Hangers should be designed adequately. To protect from damage by building occupants, al- low at least a lb See Data Book, Volume 4, Chapter 6 for further information. Seismic restraint must also be considered. Corrosive wastes require suitably acid-resistant materials such as high-silicon cast iron, boro- silicate glass, polypropylene, etc. Note: Some blood analyzers disharge sodium azide. It forms a very dangerous, explosive compound with cop- per pipes.
Either other piping must be used or the sodium azide must be kept out of the sys- tem. The materials used for pipe fittings must be compatible with the materials utilized for pip- ing.
Fittings should sweep in the direction of flow and have smooth interior surfaces without ledges, shoulders, or reductions that may ob- struct the flow in piping. Drains specified with cast-iron or PVC bod- ies should be suitable for most installations.
Where extra corrosion resistance is required, high-silica cast iron, polypropylene, borosilicate glass, stainless steel, galvanized iron, or other acid-resisting material should be selected. Where a sediment bucket is used, it should be bronze or galvanized or stainless steel. Enameled sedi- ment buckets are impractical because they chip when cleaned. In the selection of materials for top surfaces, such as grates, where floor drains are visible in finished areas, appearance is a prime consider- ation.
As cast iron will rust and galvanizing and 15 Chapter 1 Sanitary Drainage Systems chrome plating will eventually be worn off by traf- fic, the preferred material is solid, cast nickel-bronze, which maintains its attractive appearance. In a swimming pool, however, chlo- rine necessitates the use of chlorine-resistant materials.
For large grates that will be subject to hand-truck or forklift traffic, a ductile iron grate with or without a nickel-bronze veneer is recom- mended. Polished brass or bronze for floor service has the disadvantage of discoloring unless there is constant traffic over it.
Cast aluminum has also been found inadequate for certain floor-service applications due to excessive oxidation and its inability to withstand abrasion. Noise Transmission Noise transmission along pipes may be reduced by avoiding direct metal-to-metal connections. Noise transmission through pipe walls is gen- erally reduced by using heavier materials. Noise transmission to the building may be reduced by isolating piping with resilient materials, such as rugs, belts, plastic, or insulation.
See Table for relative noise-insulation absorption values. In- adequate bedding in poor soils may allow the sewer to settle, causing dips and low points in the sewer. The settlement of sewers interrupts flow, diminishes minimum cleansing velocity, reduces capacity, and creates a point where sol- ids can drop out of suspension and collect. Compacted fill.
Where natural soil or com- pacted fill exists, the trench must be excavated in alignment with the proposed pitch and grade of the sewer. Depressions need to be cut out along the trench line to accept the additional diameter at the piping joint or bell hub. A layer of sand or pea gravel is placed as a bed in the excavated trench because it is easily compacted under the pipe, allowing more accurate alignment of the pipe pitch.
The pipe settles into the bed and is firmly supported over its entire length. Shallow fill. Where shallow amounts of fill exist, the trench can be over excavated to accept a bed of sand, crushed stone, or simi- lar material that is easily compacted. Bedding should be installed in lifts layers , with each lift compacted to ensure optimum compac- tion of the bedding.
The bed must be compacted in alignment with the proposed pitch and grade of the sewer. It is recom- mended that pipe joints or bell hub depressions be hand prepared due to the coarser crushed stone. The soil bearing weight determines trench widths and bed- ding thickness. Deep fill. Where deep amounts of fill exist, the engineer should consult a geotechnical engineer, who will perform soil borings to de- termine the depths at which soils with proper bearing capacities exist.
Solutions include compacting existing fill by physical means or removing existing fill and replacing it with crushed stone structural fill. Backfilling of the trench is just as critical as the compaction of the trench bed and the strength of existing soils. Im- proper backfill placement can dislodge pipe and cause uneven sewer settlement, with physical depressions in the surface.
The type of backfill material and compaction require- ments need to be reviewed to coordinate with the type of permanent surface. Landscaped areas are more forgiving of improper backfill placement than hard surface areas, such as concrete or bituminous paving.
Care must be taken when using mechanical means to compact soils above piping. Me- chanical compaction of the first layer above the pipe by vibrating or tamping devices should be done with caution. Compacting the soil in 6-in. Proper sewer bedding and trench backfill re- sults in an installation that can be counted upon for long, trouble-free service.
The rough surfaces of either brass or iron castings collect and hold germs, fungus- laden scum, and fine debris, which usually accompany drain waste.
There is no easy or sat- isfactory way to clean these rough surfaces; the most practical approach is to enamel them. The improved sanitation compensates for the added expense. However, pipe threads cannot be cut into enameled metals because the enameling will chip off in the area of the machining.
Also, pipe threads themselves cannot be enameled; there- fore, caulked joints should be specified on enameled drains. Most adjustable floor drains utilize a threaded head that allows elevation ad- justments. The drains cannot be enameled because of this adjusting thread. However, there are other adjustable drains that use sliding lugs on a cast thread and may be enameled.
Another point to remember is that a grate or the top ledge of a drain can be enameled, but the enamel will not tolerate traffic abrasion with- out showing scratches and, eventually, chipping.
The solution to this problem is a stainless-steel or nickel-bronze rim and grate over the enam- eled drain body, a common practice on indirect waste receptors, sometimes referred to as floor sinks. Specifiers seem to favor the square, indi- rect waste receptor, but the round receptor is easier to clean and has better antisplash char- acteristics.
For cases where the choice of square or round is influenced by the floor pattern, round sinks with square tops are available.
In applications such as hospital morgues, cystoscopic rooms, autopsy laboratories, slaugh- terhouses, and animal dens, the enameled drain is fitted with a flushing rim. This is most advis- able where blood or other objectionable materials might cling to the side walls of the drain. Where the waste being drained can create a stoppage in the trap, a heel inlet on the trap with a flushing connection is recommended in addi- tion to the flushing rim, which merely keeps the drain sides clean.
This option may not be al- lowed by certain codes. A 2-in. A valve in the water line to the drain is the best way to operate the flushing-rim drain.
Flush valves have been used and save some wa- ter; however, they are not as convenient or effective as a shutoff valve. In any flushing wa- ter-supply line to a drain, a vacuum breaker in- stalled according to code must be provided. KITCHEN AREAS When selecting kitchen drains, the designer must know the quantity of liquid and solid waste the drains will be required to accept, as well as which equipment emits waste on a regular basis and which produces waste only by accidental spillage.
Floor-cleaning procedures should be ascer- tained to determine the amount of water used. If any amount of solid waste is to be drained, re- ceptors must be specified with removable sediment buckets made of galvanized or stain- less steel. Also, there must be enough vertical clearance over these drains to conveniently re- move the sediment buckets for cleaning.
Many kitchen planners mount kitchen equip- ment on a 5-in. Placing the drain on top of the curb and under the equipment makes connection of indirect drain lines diffi- cult and the receptor inaccessible for inspection and cleaning.
Mounting the receptor in front of the curb takes up floor space, and the myriad indirect drains that discharge into it create a potential hazard for employees who may trip over them.
The solution requires close coordination between the engineer and the kitchen designer. Figure Combination Floor Drain and Indirect Waste Receptor 17 Chapter 1 Sanitary Drainage Systems with adjustable tops to attain an installation that is flush with the finished floor. Inside caulk. In this arrangement, the pipe extends up into the drain body and oakum is packed around the pipe tightly against the in- side of the outlet.
Molten lead is then poured into this ring and later stamped or caulked to correct for lead shrinkage. Current installa- tion methods use a flexible gasket for a caulking material. See Figure Spigot outlet. This type utilizes the caulking method as outlined above, except that the spigot outlet is caulked into the hub or bell of the downstream pipe or fitting. Push-seal gasketed outlet.
This type utilizes a neoprene gasket similar to standard ASTM C neoprene gaskets approved for hub- and-spigot, cast-iron soil pipe. A ribbed neoprene gasket is applied to the accepting pipe thus allowing the drain outlet to be pushed onto the pipe.
This type utilizes a spigot with no bead on the end that is stubbed into a neo- prene coupling with a stainless-steel bolting band or other type of clamping device , which, in turn, accepts a downstream piece of pipe or headless fitting.
IPS or threaded. This type is a tapered female thread in the drain outlet designed to accept the tapered male thread of a downstream piece of pipe or fitting. Figure shows an arrangement whereby any spillage in front of the curb can be drained by half of the receptor, while indirect drains are neatly tucked away. Where equipment is on the floor level and an indirect waste receptor must be provided under the equipment, a shallow bucket that can easily be removed is recommended.
One is the constant wet area in the crevice around the drain that promotes mildew odor and the breeding of bacteria. Seepage to the floor below is also a possibility. This problem can be cor- rected by a seepage or flashing flange. Weep holes in the flashing flange direct moisture into the drain. Also, this flange accepts membrane ma- terial and, when used, the flashing ring should lock the membrane to the flange. One prevalent misconception about the flash- ing flange is that it can have weep holes when used with cleanouts.
In this case, there can be no weep holes into the cleanout for the moisture to run to. Weep holes should also be eliminated from the flashing flanges of drains, such as re- flection-pool drains, where the drain entrance is shut off by an overflow standpipe to maintain a certain water level.
The term nonpuncturing, used in reference to membrane-flashing, ring-securing methods, is now obsolete as securing bolts have been moved inboard on flashing L flanges and the membrane need not be punctured to get a seal. Of the vari- ous arrangements, this bolting method allows the greatest squeeze pressure on the membrane. FLOOR LEVELING A major problem in setting floor drains and cleanouts occurs when the concrete is poured level with the top of the unit, ignoring the fact that the addition of tile on the floor will cause the drain or cleanout to be lower than the sur- rounding surface.
To solve the problem, cleanouts can be specified with tappings in the cover rim to jack the top part of the cleanout up to the finished floor level. This may be done by anchoring, using expansion joints, or using expansion loops or bends. When an- choring, avoid excessive stress on the structure and the pipe. Piping or mechanical engineering handbooks should be consulted if stress analy- Figure Spigot-Outlet Drain Body sis is to be performed due to excessive stresses or to the differing expansion characteristics of materials.
See Data Book, Volume 2, Chapter 5 for further information. Insulation where copper pipe leaves slab. Condensation Insulation on piping. Corrosion See Data Book, Vol. Earth loads Stronger pipe or pipe sleeves. Expansion and Flexible joints, loops, swing contraction joints, or offsets.
Fire Building construction around pipe. Some jurisdic- tions require metal piping within 2 ft 0. Must maintain fire ratings.
Heat Keeping thermoplastic pipe away from sources of heat or using insulation. Nails Using ferrous pipe, steel sleeves, steel plates or space pipe away from possible nail penetration zone. Seismic Bracing pipe and providing flexible joints at connection between piping braced to walls or structure and piping braced to the ceiling and between stories where there will be differential movements. Settlement Sleeves or flexible joints. When embedded in concrete, covering with three layers of lb 6.
Sunlight Protecting thermoplastic pipe by insulation and jacket or shading to avoid warping. Support piping well enough to withstand lb Wood shrinkage Providing slip joints and clearance for pipe when wood shrinks.
Approxi- mately s in. Shrinkage along the grain does not usually exceed 0. The basic design criteria for sovent drainage plumbing systems for multistory buildings is based on experience gained in the design and construction of sovent systems serving many liv- ing units and on extensive experimental work on a plumbing test tower.
The sovent system has four parts: a drain, waste, and vent DWV stack; a sovent aerator fitting at each floor level; drain, waste, and vent DWV horizontal branches; and a sovent deaerator fitting at the base of the stack. The two special fittings, the aerator and deaerator, are the basis for the self-venting features of the sovent system. The functions of the aerator are 1 to limit the velocity of both liquid and air in the stack, 2 to prevent the cross section of the stack from filling with a plug of water, and 3 to mix effi- ciently the waste flowing in the branches with the air in the stack.
The deaerator fitting sepa- rates the air flow in the stack from the liquid, ensuring smooth entry into the building drain and relieving the positive pressure at the bottom of the stack. The result is a single stack that is self venting with the fittings balancing positive and negative pressures at or near the zero line throughout the system.
Soil stack and vent com- bine into a single sovent stack. Figure illustrates a typical sovent single-stack plumb- ing system. RESEARCH The advent and use of ultra-low-flow water clos- ets, and to some extent other water-saving fixtures, has brought into question the loading on drainage systems and how the reduced amount of water carries solids in the system. Still to be confirmed is that the slope of conven- tional drainage piping allows solids to remain in suspension until mixed with other flows in the drainage system.
Further research is required to determine the proper slopes of drainage pip- ing and that the release of water from fixtures is properly timed to ensure that solids are carried sufficient distances. There have been numerous studies, particu- larly in the United Kingdom, of reduced-size venting. These studies are discussed in more depth in Chapter 3 of this volume, Vents and Venting Systems. Daugherty, Robert L. Franzini, and E. John Finnemore. Fluid mechanics with engineering applications.
New York: McGraw-Hill. Dawson, F. Report on hydraulics and pneumatics of plumbing drain- age systems. Wyly and Eaton. Nonpotable water systems that use recycled water are commonly referred to as gray- water systems. There is no single definition of gray water. The definitions of a variety of recycled waters are interchangeable. In general, the term gray water is intended to include appropriately treated water that has been recovered from typi- cal fixtures, such as lavatories, bathtubs, showers, and clothes washers.
Waste potentially containing grease, such as that from kitchens and dishwashers, as well as waste from food dis- posals in kitchens is excluded due to the possibility of solid articles. Recycled water is in- tended to include clean water additionally treated to remove bacteria, heavy metals, and organic material.
Black water, on the other hand, is water recovered from plumbing fixtures discharging human excrement, such as water closets and urinals, and cooling-tower water be- cause of the chemicals involved in its treatment. Rainwater is another excellent source of water. It can be collected in cisterns for use in a wide variety of nonpotable uses with little or no treat- ment. Rainwater in cisterns can also be used for an emergency supply of drinking water if it is appropriately treated prior to use.
This chapter is limited to the discussion of gray water only. Gray-water systems have been used in vari- ous areas of the world.
In many regions, water is a critical resource and extreme measures to op- timize the use of water are sometimes necessary. Water reuse offers a considerable savings of wa- ter resources, which is appealing in localities where the underground aquifers are in danger of depletion or where adequate supplies of water are not available. Waste-water management is also a significant reason for the use of gray-wa- ter systems. On-site reclamation and recycling of relatively clean, nonpotable water is considered for the fol- lowing reasons: 1.
In areas where the code mandates that gray water be used where the availability of po- table water is in short supply or restricted. For projects where public liquid sewage disposal capacity is either limited or inad- equate. For economic reasons because obtaining po- table water or disposing of liquid waste is very costly.
For economic reasons, where payback will occur in less than 2 years and where recy- cling will reduce sewer and water usage fees, resulting in substantial savings in operating costs. Appropriately treated gray water is commonly used for the following proposes: 1. Flushing water for water closets and urinals. Landscape irrigation. Cooling-tower makeup. Note: This chapter is written primarily to familiarize the reader with the general subject area.
It is not intended to be used for system design without reference and adherence to other technical data and local code requirements. Decorative pool and fountain fill water. Floor and general hard surface wash down. Laundry prerinse water. The most common purpose is to provide water for the flushing of urinals and water closets, es- pecially in high-rises, hotels, and large dwellings.
The Uniform Plumbing Code discusses gray wa- ter but limits the discussion to single-family dwellings. Many specific local areas have estab- lished standards and guidelines for the use of gray water in facilities and homes.
Where gray- water use is permitted, local health departments have established minimum-treatment standards. In these localities, the engineer must check for regulations applicable to gray water, as is done for plumbing and building codes.
The National Sanitation Foundations Stan- dard 41, which regulates the minimum water quality for recycled waste water, is shown in Table The gray-water quality must be verified against Table and existing local regulations, if any, before use. The piping network distributes it to sources not used for human con- sumption in a safe and distinctive manner. Figure shows flow charts for a conven- tional plumbing system and a recycled water system.
In the recycled-water flow system, the gray water and black water sources are clearly defined. The use of the gray-water system is also defined, namely, for all nonpotable water sys- tems, cooling-tower water requirements, and the irrigation system. Figure A shows single-line diagrams of a gray-water plumbing system to bathtubs and lavatories and a recycled, gray-water system with a gray-water treatment plant from bathtubs, lavatories, and water closets.
The reused water gray water from the fixtures is pumped for re- use in the water closets. This figure shows the isometric piping of a gray-water system with the supply and drainage piping arrangement. The basic plumbing supply with hot water system feeds the lavatories and the bathtubs, which, in turn, act as a source for the gray-water system. In Figure B , the effluent storage as well as the sewage treatment plant STP utilize the gray water to route to the cooling tower, irrigation, and wash-down systems, and the water-closet fixtures.
A gray-water system requires modifications to the standard plumbing systems throughout a facility. There will be duplicate drainage systems. Instead of all the liquid discharged from all the plumbing fixtures going to the sanitary sewer, selected fixtures will have their effluent routed for recovery by the gray-water treatment system. The remainder will go to the sanitary sewer. There also will be duplicate water supplies: potable water will go to lavatories, sinks, showers, etc.
Special care must be taken during the installation of a gray-water system. Clear identi- fication and labeling of the gray-water system is mandatory. This will minimize the risk of cross connection during installation or repair of the system. Many newly formed, planned communities have adopted gray-water systems for their irri- gation systems. Warning signs of nonpotable water or colored PVC piping are now visible across city landscapes.
Blue dye has become a clear identification of the use of gray water. Their arrangement and type de- pend on the specific treatment system selected. A separate gray-water collection piping sys- tem. A primary waste-treatment system consist- ing of turbidity removal, storage, biological treatment, and filtering.
Disinfecting systems consisting of ozone, ul- traviolet irradiation, chlorine, or iodine. Treated water storage and system distribu- tion pressure pumps and piping. The remaining waste water that is, 3 of the discharge is black water from water closets. The discharge from the separate piping system supplying the gray-water system should be sized based on the applicable plumbing code. The following issues should be considered in the design of any gray-water system: 1.
The design flow is based on the number of people in a facility. Notes, Figure A Gray water can also be utilized for other uses, such as irrigation, cooling tower makeup, etc.
Common vent for both drainage stacks. In shopping centers, flow rates are based on square feet m 2 of space, not the number of per- sons. The flow demand is gallons per day per square foot 0. The calculations in food service resemble those for grease interceptor sizing.
The number of seats, the hours of operation, single-serving utensils, and other, similar factors change the equations for gray-water calculations. Lavatory use is estimated at 0. The average person uses a toilet 3 times a day. Design Estimates for Commercial Buildings Gray-water supply Estimates of gray-water sup- ply sources vary in commercial buildings.
Additional requirements are noted for the reuse of gray- water systems for irrigation systems. Some of the parameters are ground-water level, geologi- cal stability of the region, plot plan, and distances of irrigation from adjacent properties, lakes, lot lines, drainage channels, water supply lines, surface slope, wells, and interaction of gray-wa- ter systems with private sewage disposals.
Inspection and testing is an inherent part of the design. System components must be securely in- stalled and the manufacturer properly identified. The holding tanks must be installed in dry lev- els, and, if underground, contamination issues must be accounted for. The authorities having jurisdiction shall review all plans, and qualified and experienced contractors shall install the sys- tem in accordance with the contract documents. To design a gray-water system, one must esti- mate the source of water supply.
Separate design parameters become important for reuse in build- ings or in irrigation systems. For irrigation systems, the required area of subsurface must be designed based on soil analysis. The follow- ing paragraph clearly defines the design issues for irrigation facilities: Each valved zone shall have a minimum effective irrigation area in square feet square meters as determined by Table for the type of soil found in the excavation.
Table gives the design criteria for the use of gray-water sys- tems in various types of soil coarse sand or gravel, fine sand, sandy loam, sandy clay, mixed clay. As the soil weight decreases and the soil becomes less porous, the minimum square feet square meters needed for leaching increases.
Coarse sand or gravel needs a ft 2 irrigation area per gal 1. Clay with a small amount of sand or gravel requires ft 2 per gal Each proposed gray-water system shall include at least three valved zones, and each zone shall be in compliance with the provisions of the section. The applicant shall supply evidence of ground-water depth to the satisfaction of the administrative authority. For example, any building or structure shall be a minimum of 5 ft 1.
The minimum distance from any property lines to a gray-water surge tank is 5 ft 1. Critical areas such as streams, lakes, seepage pits, or cesspools shall be a minimum of 50 ft Simi- larly, the distance from the public water main to a surge tank shall be a minimum of 10 ft 3. The table also identifies additional restric- tions. See Table for the design of the gray-wa- ter distribution in subsurface drip systems for various types of soil.
The treatment system conditions the recovered water to a de- gree consistent with both the intended use of the conditioned water and the design require- ments of the design engineer, the applicable code, or the responsible code officialwhichever is the most stringent.
Typical waste-water gray-water and black-water treatments used for various types of project are depicted in Figure The size of the treatment systems available vary from those installed for individual private dwellings to those serving multiple facilities. As the treat- ment facility becomes more complex, the number of treatment activities increases and the quality of the water improves.
Some of the treatment activities are basic screening, flow equalization, biological treatment, filtration, coagulation, sedi- mentation, disinfections, reclaimed water tank, membrane filtration, and activated carbon filtration. The selection of a treatment system also depends on the quality and type of the influent water. To decide which is the most appropriate treatment, the kinds of fixture discharge to be used for reclaiming and the treatment require- ments of the authorities must be determined.
Table describes the types of filtration and water-treatment processes most commonly used in the gray-water treatment process. Depending on the types of filtration, the degree and types of components filtered vary. Basic filtration con- centrates on reducing suspended solids and does not absorb nitrogen or phosphates. Coagulation assists in building up the solid filtration and adds phosphates to the list. Tertiary treatment includes filtration of all categories.
Absorphan, or carbon filtration, concentrates primarily on biological and chemical oxygen demands. Table shows the design elements of gray- water system treatments.
In the type A treatment, separate gray-water riser piping and water-closet piping is required. This type of treatment con- sists of filtration, chlorination, and color modifications. The system re-feeds the water clos- ets. The enhanced version of the type A treatment adds color as well as chemical treatments. If the water source contains high percentages of soaps or foaming agents, the addition of defoaming agents is highly recommended.
Increased condi- tioning of the water will increase the use of the water for other applications, such as cooling tow- ers. Type B treatments give the complete tertiary treatment of the water and permit the use of water for a wide variety of reuse applications.
The biological and chemical oxygen treatments are mandatory for the high concentrations of fe- cal matter. Treat- ment quality also must take into account the chemical compound of the water required for use in piping, cooling towers, industrial applications, and plant life to prevent scaling of pipes and foul- ing of valves or equipment. The cost of the conventional system is based on water and sewer annual consumption.
This annual cost, plus the water and sewer cost, plus the treatment equipment main- tenance cost is near the annual cost for the hotel management. With maximum gray-water treat- ment, Type B, the total annual cost does not decrease very much. In fact, statistically they are nearly the same. Given this data, the only reasons to provide gray water in facilities are gov- ernmental or institutional incentives.
In addition, the cost of sewage as well as the cost of water consumption may become the decisive factors. Any increase in the cost of sewage or water, caused perhaps by a drought in a region, can alter the life-cycle economics. As depicted in Table , the water-flow-rate savings are clearly defined. Before one considers using a gray-water sys- tem, it is desirable to be able to evaluate quickly, on a preliminary basis, the potential economic feasibility of the proposed scheme.
To facilitate this, a nomograph such as that shown in Figure can be used. This analysis shows the varia- tion in interest rates, variation in cost of combined water and sewage, the water daily use, and cost of total systems based on two types of treatments, A and B.
Movement through the chart from an interest rate based on the cur- rent economy to the combined cost of sewage and water based on municipalities to the water consumption based on building occupancy and to the type of treatment facility based on the purity required can provide an approximate cost for a gray-water system.
To use the nomograph, proceed as follows: 1. Enter the lower right portion of the nomo- graph with the anticipated total potable water consumption for all users based on a con- ventional system. Move vertically up to the combined utility cost for water purchase and sanitary sewage charges e. Move horizontally to the left to form baseline X. Enter the upper right portion of the nomo- graph with the estimated additional cost of the gray-water system additional piping, storage, and treatment equipment.
Move vertically down to the annual interest rate cost of money used in the analysis. Move horizontally to the left to form baseline Y. If the proposed system is a Type A gray-wa- ter system, go to the intersection of baseline X and the system A curve lower left quad- rant of the nomograph. If a Type B gray-water system is being stud- ied, go to the intersection of baseline X and the system B curve. From the appropriate intersection, move ver- tically up to the horizontal separation line and then up and left at the indicated 45 angle to an intersection with baseline Y.
From this intersection point, move vertically down once again to the intersection with baseline X. If this final circled intersection is in the lower right field, the system appears preliminarily feasible and should be subjected to a more detailed economic analysis.
If the final intersection falls to the left and above the sector dividing line, then the eco- nomic feasibility of the scheme is strongly suspect.
Note: Obviously, the many variable inputs that must be considered in a detailed economic analysis do not lend themselves to an easy-to-use nomograph. Many of these inputs have been simplified by making normal assumptions about such things as ratios of reuse, relative quantities of water consumption, and sewage discharge. Thus, while the nomograph does give a quick and relatively good indication of feasibility, it does not replace a detailed economic evaluation.
This is particularly true if the scheme under consideration has anticipated hydraulic flow patterns that differ markedly from the relative uses outlined in Figure In addi- tion, the economic capabilities of a municipality determine its capability for adding sewage-treat- ment facilities and meeting the demands of the community. One of the greatest dangers is the possibility that the gray water will be inadvertently connected to the potable-water system. To avoid this possibility, the water itself and the piping must be made easily distinguish- able, anti-cross-connection precautions must be taken, and appropriate alarms must be installed.
Fixtures could be bought in the color of the water if the water color will be found objectionable. The piping system itself must be clearly iden- tified with labels placed visibly along the run of the pipe.
If possible, the piping material should be different so that the possibility of mistaking and interconnecting the two systems will be unlikely.
The most important consideration is the edu- cation of individuals and the staff of a facility with a gray-water system. An explanation of the dangers and proper operating instructions will ensure that an informed staff will operate and maintain the system in a correct manner. An exception is the Baha- mas, where the local code mandates dual or gray-water systems in all occupancies. Although the use of gray water is a proven cost-effective alternative to the use of potable water in various systems, there is reluctance on the part of authorities to approve it.
Some rea- sons include: 1. There is no generally accepted standard for the quality of recycled water. Several states in the US, Japan, and the Caribbean have adopted codes and guidelines, but for most of the world there is no standard.
This has resulted in rejection of the systems or long delays during the approval process of projects while the quality of the water is in question. Regulatory and plumbing codes that do not have any specific restrictions against using gray water or have ambiguous language that could be interpreted for its use but whose officials impose special standards due to their lack of experience.
Although the use of gray water is ideal in certain circumstances, the success of gray wa- ter will depend solely on public acceptance, and that will require an adequate educational effort. The use of colored water in water closets may not be attractive to the occupants of a newly oc- cupied high-rise. Educating the users of gray water is imperative. An understanding of the source and the associated dangers and limita- tions of gray water is essential to acceptance by the general public.
To draw a parallel, the gen- eral public is now fully aware of the dangers of electricity, yet life without electricity is consid- ered to be abnormal. An economic analysis of gray-water systems in health-care facilities may favor dual plumb- ing systems. However, the presence of viruses, bacteria, and biological contamination in health- care gray-water systems through lavatories, bathtubs, showers, and sinks may increase the cost of water treatment.
Also there is a legiti- mate concern regarding the spread of disease through such gray-water systems that must not be overlooked. Therefore, the application of gray- water systems in health-care facilities may be a less attractive option because of the possibility of biological contamination. It touched briefly on the de- sign elements of the plumbing system and identified the variations among different facilities. The economic analysis of the gray-water system can become the decisive issue that determines whether a gray-water system is even considered for a project.
This analysis can be extrapolated for any other projects and variations. For the full design of gray-water systems, the reader should refer to other technical data books.
Water treatment is one of the backbones of the gray-water system. For the water-flow calcula- tions with all the required pumps, piping, and controls, the reader is referred to the ASPE Manual on Gray Water forthcoming. Finally, water shortages, government subsi- dies, tax incentives, the facility limitations of local governments, and population growth will be the primary motivators for designers and project engineers to consider gray-water system selec- tions in their designs.
Atienze, J. Plumbing effi- ciency through gray-water recycling. Consulting Specifying Engineer. March : Baltimore, MD, Dept. June Commercial water use research project, by J. Wolf, F. Linaweaver, and J. Water uses study, by G. Gray and J. California plumbing code. Walnut, CA. Uniform plumbing code. Konen, Thomas P. Water use in office buildings. Plumbing Engineer Magazine. Lehr, Valentine A. Gray-water systems. Water: Use of treated sewage on rise in state.
Los Angeles Times, August A Siegrist, R. Characteris- tics of rural household waste water. Journal of the Environmental Engineering Division, June : US Dept. Management of small waste flows, by Wisconsin University, PB US General Services Administration. Wa- ter management: A comprehensive approach for facility managers. The com- plete venting of a building drainage system is a very complicated subject, as can be seen from the great variety of venting systems that may be involved.
It is not feasible to cover all the vent- ing variations in this chapter. However, to foster understanding, the preparation of venting tables for stacks and for horizontal branches for vari- ous venting systems is discussed. Owing to the fact that the conditions that tend to produce pneumatic pressures in the vent- ing system that exceed or are below atmospheric pressure by considerable amounts vary so greatly from case to case, and since the building drain may be wholly or partly submergedor not sub- merged at allwhere it enters the street sewer, it is not feasible to lay down rules that will apply to the venting of all designs.
Trap siphonage reduces or eliminates the trap seal and leads to an insanitary and hazardous condition. Pressure and vacuum surges cause objectionable move- ments of the water in the highly visible water closet traps as well as affect the trap seals in all fixtures. Excessive pressure causes bubbles of sewer gas to flow through traps. Unvented traps lead to gurgling noises and sluggish waste flow.
Sewer ventilation is required by some local au- thorities to promote flow in the sewer and to reduce the concentration of dangerous and cor- rosive gases. Vent Stack Terminal A vent stack terminal is the part of the venting system that extends through the roof, thus keep- ing the drainage system open to atmospheric pressure.
Though it may be small by compari- son to the overall sanitary drainage piping, the vent stack terminal is an important portion of the system. Through the terminal vent, air at atmospheric pressure enters the drainage sys- tem to hold in balance the water seal contained in each fixture trap.
The balance of atmospheric air pressure and gravitational pull on the waste- water mass follows the principles outlined in Chapter 1 of this volume, Sanitary Drainage Systems.
Good engineering practices include the fol- lowing: 1. Increase the terminal pipe by two sizes at 18 in. This allows for the interior building space which is usu- ally warmer to provide a convecting flow of interior building heat, keeping the vent ter- minal at the roof from freezing closed.
Project the vent terminal in accordance with jurisdictional building codes and in a distant relationship from air intake louvers, windows, doors, and other roof openings, 10 ft 3 m ASPE Data Book Volume 2 36 minimum. Sewer gases will be forced upward through the terminal stack by the weight of the waste water, therefore, the vent pressures versus the air intake volumes need to be con- sidered.
Provide minimum 4-in. Experience has proved that a 4-in. It should be noted that most codes require only that one 3-in. Winds of sufficient force can affect the func- tion of the venting system. A strong wind blowing across the effective opening of the vent stack ter- minal can create unbalanced air pressures within the system.
Protective devices are available but may be susceptible to frost closure. Care must also be taken in locating the vent terminals with respect to building walls, higher adjacent roofs, parapet walls, etc.
Traps and Trap Seals Traps are installed at the plumbing fixtures to prevent sewer gas and odors from escaping into the building and to keep insects and vermin out- side.
They are usually required to be of the water-seal, self-scouring type. Other types may be necessary to save pre- cious metal or to keep harmful material out of the drainage system. Special code approvals may be necessary in these cases. The trap seal may be lost when a fixture is drained. During drain- age, water drops through the fixture outlet down the tailpiece, acquiring momentum.
This momen- tum is transferred to trap-seal water. The combined water then flows out of the trap down the trap arm at a rate depending on slope and momentum. The momentum will be increased if there is a vacuum in the drainage system. If the trap arm fills with water either actually or effec- tively because of suds in the trap arm , the trap water may siphon. For this reason, most codes limit the distance from the fixture to the trap weir to 24 in. Some water will remain in the trap, but the water seal will be lost or re- duced.
The trap is usually replenished to some extent as the fixture gradually empties after the siphon is broken. Glass plumbing is a convenient way to observe this phenomenon.
Water-closet traps must always be siphoned to achieve a flush. Water closets are designed so that the water- closet trap is refilled. Traps can also be siphoned when there is excessive vacuum in the system. Factors Affecting Trap Seal Loss Based on the preceding, the following will reduce the danger of seal siphonage of the trap: 1. Reduce the depth of the overflow rim in fix- tures. Flatten the bottoms of fixtures. Avoid high-suds detergents.
Provide smaller discharge openings on the fixtures. Reduce the distance tailpiece length between the fixture and the trap. Increase the size of the trap and trap arm. Reduce the vacuum on the discharge side of the trap.
Provide a vent near the trap outlet. There are three predominant ways in which traps seals are reduced. The first way occurs when the pneumatic-pressure fluctuations caused by the discharge of fixtures other than the fixture to which a particular trap is attached siphon water out of the trap until the positive part of the fluctuation occurs.
The second way is by the discharge of the fixture to which the trap is attached. The third way of reducing trap seals is by the buildup of high-suds detergents. It is recommended that the first phenomenon described be called induced siphonage and the second self-siphonage.
Suds Venting High-sudsing detergents may be expected to be used in kitchen sinks, dishwashers, and clothes- washing machines in residential occupancies. These suds disrupt the venting action and spread through the lower portions of multistory drain- age systems. The more turbulence, the greater the suds.
In some cases, suds back up through the traps and even spill out on the floor. They cause an increase in the pressure and vacuum levels in the systems. They affect both single- stack and conventional systems. Solutions to the 37 Chapter 3 Vents and Venting problem may involve avoiding suds pressure zones, connecting the suds-producing stack downstream of all other stacks, and increasing the size of the horizontal building drain to achieve less restrictive flow of air and water. Using streamline fittings, such as wyes, tends to re- duce suds formation.
Check valves in fixture tailpieces have been used to fix problem instal- lations. The National Standard Plumbing Code, one of the traditional codes, lists the following spe- cial requirements to avoid suds problems: 1.
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