If we bring a branch waste to a fixture just as though it was to be a "dead-end" con nection, and then put in a liberal crown vent continued to the roof, as shown in Fig. 153, we have filled the letter of most specifications, be cause we then have crown ventilation and stack ventilation. But this is not the spirit of the work specified, nor is it up to the standard of intelligent workmanship. The current to the roof passes up the trap leg, and thence through the crown vent directly to the open, being brought on its way in close proximity to the seal of the trap; and it is no cause for wonder that such a connection would rob an ordinary trap of its seal within a surprisingly short time, if the fixture is left unused. This is the type of installation found in the wake of speculative builders, scrimping plumbing contractors, and ignorant or unscrupulous journeymen. Many examples of this double-duty vent pipe are seen, in which the workman foresaw the result to some extent, and, in attempting to counteract the supposed ills of evaporation, made the vent useless as a siphon-preventer by connecting the vent 10 inches or more below the crown of the trap, as shown in rig 154. The proper way is to make both the waste and the crown vent branches from other lines. Of course, if it is the top fixture, or there is only one on the line, the waste stack may end in the beginning of the vent stack or connect into the vent stack, as in Fig. 155, according to circumstances. The main current goes by the most direct route —up the main waste and vent stacks of the string. If the crown vent and waste stacks stand close together, as in Fig. 156, we have the loop effect before spoken of; and with the fixtures near the stacks, the waste and crown-vent connections are both short—which is proper. It is poor practice to have the stacks far away from the fixtures, because one is then likely to fall into the error of allowing the crown vent to act also as a direct line vent for the branch waste. This plan is such a short-cut to accomplishing the work of roughing-in, that the temptation to err is great. If the waste stack cannot come near the fixture, then follow the loop principle, and turn up and into the vent stack, branching the trap into the waste branch, and taking the crown vent into the vent stack, as shown in Fig. 157, or into a vent continuation of the branch waste, as preferred. If neither main stack can come near the fixtures, then loop out from the soil or waste stack to the fixture, and back into the main vent, leaving enough upright pipe at the fixture end of each loop to branch the waste and crown vent into, as illustrated in Fig. 158. In this way, half of the branch loop acts as a waste, and half as a vent, and there is ventilation through the soil or waste branch part without continually pulling the air into juxtaposition with the trap seal. Also, the local branch waste to the trap and the crown vent pipe are thus permitted to be as short as desired.
To avoid separate stacks for scat tered fixtures, what is termed the contin uou8 system of soil pipe is frequently em ployed when practicable. This means offsetting the main so as to be able to in clude all the fixtures• of a toilet-room without making long branch wastes. If vent lines are also offset in this manner, some provision for water-washing the off set should be made, as the products of corrosion or other foreign matter might otherwise fall into and choke the bend at the foot of the upper vertical part. Espe cially is this true when plain wrought pipe is used. Lavatory wastes are gen erally used to wash vent lines in such cases.
Some city ordinances permit the continuous system practically without vents, merely requiring the fixture con nections to be not over 3 feet in length, and requiring either vents or non-siphon ing traps where the stack cannot be brought within reach of the 3-foot limit placed on branch connections.
A plan of offsetting, some modification of which may be used in any kind of system, is shown in Fig. 159, which makes plain the work of offsetting soil waste and vent lines without incurring the risk of having trouble with the vent pipe sooner or later. It provides for throwing the corrosion of the vent line, both above and below the set, into the soil line, where it will be washed into the sewer by the water discharged from the closets and other fixtures. By simply offsetting the vent line, the corrosion from the pipe above the offset will fall into the bend, drift out into the horizontal part slightly, and finally choke up the horizontal vent altogether. As shown by the engraving, commencing with the main soil line at the first fixture, a branch line is made, and the branch then becomes the main soil line, leaving the vertical part for the vent. Next comes the offset, and after that another branch line for soil fixtures, again • ing the vertical pipe for the vent, so that whatever falls down the vent, either above or below the offset, lands in the soil pipe and is ried away with the water. With this arrangement, t h e only possible chance for the vent to clog with sion is in the zontal part of the vent offset. What corrosion takes plac€ in a piece of horizontal pipe, is not sufficient to warrant con sideration in itself. There is no other corrosion to be taken care of, except that which forms in the few feet of vertical pipe between A and B, which will not be enough to restrict materially the area of the pipe. It is best to make the piece of pipe between A and B as short as possible.
With the continuous system, several offsets, simple or more or less complex, as shown in Fig. 159, may be necessary in the same stack, according to location of fixtures and the scheme of venting and trapping. Fig. 153 shows a group of fixtures piped diametrically opposite to the continuous stack idea. The main does not deviate in favor of odd fixtures. Regular open wall-traps are used. The crown vents are assembled into one stack, and carried up inde pendently or into the stack above the highest fixture. As before stated, the plan shown in Fig. 153 is faulty in that it favors evaporation of the trap seals by putting the extra duty of a line-vent current on the siphon or crown-vent branch.
Anti-siphon traps Often simplify ventilation problems, especially in awkward situations where it would be very difficult to vent a fixture properly with pipe. Fig. 160 illustrates an example of this kifid, in which non-siphon ing traps are used on bath and lava tory without any form of crown or branch line vents.
In good practice, bath traps are placed convenient to reach, having screw-top h a n d hole with cover in full view at the floor-level.
Soil Stacks. The size to make a soil stack is largely a matter of opinion. There are examples of 10-inch stacks serving 40 closets with the usual complement of lavatories and urinals. There are also instances where as many as 75 closets and numerous other fixtures all discharge into a 5-inch stack which has never given any indication of being too small. Although com mon usage requires a 4-inch soil stack, there seems little ad vantage in adhering to this dimension in small and simple installations. When the plumbing was designed for the city of Pullman, Ill., more than twenty years ago, 3-inch soil stacks were used for small dwellings, and in some cases they were placed in a party wall, so as to afford service for two adjoining houses. The plumbing regulations of Washington, D. C., have allowed for some years past the construction of 3-inch soil stacks for dwellings having only a single bathroom, and the practice has been justified by favor able results. When it is considered that the outlet of a closet is rarely more than 2i inches in diameter, it appears that a size smaller than 4 inches is often allowable.