Fig. 66 shows a valve trap invented by Col. Waring, but afterwards frankly condemned by him in his general condemnation of all mechanical traps. The valve chamber is, however, reduced to a minimum, and the trap in operation is perhaps as a whole as self-scouring as any mechanical seal trap known. The arrangement of the valve is such as to preserve the water seal of the trap for a considerable time, even under a powerful ventilating current. Siphon-age unseals it, nevertheless, quite easily. This and other mechanical seal traps would be useful on account of their power of resisting the back pressure were there no simpler means of accomplishing the same result.
Fig. 67 represents a trap which has enjoyed a great popularity. In resistance to siphonage it is equal to a bottle trap of the same size, but has the advantage in this respect over such a bottle trap that when the water seal is broken the ball would still float up against its seal, and form under some circumstances a partial seal of itself. Unfortunately the roughness of the ball surface or of any form of mechanical closure would prevent its providing proper protection against the passage of sewer air in such a case.
Under the ventilating current produced by back venting this type of trap suffers precisely as much as an ordinary bottle trap holding the same quantity of water, the evaporation proceeding from the sewer side. The ball affords no protection against evaporation because it is on the house side where the evaporation is so slow as to be practically negligible compared with the sewer side. The amount of water which the ball displaces more than offsets the delay to evaporation caused by its partial closure of the inlet pipe.
(d) Gravity Ball Trap.
Figs. 68 to 73 represent different forms of gravity ball traps, or traps in which the mechanical seal is formed by a ball resting on the top of a bend in the inlet pipe, and partially closing the passageway by its weighty bulk. The seal, as in all mechanical traps, is dependent upon the accuracy of the fit of the valve or ball and its seat. This fit is never absolutely air tight, even when new, as may be seen by emptying a new trap of its water, and, when quite dry, testing it for the passage of air or gas between the mechanical closure and its seat. However smooth and accurate their surfaces may appear to the eye, the particles forming them are colossal masses, as will be seen under a microscope, compared with the infinitesimal atoms forming the elements of air and gas, which defy the highest magnifying power to render them visible. These surfaces, rough as they are, even when new, as compared with the substances they are intended to exclude, very soon become still rougher by the deposit of a sediment composed of all kinds of impurities carried by the waste water, so that the fit can never be tight, of whatever substances the valve and seat be made. When somewhat stiffened with age the sphere becomes still more defective in shape, and its weight cannot press out the irregularities of the surfaces. When the valve and seat are wet, a seal may sometimes be formed against the passage of air, but the seal is due to the water and not to the valve, and the water seal alone would be equally efficient, since, as we have already seen, we have to do with air and gases in their normal condition and not under pressure. None of these traps are siphon proof unless ventilated. Like the gravity valve, they resist evaporation under the ventilating current for a long time, and in this respect are better than the floating ball trap, for the gravity ball and valves, as will be seen by referring to the drawings, hinder the ventilating current from licking up the water seal beneath the ball. The floating ball offers no such resistance. Evaporation goes on as rapidly as if no ball existed. This is, under the present law requiring special trap ventilation, a matter of great importance, though one which is generally overlooked in comparing mechanical seal traps with one another.
Fig. 82 represents a gravity ball or valve trap designed for kitchen sinks. It is intended to take the place of the unfortunate bell trap, now so universally condemned.
It consists of a lead receiver with a brass grating on top. The receiver holds about half an inch of water, into which the hollow valve or ball dips. The valve has a circular rim around its bottom, corresponding to the groove in the receiver which holds the few drops of water, and with it forms the feeble seal. The quantity of water is so small that evaporation easily destroys the seal in a short time, even without special vent. The trap is extremely liable to become clogged with the substances passing through kitchen sinks. This often leads to a removal, by ignorant servants, of both valve and strainer, which, of course, destroys the seal. Such a trap is little better than the ordinary bell trap, even though there is the slight advantage claimed for it by Baldwin Latham that the bell is not attached to the strainer. All such forms of sink traps are to be unconditionally condemned.