more nearly fills the pipe, with a consequent greater danger of producing a vacuum followed by the siphonage of trap seals.

These conditions that have been described are the cause of many of the rules regulating the construction of plumbing, such as the prohibition of quarter-bends on the drainage system, for instance, the use of which would impede the outflow of waste far more than the Y branch and eighth-bend form of connection between vertical and horizontal lines.

In Fig. A of Plate 37 and Fig. E of Plate 38 are shown two views, front and end, of double batteries of lavatories installed at the center of the public toilet room, or in such location that no partition may be used for concealing the waste and vent piping.

Each individual lavatory is separately trapped and provided with a continuous vent, this work showing the principle of continuous venting applied somewhat differently than in Plates 26, 27, and 28, though with equal effectiveness. In Fig. A, Plate 37, it is intended to show the main horizontal waste pipe run above the floor, while in Fig. E, Plate 38, the main is run below the floor, and branch wastes connected from each fixture.

Plate XXXVIII. Plumbing For Public Toilet Rooms

Plumbing for

Public Toilet Rooms

Plumbing For Public Toilet Rooms 94

Fig. A.

Plumbing For Public Toilet Rooms 95

Fig. b.

Plumbing For Public Toilet Rooms 96

Fig. C.

Plumbing For Public Toilet Rooms 97

Fig. D.

Plumbing For Public Toilet Rooms 98

Either method that is most desirable may be used. The chief feature of this work is the concealment of the main vent line and branch vents inside a box formed by the marble backs of the two lines of fixtures, and a piece of marble set on top. The marble box runs the entire length of the line, which may rise vertically to run to a vertical vent stack at any intermediate point, as in Fig. A, or at either end. The lavatories in both illustrations are of porcelain or porcelain-lined ware, and supported on cast-iron standards. In Fig. A, the marble backs run down to the floor, allowing all but the traps to be concealed in the space between the two marble back slabs, while in the case of Fig. E the space below the lavatories is open, and a part of the work is in sight.

The use of continuous vents is of great advantage in this instance, as it not only allows the work to be done in a more sanitary manner, more neatly and compactly than by ordinary methods, but at far less cost of labor and material. This last advantage is gained in the use of continuous vents on nearly all work where fixtures back up to each other in pairs, whether under such circumstances as these or on opposite sides of a partition.

Under ordinary circumstances, it is not difficult to so construct the toilet room that much of the work may be concealed in open spaces behind partitions.

In Fig. C, for instance, the flush valves for a line of water closets may be thus concealed, and as in Fig. D, the flush tanks, whether high or low, and the horizontal soil pipe may both be concealed.

Concealment of working parts, such as flush valves and tanks, with their chains and pulls, is often very desirable, especially in school and factory work, where there is danger of damage due to mischievous tampering with such devices. When so concealed, however, the working parts should be made accessible for repairs and inspection.

The use of the circuit system of venting is often of much advantage in public toilet rooms, especially in connection with lines of water closets. It is applied in the case of Fig. A, and might be applied to equal advantage in Fig. D.

The choice of water closets for public toilet-room work is almost unlimited, if the matter of expense is not to be considered. Fig. D shows a very desirable form in many respects. It is so constructed that it fits squarely into the corner made by the partition, and may be made much more firm and secure against accidental blows by being bolted both to the floor and to the partition. It has a rear outlet which allows the soil pipe to be run above the floor. This method of running the soil pipe and connecting the water closets is of special value in fire-proof buildings and for public buildings of various kinds. The soil pipe is supported on standards, the entire work presenting a very neat appearance. In Fig. B a very convenient form of water closet is shown, provided with a large local vent connection, which is a part of the bowl itself. This local vent connection gives a much more finished appearance to the fixture than a connection made with metal pipe. The connection is designed to project into a foul-air flue located back of the partition against which the water closets are set.

When water closets of public toilet rooms are flushed by individual flush tanks, the capacity of the latter should not be less than for other uses, that is, not less than of 5 gallons capacity.

When supplied from an automatic flush tank, however, the latter should be of such capacity that each water closet on the line shall be flushed by at least four gallons of water at each discharge of the tank.

All lip urinals, water closets, and slop sinks used in public toilet rooms should be of the flushing-rim type, this form of fixture being flushed and cleansed more thoroughly than others.