There is also a class of traps so constructed as to give the waste in passing through it a centrifugal motion. This result is obtained by connecting the inlet into the trap on a tangent instead of into the center. This causes the waste to take a whirling and lifting motion. This trap is made in the form of the drum or round trap, but while possessing very great scouring and self-cleansing properties, it is liable to lose a portion of its seal, due to the momentum acquired. Thus, many different classes of traps might be named, each presenting some feature that would appear of value. Many of these features have much merit, especially when the trap is new, but when put to the test of time under actual working conditions, many apparently excellent traps have either failed entirely or only partially achieved the results claimed for them.
In Fig. 30 may be seen several additional forms of traps. Each of these traps is of patented form, having advantages and disadvantages which the reader may discern after having followed the foregoing remarks on trap construction.
It will be noted that two of the traps shown in Fig. 30 are specially adapted to use under floors, and have the advantage of a cleanout accessible without the removal of flooring. The trap constantly being sought for, and which may some day be brought out, should be simple in construction, self-cleansing, nonsiphonable, have a good seal, and no internal partitions, depend upon no mechanical device, and have as few corners or places where filth may collect as possible. In addition, facilities must be provided for the cleaning of such a trap. Although there are many excellent traps now on the market, it does not appear that perfection has yet been reached, and therefore until such a trap does appear, the present forms must be used, and judgment exercised in deciding which form is best adapted to the special work in hand. For the past few years there has been much money and energy expended by manufacturers in the attempt to produce a trap that would be nonsiphonable, siphonage, by the way, being the greatest obstacle to the attainment of a perfect trap. Many times the manufacturer has flattered himself that the desired result had been reached, and in many cases has been successful in convincing city health officials to that effect, and in procuring from them permission to install his form of trap without venting, a subject which will soon be considered. It is extremely questionable, however, whether the trap has yet been produced which can honestly be said to be entirely free from the danger of siphonage under all practical working conditions, and after the trap has reached a more or less foul condition incident to its use for a considerable length of time. It is not to be questioned that great strides have been made in the right direction, but it would appear that any trap for use in connection with a plumbing fixture should still be provided with special means to protect it against the action of siphonage. The nearest approach to the desired end is to be found in the modified forms of the drum trap, of which there are many excellent makes.
Fig. 30. - Various Patented Forms of Traps.
The results which have been obtained in testing several of the modern traps which are claimed to be nonsiphonable are of much interest, and tend to show how closely some of them are approximating in their operation the result which is desired.
Fig. 31. - The Testing of Traps.
The general method of testing traps is illustrated in Fig. 31. A tank holding about 200 gallons is generally used to provide the flush, and from this tank a 1 1/2-inch pipe is carried down a distance of 35 or 45 feet the end of the pipe being open, to allow the waste to be emptied upon the ground or to be connected to a drain.
At a point several feet below the tank a branch is taken out, at the end of which the trap to be tested is attached, as shown.
A quick-opening valve having a full water-way should control the flush, by which means the pipe may be quickly and completely filled. The suction created through this length of pipe is great, and puts a most severe test upon the trap, a test much more severe than it is subjected to under ordinary working conditions.
There is no trap, it might be said, which will not lose at least a small part of its seal under an extreme test of this nature.
Traps having a 4- or 5-inch seal have lost in these tests, within the first minute, from 1 to 2 inches of their seal, and often a greater amount. However, in many cases a continuation of the test did not result in further loss of seal.
Many traps under this severe test lose their entire contents, and traps, by the way, which are widely advertised as nonsiphon-able.
Those traps having the characteristics of the drum trap, have in general withstood severe tests better than those forms which follow the S type.
It should be noted that traps thus tested are new traps, having no collection of filth in them that is the result of use in actual work, and it is a question whether traps that had been in use for a few years would give such good results under test.
When the nonsiphonable trap becomes an accomplished fact from all practical points of view, there would seem to be no end to the changes that would result in the plumbing system. It will not be a matter of great surprise to see within the next few years, the plumbing system installed without the use of trap vents. When this result comes the decrease in the complex form and in the cost of the plumbing system will be very great. Such a system, however, will not be acceptable until the problems involved shall have been solved beyond a question of doubt.
In considering the perfect trap, especially if of the drum-trap form, an additional danger occurs to us which should be overcome. We refer to the entrance of sewer gas through the trap when the cleanout cover is removed from a trap connected as shown in Fig. 28. This will happen in any trap whose cleanout is not submerged, and it will also happen if the gasket on the cleanout does not make tight. It is seldom that after the trap is opened the old gasket will make a tight joint, even though it is not destroyed in removing the cover, and it is also seldom that the joint made by a new gasket is tested. Therefore, the perfect trap should be so constructed as to overcome this danger.
The term "trap seal" has been used several times, and it is a matter of importance. Fig. 32 is given as a means of defining it. Under normal conditions, the water in the trap stands at the level A. If, however, it drops below the level B, the trap becomes ineffective, as it no longer prevents the entrance of sewer gas. The water standing between the levels A and B is called the seal of the trap. This seal may be broken or destroyed in a variety of ways. It may be destroyed by siphonage, by capillary attraction, by evaporation, by back pressure, by momentum, and by gusts of wind. Its destruction by siphonage is a matter of such importance that the following chapter will be reserved for its consideration. Defined, capillary attraction is the power possessed by liquids of rising through very fine tubes to a higher level than that of the liquid in which the tubes dip. It is this action which causes a sponge to fill with water. Its application to the breaking of the trap seal may be seen in Fig. 33, which represents string or a collection of lint or other like substances dipping down into the seal of the trap and terminating in the outlet. Capillary action will cause the water in the trap to follow up through this collection of lint and drop over into the outlet. This constitutes a serious danger to the trap seal, and one for which there would seem to be no remedy. It may readily be seen that in the case of a fixture seldom used, whose trap seal therefore is seldom renewed, capillary action by withdrawing the water from the seal a drop at a time, may eventually destroy it entirely, and the length of time in which such a result might be reached is surprisingly short.
Fig. 32. - The Trap Seal.
Fig. 33. - Trap Seal Broken by Capillary Action.
As to the breaking of the seal by evaporation, it may be said that the danger is far less in the unvented trap than in the properly vented trap This is due to the fact that the vent brings in upon the seal a supply of air which naturally increases the rate of evaporation.
Causes which tend to increase the rate of evaporation are increase of temperature, exposure of surface, and air currents passing over the surface of the liquid.
Back pressure exerted upon the trap seal is a pressure generated in the sewer, and acts upon the sewer side of the trap. A poorly vented sewer may produce such a pressure owing to the expansion caused by a sudden rise in temperature, as might be occasioned by the sudden entrance into the sewer of a large amount of steam or hot water. Tide water backing into the sewer might also produce back pressure. The result of this pressure, unless certain precautions are taken in the construction of the plumbing system, is the saturation of the trap seals with sewer gases, which finally are given off into the interior of the house.
The breaking of the trap seal by momentum is occasioned by the rushing out of the waste from the trap with such force that a part or the whole of the seal is carried with it. This is a danger that exists to some extent in traps working under centrifugal motion.
The breaking of the trap seal by gusts of wind is not a common occurrence, although it sometimes happens. The trap of a water-closet, for instance, located on a top floor, and connected to a soil pipe running through the roof, may lose a few drops of its seal from time to time, owing to gusts of wind passing over the opening of the roof pipe.