Traps may be divided into two principal classes:
I. Mechanical traps.
II. Water seal traps.
Each of these may be again subdivided as follows:
I. Mechanical traps may be subdivided into:
(a) Hinged-valve trap.
(b) Gravity-valve trap.
(c) Floating-ball trap.
(d) Gravity-ball trap.
(e) Mercury seal trap.
II. Water seal traps may be subdivided into:
(a) Sediment traps.
(b) Self-cleansing traps.
These two classes may again be subdivided as follows:
(a) Sediment traps may be subdivided into: (1) Air-vent traps.
(2) Reservoir traps.
(b) Self-cleansing traps may be subdivided into:
(1) Siphonable trap.
(2) Anti-siphon trap.
Finally self-cleansing anti-siphon traps may again be subdivided into:
(a) Deep seal traps.
(b) Shallow seal traps.
Mechanical closures alone, without the water seal, are of as little use in plumbing traps, in excluding sewer gas, as could be the mechanism shown in Fig. 63, which shows the peculiar form of mechanical trap found under all the sinks of a tenement house whose landlady had received orders from the Board of Health to have "traps put under every plumbing fixture." The old lady obeyed the order to the letter, but in doing so exposed an ignorance of household sanitation so dense that even the rats themselves became rudely derisive and hilarious. They carried their ridicule so far as to withdraw the cheese from the traps by means of skewers in order to demonstrate the futility of mechanical gates in traps. Two investigators climbed up into the sink to ascertain the result of the woman's stupidity and, in still further contempt, simulated instant death, as you see, from the "deadly" sewer gas which emanated from the unprotected waste pipe, while four others were obliged to hold their sides to prevent them from splitting with their vulgar laughter.
Fig. 63. Peculiar form of trap found under the sinks of a tenement house whose landlady had received notice from the Board of Health to have traps put under every plumbing fixture.
These almost incredible facts are recorded to show the astonishing amount of ignorance displayed by the public of the functions of traps and plumbing work generally. All our good lady knew about drainage was that she emptied slops into the sink, and that the slops then went "the devil knew where."
Mechanical seal traps, like pan, valve and plunger water-closets, have served their purpose, and must now be laid aside in the general march of progress.
Before the necessity of ventilating the main soil pipe was felt, and when the science of plumbing was still more undeveloped, back pressure in every trap from the sewers was a thing to be guarded against where the sewers were foul, and balls, gates and valves in traps were invented to supply an actual want. Now, however, the universal and most desirable custom of ventilating every stack of soil pipes, and a better understanding of the hydraulics and pneumatics of plumbing has done away with this requirement, and the mechanical seal serves no longer any other purpose than to obstruct the proper flow of the waste water through the pipe, and to collect sediment, besides causing a false sense of security in case of evaporation or siphonage of the water seal. It is evident that the mechanical seal is entirely superfluous, since everything a trap is required to do can be done by other better and simpler means. Moreover, we cannot apply mechanical seals to water-closet traps, and this fact alone shows the uselessness of applying them to smaller traps, since we must rely on the water seal alone in some of the fixtures in all houses.
It has been claimed by some makers of ball traps that the rotary movement of the ball in the water scours the sides of the trap and prevents the collection of sediment, just as places. Experience proves this to be the case, for the hollow ball traps burst like other traps when exposed to frost severe enough to freeze suddenly the water beyond the parts occupied by the ball, and to break a glass of the same form and size not containing a ball.
In our drawings illustrating various types of traps in use, all the traps have been drawn to substantially the same scale and size of inlet pipe, so that their relative sizes can at once be seen. This will prove very useful in enabling us to judge of their merits, especially as far as concerns the probable scouring effect of the water current on their walls.
Fig. 64 his.
(a) Hinged-Valve Trap.
Figs. 64, 64 bis and 65 show three forms of the hinged valve." If the valves in these traps could only be maintained clean and operative, they would somewhat protect the water seal from evaporation produced by the ventilating current. The swellings in the bodies of these traps very slightly increase their power of resistance to siphonage, but the enlargement would have to be carried much further before they could be safely used without ventilation, and the retardation of the water passage due to the valve would then increase the rapidity of fouling inevitable with all forms of pot traps. The hinged valve is the worst kind of mechanical closure that can be used in the smaller house traps, the slightest corrosion or sediment at the hinge rendering the mechanism inoperative.