plumbing—water-supply, sprinkler, and

plumbing—water-supply, sprinkler, and
Source: BUILDING DESIGN AND CONSTRUCTION HANDBOOK
SECTION FOURTEEN
PLUMBING—WATER-SUPPLY,
SPRINKLER, AND
WASTEWATER SYSTEMS
Gregory P. Gladfelter
Gladfelter Engineering Group
Kansas City, Missouri
Brian L. Olsen
Poole Consulting Services, Inc.
Olathe, Kansas
This section treats the major subsystems for conveyance of liquids and gases in
pipes within a building. The pipes generally extend beyond the building walls to a
supply source or a disposal means, such as a sewer.
14.1
PLUMBING AND FIRE PREVENTION CODES
Plumbing codes were created to prevent illness and death from unsanitary or unsafe
conditions in supply of water and gases in buildings and removal of wastes in pipes.
There are two commonly recognized model plumbing and fire prevention codes:
‘‘International Plumbing Code’’ and ‘‘International Fire Code,’’ International
Code Council Inc., Falls Church, VA.
‘‘Uniform Plumbing Code’’ and ‘‘Uniform Fire Code,’’ International Association
of Plumbing and Mechanical Officials, Walnut, Calif.
These codes are generally revised on 3-year cycles.
In addition to these model codes, several cities and states have adopted their
own plumbing and fire prevention codes. The ‘‘National Standard Plumbing Code,’’
administered by the National Association of Plumbing, Heating and Cooling Contractors, Inc., Washington, D.C., has been adopted in some localities. The American
National Standards Institute (ANSI) has also adopted the ‘‘National Plumbing
14.1
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14.2
SECTION FOURTEEN
Code,’’ ANSI A.40.8, which is administered by the Mechanical Contractors Association of America, Rockville, Md. Also, numerous fire-safety codes and standards
are contained in ‘‘National Fire Codes,’’ National Fire Protection Association,
Quincy, Mass.
Persons involved in the design and installation of plumbing systems should
check with all local code authorities to determine which code is in effect prior to
beginning a project. Also, local governmental authorities should be contacted about
special regulations relating to sewer and water systems. Those involved in the design of plumbing systems should also be familiar with ANSI A117.1 and the Americans with Disabilities Act (ADA), which require that provision be made in buildings for accessibility and usability of facilities by the physically handicapped.
Plumbing designers and architects should work together to assure strict compliance
with these requirements.
14.2 HEALTH REQUIREMENTS FOR PLUMBING
Plumbing codes place strict constraints on plumbing installations in the interest of
public health. Following are typical basic provisions:
All buildings must be provided with potable water in quantities adequate for the
needs of their occupants. Plumbing fixtures, devices, and appurtenances should be
supplied with water in sufficient volume and at pressures adequate to enable them
to function properly. The pipes conveying the water should be of sufficient size to
provide the required water without undue pressure reduction and without undue
noise under all normal conditions of use.
The plumbing system should be designed and adjusted to use the minimum
quantity of water consistent with proper performance and cleansing of fixtures and
appurtenances.
Devices for heating and storing water should be designed, installed, and maintained to guard against rupture of the containing vessel because of overheating or
overpressurization.
The wastewater system should be designed, constructed, and maintained to guard
against fouling, deposit of solids, and clogging.
Provision should be made in every building for conveying storm water to a storm
sewer if one is available.
Recommended tests should be made to discover any leaks or defects in the
system. Pipes, joints, and connections in the plumbing system should be gastight
and watertight for the pressure required by the tests.
Plumbing fixtures should be located in ventilated enclosures and should be readily accessible to users.
Plumbing fixtures should be made of smooth, nonabsorbent materials. They
should not have concealed fouling surfaces. Plumbing fixtures, devices, and appliances should be protected to prevent contamination of food, water, sterile goods,
and similar material by the backflow of wastewater. Indirect connections with the
building wastewater system should be provided when necessary
Every fixture directly connected to the wastewater system should be equipped
with a liquid-seal trap. This is a fitting so constructed that passage of air or gas
through a pipe is prevented while flow of liquid through the pipe is permitted.
Foul air in the wastewater system should be exhausted to the outside, through
vent pipes. These should be located and installed to minimize the possibility of
clogging and to prevent sewer gases from entering the building.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.3
If a wastewater system is subject to the backflow of sewage from a sewer,
suitable provision should be made to prevent sewage from entering the building.
The structural safety of a building should not be impaired in any way as a result
of the installation, alteration, renovation, or replacement of a plumbing system.
Pipes should be installed and supported to prevent stresses and strains that would
cause malfunction of or damage to the system. Provision should be made for expansion and contraction of the pipes due to temperature changes and for structural
settlements that might affect the pipes.
Where pipes pass through a construction that is required to have a fire-resistance
rating, the space between the pipe and the opening or a pipe sleeve should not
exceed 1⁄2 in. The gap should be completely filled with code-approved, fire-stopping
material and closed off with close-fitting metal escutcheons on both sides of the
construction.
Pipes, especially those in exterior walls or underground outside the building,
should be protected, with insulation or heat, to prevent freezing. Underground pipes
should be placed below established frost lines to prevent damage from heaving and
in high traffic areas should be encased in concrete or installed deep enough so as
to not be damaged by heavy traffic. Pipes subject to external corrosion should be
protected with coatings, wrappings, cathodic protection, or other means that will
prevent corrosion. Dissimilar metals should not be connected to each other unless
separated by a dielectric fitting. Otherwise, corrosion will result.
Each plumbing system component, such as domestic water, natural gas, and
wastewater pipes and fixtures, should be tested in accordance with the plumbing
code. All defects found during the test should be properly corrected and the system
retested until the system passes the requirements of the test.
WATER SUPPLY
Enough water to meet the needs of occupants must be available for all buildings.
Further water needs for fire protection, heating, air conditioning, and possibly process use must also be met. This section provides specific data on all these water
needs, except those for process use. Water needs for process use must be computed
separately because the demand depends on the process served.
14.3
WATER QUALITY
Sources of water for buildings include public water supplies, groundwater, and
surface water. Each source requires careful study to determine if a sufficient quantity
of safe water is available for the building being designed.
Water for human consumption, commonly called potable water, must be of suitable quality to meet local, state, and national requirements. Public water supplies
generally furnish suitably treated water to a building, eliminating the need for treatment in the building. However, ground and surface waters may require treatment
prior to distribution for human consumption. Useful data on water treatment are
available from the American Water Works Association, Denver, Col.
Useful data on water supplies for buildings are available in the following
publications: American Society of Civil Engineers, ‘‘Glossary-Water and Sewer
Control Engineering;’’ E. W. Steel, ‘‘Water Supply and Sewerage,’’ McGraw-Hill
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.4
SECTION FOURTEEN
Publishing Company, New York; G. Fair, J. C. Geyer, and D. A. Okun, ‘‘Water and
Wastewater Engineering,’’ John Wiley & Sons, Inc., New York; and E. Nordell,
‘‘Water Treatment for Industrial and Other Uses,’’ Van Nostrand Reinhold, New
York. The ASTM ‘‘Manual on Industrial Water’’ contains extensive data on processwater and steam requirements for a variety of industries. Data on water for fire
protection are available from the American Insurance Association, New York, and
the National Fire Protection Association (NFPA), Quincy, Mass.
Water for buildings is transmitted and distributed in pipes, which may be run
underground or aboveground. Useful data on pipeline sizing and design are given
in J. Church, ‘‘Practical Plumbing Design Guide,’’ and C. E. Davis and K. E.
Sorenson, ‘‘Handbook of Applied Hydraulics,’’ McGraw-Hill Publishing Company,
New York. The American Insurance Association promulgates a series of
publications on water storage tanks for a variety of services.
Characteristics of Water. Physical factors of major importance for raw water are
temperature, turbidity, color, taste, and odor. All but temperature are characteristics
to be determined in the laboratory from carefully procured samples by qualified
technicians utilizing current testing methods and regulations.
Turbidity, a condition due to fine, visible material in suspension, is usually due
to presence of colloidal particles. It is expressed in parts per million (ppm or mg /
L) of suspended solids. It may vary widely in discharges of relatively small streams
of water. Larger streams or rivers tending to be muddy are generally muddy all the
time. The objection to turbidity in potable supplies is its ready detection by the
drinker. The U.S. Environmental Protection Agency (USEPA) limit is one nephelometric turbidity unit (NTU).
Color, also objectionable to the drinker, is preferably restricted to 15 color units
or less. It is measured, after all suspended matter (turbidity) has been centrifuged
out, by comparison with standard hues.
Tastes and odors due to organic material or volatile chemical compounds in the
water should be removed completely from drinking water. But slight, or threshold,
odors due to very low concentrations of these compounds are not harmful-just
objectionable. Perhaps the most common source of taste and odor is decomposition
of algae.
Chemical Content. Chemical constituents commonly found in raw waters intended for potable use and measured by laboratory technicians include hardness,
pH, iron, and manganese, as well as total solids. Total solids should not exceed
500 ppm. Additionally, the USEPA is continually developing, proposing, and adopting new drinking water regulations as mandated by the Safe Drinking Water Act.
Hardness, measured as calcium carbonate, may be objectionable in laundries
with as little as 150 ppm of CaCO3 present. But use of synthetic detergents decreases its significance and makes even much harder waters acceptable for domestic
uses. Hardness is of concern, however, in waters to be used for boiler feed, where
boiler scale must be avoided. Here, 150 ppm would be too much hardness and the
water would require softening (treatment for decrease in hardness).
Hydrogen-ion concentration of water, commonly called pH, can be a real factor
in corrosion and encrustation of pipe and in destruction of cooling towers. A pH
under 7 indicates acidity; over 7 indicates alkalinity; 7 is neutral. Tests using color
can measure pH to the nearest tenth, which is of sufficient accuracy.
Iron and manganese when present in more than 0.3-ppm concentrations may
discolor laundry and plumbing. Their presence and concentration should be determined. More than 0.2 ppm is objectionable for most industrial uses.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.5
Organic Content. Bacteriological tests of water must be made on carefully taken
and transported samples. A standard sample is five portions of 10 cm3, each sample
a different dilution of the water tested. A state-certified laboratory will use approved
standard methods for analyses.
Organisms other than bacteria, such as plankton (free-floating) and algae, can
in extreme cases be important factors in design of water treatment systems; therefore, biological analyses are significant. Microscopic life and animal and vegetable
matter can be readily identified under a high-powered microscope.
Maintenance of Quality. It is not sufficient that potable water just be delivered
to a building. The quality of the water must be maintained while the water is being
conveyed within the building to the point of use. Hence, the potable-water distribution system must be properly designed to prevent contamination.
No cross connections may be made between this system and any portion of the
wastewater-removal system. Furthermore, the potable-water distribution system
should be completely isolated from parts of plumbing fixtures or other devices that
might contaminate the water. Backflow preventers or air gaps may be used to prevent backflow or back siphonage. Many states or municipal water systems now
have regulations which require that backflow prevention devices be installed at the
building potable and fire system services. These devices are required to protect the
municipal water systems from contamination. All backflow prevention devices are
required to have annual inspection, testings and certification.
Backflow is the flow of liquid into the distribution piping system from any
source other than the intended water-supply source, such as a public water main.
Back siphonage is the suction of liquid back into the distribution piping system
because of a siphonage action being applied to the distribution pipe system. The
type of backflow preventer to use depends on the type of reverse flow expected
(backflow or back siphonage) and the severity of the hazard. In general, double
check-valve-type backflow preventers are normally approved for low-hazard backflow conditions and vacuum breakers are approved for low-hazard back-siphonage
conditions. Where the hazard is great, reduced-pressure principal backflow preventers are normally required. The local code authorities should be consulted about
local and state regulations pertaining to backflow prevention.
14.4
WATER TREATMENT
To maintain water quality within acceptable limits (Art. 14.3), water supplied to a
building usually must undergo some form of treatment. Whether treatment should
be at the source or after transmission to the point of consumption is usually a
question of economics, involving hydraulic features, pumping energies and costs,
and possible effects of raw water on transmission mains.
Treatment, in addition to disinfection, should be provided for all water used for
domestic purposes that does not fall within prescribed limits. Treatment methods
include screening, plain settling, coagulation and sedimentation, filtration, disinfection, softening, and aeration. When treatment of the water supply for a building is
necessary, the method that will take the objectionable elements out of the raw water
in the simplest, least expensive manner should be selected.
Softening of water is a process that must be justified by its need, depending on
use of the water. With a hardness in excess of about 150 ppm, the cost of softening
will be offset partly by the reduction of soap required for cleaning. When synthetic
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14.6
SECTION FOURTEEN
detergents are used instead of soap, this figure may be stretched considerably. But
when some industrial use of water requires it, the allowable level for hardness must
be diminished appreciably.
Since corrosion can be costly, corrosive water must often be treated in the interest of economics. In some cases, it may be enough to provide threshold treatment
that will coat distribution lines with a light but protective film of scale. But in other
cases—boiler-feed water for high-pressure boilers, for example—it is important to
have no corrosion or scaling. Then, deaeration and pH control may be necessary.
(The real danger here is the failure of boiler-tube surfaces because of overheating
due to scale formation.)
(American Water Works Association, ‘‘Water Quality and Treatment,’’ McGrawHill Publishing Company, New York; G. M. Fair, J. C. Geyer, and D. A. Okun,
‘‘Elements of Water Supply and Wastewater Disposal,’’ John Wiley & Sons, Inc.,
New York.)
14.5 WATER QUANTITY AND PRESSURES
Quantity of water supplied must be adequate for the needs of occupants and processes to be carried out in the building. The total water demand may be calculated
by adding the maximum flows at all points of use and applying a factor less than
unity to account for the probability that only some of the fixtures will be operated
simultaneously (Art. 14.8).
In addition, the pressure at which water is delivered to a building must lie within
acceptable limits. Otherwise, low pressures may have to be increased by pumps
and high pressures decreased with pressure-reducing valves. Table 14.1 lists minimum flow rates and pressures generally required at various water outlets. The pressure in Table 14.1 is the pressure in the supply pipe near the water outlet while the
outlet is wide open and water is flowing.
In delivery of water to the outlets, there is a pressure drop in the distribution
pipes because of friction. Therefore, water supplied at the entrance to the distri-
TABLE 14.1 Required Minimum Flow Rates and Pressures during Flow for Fixtures
Fixture
Pressure, psi*
Flow, gpm
Basin faucet
Basin faucet, self-closing
Sink faucet, 3⁄8-in
Sink faucet, 1⁄2-in
Dishwasher
Bathtub faucet
Laundry tub cock, 1⁄4-in
Shower
Water closet ball cock
Water closet flush valve
Urinal flush valve
Garden hose, 50 ft, and sill cock
8
12
10
5
15–25
5
5
12
15
15–20
15–20
30
3
2.5
4.5
4.5
†
6
5
3–10
3
15–40
15
5
* Residual pressure in pipe at entrance to fixture. 20 psi minimum required at water conserving type
fixture. Verify minimum pressure reqirements with fixture manufacturer.
† As specified by fixture manufacturer.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.7
bution system must exceed the minimum pressures required at the water outlets by
the amount of the pressure loss in the system. But the entrance pressure should not
exceed 80 psi, to prevent excessive flow and damage to system components. Velocity of water in the distribution system should not exceed 10 ft / s.
A separate supply of water must be provided for fire-fighting purposes. This
supply must be of the most reliable type obtainable. Usually, this requirement can
be met with water from a municipal water supply. If the municipal water supply is
not adequate or if a private water supply is utilized, pumps or storage in an elevated
water tank should be provided to supply water at sufficient quantities and pressures.
Generally, such water should be provided at a pressure of at least 15 psi residual
pressure at the highest level of fire-sprinkler protection for light-hazard occupancies
and 20 psi residual pressure for ordinary-hazard occupancies. Acceptable flow at
the base of the supply riser is 500 to 700 gpm for 30 to 60 minutes for light-hazard
occupancies and 850 to 1500 gpm for 60 to 90 minutes for ordinary-hazard occupancies.
If a building is so located that it cannot be reached by a fire department with
about 250 ft of hose, a private underground water system, installed in accordance
with NFPA 24, ‘‘Installation of Private Fire Service Mains and Their Appurtenances,’’ may have to be provided. Many municipalities require that the water system for a building site be a type generally called a ‘‘loop-to-grid’’ system. It consists
of pipes that loop around the property and has a minimum of two municipal-watersystem connections, at opposite sides of the loop, usually at different water mains
of the municipal system. Hydrants should be placed so that all sides of a building
can be reached with fire hoses. The requirements for fire hydrants should be verified
with the local code officials or fire marshal.
14.6
WATER DISTRIBUTION IN BUILDINGS
Cold and hot water may be conveyed to plumbing fixtures under the pressure of a
water source, such as a public water main, by pumps, or by gravity flow from
elevated storage tanks.
The water-distribution system should be so laid out that, at each plumbing fixture
requiring both hot and cold water, the pressures at the outlets for both supplies
should be nearly equal. This is especially desirable where mixing valves may be
installed, to prevent the supply at a higher pressure from forcing its way into the
lower-pressure supply when the valves are opened to mix hot and cold water. Pipe
sizes and types should be selected to balance loss of pressure head due to friction
in the hot and cold-water pipes, despite differences in pipe lengths and sudden large
demands for water from either supply.
Care should be taken to assure that domestic water piping is not installed in a
location subject to freezing temperatures. When piping is installed in exterior walls
in cold climate areas, the piping should be insulated and should be installed on the
building side of the building wall insulation. Piping installed in exterior cavity walls
or chases may require heat tracing, although the installation of high and low wallmounted grilles, which allow heated air from the building to naturally flow through
the cavity, will usually prevent the temperature in the cavity from falling below a
temperature where water in the piping will freeze. Designers should thoroughly
investigate local climatic conditions and building methods to assure proper installation. Designers should also specify freeze-proof-type hydrants (hose bibs) for
exterior applications.
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14.8
14.6.1
SECTION FOURTEEN
Temperature Maintenance in Hot-Water Distribution
In large, central, hot-water distribution systems, many fixtures that require hot water
are not located very close to the water-heating equipment. If some means of maintaining the temperature of the hot water in the piping is not provided, the water
temperature will fall, particularly during periods of low demand. The supply to
remote fixtures would have to run for a long period before hot water would be
available at the outlet thereby wasting precious water. For this reason, designers
should provide a temperature maintenance system whenever a fixture requiring hot
water is over 25 ft away from the source of hot water.
One method of temperature maintenance is to use a hot-water recirculating system, which consists of a hot-water return piping system, a circulating pump, and a
water-temperature controller to operate the pump. The return piping system starts
at the end of each remote branch main and runs back to the water-heater coldwater-supply pipe connection. The circulating pump circulates hot water through
the supply piping, return piping, and the water heater whenever the controller senses
that the water temperature has fallen below a preselected set point. To reduce heat
loss, all hot-water supply and return piping should be insulated.
Another method employs self-regulating, electric heat tracing that is applied
directly to the hot-water supply piping prior to the installation of the piping insulation. The self-regulating heat tracing is made of polymers, which have variable
electric resistances, depending on the surface temperature of the pipe. As the surface
temperature of the pipe falls, the resistance increases and more heat is given off by
the heat tracing. The opposite is true if the surface of the piping is hot. This type
of system requires less maintenance once it is installed and less energy to maintain
the hot-water temperature in the piping.
Horizontal pipe runs should not be truly horizontal. They should have a minimum slope of about 1⁄4 in / ft toward the nearest drain valve when possible. An
adequate number of drain valves should be provided to drain the domestic water
system completely.
14.6.2
Up-Feed Water Distribution
To prevent rapid wear of valves, such as faucets, water should only be supplied to
building distribution systems at pressures not more than about 80 psi. This pressure
is large enough to raise water from 8 to 10 stories upward and still retain desired
pressures at plumbing fixtures (Table 14.1). Hence, in low buildings, cold water
can be distributed by the up-feed method (Fig. 14.1), in which at each story plumbing fixtures are served by branch pipes connected to risers that carry water upward
under pressure from the water source.
In Fig. 14.1, cold water is distributed under pressure from a public water main.
The hot-water distribution is by a discontinuous system. Hot water rises from the
water heater in the basement to the upper levels under pressure from the cold-water
supply to the water heater.
When an up-feed distribution system is desired, but the city water pressure is
not sufficient to provide adequate water pressure, the water pressure may be boosted
to desired levels by the installation of a packaged, domestic water-booster pump
system. This equipment usually consists of a factory-built system with multiple
pumps, a pressure tank, and all operating controls to maintain the required water
pressure. This type of system may also be used in buildings in excess of 10 stories
by proper zoning and the use of pressure-reducing valves at each zone.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.9
FIGURE 14.1 Up-feed water-distribution system for a two-story apartment building. (Reprinted
with permission from F. S. Merritt, ‘‘Building Engineering and Systems Design,’’ Van Nostrand
Reinhold Company, New York.)
14.6.3
Down-Feed Water Distribution
For buildings more than 8 to 10 stories high, designers have the option to pump
water to one or more elevated storage tanks, from which pipes convey the water
downward to plumbing fixtures and water heaters. Water in the lower portion of an
elevated tank often is reserved for fire-fighting purposes (Fig. 14.2). Generally, also,
the tank is partitioned to provide independent, side-by-side chambers, each with
identical piping and controls. During hours of low demand, a chamber can be
emptied, cleaned, and repaired, if necessary, while the other chamber supplies water
as needed. Float-operated electric switches in the chambers control the pumps supplying water to the tank. When the water level in the tank falls below a specific
elevation, a switch starts a pump, and when the water level becomes sufficiently
high, the switch stops the pump.
Usually, at least two pumps are installed to supply each tank. One pump is used
for normal operation. The other is a standby, for use if the first pump is inoperative.
For fire-fighting purposes, a pump must be of adequate size to fill the tank at the
rate of the design fire flow.
When a pump operates to supply a tank, it may draw so much water from a
public main that the pressure in the main is considerably reduced. To avoid such a
condition, water often is stored in a suction tank at the bottom of the building for
use by the pumps. The tank is refilled automatically from the public main. Because
refilling can take place even when the pumps are not operating, water can be drawn
from the public main without much pressure drop.
Figure 14.2 is a simplified schematic diagram of a down-feed distribution system
of a type that might be used for buildings up to 20 stories high.
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14.10
SECTION FOURTEEN
FIGURE 14.2 Down-feed water-distribution system for a tall building. (Reprinted with permission from F. S. Merritt, ‘‘Building Engineering and Systems Design,’’ Van Nostrand and Reinhold
Company, New York.)
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14.11
Tall buildings may be divided into zones, each of which is served by a separate
down-feed system. (The first few stories may be supplied by an up-feed system
under pressure from a public main.) Each zone has at its top its own storage tank,
supplied from its own set of pumps in the basement. All the pumps draw on a
common suction tank in the basement. Also, each zone has at its base its own water
heater and a hot-water circulation system. In effect, the distribution in each zone
is much like that shown in Fig. 14.2.
If space is not available to install storage tanks at the top of each zone, the main
water supply from a roof-mounted storage tank may be supplied to the zones if
pressure-reducing valves are utilized to reduce the supply-water pressure to an acceptable level at each zone.
14.6.4
Prevention of Backflow
All water-supply and distribution piping must be designed so there is no possibility
of backflow at any time. The minimum code-required air gap (distance between the
fixture outlet and the flood-level rim of the receptacle) should be maintained at all
times. Domestic water systems that are subject to back siphonage or backflow
should be provided with approved vacuum breakers or backflow preventers (Art.
14.3). Before any potable-water piping is put into use, it must be disinfected using
a procedure approved by the local code authorities.
14.6.5
Pipe Materials
Pipes and tubing for water distribution may be made of copper, brass, polyvinyl
chloride (PVC), polybutylene, ductile iron, or galvanized steel, if they are approved
by the local code. When materials for potable-water piping are being selected, care
should be taken to ensure that there is no possibility of chemical action or any
other action that might cause a toxic condition.
14.6.6
Fittings
These are used to change the direction of water flow (because it usually is not
practical to bend pipe in the field), to make connections between pipes, and to plug
openings in pipes or close off the terminal of a pipe. In a water-supply system,
fittings and joints must be capable of containing pressurized water flow. Fittings
should be of comparable pressure rating and of quality equal to that of the pipes
to which they are connected.
Standard fittings are available and generally may be specified by reference to an
American National Standards Institute or a federal specification. Fitting sizes indicate the diameters of the pipes to which they connect. For threaded fittings, the
location of the thread should be specified: A thread on the outside of a pipe is
called a male thread, whereas an internal thread is known as a female thread.
Ductile-iron pipe is generally available with push-on mechanical joint or flanged
fittings. Brass or bronze fittings for copper or brass pipe also may be flanged or
threaded. Flanges are held together with bolts. In some cases, to make connections
watertight, a gasket may be placed between flanges, whereas in other cases, the
flanges may be machine-faced. Threaded fittings often are made watertight by coating the threads with an approved pipe compound or by wrapping the threads with
teflon tape before the fittings are screwed onto the pipe.
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14.12
14.6.7
SECTION FOURTEEN
Valves
These are devices incorporated in pipelines to control the flow into, through, and
from them. Valves are also known as faucets, cocks, bibs, stops, and plugs. The
term cock is generally used with an adjective indicating its use; for example, a sill
cock (also called a hose bib) is a faucet used on the outside of a building for
connection with a garden hose. A faucet is a valve installed on the end of a pipe
to permit or stop withdrawal of water from the pipe.
Valves usually are made of cast or malleable iron, brass, or bronze. Faucets in
bathrooms or kitchens are usually faced with nickel-plated brass.
The types of valves generally used in water-supply systems are gate, globe,
angle, ball, and check valves.
Gate valves control flow by sliding a disk perpendicular to the water flow to fit
tightly against seat rings when a handwheel is turned. This type of valve is usually
used in locations where it can be left completely open or closed for long periods
of time.
Globe valves control the flow by changing the size of the passage through which
water can flow past the valves. Turning a handwheel moves a disk attached at the
end of the valve stem to vary the passage area. When the valve is open, the water
turns 90⬚ to pass through an orifice enclosed by the seat and then turns 90⬚ again
past the disk, to continue in the original direction. Flow can be completely stopped
by turning the handwheel to compress the disk or a gasket on it against the seat.
This type of valve usually is used in faucets.
Angle valves are similar to globe valves but eliminate one 90⬚ turn of the water
flow. Water is discharged from the valves perpendicular to the inflow direction.
Check valves are used to prevent reversal of flow in a pipe. In the valves, water
must flow through an opening with which is associated a movable plug (or flapper).
When water flows in the desired direction, the plug automatically moves out of the
way; however, a reverse flow forces the plug into the opening, to seal it.
Ball valves are quick-closing (1⁄4 turn to close) valves, which consist of a drilled
ball that swivels on its vertical axis. This type of valve creates little water turbulence
owing to its straight-through flow design.
14.6.8
Pipe Supports
When standard pipe is used for water supply in a building, stresses due to ordinary
water pressure are well within the capacity of the pipe material. Unless the pipe is
supported at short intervals, however, the weight of the pipe and its contents may
overstress the pipe material. Generally, it is sufficient to support vertical pipes at
their base and at every floor. Maximum support spacing for horizontal pipes depends on pipe diameter and material. The plumbing code should be consulted to
determine maximum horizontal and vertical hanger spacings allowed.
While the supports should be firmly attached to the building, they should permit
pipe movement caused by thermal dimensional changes or differences in settlement
of building and pipe. Risers should pass through floors preferably through sleeves
and transfer their load to the floors through tight-fitting collars. Horizontal pipe runs
may be carried on rings or hooks on metal hangers attached to the underside of
floors. The hangers and anchors used for plumbing piping should be metal and
strong enough to prevent vibration.
Each hanger and anchor should be designed and installed to carry its share of
the total weight of the pipe.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.13
All piping installed should be restrained according to the requirements specific
to the exact earthquake zone where the building is located. The local code authorities should be consulted about these requirements.
14.6.9
Expansion and Contraction
To provide for expansion and contraction, expansion joints should be incorporated
in pipelines. Such joints should be spaced not more than 50 ft apart in hot-water
pipe. While special fittings are available for the purpose, flexible connections are a
common means of providing for expansion. Frequently, such connections consist
of a simple U bend or a spiral coil, which permits springlike absorption of pipe
movements.
14.6.10
Meters
These are generally installed on the service pipe to a building to record the amount
of water delivered. The meters may be installed inside the building, for protection
against freezing, or outside, in a vault below the frost line. Meters should be easily
accessible to meter readers. Meter size should be determined by the maximum
probable water flow, gal / mm.
14.6.11
Water Hammer
This is caused by pressures developing during sudden changes in water velocity or
sudden stoppage of flow. The result is a banging sound or vibration of the piping
system. It frequently results from rapid closing of valves, but it also may be produced by other means, such as displacing air from a closed tank or pipe from the
top.
Water hammer can be prevented by filling a closed tank or pipe from the bottom
while allowing the air to escape from the top. Water hammer also can be prevented
by installing on pipelines air chambers or other types of water-hammer arresters.
These generally act as a cushion to dissipate the pressures.
14.7
PLUMBING FIXTURES AND EQUIPMENT
The water-supply system of a building distributes water to plumbing fixtures at
points of use. Fixtures include kitchen sinks, water closets, urinals, bathtubs, showers, lavatories, drinking fountains, laundry trays, and slop (service) sinks. To ensure
maximum sanitation and health protection, most building codes have rigid requirements for fixtures. These requirements cover such items as construction materials,
connections, overflows, installation, prevention of backflow, flushing methods, types
of fixtures allowed, and inlet and outlet sizes. Either the building code or the plumbing code lists the minimum number of each type of fixture that must be installed
in buildings of various occupancies (Table 14.2). Since these numbers are minimums, each project should be reviewed to determine if additional fixtures should
be provided. This is especially true for assembly occupancies, where large numbers
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Male
1 for 1–100
2 for 101–200
3 for 201–400
Female
3 for 1–50
4 for 51–100
8 for 101–200
11 for 201–400
Over 400, add one fixture for
each additional 500 males and 2
for each 300 females
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for each
additional 40 persons
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
2 for 16–35
3 for 36–55
3 for 36–55
Over 55, add 1 fixture for each
additional 40 persons
Male
Female
1 for 1–20
1 for 1–20
2 for 21–50
2 for 21–50
Over 50, add 1 fixture for each
additional 50 persons
Male
Female
1 per 30
1 per 25
Male
Female
1 per 40
1 per 30
Office or public building
Office or public buildings—
for employee use
Schools—for staff use
All schools
Schools—for student use
Nursery
Secondary
Elementary
1 for each dwelling or apartment
unit
Water closets b
Dwelling or
apartment house d
Type of building
or occupancy
Urinals
1 per 35
1 per 75
1 per 50
0 for 1–9
1 for 10–50
Add one fixture for each
additional 50 males
1 for 1–100
2 for 101–200
3 for 201–400
4 for 401–600
Over 600 add 1 fixture for
each additional 300 males
TABLE 14.2 Minimum Plumbing Fixtures for Various Occupancies a
Female
1 per 40
Female
1 per 40
Male
Female
1 for 1–25
1 for 1–25
2 for 26–50
2 for 26–50
Over 50, add 1 fixture for
each additional 50 persons
Male
Female
1 per 35
1 per 35
Male
Female
1 per 40
1 per 40
Male
1 per 40
Male
1 per 40
Male
Female
1 for 1–200
1 for 1–200
2 for 201–400
2 for 201–400
3 for 401–750
3 for 401–750
Over 750, add one fixture for
each additional 500 persons
1 for each dwelling or
apartment unit
Lavatories
1 for each dwelling
or apartment unit
Bathtubs or
showers
1 per 75
1 per 75
1 per 75
1 per first 75 e
Drinking
fountains c
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.14
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Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for
each additional 40 persons
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for each
additional 40 persons
Male
1 for 1–100
2 for 101–200
3 for 201–400
Dormitories—
for staff use
Assembly places—
theaters, auditoriums,
convention halls—for
permanent employee use
Assembly places—
theaters, auditoriums,
convention halls—for
public use
Female
3 for 1–50
4 for 51–100
8 for 101–200
11 for 201–400
Over 400, add one fixture for
each additional 500 males and
2 for each 300 females
Male
Female
1 per 10
1 per 8
Add 1 fixture for each
additional 25 males (over 10)
and 1 for each additional 20
females (over 8)
Dormitories—
school or labor ƒ
Female
1 per 75
2 for 76–125
3 for 126–250
Female
1 per 30
Male
1 per 125
2 for 126–250
Male
1 per 40
Worship places—educational
and activities unit
Other (colleges,
universities, adult centers)
1 for 1–100
2 for 101–200
3 for 201–400
4 for 401–600
Over 600, add 1 fixture for
each additional 500 males
Add one fixture for each
additional 50 males
0 for 1–9
1 for 10–50
1 per 50
1 per 25
Over 150, add 1 fixture for
each additional 50 males
1 per 125
1 per 35
Female
1 per 40
Female
1 per 40
Female
1 per 40
Male
Female
1 for 1–200
1 for 1–200
2 for 201–400
2 for 201–400
3 for 401–750
3 for 401–750
Over 750, add one fixture
for each additional 500
persons
Male
1 per 40
Male
1 per 40
Male
Female
1 per 12
1 per 12
Over 12 add one fixture for
each additional 20 males
and 1 for each 15
additional females
1 per 2 water closets
Male
1 per 40
1 per 8
1 per 8
For females, add 1
bathtub per 30.
Over 150, add 1
per 20
1 per first 75 e
1 per first 75 e
1 per 75
1 per 75
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.15
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1 per room
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for
each additional 40 persons
Hospital waiting rooms
Hospitals—
for employee use
Penal Institutions—
for prison use
1 per room
1 per 8 patients
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for each
additional 40 persons
Hospitals
Individual room
Ward room
Institutional—other than
hospitals or penal
institutional (on each
occupied floor)—
for employee use
Male
1 per 25
Institutional—other than
hospitals or penal
institution (on each
occupied floor)
Female
1 per 20
Male
Female
1 for 1–10
1 for 1–10
2 for 11–25
2 for 11–25
3 for 26–50
3 for 26–50
4 for 51–75
4 for 51–75
5 for 76–100
5 for 76–100
Over 100, add 1 fixture for
each additional 30 persons
Water closets b
Industrial, warehouses,
workshops, foundries, and
similar establishments—
for employee use g
Type of building
or occupancy
Add one fixture for each
additional 50 males
0 for 1–9
1 for 10–50
0 for 1–9
1 for 10–50
Add one fixture for each
additional 50 males
0 for 1–9
1 for 10–50
Add one fixture for each
additional 50 males
Urinals
TABLE 14.2 Minimum Plumbing Fixtures for Various Occupancies a (Continued )
Male
1 per 40
1 per room
1 per room
1 per 10 patients
Male
1 per 40
Male
1 per 10
Female
1 per 40
Female
1 per 40
Female
1 per 10
Over 100, 1 per 15
persons h
Up to 100, 1 per 10
persons
Lavatories
1 per room
1 per 20 patients
1 per 8
1 per 8
1 shower for each
15 persons
exposed to
excessive heat or
to skin contamination with poisonous, infectious, or
irritating material
Bathtubs or
showers
1 per cell block
floor
1 per 75
1 per 75
1 per 75
1 per 75
1 per 75
Drinking
fountains c
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.16
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Male
1 per 150
2 for 151–300
Male
Female
1 for 1–50
1 for 1–50
2 for 51–150
2 for 51–150
3 for 151–300
4 for 151–300
Over 300, add 1 fixture for
each additional 200 persons
Worship places, principal
assembly place
Restaurants, pubs, and
lounges i
1 for 1–150
Over 150, add 1 fixture for
each additional 150 males
1 per 150
0 for 1–9
1 for 10–50
Add one fixture for each
additional 50 males
1 per exercise room
Female
1 per 40
Mae
Female
1 for 1–150
1 for 1–150
2 for 151–200
2 for 151–200
3 for 210–400
3 for 201–400
Over 400, add 1 fixture for
each additional 400 persons
1 per 2 water closets
Male
1 per 40
1 per cell
1 per exercise room
1 per 75
1 per 75
1 per exercise
room
a
Based on ‘‘Uniform Plumbing Code,’’ 1990, International Association of Plumbing and Mechanical Officials, Walnut, Calif.
The table lists the number of fixtures required for the number of persons indicated. Minimum exiting requirements determine the minimum number of occupants to be
accommodated.
Every building should include provisions for the physically handicapped. (Refer to local authorities or ‘‘Specifications for Making Buildings and Facilities Accessible to, and
Usable by, the Physically Handicapped,’’ ANSI A117.1, American National Standards Institute.)
Building categories not listed in the table should be considered separately by the administrative authority.
Consideration should be given to the accessibility of the fixtures. Application of the table data strictly on a numerical basis may not produce an installation suited to the needs
of building occupants. For example, schools should have toilet facilities on every floor on which there are classrooms.
Temporary facilities for workers: one water closet and one urinal for every 30 male workers and every 30 female workers, or fraction thereof. Through urinals are prohibited.
Walls and floors around every urinal should be lined with nonabsorbent materials. The lining should extend on the floor from the wall to 2 ft in front of the urinal lip, and on the
wall, 4 ft above the floor and at least 2 ft on both side of the urinal.
b
The total number of water closets for females should be at least equal to the sum of the water closets and urinals required for men.
c
There should be at least one drinking fountain per occupied floor in schools, theaters, auditoriums, dormitories, and office and public buildings. Drinking fountans should not
be installed in toilet rooms. Where food is consumed indoors, water stations may be substituted for drinking fountains.
d
One kitchen sink for each dwelling or apartment unit. One laundry tray or automatic washer standpipe for each dwelling and two laundry trays or two automatic washer
standpipes or combination of these for every 10 apartments.
e
One additional fountain for each additional 150 persons.
f
One laundry tray for every 50 persons. One slop sink for every 100 persons.
g
As required by local authorities or ‘‘Sanitation in Places of Employment,’’ ANSI Z4.1.
h
Where there is exposure to skin contamination from poisonous, infectious, or irritating materials, one lavatory should be provided for every 5 persons. A wash sink 24 in long
or a circular basin 18 in in diameter, when equipped with water outlets for these dimensions, may be considered equivalent to one lavatory.
i
Any business that sells food for consumption on th epremises is considered a restaurant. Employee toilet facilities should not be counted toward meeting the restaurant
requirements in the table. Hand washing must be available in the kitchen for employees. The number of occupants for a drive-in restaurant should be taken equal to the number of
parking stalls.
Female
1 per 75
2 for 76–150
3 for 151–300
Male
Female
1 for 1–15
1 for 1–15
2 for 16–35
3 for 16–35
3 for 36–55
4 for 36–55
Over 55, add 1 fixture for each
additional 40 persons
1 per cell
1 per exercise room
Penal Institutions—for
employee use
Cell
Exercise room
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.17
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14.18
SECTION FOURTEEN
of people may utilize the restroom facilities in a short period of time; for example,
at half-time at a football game.
The plumbing fixtures are at the terminals of the water-supply system and the
start of the wastewater system. To a large extent, the flow from the fixtures determines the quantities of wastewater to be drained from the building.
Traps. Separate traps are required for most fixtures not fitted with an integral trap.
The trap should be installed as close as possible to the unit served. More than one
fixture may be connected to a trap if certain code regulations are observed. For
specific requirements, refer to the governing code.
A water seal of at least 2 in, and not more than 4 in, is generally required in
most traps. Traps exposed to freezing should be suitably protected to prevent ice
formation in the trap body. Clean-outs of suitable size are required on all traps
except those made integral with the fixture or those having a portion which is easily
removed for cleaning of the interior body. Most codes prohibit use of traps in which
a moving part is needed to form the seal. Double trapping is also usually prohibited.
Table 14.4 lists minimum trap sizes for various fixtures.
Showers. Special care should be taken in selection of showers, especially shower
valves. To ensure that a user is not scalded when pressure fluctuations occur in the
water distribution system, pressure-balancing or temperature-limiting shower valves
that prevent extreme variations in the outlet water temperature may be specified. In
facilities with large numbers of showers, a central tempered water system may be
used to serve the showers. As with the shower valves, the mixing valve serving a
tempered water system should also be of a pressure-balancing or temperaturelimiting type.
Water Closets. These consist of a bowl and integral trap, which always contains
water, and a tank or a flushometer valve, which supplies water for flushing the bowl
(Fig. 14.3). The passage through the trap to the discharge usually is large enough
to pass a solid ball 2 to 3 in in diameter. Siphon-jet flushometer valves generally
require a pressure of at least 15 psi for operation and blowout flushometer valves
generally require 25 psi for operation. The water level in a tank of a tank-type
water closet is raised above the water level in the bowl so that gravity provides
sufficient pressure for flushing.
The cleansing action of water flow in the bowl may be achieved in any of several
different ways. One method is illustrated by the siphon jet in Fig. 14.3b. The tank
discharges water around the rim and also jets water into the up leg of the trap. As
a result, the contents of the bowl are siphoned out of the down leg of the discharge
pipe. Other types of action include the reverse trap (Fig. 14.3c ), which is similar
to the siphon-jet type but smaller; the siphon vortex (Fig. 14.3a ), in which water
from the rim washes the bowl, creates a vortex, becomes a jet, and discharges by
siphonage; the washdown (Fig. 14.3d ), in which pressure buildup causes the up
FIGURE 14.3 Typical water closets: (a ) siphon-vortex; (b ) siphon-jet; (c ) reverse trap; (d )
washdown; (e ) blowout.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.19
leg to overflow and create a discharge siphon; and the blowout (Fig. 14.3e ), used
with a flushometer valve, which projects a strong jet into the up leg to produce the
discharge. Blowout-type water closets are generally reserved for use where clogs
due to solids in the bowl are common, such as in penal institutions, stadiums, or
arenas. Because of the large amount of water consumed during the flush of a blowout type of water closet, these types of fixtures are not used to the extent they once
were. Siphon-jet type water closets are the most common type of water closets
specified.
As part of the Energy Policy Act of 1992, all water closets manufactured after
January 1, 1994, for use in the United States were required to have a maximum
water use of 1.6 gallons per flush. Blowout water closets were required to have a
maximum water use of 3.5 gallons per flush and urinals were required to have a
maximum water use of 1.0 gallon per flush.
Air Gaps. These should be provided to prevent backflow of wastewater into the
water supply (Art 14.6.4). At plumbing fixtures, an air gap must be provided between the fixture water-supply outlet and the flood-level rim of the receptacle.
Building codes usually require a minimum gap of 1 to 2 in for outlets not affected
by a nearby wall and from 11⁄2 to 3 in for outlets close to a wall. Table 14.3 lists
minimum air gaps usually used.
In addition to the usual drain at the lowest point, receptacles generally are provided with a drain at the flood-level rim to prevent water from overflowing. The
overflow should discharge into the wastewater system on the fixture side of the
trap.
Floor and Equipment Drains. Floor drains should be installed at all areas where
the possibility of water spillage occurs. Common areas that are provided with floor
drains include restrooms, mechanical rooms, kitchens, and shower and locker
rooms. Equipment that requires piped discharge from drains or relief devices, such
as boilers, require recessed-type drains of adequate size, preferably with a funnel
receptor. Large commercial kitchens often require deep, receptor floor sinks to
receive indirect wastes from kitchen equipment.
14.8
WATER DEMAND AND FIXTURE UNITS
For each fixture in a building, a maximum requirement for water flow, gal / min,
can be estimated. Table 14.1 indicates the minimum flow rate and pressure required
by code. The maximum flow may be considerably larger. Branch pipes to each
fixture should be sized to accommodate the maximum flow and minimum pressure
the fixture will require. Mains serving these branches, however, need not be sized
to handle the sum of the maximum flows for all branches served. It is generally
unlikely that all fixtures would be supplying maximum flow simultaneously or even
that all the fixtures would be operating at the same time. Consequently, the diameters of the mains need be sized only for the probable maximum water demand.
In practice, the probable flow is estimated by weighting the maximum flow in
accordance with the probability of fixtures being in use. The estimate is based on
the concept of fixture units.
Fixture unit is the average discharge, during use, of an arbitrarily selected fixture, such as a lavatory or water closet. Once this value is established, the discharge
rates of other types of fixtures are stated in terms of the basic fixture. For example,
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14.20
SECTION FOURTEEN
TABLE 14.3 Minimum Air Gaps for Generally Used Plumbing Fixtures
Minimum air gap A, in
Fixture
Away from
a wall*
Close to
a wall*
1.0
1.50
1.5
2.25
2.0
3.00
1.0
†
1.5
§
Lavatories with effective openings not greater than 1⁄2-in
diameter
Sink, laundry trays, and goose neck bath faucets with effective
openings not greater than 3⁄4-in diameter
Overrim bath fillers with effective openings not greater than 1-in
diameter
Drinking fountains with a single orifice not more than 7⁄16 in in
diameter or multiple orifices with a total area of 0.150 in2 (area
of a 7⁄16-in-diameter circle)
Effective openings greater than 1-in
* Side walls, ribs, or similar obstructions do not affect the air gaps when spaced from inside edge of
spout opening a distance c greater than three times the diameter of the effective opening for a single wall,
or a distance greater than four times the diameter of the effective opening for two intersecting walls (see
figure).
† Vertical walls, ribs, or similar obstructions extending from the water surface to or above the horizontal
plane of the spout opening require a greater air gap when spaced closer to the nearest inside edge of spout
opening than specified in note* above.
‡ 2 ⫻ effective opening.
§ 3 ⫻ effective opening.
when the basic fixture is a lavatory served by as 11⁄4-in trap, the average flow during
discharge is 7.5 gal / min. So a bathtub that discharges 15 gal / min is rated as two
fixture units (2 ⫻ 7.5). Thus, a tabulation of fixture units can be set up, based on
an assumed basic unit.
A specific number of fixture units, as listed in Table 14.4, is assigned to each
type of plumbing fixture. These values take into account:
• Anticipated rate of water flow from the fixture outlet, gal / min
• Average duration of flow, min, when the fixture is used
• Frequency with which the fixture is likely to be used
The ratings in fixture units listed in Table 14.4 represent the relative loading of
a water-distribution system by the different types of plumbing fixtures. The sum of
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.21
the ratings for any part or all of a system is a measure of the load the combination
of fixtures would impose if all were operating. The probable maximum water demand, gal / min, can be determined from the total number of fixture units served by
any part of a system by use of graphs shown in Fig. 14.4.
The demand obtained from these curves applies to fixtures that are used intermittently. If the system serves fixtures, such as air-conditioning units, lawn sprinklers, or hose bibs, that are used continuously, the demand of these fixtures should
be added to the intermittent demand. For a continuous or semicontinuous flow into
a drainage system, such as from a pump, pump ejector, air-conditioning system, or
similar device, two fixture units should be used for each gallon per minute of flow.
When additional fixtures are to be installed in the future, pipe and drain sizes should
be based on the ultimate load, not on the present load.
14.9
WATER-PIPE SIZING
The required domestic-water pipe sizes should be determined by application of the
principles of hydraulics. While economy dictates use of the smallest sizes of pipe
permitted by building-code requirements, other factors often make larger sizes advisable. These factors include:
1. Pressure at the water-supply source, usually the public main, psi
2. Pressure required at the outlets of each fixture, psi
3. Loss of pressure because of height of outlets above the source, pressure loss due
to friction caused by the flow of water through water meters and backflow preventers, and friction from water flow in the piping
4. Limitations on velocity of water flow, ft / s, to prevent noise and erosion
5. Additional capacity for future expansion (normally 10% minimum)
14.9.1
Method for Determining Pipe Sizes
1. Sketch all the proposed risers, horizontal mains, and branch lines, indicating the
number and the type of fixtures served, together with the required flow
2. Compute the demand weights of the fixtures, in fixture units, using Table 14.4
3. From Fig. 14.4 and the total number of fixture units, determine the water demand, gal / mm
4. Compute the equivalent length of pipe for each stack in the system, starting
from the street main
5. Obtain by test or from the water company the average minimum pressure in the
street main. Determine the minimum pressure needed for the highest fixture in
the system
6. Compute the pressure loss in the piping with the use of the equivalent length
found in item 4
7. Choose the pipe sizes from a chart like that in Fig. 14.5 or 14.6, or from the
charts given in the plumbing code being used
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2
2
3
4
Bathtub† (with or without overhead shower
Bidet
Combination sink and tray
Combination sink and tray with food-disposal unit
Dental unit or cuspidor
Dental lavatory
Dishwasher, domestic
Drinking fountain
Floor drains‡
Kitchen sink
Kitchen sink, domestic, with food-waste grinder
Lavatory
1
2
1
1
2
3
1
Private
Fixture type
3
1
2
1
4
⁄8
3
⁄2
⁄8
3
2
1
⁄8
⁄2
1
⁄8
3
⁄2
1
⁄2
1
1
⁄2
⁄2
1
⁄2
1
1
⁄2
⁄2
1
⁄2
Hot
water
Cold
water
Min size of
connections, in
4
4
Public
Fixture-unit value
as load factors
Domestic water
TABLE 14.4 Fixture Units and Trap and Connection Sizes for Plumbing Fixtures
2
2
2
3
1
2
2
1
2
2 or 3
2
1
Fixture-unit value
as load factors
11⁄2
Nominal 11⁄2
11⁄2
11⁄2
11⁄4
11⁄4
11⁄2
11⁄4
2
11⁄2
11⁄2
Small P.O. 11⁄4
Min size of trap,
in
Drainage
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.22
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3
6
3
2
3
2
2
2
4
4
10
5
5
3
2
5
10
2
4
4
2
2
⁄2
⁄2
⁄2
⁄2
2
1
1
⁄2
⁄8
1
3
⁄2
3
1
⁄2
3
⁄4
1
3
⁄2
⁄4
1
⁄2
1
⁄2
1
1
1
⁄2
1
⁄2
⁄4
1
⁄2
1
⁄2
1
1
1
⁄2
1
* Fixture units listed in the table give the total water-supply demand of fixtures with both hot-water and cold-water
supply. Fixture units for the maximum demand of either cold water or hot water alone may be taken as 75% of the
fixture units in the table.
† A shower head over a bathtub does not increase the fixture value.
‡ Size of floor drain should be determined by the area of surface water to be drained.
Lavatories with 11⁄4- or 11⁄2-in trap have the same load value; larger P.O. (plumbing orifice) plugs have greater
flow rate.
Lavatory
Lavatory, barber, beauty parlor
Lavatory, surgeon’s
Laundry tray (1 or 2 compartments)
Shower, per head
Sinks:
Surgeon’s
Flushing rim (with valve)
Service (trap standard)
Service (P trap)
Pot, scullery, etc.
Urinal, pedestal, siphon jet, blowout
Urinal, wall lip
Urinal stall
Urinal with flush tank
Wash sink (circular or multiple) each set of faucets
Water closet, tank-operated
Water closet, valve-operated
3
6
3
3
3
6
2
2
2
3
4
6
2
2
2
2
2
11⁄2
3
3
2
11⁄2
Nominal 3
11⁄2
2
11⁄2
Nominal 11⁄2
Nominal 3
3
Large P.O. 11⁄2
11⁄2
11⁄2
11⁄2
2
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.23
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.24
SECTION FOURTEEN
FIGURE 14.4 Estimate curves for domestic water demand. (a ) The number of fixture units
served determines the rate of flow. (b ) Enlargement of the low-demand portion of (a ).
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.25
FIGURE 14.5 Chart for determination of flow in copper tubing and other pipes that will
be smooth after 15 to 20 years of use.
14.9.2
Effects of Pressure
Rate of flow, ft3 / s, in a pipe is determined by
Q ⫽ AV
(14.1)
where A ⫽ pipe cross-sectional area, ft2
V ⫽ water velocity, ft / s
In general, V should be kept to 8 ft / s or less to prevent noise and reduce erosion
at valve seats. Hence, pipe area should be at least the flow rate Q divided by 8.
Mains may be allowed to have a velocity of 10 ft / s, but lower velocities are preferred.
The minimum pressures at plumbing fixtures generally required by building
codes are listed in Table 14.1. These pressures are those that remain when the
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.26
SECTION FOURTEEN
FIGURE 14.6 Chart for determination of flow in pipes such as galvanized steel and
wrought iron that will be fairly rough after 15 to 20 years of use.
pressure drop due to height of outlet above the water source and the pressure lost
by friction in pipes are deducted from the pressure at the water source. The pressure
loss due to height can be computed from
p ⫽ 0.433h
(14.2)
where p ⫽ pressure, psi
h ⫽ height or pressure head, ft
The total head H, ft, on water at any point in a pipe is given by
H⫽Z⫹
p
V2
⫹
w 2g
(14.3)
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
where Z
p/w
w
V 2 / 2g
g
⫽
⫽
⫽
⫽
⫽
14.27
elevation, ft, of the point above some arbitrary datum
pressure head, ft
specific weight of water ⫽ 62.4 lb / ft3
velocity head, ft
acceleration due to gravity, 32.2 ft / s2
When water flows in a pipe, the difference in total head between any two points
in the pipe equals the friction loss hƒ, ft, in the pipe between the points.
Any of several formulas may be used for estimating hƒ. One often used for pipes
flowing full is the Hazen-Williams formula:
hƒ ⫽
where Q
D
L
C1
⫽
⫽
⫽
⫽
4.727 Q1.85
L
D4.87
C1
(14.4)
discharge, ft3 / s
pipe diameter, ft
length of pipe, ft
coefficient
The value of C1 depends on the roughness of the pipe, which, in turn, depends
on pipe material and age. A new pipe has a larger C1 than an older one of the same
size and material. Hence, when pipe sizes are being determined for a new installation, a future value of C1 should be assumed to ensure adequate flows in the
future. Design aids, such as charts (Figs. 14.5 and 14.6) or nomograms, may be
used to evaluate Eq. (14.4), but if such computations are made frequently, a computer solution is preferable.
In addition to friction loss in pipes, there are also friction losses in meters,
valves, and fittings. These pressure drops can be expressed for convenience as
equivalent lengths of pipe of a specific diameter. Table 14.5 indicates typical allowances for friction loss for several sizes and types of fittings and valves.
The pressure reduction caused by pipe friction depends, for a given length of
pipe and rate of flow, on pipe diameter. Hence, a pipe size can be selected to create
a pressure drop in the pipe to provide the required pressure at a plumbing fixture,
when the pressure at the water source is known. If the pipe diameter is too large,
the friction loss will be too small and the pressure at the fixture will be high. If
the pipe size is too small, the friction loss will be too large and the pressure at the
fixture will be too small.
14.9.3
Minimum Pipe Sizes
The minimum sizes for fixture-supply pipes are given for cold water and hot water
in Table 14.4.
Sizes of pipes for small buildings, such as single-family houses, can usually be
determined from the experience of the designer and applicable building-code requirements, without extensive calculations. For short branches to individual fixtures,
for example, the minimum pipe diameters listed in Table 14.4 generally will be
satisfactory. Usually also, the following diameters can be used for the mains supplying water to the fixture branches:
1
3
⁄2 in for mains with up to three 3⁄4-in branches
⁄4 in for mains with up to three 1⁄2-in or five 3⁄8-in branches
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1
2
2.5
3
4
5
7
8
10
14
17
20
90⬚
standard
elbow
0.6
1.2
1.5
1.8
2.4
3
4
5
6
8
10
12
45⬚
standard
elbow
1.5
3
4
5
6
7
10
12
15
21
25
30
Standard
90⬚ tee
0.3
0.6
0.8
0.9
1.2
1.5
2
2.5
3
4
5
6
Coupling or
straight run
of tee
* Allowances based on nonrecessed threaded fittings. Use one-half the allowances for recessed threaded fittings or
streamlined older fittings.
1
⁄8
⁄2
3
⁄4
1
11⁄4
11⁄2
2
21⁄2
3
4
5
6
3
Diameter
of fitting,
in
0.2
0.4
0.5
0.6
0.8
1
1.3
1.6
2
2.7
3.3
4
Gate
valve
TABLE 14.5 Allowances for Friction Losses in Valves and Fittings, Expressed as Equivalent Length of Pipe, Ft*
8
15
20
25
35
45
55
65
80
125
140
165
Globe
valve
4
8
12
15
18
22
28
34
40
55
70
80
Angle
valve
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.28
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.29
1 in for mains with up to three 3⁄4-in or eight 1⁄2-in or fifteen 1⁄8-in branches
The adequacy of these sizes, however, depends on the pressure available at the
water source and the probability of simultaneous use of the plumbing fixtures.
14.10
DOMESTIC WATER HEATERS
The method of heat development for water heaters may be direct (heat from combustion of fuels or electrical energy directly applied to water) or indirect (heat from
a remote heat source utilizing some other medium, such as steam, to heat water).
Direct-heat-type water heaters are classified as follows:
1. Automatic storage heaters, which incorporate burners or heating elements, storage tank, outer jacket, insulation, and controls as a packaged unit
2. Circulating tank heaters, which consist of what is essentially an instantaneous
heater and an accessory storage tank. Hot water is circulated through the heating
section by means of a circulating pump
3. Instantaneous heaters, which have little water storage capacity and generally
have controls that modulate the heat output based on the demand
4. Hot-water supply boilers, which provide high-temperature hot water in a manner
similar to hot-water heating boilers
Fuel for direct-fired water heaters is generally one of the fossil fuels, such as
natural gas or oil, or electric power.
Indirect-type water heaters are classified as follows:
1. Storage type, which consists of a heat exchanger installed in a storage tank (Fig.
14.7) or in a separate storage tank and stand-alone heat exchanger provided with
a circulating water system.
FIGURE 14.7 Storage heater for domestic hot water.
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.30
SECTION FOURTEEN
2. Indirect immersion type, a self-contained water heater, utilizing one of the fossil
fuels as a heating medium for a horizontal fire tube containing a finned-tube
bundle. Water, or some other heat-transfer fluid, is heated in the finned bundle
in the burner section and is pumped to a water-heating bundle located in the
shell or storage tank installed below the fire tube.
3. Instantaneous type, which is suited for facilities requiring steady, continuous
supplies of hot water (Fig. 14.8). The rate of flow is indirectly proportional to
the temperature of the water being supplied.
4. Semi-instantaneous type, which have limited storage to meet momentary hotwater peak demands. These types of heaters consist of a heating element and a
control system that closely controls leaving-water temperature. A hot-water storage tank provides additional hot water when required during periods of peak
momentary hot-water demand.
The heat-transfer media normally utilized for indirect domestic hot-water heaters
are steam and heating hot water. The heat-transfer media use heat provided by
boilers and, in some instances, solar collectors, which collect heat from the sun.
(For detailed guidance in the sizing of domestic water heating systems, see ‘‘Service
Hot-Water Systems,’’ Chap. 4, ASPE Data Book, American Society of Plumbing
Engineers, Westlake, CA 91362. Recovery versus storage curves that have been
developed based on extensive research can be utilized to compare various combinations available.)
Plumbing designers should also assure that all required safety devices and controls have been provided to prevent an explosion of the storage vessel. There have
been numerous instances of injury and death to occupants due to overfiring conditions caused by malfunctioning controls and safety-relief devices that did not
operate properly. All storage vessels should be provided with AGA / ASME-rated
pressure and temperature (P&T) relief valves, installed as directed by the vessel
manufacturer. The rating of the P&T valves should meet or exceed the Btu input
rating of the water-heating apparatus.
As water is heated, the volume required to contain the heated water increases.
In the past, the increased volume and resulting increased pressure was allowed to
FIGURE 14.8 Instantaneous heater for domestic hot water.
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.31
expand back into the domestic cold water system. With the increased use of backflow prevention devices in domestic water systems, the potential for expansion of
hot water has been limited. In many instances, water heater tanks have failed due
to variations in pressure associated with expansion during heating. Most plumbing
codes now require the installation of an expansion tank on domestic hot water
systems to prevent premature tank failure.
Most storage tanks are constructed of steel and therefore are subject to rusting
when in direct contact with water. Various liners are available such as cement, glass,
copper, and nickel. The designer should select a liner that best meets the needs of
the building being designed. Storage tanks should be ASME certified.
The hot-water load for a given building is computed in a manner similar to that
described in Art. 14.8 but with Table 14.6 and the tabulated demand factor for the
particular building type. The heating-coil capacity of the heater must at least equal
the maximum probable demand for hot water.
For storage-type heaters, the storage capacity is obtained by multiplying the
maximum probable demand by a suitable factor, such as 1.25 for apartment buildings to 0.60 for hospitals. Table 14.7 lists representative hot-water utilization temperatures for various services. It should be noted that service-water temperatures in
the 140⬚F range should be provided, to prevent the growth of Legionella pneumophila bacteria which causes Legionnaires’ disease.
Example. Determine heater and storage tank size for an apartment building from
a number of fixtures.
Solution. Calculation of the maximum possible demand with the use of Table
14.6 is shown in Table 14.8. Table 14.6 also gives a demand factor of 0.30 for
apartment buildings.
Probable maximum demand ⫽ 2520 ⫻ 0.30 ⫽ 756 gph
This determines the minimum heater or coil capacity, 756 gph. From Table 14.6
also, the storage capacity factor is 1.25
Storage tank capacity ⫽ 756 ⫻ 1.25 ⫽ 945 gal
WASTEWATER PIPING
Human, natural, and industrial wastes resulting from building occupancy and use
must be disposed of in a safe, quick manner if occupant health and comfort are to
be safeguarded. Design of an adequate plumbing system requires careful planning
and adherence to the codes in effect and to state or municipal regulations governing
these systems.
14.11
WASTEWATER DISPOSAL
There are three main types of wastewater: domestic, storm, and industrial. Separate
plumbing systems are generally required for each type.
Domestic wastewater is primarily spent water from the building water supply,
to which is added wastes from bathrooms, kitchens, and laundries. It generally can
be disposed of by discharge into a municipal sanitary sewer, if one is available.
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3
10
20
5
30
20
0.30
1.25
Foot basins
Kitchen sink
Laundry, stationary tubs
Pantry sink
Showers
Service sink
Hydrotherapeutic showers
Hubbard baths
Leg baths
Arm baths
Sitz baths
Continuous-flow baths
Circular wash sinks
Semicircular wash sinks
Demand factor
Storage capacity factor‡
0.40
1.00
225
12
2
8
30
Gymnasiums
0.25
0.60
Factors
2
6
20
50
190
3
20
28
10
75
20
400
600
100
35
30
165
20
10
Hospitals
0.25
0.80
0.40
1.00
30
15
20
10
0.30
2.00
20
10
10
30
20
20
20
76
12
20
225
20
2
6
Office
buildings
2
12
Industrial
plants
2
8
20
50
190
3
30
28
10
75
30
Hotels
* Based on data in ‘‘ASPE Data Book,’’ American Society of Plumbing Engineers, Westlake, Calif.
† Dishwasher requirements should be taken from this table or from manufacturers’ data for the model to be used,
if this is known.
‡ Ratio of storage-tank capacity to probable maximum demand per hour. Storage capacity may be reduced where
an unlimited supply of steam is available from street steam system or large boiler plant.
2
4
20
15
Lavatory, private
Lavatory, public
Bathtubs
Dishwashers†
Apartment
buildings
[Based on average conditions for the building type, gal / h of water per fixture at 140⬚F (60⬚C )]
TABLE 14.6 Hot-Water Demand per Fixture for Various Building Types*
0.30
0.70
3
10
20
5
30
15
20
15
2
Dwellings
0.40
1.00
30
15
10
225
20
20
76
3
20
2
15
Schools
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.32
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.33
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
TABLE 14.7 Hot-Water Temperatures for Various Services
Temperature
Use
Lavatory
Hand washing
Shaving
Showers and tubs
Therapeutic baths
Commercial and institutional laundry
Residential dishwashing and laundry
Commercial spray-type dishwashing
Single or multiple tank hood or rack type
Wash minimum temperature
Final rinse
Single tank conveyor type
Wash minimum temperature
Final rinse
Single tank rack or door type
Single-temperature wash and rinse
Surgical scrubbing
Chemical sanitizing types (consult manufacturer for actual
temperature required)
Multiple-tank conveyor type
Wash minimum temperature
Pumped rinse minimum temperature
Final rinse
Chemical sanitizing glasswasher
Wash
Rinse minimum temperature
⬚F
⬚C
105
115
110
95
180
140
40
45
43
35
82
60
150
180–195
65
82–90
160
180–195
71
82–90
165⫹
110
74⫹
43
140
60
150
160
180–195
65
71
82–90
140
75
60
24
TABLE 14.8 Hot-Water Demand for Apartment-Building Example
Number of fixtures
60 lavatories
30 bathtubs
30 showers
60 kitchen sinks
15 laundry tubs
Possible maximum demand
Flow per fixture,
gal / h (from Table 14.6)
Hot-water demand,
gal / hr
2
20
30
10
20
120
600
900
600
300
2520
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.34
SECTION FOURTEEN
Storm water is primarily the water that runs off the roof or the site of the
building. The water usually is directed to roof drains or gutters. These then feed
the water to drainpipes, which convey it to a municipal or private storm-water sewer
system. Special conditions at some building sites, such as large paved areas or steep
slopes, may require the capture of storm water in retention areas or ponds to prevent
the municipal storm sewer systems from being overloaded. From these areas or
ponds, the storm water is generally conveyed to the storm sewers through outfall
structures designed to delay and control the flow of storm water to the municipal
storm sewer systems. Discharge into sanitary sewers is objectionable, because the
large flows interfere with effective wastewater treatment and increase treatment
costs. If kept separate from other types of wastewater, storm water usually can be
safely discharged into a large body of water. Raw domestic wastewater and industrial wastes, on the other hand, have objectionable characteristics that make some
degree of treatment necessary before they can be discharged. Nevertheless, municipal combined sewers (sanitary and storm wastes) exist in some areas. Appropriate
local authorities should be consulted to determine which type of system is available
and specific regulations that relate to connection to these systems.
In areas where municipal sanitary sewers are not available, some form of wastewater treatment is required. Prefabricated treatment plants are available in various
sizes and configurations. Most treatment systems are complex and require many
steps. These include filtration and activated-sludge and aeration methods. The degree of treatment necessary generally depends on the assimilation potential of the
body of water to receive the effluent, primarily the ability of the body to dilute the
impurities and to supply oxygen for decomposition of organic matter present in the
wastewater.
Industrial waste may present special problems because (1) the flow volume may
be beyond the public sewer capacity, and (2) local regulations may prohibit the
discharge of industrial waste into public sewers. Furthermore, many pollution regulations prohibit discharge of industrial waste into streams, lakes, rivers, and tidal
waters without suitable prior treatment. Industrial wastes generally require treatments engineered to remove the specific elements injected by industrial processes
that make the wastes objectionable. Often, these treatments cannot be carried out
in public wastewater treatment plants. Special treatment plants may have to be built
for the purpose. Treatment methods for a variety of industrial wastes are discussed
in W. W. Eckenfelder, Jr., ‘‘Industrial Water Pollution Control,’’ McGraw-Hill Publishing Company, New York. Specific design procedures for sewers, drains, and
wastewater treatment, with accompanying numerical examples, are given in T. G.
Hicks, ‘‘Standard Handbook of Engineering Calculations,’’ McGraw-Hill Publishing
Company, New York.
14.12
SEWERS
A sewer is a conduit for water carriage of wastes. For the purpose of this section,
any piping for wastewater inside a building will be considered plumbing or process
piping; outside the building, wastewater lines are called sewers.
Sewers carry wastewater. And a system of sewers and appurtenances is sewerage. Sanitary sewers carry domestic wastes or industrial wastes. Where buildings
are located on large sites, or structures with large roof areas are involved, a storm
sewer is used for fast disposal of rain and is laid out to drain inlets located for best
collection of runoff.
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.12.1
14.35
Determination of Runoff
For figuring rates of runoff to determine storm-sewer requirements, the so-called
rational method may be used. It employs the formula
Q ⫽ CIA
where Q
C
I
A
⫽
⫽
⫽
⫽
(14.5)
maximum rate of runoff, ft3 / s
runoff coefficient of the runoff area
rainfall intensity, in / hr
watershed area, acres
The runoff coefficient C indicates the degree of imperviousness of the land. It
ranges from 0.6 to 0.9 for built-up areas and paved surfaces and from 0.30 to 0.50
for unpaved surfaces, depending on the surface slope. In storm-sewer design, however, it is necessary to know not only rate of runoff and total runoff, but also at
what point in time after the start of a storm the rate of runoff reaches its peak. It
is this peak runoff for which pipe must be sized and sloped. (The conduit designed
to handle the peak runoff is for conveyance of runoff volume only and should not
be considered for storage.)
14.12.2
Determination of Sewer Size
Sanitary sewers or lines carrying exclusively industrial wastes from a building to
disposal must be sized and sloped according to best hydraulic design. The problem
is generally one of flow in a circular pipe. (C. V. Davis and K. E. Sorenson, ‘‘Handbook of Applied Hydraulics,’’ McGraw-Hill Publishing Company, New York.)
Gravity flow is to be desired, but pumping is sometimes required.
Pipe should be straight and of constant slope between access holes, and access
holes should be used at each necessary change in direction, slope, elevation, or size
of pipe. Access holes should be no farther apart than 200 ft for pipes 24 in and
smaller, and 500 ft for pipes 30 in and larger.
The sewer from a building must be sized to carry out all the water carried in
by supply mains or other means. Exceptions to this are the obvious cases where
losses might be appreciable, such as an industrial building where considerable water
is consumed in a process or evaporated to the atmosphere. But, in general, water
out about equals water in, plus all the liquid and water-borne solid wastes produced
in the building.
Another factor to consider in sizing a sewer is infiltration. Sewers, unlike water
mains, often flow at less pressure than that exerted by groundwater around them.
Thus, they are more likely to take in groundwater than to leak out wastewater. An
infiltration rate of 2000 to 200,000 gal / (day mi) might be expected. It depends
on diameter of pipe (which fixes length between joints), type of soil, groundwater
pressure, and workmanship.
In an effort to keep infiltration down, sewer-construction contracts specify a
maximum infiltration rate. Weir tests in a completed sewer can be used to check
the contractor’s success in meeting the specification; but unless the sewer is large
enough for workers to traverse, prevention of excessive infiltration is easier than
correction. In addition to groundwater infiltration through sewer-pipe joints, the
entry of surface runoff through access hole covers and thus into sewers is often a
factor. Observers have gaged as much as 150 gal / min leaking into a covered access
hole.
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14.36
SECTION FOURTEEN
Size and slope of a sanitary sewer also must satisfy a requirement that velocity
under full flow be kept to at least 2.5 ft / s to keep solids moving and preventing
clogging. In general, no drain pipe should be less than 6 in in diameter; an 8-in
minimum is safer.
14.12.3
Sewer-Pipe Materials
Vitrified clay, concrete, ductile iron, polyvinyl chloride (PVC), acrylonitrile butylene styrene (ABS) composite pipe, or steel may be used for pipe to carry wastewater
and industrial wastes. PVC or ABS are used for the smaller diameters. Steel or
reinforced concrete are generally used for larger sizes (⬎24 in).
Choice of pipe material depends on required strength to resist load or internal
pressure; corrosion resistance, which is especially vital for pipe carrying certain
industrial wastes; erosion resistance in sewers carrying coarse solids; roughness
factor where flat slopes are desirable; and cost in place. Sewer piping installed on
the discharge side of pumps should have a pressure rating well in excess of the
pressure that will be experienced.
Reinforced concrete pipe must be made well enough or protected to withstand
effects of damaging sewer gas (hydrogen sulfide) or industrial wastes. Ductile-iron
sewer pipe is good under heavy loads, exposed as on bridges, in inverted siphons,
or in lines under pressure. Steel is used chiefly for its strength or flexibility. Corrugated steel pipe with protective coatings is made especially for sewer use; its
long lengths and light weight and ease of handling and jointing. Plastic pipes are
used because of corrosion resistance, light weight, and low installation cost.
14.13
WASTEWATER-SYSTEM ELEMENTS
The usual steps in planning a plumbing system are: (1) secure a sewer or wastedisposal plan of the site; (2) obtain architectural and structural plans and elevations
of the building; (3) tabulate known and estimated occupancy data, including the
number of persons, sex, work schedules, and pertinent details of any manufacturing
process to be performed in the building; (4) obtain copies of the latest edition of
the applicable codes, (5) design the system in accordance with code requirements,
and (6) have the design approved by local authorities before construction is begun.
The typical plumbing layout in Fig. 14.9 shows the major elements necessary
in most plumbing systems. Fixtures (lavatories, water closets, bathtubs, showers,
etc.) are located as needed on each floor of the structure (Art. 14.7).
Each fixture is served by a soil stack, or waste stack, a vent or vent stack, and
a trap (Fig. 14.9). Vertical soil or waste stacks conduct waste solids and liquids
from one or more fixtures to a sloped house drain, or building drain, generally
located below the lowest floor of the building. Each vent stack extends to a stack
vent that projects above the building roof to a vent through roof (VTR). The vent
stack may or may not have branch vents connected to it. Vents and vent stacks
permit the entrance of fresh air to the plumbing system, diluting any gases present
and balancing the air pressure in various branches. (See also Art. 14.20.)
Traps on each fixture provide a water seal, which prevents sewer gases from
entering the working and living areas. In some areas, the plumbing regulations
require installation of a building or house trap. The building drain delivers the
discharge from the various stacks to the house trap, or building trap (Fig. 14.9),
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WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.37
FIGURE 14.9 Wastewater-removal system for a multistory building. (Reprinted with permission from F. S. Merritt, ‘‘Building Engineering and Systems Design,’’ Van Nostrand Reinhold
Company, New York.)
which is generally provided with a separate vent. Between the building trap and
public sewer, or other main sewer pipe, is the building sewer. The building sewer
is outside the building structure, while the building trap is just inside or outside of
the building foundation wall.
Where the building drain is below the level of the public sewer line, some
arrangement for lifting the wastewater to the proper level must be provided. This
can be done by allowing the building drain to empty into a suitably sized sump
pit. The wastewater is discharged from the sump pit to the public sewer by a
pneumatic ejector or motor-driven sewage ejector pump.
Pipe Supports. Pipes of wastewater-removal systems should be supported and
braced in the same way as pipes of water-supply systems (Art. 14.8). Vertical pipes
generally should be supported at every floor. Horizontal pipes should be supported
at intervals not exceeding the following: cast-iron soil pipe, 5 ft and behind every
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.38
SECTION FOURTEEN
hub; threaded pipe, 12 ft; copper tubing, 10 ft. Supports also should be provided
at the bases of stacks.
Consideration should be given to the possibility of building settlement and its
effects on vertical pipes and to thermal expansion and contraction of pipes, especially when the pipes have a high coefficient of expansion or are made of copper.
Clean-outs. A clean-out is an opening that provides access to a pipe, either
directly or through a short branch, to permit cleaning of the pipe. The opening is
kept plugged, until the plug has to be removed for cleaning of the sewer. In horizontal drainage lines, at least one clean-out is required for each 100 ft of pipe.
Clean-outs should be installed at the base of all stacks, at each change of direction
in excess of 45⬚, and at the point where the building sewer begins. For underground
drainage lines, the clean-out must be extended to the floor or ground level to allow
easier cleaning. Clean-outs should open in a direction opposite to that of the flow
in the pipe, or at right angles to it.
In pipes up to 4 in, the clean-out should be the same size as the pipe itself. For
pipes larger than 4 in, the clean-out should be at least 4 in in diameter but may be
larger, if desired. When underground piping over 10 in in diameter is used, an
access hole is required at each 90⬚ bend and at intervals not exceeding 150 ft.
14.14
WASTE-PIPE MATERIALS
Cast iron is the most common pipe material for systems in which extremely corrosive wastes are not expected. Polyvinyl chloride (PVC) is often used because it
is inexpensive, lightweight, and easy to install. Galvanized steel, copper, and acrylonitrile butylene styrene (ABS) also are used.
Plumbing piping should conform to one or more of the accepted material standards approved by the plumbing code applicable in the area in which the building
is located.
For cast-iron pipe, the fitting joints are calked (with oakum or hemp and filled
with molten lead at least 1 in deep), push-on which use rubber gaskets inserted
into the bell of the pipe, or are no-hub (drawn stainless steel bands with neoprene
gaskets). Copper pipe is commonly soldered or brazed, while steel and wroughtiron pipe have screwed, flanged, or welded connections.
When planning a plumbing system, designers should check with the applicable
code before specifying the type of joint to be used in the piping. Joints acceptable
in some areas may not be allowed in others.
14.15
LAYOUT OF WASTE PIPING
Sanitary sewer systems should be sized and laid out to permit use of the smallestdiameter pipes capable of rapidly carrying away the wastewater from fixtures without clogging the pipes, without creating annoying noises, and without producing
excessive pressure fluctuations at points where fixture drains connect to soil or
waste stacks. Such pressure changes may siphon off the liquid seals in traps and
force sewer gases back through the fixtures into the building. Positive or negative
air pressure at the trap seal of a fixture should never be permitted to exceed 1 in
of water.
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.39
Flow in Stacks. The drainage system is considered a nonpressure system. The
pipes generally do not flow full. The discharge from a fixture drain is introduced
to a stack through a stack fitting, which may be a long-turn tee-wye or a short-turn
or sanitary tee. The fitting gives the flow a downward, vertical component. As the
water accelerates downward under the action of gravity, it soon forms a sheet
around the stack wall. If no flows enter the stack at lower levels to disrupt the
sheet, it will remain unchanged in thickness and will flow at a terminal velocity,
limited by friction, to the bottom of the stack. A core of air at the center of the
stack is dragged downward with the wastewater by friction. This air should be
supplied from outdoors through a vent through roof (Fig. 14.9), to prevent creation
of a suction that would empty trap seals.
When the sheet of wastewater reaches the bottom of the stack, a bend turns the
flow 90⬚ into the building drain. Within a short distance, the wastewater drops from
the upper part of the drain and flows along the lower part of the drain.
Slope of Horizontal Drainage Pipes. Plumbing codes generally require that horizontal pipes have a uniform slope sufficient to ensure a flow with a minimum
velocity of 2 ft / s. The objective is to maintain a scouring action to prevent fouling
of the pipes. Codes therefore often specify a minimum slope of 1⁄4 in / ft for horizontal piping 31⁄2 in in diameter or less and 1⁄8 or 1⁄4 in / ft for larger pipes.
Because flow velocity increases with slope, greater slopes increase pipe-carrying
capacity. In branch pipes, however, high velocities can cause siphonage of trap
seals. Therefore, use of larger-size pipes is preferable to steeper slopes for attaining
required capacity of branch pipes.
See also Art. 14.20.
14.16
INTERCEPTORS
These are devices installed to separate grease, oil, sand, and other undesirable matter from the wastewater and retain them, while permitting normal liquid wastes to
discharge to the sewer.
Grease interceptors are used for kitchens, cafeterias, restaurants, and similar
establishments where the amount of grease discharged might obstruct the pipe or
interfere with disposal of the wastewater. Oil separators are used where flammable
liquids or oils might be discharged to the sewer. Sand interceptors are used to
remove sand or other solids from the wastewater before it enters the building sewer.
They are provided with large clean-outs for easy removal of accumulated solids.
Other types of applications in which interceptors are usually required include
laundries, beverage-bottling firms, slaughterhouses, and food-manufacturing establishments. The local authorities should be contacted to determine applicable local
code or municipal regulations.
14.17
PIPING FOR INDIRECT WASTES
Certain wastes like those from food-handling, dishwashing (commercial), and sterile-materials machines should be discharged through an indirect waste pipe. This
pipe is not directly connected with the building drainage pipes. Instead, it discharges
waste liquids into a plumbing fixture or receptacle from where they flow directly
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.40
SECTION FOURTEEN
to the building sanitary drainage system. Indirect-waste piping is generally required
for the discharge from rinse sinks and such appliances as laundry washers, steam
tables, refrigerators, egg boilers, iceboxes, coffee urns, dishwashers, stills, and sterilizers. It is also required for units that must be fitted with drip or drainage connections but are not ordinarily regarded as plumbing fixtures.
An air gap is generally required between the indirect-waste piping and the regular drainage system. The gap should be at least twice the effective diameter of the
drain it services, but not less than 1 in. A common way of providing the required
air gap is to lead the indirect-waste line to a floor drain, slop sink, or similar fixture
that is open to the air and is vented or trapped in accordance with the governing
code. To provide the necessary air gap, the indirect-waste pipe is terminated above
the flood level of the fixture.
For a device that discharges only clear water, such as water from engine-cooling
jackets, air-handling-unit coil condensate, sprinkler systems, or overflows, an indirect-waste system must be used. Clear water wastes from roof-mounted airconditioning equipment can usually be discharged to roof drains or rainwater gutters. Although some jurisdictions require clear water wastes to be discharged to
sanitary sewers, others allow or require clear water wastes to be discharged to the
storm sewer system or dry wells.
Hot water above 140⬚F and steam pipes usually must be arranged for indirect
connection into the building drainage system or into an approved interceptor.
To prevent corrosion of plumbing piping and fittings, any chemicals, acids, or
corrosive liquids are generally required to be automatically diluted or neutralized
before being discharged into the plumbing piping. Sufficient fresh water for satisfactory dilution, or a neutralizing agent, should be available at all times. A similar
requirement is contained in most codes for liquids that might form or give off toxic
or noxious fumes.
14.18
RAINWATER DRAINAGE
Exterior sheet-metal gutters and leaders for rainwater drainage are not normally
included as part of the plumbing work. Interior leaders or storm-water drains, however, are considered part of the plumbing work. Depending on local codes or ordinances in the locality, rainwater from various roof areas may or may not be led
into the sanitary sewer (Art. 14.11). Where separate rainwater leaders or storm
drains are used, the building drains are then called sanitary drains because they
convey only the wastes from the various plumbing fixtures in the building.
Interior storm-water drain pipes may be made of cast iron, steel, plastic, or
wrought iron. All joints must be tight enough to prevent gas and water leakage.
When a combined system is utilized, it is common practice to insert a cast-iron
running trap between the storm drain and the building drain to maintain a trap seal
on the storm drain at all times. Use of a combined system does not eliminate the
need for separate drains and vents for wastewater. All codes prohibit use of storm
drains for any type of wastewater.
Water falling on the roof may be led either to a gutter, from where it flows to
a downspout (Fig. 14.10a ), or it may be directed to a roof drainage device by
means of a slope in the roof surface. Many different roof drainage devices, such
as roof drains (Fig. 14.10b ) and parapet drains, are available for different roof
constructions and storm-water conditions.
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.41
FIGURE 14.10 Elements of a storm-drainage system: (a ) roof gutter, exterior leader, and
splash pan; (b ) roof drain and top portion of interior leader; (c ) piping to a storm sewer; (d )
piping to a combined sewer. (Reprinted with permission from F. S. Merritt, ‘‘Building Engineering
and Systems Design,’’ Van Nostrand Reinhold Company, New York.)
Most plumbing codes include provisions to prevent the collapse of the building
structure due to water ponding on the roof because of a clogged storm drainage
system. In most cases, these codes require installation of overflow roof drains or
parapet overflow scuppers to relieve water from the roof in the event of such a
condition. Local authorities should be contacted to determine what requirements
apply in their jurisdiction.
When vertical leaders are extremely long, it is common practice to install an
expansion joint between the leader inlet and the leader itself. Figure 14.10c shows
an example of a connection of a building storm drain to a storm sewer. When the
drain must be connected to a combined sanitary-storm sewer, a trap should be
installed before the connection to the sewer (Fig. 14.10d ).
Sizes of vertical leaders and horizontal storm drains depend on the roof area to
be drained. Table 14.9 indicates the maximum horizontal projection of roof area
permitted for various sizes of leaders and horizontal storm drains.
Semicircular gutters are sized on the basis of the maximum projected roof area
served. Table 14.10 shows how gutter capacity varies with diameter and pitch.
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PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.42
SECTION FOURTEEN
TABLE 14.9 Sizes of Vertical Leaders and Horizontal Drains*
Vertical conductors and leaders
Size of leader or conductor, in†
Maximum projected area, ft2
Flow, gal / min
2
21⁄2
3
4
5
6
8
2,176
3,948
6,440
13,840
25,120
40,800
88,000
23
41
67
144
261
424
913
Horizontal building storm drains and building storm sewers
Maximum projected roof area, ft2, and flow, gal / min, for
various slopes
1
1
⁄8 in per ft slope
1
⁄4 in per ft slope
⁄2 in per ft slope
Drain diameter, in
Area
Flow
Area
Flow
Area
Flow
3
4
5
6
8
10
12
15
3,288
7,520
13,360
21,400
46,000
82,800
133,200
238,000
34
78
139
222
478
860
1,384
2,473
4,640
10,600
18,880
30,200
65,200
116,800
188,000
336,000
48
110
196
314
677
1,214
1,953
3,491
6,576
15,040
26,720
42,800
92,000
165,600
266,400
476,000
68
156
278
445
956
1,721
2,768
4,946
* Roof areas and flows are based on a maximum rainfall intensity of 1 in / hr for a duration of 1 hr. For
regions with different maximum rainfall intensity in storms with a 100-year recurrence interval, divide
tabulated areas and flows by that intensity, in / hr.
† The area of rectangular leaders should equal or exceed that of the circular leader required. The ratio
of width to depth of rectangular leaders should not exceed 3 to 1.
TABLE 14.10 Sizes of Semicircular Roof Gutters*
Maximum projected roof area, ft2, and flow, gal / min, for gutters of
various slopes
1
⁄16 in per ft
slope
1
⁄8 in per ft
slope
1
⁄4 in per ft
slope
1
⁄2 in per ft
slope
Gutter diameter, in
Area
Flow
Area
Flow
Area
Flow
Area
Flow
3
4
5
6
7
8
10
680
1,440
2,500
3,840
5,520
7,960
14,400
7
15
26
40
57
83
150
960
2,040
3,520
5,440
7,800
11,200
20,400
10
21
37
57
81
116
212
1,360
2,880
5,000
7,680
11,040
14,400
28,800
14
30
52
80
115
165
299
1,920
4,080
7,080
11,080
15,600
22,400
40,000
20
42
74
115
162
233
416
* See assumption of rainfall intensity and duration in note for Table 14.9.
† Gutters other than semicircular may be used if they have an equivalent cross-sectional area.
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14.43
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
Where maximum rainfall is either more than, or less than, 1 in / hr, refer to the
plumbing code for suitable correction factors.
Drains for building yards, subsoil drainage systems, and exterior areaways may
also be connected to the storm drainage system. Where this is not possible, these
drains may be run to a dry well. When a dry well is used, only the discharge from
these devices may be run to the dry well.
14.19
WASTE-PIPE SIZING
There are two ways of specifying the pipe size required for a particular class of
plumbing service: (1) directly in terms of area served, as in roof-draining service
(Table 14.9) and (2) in terms of fixture units (Table 14.11).
As can be seen from these tables, the capacity of a leader or drain varies with
the pitch of the installed pipe. The greater the pitch per running foot of pipe, the
larger the capacity allowed, in terms of either the area served or the number of
fixture units. The reason for this is that the steeper the pitch the larger is the static
head available and hence the larger is the amount of liquid that the pipe can handle.
The steps in determination of pipe sizes by means of fixture units (Art. 19.8)
are: (1) list all fixtures served by one stack or branch; (2) alongside each fixture
list its fixture unit (Table 14.4, p. 14.22); (3) add the fixture units and enter the
proper table (Tables 14.4, 14.11, or 14.13) to determine the pipe size required for
the stack or the branch.
Fixture branches connecting one or more fixtures with a soil or waste stack are
usually sized on the basis of the maximum number of fixture units for a given size
of pipe or trap (Table 14.4). Where a large volume of water or other liquid may
be contained in a fixture, such as in bathtubs or slop sinks, an oversize branch drain
may be provided to secure more rapid emptying.
TABLE 14.11
Maximum Capacities of Building Drains and Building Sewers, Fixture
Units*
Slope of pipe, in / ft
Pipe diameter, in
2
21⁄2
3
4
5
6
8
10
12
15
1
⁄16
1,400
2,500
2,900
7,000
1
⁄8
180
390
700
1,600
2,900
4,600
8,300
1
⁄4
21
24
42†
216
480
840
1,920
3,500
5,600
10,000
1
⁄2
26
31
50†
250
575
1,000
2,300
4,200
6,700
12,000
* Maximum number of fixture units that may be connected to any portion of a building drain or building
sewer. Consult the administrative authority for public sewers for sizing of on-site sewers that serve more
than one building.
† A maximum of three water closets or three bathroom groups (water closet, lavatory, and bathtub or
shower, or both) may be installed in single-family dwellings and two water closets or bathroom groups, in
other types of construction.
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Fixture units connected
2
8
10
12
20
42
10
30
60
100
200
500
200
500
1100
350
620
960
1900
600
1400
2200
3600
1000
2500
3800
5600
11⁄4
11⁄2
11⁄2
2
2
21⁄2
3
3
3
4
4
4
5
5
5
6
6
6
6
8
8
8
8
10
10
10
10
Size and Length of Vents
Size of soil or waste stack, in
TABLE 14.12
30
50
30
30
26
1 ⁄4
1
150
100
75
50
30
30
1 ⁄2
1
200
150
100
100
60
50
35
30
20
2
3
4
300
200
200
80
100
90
70
35
30
20
25
15
600
500
400
260
250
180
80
70
50
50
30
24
20
1000
900
700
350
300
200
200
125
100
70
50
40
30
25
Maximum length of vent, ft
21⁄2
Required vent diameter, in
1000
900
700
400
300
250
200
150
100
80
60
75
50
30
25
5
1300
1100
1000
700
500
400
350
250
125
100
80
60
6
1300
1200
1100
800
1000
500
350
250
8
PLUMBING—WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
14.44
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14.45
WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS
TABLE 14.13
Horizontal Fixture Branches and Stacks
Max number of fixture units that may be connected to
Pipe diameter, in
Any horizontal
fixture branch*
11⁄4
11⁄2
2
21⁄2
3
4
5
6
8
10
12
15
1
3
6
12
20†
160
360
620
1400
2500
3900
7000
More than 3 branch intervals
One stack of 3
stories in height
or 3 intervals,
or less
Total for
stack
Total at one story
or branch interval
2
4
10
20
30‡
240
540
960
2200
3800
6000
2
8
24
42
72‡
500
1100
1900
3600
5600
8400
1
2
6
9
20†
90
200
350
600
1000
1500
* Does not include branches of the building drain.
† Not over two water closets or bathroom groups in each branch interval.
‡ Not over six water closets or bathroom groups on the stack.
14.20
VENTING
Waste pipes are vented to the outside to balance the air pressure in various branches
and to dilute any gases present. The availability of air prevents back pressure and
protects traps against siphonage.
14.20.1
Types of Vents
The main vent is the principal artery of the venting system. It supplies air to
branch vents, which, in turn, convey it to individual vents and wastewater pipes.
Every building should have at least one main vent stack. It should extend undiminished in size and as directly as possible from outdoor air at a level at least 6
in above the roof to the building drain. The main vent should be so located as to
provide a complete loop for circulation of air through the wastewater-removal system. As an alternative to direct extension through the roof, a vent stack may be
connected with a stack vent, if the connection is made at least 6 in above the floodlevel rim of the highest fixture.
A stack vent is the extension of a soil or waste stack above the highest horizontal drain connected to the stack. This vent terminates above the roof.
A vent through roof (VTR) is any vent that extends through the roof to allow
escape of sewer gases and to equalize pressures in the drainage system to prevent
siphonage from trap seals. In colder climates, a VTR should be at least 4 in in
diameter to prevent blockage from formation of frost and should terminate at least
12 in above the roof, but higher if the VTR is installed in regions with high snowfall
rates.
An individual vent, or back vent, is a pipe installed to vent a fixture trap and
is connected to the venting system above the fixture served or terminated outdoors.
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14.46
SECTION FOURTEEN
To ensure that the vent will adequately protect the trap, plumbing codes generally
limit the distance downstream that the vent opening may be placed from the trap.
This distance generally ranges from 21⁄2 ft for a 11⁄4-in fixture drain to 10 ft for a
4-in fixture drain, but not less than two pipe diameters. The vent opening should
be located above the bottom of the discharge end of the trap (Fig. 14.11). In general,
all trapped fixtures are required to have an individual vent, although vents may be
eliminated under some exceptional conditions. The plumbing code should be reviewed to determine where and how individual vents are to be installed.
To reduce the amount of piping required, two fixtures may be set back to back,
on opposite sides of a wall, and vented by a single vent (common vent). In that
case, however, the fixtures should discharge wastewater separately into a double
fitting with inlets at the same level.
A branch vent is a pipe used to connect one or more individual vents to a vent
stack or to a stack vent.
A wet vent is a pipe that serves both as a vent and as a drainage pipe for wastes
other than those from water closets. This type of vent reduces the amount of piping
from that required with individual vents. For example, a bathroom group of fixtures
may be vented through the drain from a lavatory, kitchen sink, or combination
fixture if such a fixture has an individual vent (Fig. 14.lla ).
A battery of fixtures is any group of similar fixtures that discharges into a common horizontal waste or soil branch. A battery of fixtures should be vented by a
circuit or loop vent. (Building codes usually set a limit on the number of fixtures
that may be included in a battery.)
A circuit vent is a branch vent that serves two or more traps and extends from
the vent stack to a connection to the horizontal soil or waste branch just downstream
from the farthest upstream connection to the branch (Fig. 14.11b ).
A loop vent is like a circuit vent but connects with a stack vent instead of a
vent stack (Fig. 14.11c ). Thus, air can circulate around a loop.
In some instances, conventional venting methods cannot be applied, such as with
island sink fixtures. Some codes allow the use of air admittance devices, commonly
known as quick vents. These devices allow air to enter the vent system while
preventing sewer gasses from escaping.
Soil and waste stacks with more than 10 branch intervals should be provided
with a relief vent at each tenth interval installed, starting with the top floor. A
branch interval is a section of stack at least 8 ft high between connections of
FIGURE 14.11 Venting of waste branches: (a ) wet venting of bathtub drainage pipe; (b ) circuit
venting, and (c ) loop venting of a battery of plumbing fixtures.
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14.47
horizontal branches. A relief vent provides circulation of air between drainage and
venting systems. The lower end of a relief vent should connect to the soil or waste
stack, through a wye, below the horizontal branch serving a floor where the vent
is required. The upper end of the relief vent should connect to the vent stack,
through a wye, at least 3 ft above that floor. Such vents help to balance the pressures
that are continuously changing within a plumbing system.
14.20.2
Slopes and Connections for Vent Pipes
While the venting system is intended generally to convey only air to and from the
drainage system, moisture may condense from the air onto the vent pipe walls. To
remove the condensation from the venting system, all individual and branch vent
pipes should be sloped and connected as to conduct the moisture back to soil or
waste pipes by gravity.
14.20.3
Sizing of Vent Pipes
Fixture units (Art. 14.19) are also used for sizing vents and vent stacks (Table
14.12). In general, the diameter of a branch vent or vent stack should be one-half
or more of that of the branch or stack it serves, but not less than 11⁄4 in. Smaller
diameters are prohibited, because they might restrict the venting action.
14.20.4
Combined Draining and Vent Systems
These offer the possibility of considerable cost savings over the separate drainage
and venting systems described in Art. 14.20.1.
One such system, introduced by the Western Plumbing Officials Association,
employs horizontal wet venting of one or more lavatories, sinks, or floor drains by
means of a common waste and vent pipe adequately sized to provide free movement
of air above the flow line of the pipe. Relief vents are connected at the beginning
and end of the horizontal pipe. The traps of the fixtures are not individually vented.
Some building codes permit such a system only where structural conditions preclude installation of a conventional system. Where this combined drainage and vent
system may be used, it may require larger than normal waste pipes and traps. Each
of the model codes has different requirements for this type of system and, therefore,
the code in effect must be carefully reviewed during the design process.
The Sovent system is another type of combination system. It requires drainage
branches and soil stacks, with special fittings, but no individual and branch vents
and no vent stacks.
The system has four basic parts: a soil or waste stack with a stack vent extending
through the roof, a Sovent aerator fitting on the stack at each floor, horizontal
branches, and a Sovent deaerator fitting on the stack at its base and at horizontal
offsets (Fig. 14.12). The aerator and deaerator provide means for self-venting the
stack. In a conventional drainage system, a vent stack is installed to supply air to
vent pipes connected to the drainage branches and to the soil or waste stack to
prevent destruction of the trap seals. In the Solvent system, however, the vent stack
is not needed because the aerator, deaerator, and stack vent avoid creation of a
strong suction.
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14.48
SECTION FOURTEEN
FIGURE 14.12 Copper single-stack Sovent plumbing system. (Courtesy of Copper Development
Association, Inc.)
The aerator does the following: It reduces the velocity of both liquid and air in
the stack. It prevents the cross section of the stack from filling with a plug of water.
And the fitting mixes the wastewater from the drainage branches with the air in the
stack.
The deaerator separates the airflow in the stack from the wastewater. As a result,
the wastewater flows smoothly into a horizontal offset or building drain. Also, air
pressure preceding the flow at 90⬚ turns is prevented from rising excessively by a
pressure relief line between a deaerator and a stack offset or the building drain to
allow air to escape from the deaerator.
An aerator is required on the stack at each level where a horizontal soil branch
or a waste branch the same size as or one tube size smaller than the stack discharges
to it. Smaller waste branches may drain directly into the stack. At any floor where
an aerator fitting is not required, the stack should have a double in-line offset, to
decelerate the flow (Fig. 14.12). No deaerators are required at stack offsets of less
than 60⬚.
14.21
PLUMBING-SYSTEM INSPECTION
AND TESTS
Plans for plumbing systems must usually be approved before construction is started.
After installation of the piping and fixtures has been completed, both the new work
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14.49
and any existing work affected by the new work must be inspected and tested. The
plumber or plumbing contractor is then informed of any violations. These must be
corrected before the governing body will approve the system.
Most plumbing codes allow air or water to be used for preliminary testing of
drainage, vent, and plumbing pipes. After the fixtures are in place, their traps should
be filled with water and a final test made of the complete drainage system.
When a system is tested with water, all pipe openings are tightly sealed, except
the highest one. The pipes are then filled with water until overflow occurs from the
top opening. With this method, either the entire system or sections of it can be
tested. In no case, however, should the head of water on a portion being tested be
less than 10 ft, except for the top 10 ft of the system. Water should be kept in the
system for at least 15 min before the inspection starts. During the inspection, piping
and fixtures must be tight at all points; otherwise approval cannot be granted.
An air test is made by sealing all pipe outlets and subjecting the piping to an
air pressure of 5 psi throughout the system. The system should be tight enough to
permit maintaining this pressure for at least 15 min without the addition of any air.
The final test required of plumbing systems uses either smoke or peppermint.
In the smoke test, all traps are sealed with water and a thick, strong-smelling smoke
is injected into the pipes by means of a suitable number of smoke machines. As
soon as smoke appears at the roof stack outlets, they should he closed and a pressure
equivalent to 1 in of water should be maintained throughout the system for 15 min
before inspection begins. For the peppermint test, 2 oz of oil of peppermint are
introduced into each line or stack.
GAS PIPING
Natural and manufactured gases are widely used for heating in stoves, water heaters,
and space heaters of many designs. Since gas can form explosive mixtures when
mixed with air, gas piping must be absolutely tight and free of leaks at all times.
Usual plumbing codes cover every phase of gas-piping size, installation, and testing.
The local code governing a particular building should be carefully followed during
design and installation.
(‘‘National Fuel Gas Code,’’ ANSI Z223.1, American National Standards Institute and National Fire Protection Association; see also model plumbing codes and
mechanical codes of the various building officials associations listed in Art. 14.1.)
14.22
GAS SUPPLY
The usual practice is for the public-service gas company to run its pipes to the
exterior wall of a building, terminating with a brass shutoff valve and gas meter.
The gas piping from the load side of the meter is generally extended to the inside
of the building. From this point, the plumbing contractor or gas-pipe fitter runs
lines through the building to the various fixture outlets. When the pressure of the
gas supplied by the public-service company is too high for the devices in the
building, a pressure-reducing valve can be installed near the point where the line
enters the building. This valve is usually supplied by the gas company.
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14.50
SECTION FOURTEEN
Besides municipal codes governing design and installation of gas piping and
devices, the gas utility serving the area will usually have a number of regulations
that must be followed. Typically, meters are required to be installed outside the
building. The gas supply should not enter the building from below grade unless
certain venting requirements are met, and gas pressure regulators installed inside
the building must be vented to the outdoors. The local authorities and gas utility
should be consulted as to special regulations relating to the installation of the gas
piping system.
14.23
GAS-PIPE SIZES
Gas piping must be designed to provide enough gas to appliances without excessive
pressure loss between the appliance and the meter. It is customary to size gas piping
so the pressure loss between the meter and any appliance does not exceed 0.3 in
of water during periods of maximum gas demand. Other factors influencing the
pipe size include maximum gas consumption anticipated, length of pipe and number
of fittings, specific gravity of the gas, and the diversity factor.
(C. M. Harris, ‘‘Handbook of Utilities and Services for Buildings,’’ McGrawHill Publishing Company, New York.)
14.24
ESTIMATING GAS CONSUMPTION
Use the manufacturer’s Btu rating of the appliances and the heating value of the
gas to determine the flow required, ft3 / hr. When Btu ratings are not immediately
available, the values in Table 14.14 may be used for preliminary estimates. The
average heating value of gas in the area can be obtained from the local gas company,
but when this is not immediately available, the values in Table 14.15 can be used
for preliminary estimates.
Example. A building has two 50-gal storage hot-water heaters and 10 domestic
ranges. What is the maximum gas consumption that must be provided for if gas
with a net heating value of 500 Btu / ft3 is used?
Solution. From Table 14.14,
Heat input ⫽ 2(55,000) ⫹ 10(65,000) ⫽ 760,000 Btu / hr
Maximum gas consumption is therefore 760,000 / 500 ⫽ 1520 ft3 / hr. The supply
piping would be sized for this flow, even though all appliances would rarely operate
at the same time.
(C. M. Harris, ‘‘Handbook of Utilities and Services for Buildings,’’ and H. E.
Bovay, Jr., ‘‘Handbook of Mechanical and Electrical Systems for Buildings,’’ McGraw-Hill Publishing Company, New York.)
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14.51
TABLE 14.14 Minimum Demand of Gas
Appliances, Btu / hr
Appliance
Demand
Barbecue (residential)
Bunsen burner
Domestic clothes dryer
Domestic gas range
Domestic recessed oven section
Domestic recessed top-burner section
Gas engineers, per horsepower
Gas refigerator
Steam boilers, per horsepower
Storage water heater:
Up to 30-gal tank
30- to 40-gal tank
41- to 49-gal tank
50-gal tank
Water heater, automatic instantaneous:
2 gal / min
4 gal / min
6 gal / min
50,000
3,000
35,000
65,000
25,000
40,000
10,000
3,000
50,000
30,000
45,000
50,000
55,000
142,800
285,000
428,400
TABLE 14.15 Typical Heating Values of
Commercial Gases, Btu / ft3
14.25
Gas
Net heating value
Natural gas (Los Angeles)
Natural gas (Pittsburgh)
Coke-oven gas
Carbureted water gas
Commercial propane
Commercial butane
971
1021
514
508
2371
2977
GAS-PIPE MATERIALS
The most common material used for gas piping is black steel pipe conforming to
ASTM A53 or ASTM A106. Malleable-iron or steel fittings should be used, except
for stopcocks and valves. Above 4-in nominal size, cast-iron fittings may be used.
Most plumbing codes require that black steel piping exposed to the elements be
treated to prevent deterioration.
Some local codes permit the use of brass or copper pipe of the same sizes as
iron pipe if the gas handled is not corrosive to the brass or copper. Brazed or
threaded fittings are generally used with these two materials.
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14.52
SECTION FOURTEEN
Polyethylene (PE) and polybutylene (PB) with heat fusion joints and polyvinyl
chloride (PVC) with solvent cement joints are used for outdoor underground installations, since these materials do not corrode and deteriorate as does black steel
piping. If black steel is to be used underground, it must be provided with an exterior
protective coating or tape or a cathodic-protection system, to prevent failure of the
piping due to corrosion.
The usual gas supplied for heating and domestic cooking generally contains
some moisture. Hence, all piping should be installed so it pitches back to the supply
main, or drips should be installed at suitable intervals. Generally, unions or bushings
are not permitted in gas piping systems owing to the danger of gas leakage and
moisture trapping. To permit moisture removal, drips are installed at the lowest
point in the piping, at the bottom of vertical risers at appliance connections, and at
any other location where moisture might accumulate. Figure 14.13 shows typical
drips for gas piping.
14.26
SPRINKLER SYSTEMS
Automatic fire sprinkler systems have been protecting property in the United States
since the late 1800’s; in fact, the Standard for the Installation of Sprinkler Systems,
1896 was the first standard developed by the National Fire Protection Association
(NFPA). Today the NFPA still develops the most widely accepted standards for the
design and installation of sprinkler systems: NFPA 13, Standard for the Installation
of Sprinkler Systems; 20, Installation of Centrifugal Fire Pumps; 24, Installation
of Private Fire Services Mains and Their Appurtenances; 231, General Storage and
231C, Rack Storage of Materials.
While intended to protect and preserve property, automatic sprinkler systems
have other inherent advantages: ‘‘The NFPA has no record of a multiple-death fire
in a completely sprinklered building. . .’’ Given this inherent advantage, the NFPA
has developed a special series of sprinkler standards, NFPA 13D, Sprinkler Systems,
Dwellings and 13R, Sprinkler Systems, Residential Occupancies up to and Including
4 Stories, which are intended to protect life safety, but at significantly less cost than
an NFPA 13 designed system.
FIGURE 14.13 Drips for gas piping.
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14.53
In today’s built environment, automatic sprinkler systems are installed as a result
of minimum building code requirements, local sprinkler ordinances, insurance underwriting stipulations and corporate policy. Consisting of a water supply, horizontal
and vertical water distribution pipes and a series of sprinklers to distribute water
on a fire, sprinkler systems are quite simple (Fig. 14.21). The simplicity of the
sprinkler system is greatly responsible for the historic time tested precedent of
success they have become known for: 96% of all fires that occur in fully sprinklered
buildings are controlled with the operation of two or fewer sprinklers.
In the design of a sprinkler system there are usually four groups of individuals
involved. There are the engineers, responsible for the specification and overall design of the system; Authorities Having Jurisdiction (AHJ’s), these include the local
building and fire official, insurance carrier, etc., who have the final authority over
accepting the design and installation of the system; the building owner; and the
sprinkler contractor, who is responsible for the system installation and is often
called upon to perform engineering design functions as well. Coordination with the
AHJ’s regarding their system design expectations is a crucial step in the design of
a fire sprinkler system. Where there are multiple AHJ’s, conflicts between design
expectations must be reconciled to avoid undue construction delays and ambiguity
for the construction bidders.
14.27
AUTOMATIC SPRINKLERS
In the past fifteen years the variety of sprinklers available has grown tremendously.
Years ago an engineer would simply specify an upright, pendent or sidewall sprinkler, a sprinkler temperature classification and thread and outlet size. Today, sprinkler specification is a much more difficult task. Characteristics such as the Response
Time Index, water spray pattern, (Fig. 14.18) operating component type and appearance must be addressed. While there have been numerous advances in sprinkler
technology, sprinklers still work in the same manner as they did 100 years ago.
Sprinklers are heat sensitive devices, which open to flow water at a preset temperature. More specifically, a sprinkler operating component releases at a specified
temperature. Upon release of the operating component, the sprinkler plug falls from
the sprinkler orifice and water flows through the orifice, hitting the sprinkler deflector and spraying into a predetermined spray pattern and onto the fuel below.
Of sprinkler components the most interesting is the operating component (see
Fig. 14.14). There are two basic types of operating components, the fusible-style
operating component, which is a soldered type element that melts when subjected
to sufficient heat, and the glass bulb operating components, which is an oil containing glass bulb that become pressurized and fails under sufficient heat. For either
type of sprinkler operating component, sufficient heat must be provided over a
sufficient period of time to cause the solder to melt or bulb to fail. Neither the
fusible or glass bulb operating component are better than the other; however, specification of a quick response operating component, available in either fusible or
glass bulb style, will result in faster operating times than a standard response operating component. This is a result of the low mass to surface area ratio of the
quick response operating component as opposed to that of a standard response
operating component. In offices and other light hazard applications quick response
sprinklers have proven superior to standard response sprinklers. As a result, it is a
current code requirement that all light hazard occupancies be protected with quick
response sprinklers.
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14.54
SECTION FOURTEEN
FIGURE 14.14 Fusible style (left) and glass
bulb style (right) sprinklers. (Reprinted with permission from Fire Protection Handbook, Copyright
1997, National Fire Protection Association,
Quincy, MA 02269.)
14.28
TYPES OF SPRINKLER SYSTEMS
The type of system that should be used depends chiefly on the temperature maintained in the building, damageability of contents, expected propagation rate of a
fire, and total fire load.
14.28.1
Wet-Pipe Systems
In the United States the wet-pipe sprinkler system is the most common and affordable sprinkler system available. In consideration of the approximately $1.50 / sqft
installation cost, minimal maintenance costs, and the impressive record for reliability, wet-pipe sprinkler systems should be every engineer’s first choice in sprinkler
protection. The wet-pipe sprinkler system is clearly established as the workhorse
of the fire protection industry.
Unless out of service, wet-pipe sprinkler systems are always water filled. Consequently, building temperature must be maintained above 40⬚F to prevent freezing.
Other than a gate valve and an alarm valve or ‘‘shot-gun’’ riser assembly, there are
no devices between the water supply and sprinklers.
To indicate the flow of water as a result of an operating sprinkler or broken
pipe, a local alarm bell on the exterior of the building being protected is required.
For a wet-pipe sprinkler system this alarm feature is accomplished in one of two
ways. In the past it was more common for engineers to specify the installation of
an alarm-check valve in the main supply pipe, i.e. system riser. The alarm-check
valve (Fig. 14.15) is a swing check valve with an interior orifice that admits water
to an alarm line onto which a water-motor-driven gong is attached. To help differentiate between a water pressure surge and a legitimate water flow, a retard chamber
is often used. The retard chamber acts to delay pressure surges so they subside
prior to causing nuisance alarms. In lieu of a water-motor-gong, and in all cases
on ‘‘slick’’ wet-pipe systems, a vane-type water-flow indicator can be installed and
connected to an electric bell to give notification of water flow. Among the advantages of using a vane-type water-flow switch are that most models include a variable
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14.55
FIGURE 14.15 Alarm-check valve.
time delay to serve as the retard function and they can easily be monitored as a
fire alarm device. Figure 14.15 shows a typical alarm-check valve.
14.28.2
Antifreeze Systems
Where a wet-pipe sprinkler system is installed but small unheated areas such as
truck docks or attics exist, an antifreeze system, normally a subsystem to a wetpipe system, will be employed. In most instances, when the capacity of an antifreeze
system exceeds 40 gallons, the cost of system maintenance becomes prohibitive
and a dry-pipe system is more appropriate.
An antifreeze system consists of an antifreeze U-Loop (Figure 14.16) which
includes an indicating control valve, antifreeze solution test ports and drain connection and a check valve or backflow preventer to restrict the migration of antifreeze from the antifreeze side of a system to the wet-pipe side. Since the waterside
of an antifreeze U-loop is subject to freezing, the U-loop must be located in a
heated area. The operation of a sprinkler on an antifreeze system is identical to that
of a wet-pipe system; however, rather than water flowing from the sprinkler immediately, it is first the antifreeze solution, followed by water. While it may be of
concern, the antifreeze solutions currently permitted by NFPA 13 are tested for
their ability to control fire and they do not detract from the characteristics of water
as an extinguishing medium.
Given today’s increasingly stringent environmental regulations, the installation
of backflow prevention devices are often required on antifreeze systems to prevent
antifreeze from flowing into wet-pipe sprinkler systems and endangering potable
water supplies. The presence of a backflow preventer in an antifreeze system causes
special problems with respect to excess system pressures and where a reducedpressure backflow (RPV) preventer is used, proper maintenance of antifreeze solution concentrations. Where backflow preventers are included in antifreeze system
design, expansion chambers must be used to absorb the excess pressures that may
build up on the antifreeze side of the system. Where RPV’s are employed, the
system owner or person in charge of antifreeze system maintenance must be aware
that the antifreeze system solution may change over time if antifreeze bleeds from
the system through the RPV’s interstitial zone.
14.28.3
Dry-Pipe Systems
In locations where it is impractical to maintain sufficient heat to prevent freezing
and the area is too large to be protected by an antifreeze system, dry-pipe systems
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14.56
SECTION FOURTEEN
FIGURE 14.16 Acceptable antifreeze u-loop configuration. (Reprinted with permission from NFPA 13, Installation of Sprinkler Systems, Copyright 1996, National Fire Protection Association, Quincy,
MA 02269. This reprinted material is not the complete and official
position of the National Fire Protection Association, on the referenced
subject, which is represented only by the standard in its entirety.)
are often specified. A dry pipe system is similar to that of a wet-pipe system;
however, it normally contains air under pressure instead of water. In a dry-pipe
system a normally high water pressure is held back by a normally low air pressure
through use of a differential type dry-pipe valve. This valve employs a combined
air and water clapper (Fig. 14.17) where the area under air pressure is about 16
times the area subject to water pressure. When a sprinkler activates, air is released
to the atmosphere through the sprinkler orifice, allowing the water to overcome the
pressure differential and enter the piping. On smaller systems, riser mounted air
compressors are used to maintain the air pressure such that the dry pipe valve does
not operate as a result of small pressure losses over time. Floor mounted air compressors or plant air systems are typically used for air pressure maintenance on
larger dry pipe systems.
In dry-pipe systems of large capacity, the relatively slow drop in air pressure
when a single head or a few heads are activated is overcome by use of an accelerator
or exhauster. The former is a device, installed near the dry-pipe valve, to sense a
small drop in pressure and transmit the system air pressure to a point under the
valve clapper. The additional air pressure on the bottom side of the clapper causes
it to move into the open and locked position faster than it would otherwise; therefore, water reaches the open sprinklers with less delay.
While a dry-pipe system is intended for use in areas of 40⬚F or less, the drypipe valve must be installed in a heated area or enclosure since there is water in
the piping up to the valve and priming water in the valve itself.
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14.57
FIGURE 14.17 Differential dry-pipe valve: (a ) air pressure keeps clapper closed; (b ) venting of air permits clapper to open and water to flow.
FIGURE 14.18 Typical distribution pattern from a standard spray sprinkler.
(Reprinted with permission from Fire Protection Handbook, Copyright 1997, National Fire Protection Association, Quincy, MA 02269.)
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14.58
SECTION FOURTEEN
The indication of water flow in a dry pipe system is accomplished in a manner
identical to that of the wet-pipe system; however, if the option of the electric bell
is desired a water pressure switch must be employed. Since a dry-pipe system is
normally empty, when a sprinkler operates water rushes into the piping. If a vanetype water-flow indicator were installed, the rushing water could dislodge the vane
and cause an obstruction in the sprinkler piping.
14.28.4
Preaction Systems
Preaction sprinkler systems are used where the presence of water, except in emergencies, is unacceptable or where a dry-pipe system is necessary and the additional
expense of a detection system can be justified. The water in these systems is controlled by a preaction deluge valve, which is operated by an integrated fire alarm
system consisting of heat or smoke detection devices installed throughout the same
area the preaction system protects. There are two basic types of preaction systems:
Single Interlock. These systems admit water to their piping upon actuation of an
associated detection system. Their primary benefit is that system piping or sprinklers can be damaged or removed without accidental water discharge. Single Interlock systems are commonly used in computer rooms and sometimes museums
although wet-pipe systems are normally adequate.
Double Interlock. A combination of a single interlock preaction system and a
dry-pipe system, these are filled with compressed air that is capable of holding the
water pressure at the preaction deluge valve back until the air pressure is released.
Water only enters the piping of a double interlock system after the associated detection system operates and the systems air pressure has been purged. The double
interlock system is most frequently used for the protection of refrigerated cold
storage / freezer warehouses where a false activation would result in frozen pipes
and long periods of business interruption. Often times double interlock sprinkler
systems are wrongly specified for the protection of high dollar areas such as computer rooms, museums, etc., where the protection of wet-pipe systems or single
interlock preaction systems are adequate.
Since preaction sprinkler systems rely on a fire alarm system, and in the case
of the double interlock system, the dry-pipe principle, they are the least reliable of
sprinkler systems and require the greatest amount of maintenance.
14.28.5
Deluge Systems
These systems are identical to that of single interlock preaction systems except
none of the sprinklers have operating components or caps. Like the sprinkler systems depicted in the movies, the operation of a deluge system results in water
flowing from all system sprinklers simultaneously. As with the preaction system, a
preaction deluge valve controls the water in these systems. Since deluge systems
are often installed in harsh environments where smoke or heat detectors are prone
to failure, pneumatic or mechanical means are commonly employed for valve operation. Operation of a pneumatically controlled preaction deluge valve can be by
means of a pilot line of small-diameter pipe on which are spaced automatic sprinkler
heads at suitable intervals. These heads can be augmented when necessary by use
of a mechanical air or water-release device, which operates on the rate-of-rise prin-
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14.59
ciple as well as the fixed temperature of the sprinkler heads. Other pneumatic means
include small copper air chambers, sensitive to rate-of-rise conditions connected by
small-diameter copper tubing to the release mechanism of the valve. In some instances specialized infrared or ultraviolet flame detectors may be used to activate
a deluge system. The nature and extent of the hazard and the surrounding ambient
conditions always determines the kind of detection required.
While a small two or three sprinkler deluge system may be used to protect an
isolated industrial hazard, a large deluge system having as many as one-thousand
sprinklers may protect an aircraft hangar, chemical plant, or a portion of a plant
where process vessels and tanks containing flammable materials are located. Deluge
systems are only justified for the protection of areas where the probability of a fire
is likely and the fire growth potential is extreme.
14.28.6
Outside Sprinklers
The types of sprinkler systems referenced above are intended for fire control and
on a limited basis fire suppression; however, sprinklers can also be used for exposure protection. In instances where buildings are located too close to one another
or to an adjacent fire hazard, such as a combustible liquid storage tank, a ‘‘hybrid’’
sprinkler system can be specified to prevent the spread of fire from a fire area to
an exposed building. Such systems have open nozzles directed onto the wall, windows, or cornices to be protected. The water supply may be taken from a point
below the inside-sprinkler-system control valve if the building is sprinklered, otherwise from any other acceptable source, with the controlling valve accessible at
all times. The system is usually operated manually by a gate valve but can be made
automatic by use of a deluge valve actuated by suitable means on the exposed side
of the building. The distribution piping is usually installed on the outside of the
wall with nozzles provided in sufficient numbers to wet the surface to be protected.
14.29
14.29.1
SYSTEM DESIGN
Establishing Pipe Sizes and Water Supply Acceptability
In the past, pipe schedules were the accepted method of determining the adequacy
of system pipe sizes; however, the current standards no longer recognize the pipeschedule method for new construction. The accepted method for the determination
of pipe sizes and water supply adequacy is the performance of hydraulic calculations as outlined in NFPA 13.
The installing contractor may perform hydraulic calculations if qualified, but
there is significant advantage to the engineer performing the hydraulic calculations
and establishing pipe sizes and water supply acceptability before the bidding process begins. In performing hydraulic calculations, the sprinkler piping layout, nature
of the hazard protected and water supply information must be known. Based on
this information the area of sprinkler operation, appropriate design density and
minimum sprinkler pressures can be used to perform the necessary hydraulic calculations. While it is beyond our scope to further describe the hydraulic calculation
procedure an excellent resource is Fire Protection Hydraulics and Water Supply
Analysis, by Pat Brock, published by Fire Protection Publications of Oklahoma
State University.
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14.60
14.29.2
SECTION FOURTEEN
Sprinkler Piping
There are numerous types of sprinkler piping currently accepted for the installation
of sprinkler systems. In all cases the piping specified for a sprinkler system must
be installed and used within the parameters of its U.L. Listing.
Most sprinkler piping specified today is black or galvanized, welded and seamless steel pipe. Normally smaller pipe sizes are specified as Schedule 40 and larger
sizes as Schedule 10 black steel pipe. The joining methods for sprinkler pipe include
the use of flanged fittings, prefabricated welded outlets, cast or malleable iron fittings or mechanical grooved fittings. In all cases, sprinkler pipe and fittings must
be capable of withstanding pressures of 175 psi. For further details NFPA 13 and
pipe manufacturer catalogs should be consulted.
Areas Protected by Sprinklers. To provide a fully sprinklered building, which is
the intent of most building codes and insurance industry sprinkler requirements, all
areas of a structure, with few exceptions, must be provided sprinkler protection.
Generally, all spaces that are accessible, combustible or intended for storage or
occupancy require sprinkler protection. The guidelines for permissible sprinkler
omissions in fully sprinkled buildings are contained in NFPA 13. Except for void
spaces in walls and noncombustible concealed spaces there are few exceptions and
where exceptions do exist they are extremely specific with respect to accessibility,
construction and dimensions.
With respect to individual sprinkler spacing requirements, the maximum area
protected by one sprinkler should not exceed the area specified for the specific
sprinkler as indicated in the manufacturer’s specification sheets. Standard spray
sprinklers are listed for light hazard, ordinary hazard and extra hazard occupancies
for 225-, 130- and 100-2 protection areas, respectively.
In most installations, the area or coverage of each sprinkler is usually less than
the maximum areas listed.
14.29.3
Sprinkler Position
In areas where construction is unobstructed, sprinkler deflectors should be parallel
to and within 12 inches of the ceiling. Where construction is obstructed sprinklers
must be within 22 inches of the roof deck above. In all cases, when locating sprinklers the maximum expected ambient temperature of the area being protected must
be considered such that unwanted sprinkler activation does not occur.
Undesirable sprinkler water spray obstructions must also be considered when
locating sprinklers. Where obstructions such as ducts are greater than 4 feet wide
and are located below sprinklers, additional sprinklers should be added to spray
below the obstruction. Furnishings such as tables are not considered obstructions
unless they are within 18-inches, measured vertically of a sprinkler. When locating
all sprinklers NFPA 13 and the sprinkler manufacturer’s guidelines must be followed to prevent unwanted water spray obstructions.
Sprinkler System Layout. A sprinkler system is generally laid out as a ‘‘Tree’’,
‘‘Loop’’ or ‘‘Grid’’ type system. Whatever the case, sprinklers are attached directly
to pipes called branch lines. Branch lines, normally the smallest of sprinkler pipes,
are supplied water from cross mains or feed mains which are directly connected to
the system riser.
The riser, configured to control the water supply and monitor water flow and
valve position, may support a single sprinkler system or if manifolded, many sys-
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14.61
tems (Fig. 14.19). In any case, the maximum area per floor to be protected by a
single riser is 52,000-2 for light and ordinary hazard areas and 40,000-2 for extra
hazard areas.
In high-rise buildings where standpipes and sprinklers are required a combined
standpipe / sprinkler system is normally used. In these situations there may be no
true system riser; rather, each floor is provided with a floor control valve (Fig.
14.20) consisting of a control valve, drain, test connection and flow switch. In this
configuration the individual floor control valves accomplish the function of the
system riser. An inherent advantage of using floor control valves is that individual
floors can be isolated so sprinkler system repairs on one floor do not reduce the
level of protection on another floor.
As a practical matter, when lying sprinkler piping out it is advantageous to
consider the pipe hanging arrangement. Where construction consists of joist construction, mains should be run parallel to the joist channels. This accommodates
FIGURE 14.19 Single riser (left), manifold system with multiple risers (right).
FIGURE 14.20 Floor control valve. (Reprinted with permission from
NFPA 13, Installation of Sprinkler Systems, Copyright 1996, National
Fire Protection Association, Quincy, MA 02269. This reprinted material
is not the complete and official position of the National Fire Protection
Association, on the referenced subject, which is represented only by the
standard in its entirety.)
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14.62
SECTION FOURTEEN
FIGURE 14.21 Water-supply piping for sprinklers.
pipe hanging since the branch lines, which out number the mains, can be hung
directly off the joists. Where construction is concrete pipe hanging is an easier task
but one should give consideration to the arrangement of beams and bays such that
unnecessary fittings and pipe lengths can be avoided.
Drainage of Sprinkler Systems. Provisions must be made for draining all parts
of a sprinkler system. For that purpose, valve-controlled drains must be provided
at low points in the system. The primary drain for most sprinkler systems is the
main drain, normally a 2 inch drain located at the system riser. All drains should
discharge directly to outdoors or to a sump capable of handling full flow drain
capacity.
Special consideration must be given to the drainage of dry-pipe systems and
portions of preaction systems subject to freezing. The branch lines of these systems
should be pitched 1⁄2 in per 10 feet and mains 1⁄4 inch per 10 feet of length towards
a suitable drain connection to accommodate total system drainage. Where trapped
piping in dry-pipe systems exceeds 5 gallons capacity, a means must be provided
to drain the trapped area without accidentally tripping the dry-pipe valve. This is
usually accomplished with use of a drum drip assemble, an assembly which permits
isolating trapped water and draining it without loosing air pressure.
Inspector’s Test Connections. All sprinkler systems should be tested periodically
to ensure their proper function. A test connection for wet- and dry-pipe systems
consists of a connection at least 1 inch in diameter with a test valve terminating in
a smooth-bore, corrosion-resistant orifice. This orifice connection should be sized
to provide a test flow equivalent to the smallest orifice size sprinkler installed in
the system. For most systems the test valve connection can be located anywhere
down stream of the alarm valve or flow switch, whichever is provided; however,
on dry-pipe and double-interlock preaction systems the alarm test valve must be
located at the hydraulically remote point of the system. This is to ensure that water
will reach the remote end of the sprinkler system without undue delay, usually 60
seconds for large systems.
Approvals of Sprinkler-System Design. In all cases, before a sprinkler system is
installed or modified, the applicable drawings and hydraulic calculations should be
submitted to the authority having jurisdiction and the insurance underwriter as nec-
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14.63
essary. Since beneficial reductions in insurance rates may be obtained by suitable
installation of sprinkler systems, it is important that the underwriter have sufficient
time for a full review of the plans before construction begins. Similarly, municipal
approval of the sprinkler-system plans is necessary before the structure can be
occupied. In actual construction, the installing contractor generally secures the necessary municipal approval. The existence of this approval should always be confirmed before construction starts.
14.30
STANDPIPES
Standpipes, hose valve connections supplied with water from a piping system that
is always under pressure or can be rapidly supplied with water under pressure are
the usual means through which firefighters are provided water to fight interior fires
in large buildings such as malls and high-rises. NFPA 14, Standpipe, Hose Systems,
is the recognized standard for the installation and design of standpipe systems.
Today, most standpipes installed are intended for use by the fire department; however, some are designed for occupant use. As with sprinkler systems, building codes
generally dictate when and where standpipes are required.
14.30.1
Class of Service
Standpipe systems are classified into the following types:
Class I. For use by fire department personnel only. These systems are provided
with 21⁄2-inch hose valves located in building stairwells and other protected areas.
Water supplies permit two hose streams to be fed simultaneously from a single
riser. Each stream provides 250 gal / min at a minimum pressure of 100 psi.
Class II. For occupant use only. Provided with 11⁄2-inch hose valves and hose
racks with a minimum 100-feet length of 11⁄2 hose, these standpipes are located in
a building such that all areas of a building are within 130-feet of a hose valve (100feet of hose plus 30-feet of water spray). It should be noted that most authorities
having jurisdiction no longer permit hose to be attached to Class II systems since
it is felt that the best option for occupants who are not trained in fire fighting
procedures is to evacuate the building and report the emergency situation.
Class III. A combination of Class I and Class II systems with both 21⁄2-in hose
valves and 11⁄2-in hose valves and hose racks with 100 ft of hose, installed as
required for a Class I and Class II system. The calculated water supply at an outlet
is the same as for a Class I system.
Riser Sizes. Standpipe pipe sizes can be established based on the performance of
hydraulic calculations or for low rise buildings the NFPA 14 Pipe Schedule System,
with the hydraulic procedure being the preferred method. The hydraulic calculations
for a Class I system are based on flowing 500 gpm at 100 psi at the most remote
standpipe and 250 gpm at the top hose connection of all other standpipes with a
total not to exceed 1250 gpm.
Maximum Pressure. Standpipe systems should be designed so the maximum gage
pressure at the inlet of any Class I hose connection does not exceed 175 psi and
Class II hose connection, 100 psi. Where pressures exceed 175-psi, pressure-
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14.64
SECTION FOURTEEN
limiting devices must be installed. Engineers must be extremely cautious in specifying pressure-limiting devices as they are frequently specified improperly.
14.31
WATER SUPPLIES FOR SPRINKLER AND
STANDPIPE SYSTEMS
Water supplies for sprinkler and standpipe systems must be reliable. When a municipal water supply has been identified as unreliable or incapable of meeting the
demand of a sprinkler or standpipe system, fire pumps and water storage tanks or
reservoirs may be required. Even in instances where a water supply is reliable and
the protected area is of high value, a secondary water supply employing water tanks
and fire pumps is often provided.
In determining the size and elevation of tanks, site conditions should be of
primary concern. Often times water storage tanks can be located advantageously at
the higher elevations of a property. Other times penstocks, flumes, rivers or lakes
may serve as a water supply. In these cases approved strainers must be provided
on the water supply inlets to prevent obstructions from entering system piping. In
all cases, whether the water supply is from a municipal source or raw source as
described above, consideration must be given to the potential effects of Microbiological Influenced Corrosion (MIC) which can rapidly damage sprinkler piping.
While water supply adequacy is heavily reliant on the presence of sufficient flow
and pressure, water supply duration is also important. For sprinkler systems the
minimum water supply duration is 30, 60 and 90-minutes for light, ordinary and
extra hazard areas, respectively. Standpipe water supply duration is 30-minutes.
Water supply duration is mandated to ensure that adequate time is available to
achieve fire control.
Fire Department Connection. With the exception of small sprinkler systems, all
sprinkler and standpipe systems must be provided with a fire department connection
(FDC). The FDC, often referred to as the siamese connection, is a means through
which fire hoses may be connected to a system to support the hydraulic requirements of the system to which it is attached. In most cases, the FDC is a backup
water supply. It should be noted that often times the FDC for standpipes in lowrise buildings is the only source of water supply. These systems are referred to as
manual standpipes. Before specifying a manual standpipe the AJH should be consulted.
Depending on the AJH, FDC’s may be installed on a side of a building or they
may be free standing. Whatever the case, the FDC should be 18- to 36-inches above
grade, and within clear sight of a fire department access-way. To speed fire ground
operations it is good practice to locate FDC’s within 75 feet of a fire hydrant. In
addition, high rise buildings should be provided with two remotely located FDC’s.
While not a code requirement, as a rule of thumb, for each 250-gpm required, as
determined in the hydraulic calculations, one 21⁄2-inch FDC outlet should be provided. For a 600-gpm-system demand three 21⁄2-inch FDC outlets should be provided.
As it is becoming common place for fire departments to use quick connecting
FDC’s, Stortz Connections, and since the fire department is the FDC end user, in
all cases the local fire official should be consulted regarding FDC type and location.
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14.32
14.65
CENTRAL STATION SUPERVISORY
SYSTEMS
Any mechanical device or system is more reliable if it is supervised or monitored.
Sprinkler systems are designed to be rugged and dependable as shown by their
impressive performance record; however, reliability improves where systems are
monitored by an approved central-station supervisory service for valve position
(open or closed) and water flow switch status.
A central station monitors the equipment specified by the engineer and provided
by the contractor and transmits appropriate signals over leased telephone lines or
other approved methods, to a constantly attended location. When a signal is received
at the central station, no matter what hour, the fire department and any other preestablished emergency contacts are summoned. When notification of a closed valve
is provided, the building owner or other acceptable contact should investigate, but
notification of water flow should always result in fire department dispatch.
Monitoring services are available across the country and are arranged by contract, usually with an installation charge and a monthly maintenance fee. Requirements for such systems are in NFPA 72, National Fire Alarm Code. Where no such
service is available, a local or proprietary substitute can be provided.
14.33
ADDITIONAL INFORMATION
Developing proficiency in the proper design and specification of fire sprinkler systems is extremely tedious. While sprinkler system design is admittedly a small
portion of the engineering design package for a construction project, the implications of inadequate system design are more than severe. There have been numerous
cases where engineers have been named in lawsuits relating to improperly designed
automatic sprinkler systems. To obtain additional information regarding the proper
design and installation of automatic sprinkler systems the NFPA or Society of Fire
Protection Engineers (SFPE) are excellent resources. In addition, to display your
proficiency in the field of fire protection engineering, registration as a fire protection
engineer is available in most states.
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