Fig. 205 illustrates a form of trap suitable for use with baths. It has a submerged inlet connection which is expanded so that the flow enters the trap at a dipping angle which produces a swirl with cleansing effect. The extension collar A is made so that the screw-cover B forms the gasket joint below the water-level. The method of pro viding the outlet in this trap makes it open to the same objection raised in connection with Fig. 203. This form, however, has the merit of being accessible for inspection without dis turbing its service, which is impos sible with the flask pattern shown in Fig. 204.
The lavatory trap shown in Fig. 206, has an interior weir as shown at A; but the wall is doubled in such a way as to betray defec tiveness by water leakage. It is made of cast metal, and is furnished with either glass or metal dome. The strong point claimed for this trap is the cleansing effect obtained by the flange extension of the exit, as shown at A, deflecting some of the water, which, together with the swirling effect produced by the tangential inlet, makes the trap self-cleansing.
Of the traps having a mechanical seal sup plementing the water-lock, Fig. 207 is a specific type. The mechanical valve D is a rubber ball, lighter than an equal bulk of water, playing in the cup C. It acts by flotation, and presses up against the inlet A with a force equal to the dif erence in weight of the ball and the water it dis places. The body is generally made of lead ; and the cup of glass, with screw joint and gasket at F. This trap is proof against back water; and, in case the waste line becomes choked below, will pre vent a fixture from flooding even when others are discharged at a higher level. It has, however, several faults that counterbalance its merits. The inlet is open to the same criticisms that an interior wall of any other trap would be; the nular space at R accumulates filth; and the mechanical seal is worthless when most needed—that is, in the absence of the water-seal.
Another mechanical seal trap, shown in Fig. 208, is the exact site of the previous example. The ball sinks by gravity, and effects a mechanical seal even when the water seal is absent. This trap is not so easily siphoned as a plain trap. It has a clean-out screw, and can be had with vent opening. Air from the sewer side acts against the clean-out cap through which access is had to the ball, and there are interior walls to become defective with little chance of discovery in practice.
A combined mechanical and water-seal trap is shown in Fig. 209, in which D is a hollow, flexible ball inclosing a metal baU Dl, thus giving a resilient seating surface that finds its place by gravity in water. The arrangement is proof against back-water, and the
mechanical seal is positive without the aid of water. A represents the basin; B, the basin coupling; C, the valve seat; F, a glass cylinder body; and GG, a clamp with thumb-screw G', for clamping the cylinder body in place. This trap holds a large amount of water, and is not likely to become unsealed from lack of use, as part of the seal is protected by the ball, and should the water evaporate, the mechanical seal is s t ill effective.
There are no in terior walls through which the trap could lose its seal without betraying the fact by leakage.
Generally speaking, mechanical seals in fixture traps cannot be depended upon.
Anti-siphoning traps are a blessing in instances where pipe ventilation is difficult. It would be better to have none of them, however, than to attempt to supplant pipe venti lation by their use to any great extent.
It would be impossible here to consider the whole list of traps individually in an adequate manner. What has been said should be enough to enable one by careful study to decide each case intelligently upon its merits. Many special traps are deserving of more favor than is generally shown them. It is the fear of seeming to indorse the horde of cheap competitive articles that causes many to ignore alike the good and bad. This fear is well grounded. The wolves will creep in if the door is opened at all.
Loss of Traps Seals. Traps may lose their seals in six ways—by waving out, by capillary action, by leakage, by evaporation, by siphon age, and—if the use of an unusual term be permissible—by in pella lion. The first, with its cause, has been described (see page 117). The last, like waving out, is caused by air-pressure, but on the house side instead of the sewer side of the trap. It occurs most frequently in intercepting traps where the fresh-air inlet has been connected too far from the trap, thus allowing heavy discharges of water and storm floods to compress the air between the fresh-air inlet and the trap. This action is of little consequence when so caused, as there is abun dance of water to re-establish the seal. Its mention, however, suggests that a portion of the pipe is left unventilated by connecting the inlet too far from the trap. This error is usually made with good intention, because the foul-air outlet and fresh-air inlet are often made in the trap proper and are therefore too close together to pipe to the surface directly. There is a singular instance on record, of a trap having its seal broken by pressure on the house side—not from pressure of air in the pipe, but of that in the room into which the trap seal opened.