Figs. 83 and 84 represent the ordinary bell sink trap, and Fig. 85 is an improvement thereon in having the water seal independent of the grating. In both of these traps the water seal is too small. Both are destroyed by the slightest disturbance of atmospheric pressure in the waste pipes, and are condemned by all sanitarians.
FIG. 143. - Turner's Trap.
This trap, Fig. 81, is far too expensive and complicated ever to become popular or practical, and is no less of a cesspool than the common round or pot trap,which is equally effective in excluding sewer air. The seal of this trap cannot be broken by siphonage, nor can that of a pot trap, if it be made large enough.
Yet the law requires the ventilation of both of these traps. The mercury seal trap must be constructed of some material not easily corroded by mercury or water.
Figs. 74 to 79 show five more ball traps, described by Mr. Gerhard. The first has a double gravity valve. "A glass in the upper side of the trap," says Mr. Gerhard, "enables one to inspect the working of the ball valves, which is as follows: When in rest there is, in addition to the water seal, a mechanical seal, which is half immersed in water. The second ball valve at the outlet also shuts off by its weight, but in case of undue pressure this would tend to lift the ball, leaving around it a waterway through which the water flows out. In rising, the first ball touches the second ball, which is also lifted, to allow the water to pass freely. As soon as the discharge ceases, both valves drop back into their seat." Under siphonage the valve nearest the outlet, and under back pressure that on the inlet side, will close, and so long as the trap continues clean these balls would aid in protecting the seal. But better methods have now been devised for accomplishing this, and the two balls form a double impediment to the water scour.
The remaining drawings in this slide show Mr. Gerhard's improvements in ball traps, which at that time were valuable, but which have since been supplanted by improved water seal.* The last is certainly ingenious and as good a mechanical trap as could be devised for resisting siphonage or back pressure.
*Wm. Paul Gerhard "Drainage and Sewerage of Dwellings." Wm. T. Comstock, N. Y.
Figs. 86, 87 and 89 represent the McClellan Trap Vent, a simple device to take the place of the back vent pipe. Figs. 86 to 88 give sections of the device, and Fig. 89 shows the manner in which it is connected up with different fixtures. Siphoning action lifts a small cup out of a mercury seal and allows air to pass from the room under the cup as shown by the arrows to break the partial vacuum in the soil pipe. This device is much better than back venting. But where grease would accumulate in the throat of the back vent pipe it would here, and the mechanical parts are open to the objections already referred to in other mechanical traps.