Plumbing Fundamentals PDF

 PLUMBING FUNDAMENTALS 12.1 BUILDING PLUMBING SYSTEMS Tidbits from Plumbing History Nearly 4000 years ago, the ancient Greeks had hot and cold water systems in buildings. The Minoan Palace of Knossos on the isle of Crete had terra cotta (baked clay) piping laid...

 PLUMBING FUNDAMENTALS 12.1 BUILDING PLUMBING SYSTEMS Tidbits from Plumbing History Nearly 4000 years ago, the ancient Greeks had hot and cold water systems in buildings. The Minoan Palace of Knossos on the isle of Crete had terra cotta (baked clay) piping laid beneath the palace floor. These pipes provided water for fountains and faucets of marble, gold, and silver that offered hot and cold run- ning water. Drainage systems emptied into large sewers con- structed of stone. Surprisingly, although hot and cold water systems were in place, for the Spartan warrior it was unmanly to use hot water. The first storm sewers of Rome were built about 2800 years ago. Over 2000 years ago, the Romans had in place highly developed community plumbing system in which water was conveyed over many miles by large aqueducts. Water was then distributed to residences in lead pipes. By the 4th century C.E., Rome had 11 public baths, over 1300 public fountains and cisterns, and over 850 private baths. The Roman plumber was an artisan who worked with lead. Both male and female plumbers soldered, installed, and repaired roofs, gutters, sewers, drains, and every part of the plumbing supply, waste, and storm drainage systems. The term plumbing is derived from the Latin word plumbum for lead (Pb). Historians theorize that lead leaching into drinking water from water supply pipes and lead from other sources poisoned the Roman aristocracy, contributing to the decline of the Roman Empire. King Minos of Crete owned the world’s first flushing water closet with a wooden seat and a small reservoir of water, over 2800 years ago. In the Far East, archaeologists in China re- cently uncovered an antique water closet in the tomb of a king of the Western Han Dynasty (206 B.C.E. to 24 C.E.). It was complete with running water, a stone seat, and a comfortable armrest. The decline of the Roman Empire and an outbreak of deadly bubonic plague that killed an estimated one-third of the European population during the Middle Ages resulted in the decline of public baths and fountains. The period from 500 to 1500 C.E. was a dark age in terms of human hygiene; commu- nity plumbing became almost nonexistent. At the end of the Middle Ages, London’s first water system was rebuilt around 1500. It consisted partly of the rehabilitated Roman system with the remainder patterned off of the Roman’s design. Pumping devices have been an important way of moving fluids for thousands of years. The ancient Egyptians invented water wheels with buckets mounted on them to move water for irrigation. Over 2000 years ago, Archimedes, a Greek mathe- matician, invented a screw pump made of a screw rotating in a cylinder (now known as an Archimedes screw). This type of pump was used to drain and irrigate the Nile Valley. The beginnings of modern plumbing began in the early 1800s, when steam engines became capable of supplying water under pressure and inexpensive cast iron pipes could be produced to carry it. Still it was considered unhealthy to bathe. In 1835, the Common Council of Philadelphia nearly banned wintertime bathing (the ordinance failed by two votes). Ten years later, Boston prohibited bathing except on specific medical advice. Finally, it was through observation of several cholera epi- demics in the mid-1800s that epidemiologists finally recog- nized the link between sanitation and public health. This discovery provided the thrust for modern water and sewage sys- tems. In 1848, England passed the national Public Health Act, which later became a model plumbing code for the world to follow. It mandated some type of sanitary disposal in every res- idence such as a flushing toilet, a privy, or an ash pit. In America, like Europe, colonial hygiene and sanitation were poor. Colonial bathing consisted of infrequent baths in ponds or streams. New World settlers emulated the Native Americans’ discharge of waste and refuse in running water, open fields, shrubs, or forests. As in Europe, colonials living in town would empty their chamber pots by tossing excrement out the front door or window onto the street. As early as 1700, local ordinances were passed to prevent people from throwing waste in a public street. Eventually, use of the privy or outhouse slowly became accepted. Drinking water in colonial America came from streams, rivers, and wells. It was commonly believed at the time that foul- tasting mineral water had medicinal value. Around the time of the American Revolution, Dr. Benjamin Rush, a signer of the Declaration of Independence and surgeon general under George Washington, had the bad fortune of having a well with horribly tasting water at the site of his Pennsylvania home. Townspeople rushed to his well to get drinking water in hopes that its medicinal value would cure ailments. Unfortunately, when Dr. Rush’s well dried out from overuse, it was discovered too late that the well was geologically connected underground to the doctor’s privy. 393  PLUMBING FUNDAMENTALS 3 Boston and later New York built the country’s first water- works to provide water for firefighting and domestic use about 1700. The wooden pipe system, laid under roads, provided water at street pumps or hydrants. Water pipes were made of bored-out logs. Wooden pipes were common until the early 1800s, when the increased pressure required to pump water into rapidly expanding streets began to split the pipes. In 1804, Philadelphia earned the distinction as the first city in the world to adopt cast iron pipe for its water mains. Chicago is credited with having the first comprehensive sewerage project in the United States, designed in 1885. Inside running water and toilets were not common in the U.S. home until well into the mid-1900s. The Census of 1910 indicated that only about 10% of American homes had inside running water. Farms during that time relied on well water, with many powered by hand pumps and windmills. Modern Plumbing Systems Water supply system consists of the piping and fittings that supply hot and cold water from the building water supply to the fixtures, such as lavatories, bathtubs, water closets, dishwashers, clothes washers, and sinks. Sanitary drainage system or drain, waste and vent (DWV) system waste disposal system consists of the piping and fittings required to take that water supplied to the fixtures out of the building and into the sewer line or disposal field. This system is typically referred to as a. Wastewater treatment is also an important component of waste disposal from building plumbing systems. Although most buildings rely upon district or community water treatment plants to dispose of their sewage, some buildings and facilities operate their own operations. These are generally known as septic or on-site sewage treatment (OSST) systems. Plumbing system is a network of pipes, fit- tings, and valves that carry and control flow of supply water and wastewater to and from points of use known as fixtures: Fixtures are components, receptacles, or pieces of equipment that use water and dispose of wastewater at the point of water use. Piping is a series of hollow channels that carry water to and wastewater from plumbing fixtures. Fittings are used to connect lengths of pipe in the piping network. Valves are used to regulate or control flow of water. Water is the name given to the liquid compound H2O. A molecule of water is composed of one oxygen atom and two hydrogen atoms. In a pure state, it is tasteless and odorless. Under standard atmospheric pressure (14.696 psi, 101.04 kPa), the boiling point temperature of water is 212°F (100°C). Fundamental Units The following are definitions of the fundamental units. Specific Weight (Density) Specific weight (w) or density is weight per unit volume. Water density varies with temperature; it is most dense at 39°F (4°C). Below this temperature, crystals begin to form, increasing its volume and therefore decreasing its density Specific Gravity The specific gravity (s.g.) of a fluid or solid is the ratio of the specific weight of the fluid or solid to the specific weight of water at a temperature of 39°F (4°C), the temperature at which water is most dense (62.42 lb/ft3 or 1.00 kg/L). It is a compari- son of its weight with the weight of an equal volume of water. Materials with a specific gravity less than 1.0 are less dense than water (e.g., oil) and will float on pure water; substances with a specific gravity more than 1.0 are denser than water and will sink. The specific gravity of water is assumed to be 1.0 at common plumbing system temperatures. Volume Volume (V) is the amount of space occupied by a substance. Water volume is typically expressed in cubic inches (in3) or cubic feet (ft3) in the customary system, and in cubic meters (m3) or liters (L) in the SI system. In plumbing system design, volume is commonly expressed in gallons (g or gal). There are 7.48 gallons in a cubic foot (ft3). A gallon is approximately 3.8 L. Volumetric Flow Rate Volumetric flow rate (Q), frequently called the flow rate, is the volume of a substance that passes a point in a system per unit of time.  4 CHAPTER 12 Velocity Velocity is the rate of linear motion of a substance in one direction. The magnitude of velocity, known as speed, is usually expressed in terms of distance covered per unit of time. In a fluidic system such as a plumbing system, water velocity is expressed as an average velocity because water molecules each have different speeds and directions of travel; Average velocity (v) of a fluid (such as water) flowing through a pipe may be found by the following equations based upon average volumetric flow rate (Q) and cross-sectional area or inside diameter (Di). Pressure Pressure (P) is the force per unit area exerted by liquid or gas on a surface such as the sidewall of a container or pipe. Although units of lb/in2 are dimensionally correct, the acronym “psi” will be used for pounds per square inch of gauge pressure because it is universally accepted in the plumbing industry. The acronym “psia” will be used for absolute pressure. Standard atmospheric pressure (Ps) is the typical barometric pressure of air at sea level and 70°F (21°C). It is equal to 14.696 psia (101 325 Pa). Atmospheric pressure varies with weather conditions and elevation. In Denver, Colorado, atmospheric pressure is about 11.8 psia because Denver is about a mile above sea level; it is above about 20% of the earth’s atmosphere. Gauge pressure (Pg) is the pressure of a fluid (gas or liquid) excluding pressure exerted by the atmosphere. Pressure can be expressed in terms of absolute and gauge pressure: Absolute pressure (Pa) is the pressure of a fluid (gas or liquid) including pressure exerted by the atmosphere: 12.2 WATER SUPPLY Water Sources Potable is clean water that is suitable for human drinking. It must be available for drinking, cooking, and cleaning. Non-potable water may be used for flushing water closets (toilets), irrigating grass and gardens, washing cars, and for any use other than drinking, cooking, or cleaning. Vacuum pressure or a suction pressure when a pressure in a system is below atmospheric pressure, it is called. It is expressed as a negative gauge pressure. Saturation vapor pressure is the pressure that water vapor molecules exert when the air is fully saturated at a given temperature. Saturation vapor pressure is directly proportional to the temperature: it increases with rising temperature and falls with decreasing temperature. In plumbing systems there are three additional classifications of pressure: ✓ Static pressure is the pressure that exists without any flow. It is the pressure available at a location in the system. ✓ Residual pressure is the pressure available at a fixture or outlet during a period of maximum demand. It is the pressure that exists after pressure losses from friction from water flow, elevation change, and other pressure losses in the system are subtracted. ✓ Discharge pressure is the pressure of the water at the point of discharge, such as at the mouth of a show- erhead, faucet, or hose bibb. The constituent gases that make up a mixture of gases such as air each exert a partial pressure that contributes to the total pressure exerted by the gas mixture. For example, atmos- pheric air consists of about 75% nitrogen, by weight, so 75% of the total pressure exerted by atmospheric air is from the nitro- gen constituent. Water vapor pressure is the pressure that the water vapor molecules alone exert in air. It is based on the amount of water vapor that exists in the air. Surface water is the rain that runs off the surface of the ground into streams, rivers, and lakes. Groundwater is water found below the surface of the earth. It is water that has percolated through porous soil until it reaches an impervious stratum, upon which it collects. Surface Water Surface water readily provides much of the water needed by cities, counties, large industry, and others. Reservoirs hold surface water during periods of high runoff and release water during periods of low runoff. Surface water can be collected in a storage tank called a cistern. PLUMBING FUNDAMENTALS 5 Groundwater Groundwater seeps through the soil and is trapped on impervious stratum, a layer of soil or rock that water cannot pass through. Aquifer is a saturated permeable stratum capable of providing a usable supply of water. Water table is the level of groundwater is referred to as the. Water table depth. distance from the ground surface to the water table. Artesian well if the water pressure is released by drilling through the top stratum or through a natural opening in the stratum, the water will be forced upward creating an Drinking Water Standards The Safe Drinking Water Act (SDWA) was originally passed by Congress in 1974, and amended in 1986 and 1996. Its purpose is to protect public health by regulating the nation’s public drinking water supply. National Primary Drinking Water Regulations are legally enforceable mandatory standards that apply to public water systems and that protect public health by limiting the levels of contaminants in drinking water. National Secondary Drinking Water Regulations are guidelines regulating contaminants that may cause undesirable cosmetic effects (such as skin or tooth discoloration), aesthetic effects (e.g., taste, odor, or color) and other characteristics (e.g., corrosivity, pH) in drinking water. Water Treatment Water quality and taste vary considerably from place to place, depending on the water source of the area, the chemical and bacteria contents of the water, and the amount and type of treatment given the water before it is put into the system. Several methods are used to improve water quality and taste: Problems with undesirable taste and odor are overcome by use of filtration equipment or by aeration of the water. Bacteria are destroyed by the addition of a few parts per million of chlorine. The taste of chlorine is then re- moved with sodium sulfite. Suspended organic matter that supports bacterial life and suspended mineral matter are removed by the addition of a flocculating and precipitating agent, such as alum, before settling or filtration. Excessive hardness, which renders the water unsuitable for many industrial purposes, is reduced by the addition of slaked, or hydrated, lime or by an ion-exchange process. In addition to treating water for quality and taste, artificial fluoridation of public water is done in many U.S. communities. It is an established method of reducing tooth decay in children. In the desalination process, saline (salt) is removed from water (e.g., seawater) thereby making the water potable. Water Use Traditionally, water use rates are described in units of gallons per capita per day (gpcd) or liters per capita per day (Lpcd). Of the potable water supplied by public water systems, only a small portion is actually used for drinking. Use of Gray Water Another approach to conserving potable water is a water reuse system. This system, known as a gray-water system, involves the processing of household wastewater for reuse. Community water supply systems are public or private entities that install and provide a central supply of water to a neighbor- hood, city or special district. Water meters are required in all community systems that charge for water usage or in systems where water consumption must be monitored. Well Systems A modern well system consists of a well, a motor-driven pump, and a storage tank Types of Wells  6 CHAPTER 12 Wells are classified according to their depth and the method used to construct the well: Classification Depth Construction Method Shallow Less than 25 ft Dug, driven, and (7.6 m) in depth shallow bored Deep 25 ft (7.6 m) or Drilled and bored more in depth There are three common types of water wells: dug driven bored/drilled( most common type for private water supply) Dug Wells Dug wells are shallow wells, generally not more than 25 ft (7.6 m) deep, and typically 3 to 6 ft (1 to 2 m) in diameter. They are typically made by excavation with a backhoe or excavator but can be hand shoveled. Driven wells, also referred to as sand point wells, consist of lengths of 11⁄4 to 2 in (32 to 50 mm) diameter pipe that is driven into the ground. In driving this type of well, a sharp well point and drive cap are attached to a pipe. Drive cap allows the assembly to be driven into the earth without the pipe end being damaged. The assembly is driven into the ground until the well point extends below the water table. As the well point is driven, additional lengths of pipe may be attached (usually 5 ft [1.5 m] lengths are used) to the assembly by the use of a coupling. Well point is a pointed perforated pipe or a pipe with a pointed well screen that allows water to be sucked up the pipe to the surface by a shallow well pump. Drilled/Bored Wells A well-drilling rig is used to create the well hole. Drilled wells have the holes formed by using rotary bits. Bored wells have the holes formed by using an auger and covered with a casing. Only the drilling method is effective in cutting through hard rock. Drilled wells typically have holes 200 feet or more in depth. Shallow wells may have to be bored or drilled if it is necessary to pass through rock to reach the water table. Well shaft, or borehole, is lined with a solid pipe that seals out contaminants and stabilizes the hole During drilling or boring a hole, a pipe-like casing is lowered into the hole. This pipe is usually 4 to 6 in (100 to 150 mm) in diameter in sections with threaded or welded joints that must be watertight. Wellhead is the top of the well, the part that rises above the surface of the soil. Usually, at least 12 in of casing must extend above the soil line, which is capped, then stabilized with a concrete slab. The slab slopes outward, and extends at least 2 ft on all sides. To seal off that channel the space between the casing and soil is filled with a mixture of gravel and cement called grout. To protect the inside of the casing, the driller installs a tight-fitting well cap. To further protect against surface drainage and contamination, a concrete apron, sloping away from the well, is generally cast around the casing at the ground surface. Well Pumps Pumps are used to bring well water to the surface. Well pumps are referred to as shallow well and deep well, depending on the type and depth of well. Pumping level, expressed in feet or meters, is the vertical distance between the pump and the lowest water level, taking into account level draw down by pumping and lower levels during dry seasons. Most well pumps are powered on 120 or 240 V AC single-phase electricity. There are two general types of well pumps: submersible well pumps and jet pumps. Well Jet Pumps The well jet pump combines centrifugal and ejection pumping. In addition to a motor, impeller, and diffuser, the jet pump includes a jet (ejector) assembly that consists of a nozzle and venturi tube. Jet pumps are self-priming, but priming (manually filling with water) prior to initial use is required for the pump to operate. PLUMBING FUNDAMENTALS 7 Shallow well jet pumps are used for wells with a pumping level up to 25 ft (7.6 m) deep, which is the pump’s suction lift limit. It has no working parts submerged in water. The jet assembly is located on the suction side of the pump impeller. Water is supplied to the nozzle under pressure from the pump. As the drive water moves through the nozzle and venturi, a partial vacuum is created, drawing more water from the well up the suction pipe. A portion of the water is directed to the discharge outlet for the distribution system; the rest is recirculated to the ejector. Deep well jet pumps can be used for wells with a pumping level up to 120 ft (37 m) deep. It works the same as the shallow well type but with the jet assembly located in the well 10 to 20 ft (3 to 9 m) below water table level. Submersible well pumps are centrifugal pumps designed to operate submersed in water near the bottom end of the well shaft. It is typically used in wells with a pumping level of at least 75 ft (23 m) deep. Centrifugal pumps work by using their rotation of impellers to push water outward and then upward through the well shaft. A small electric motor, called a driver, is installed in the well shaft, usually below the pump itself. An electric cable is at- tached to the pump’s motor. Well Tanks Water drawn from a well is pumped into a storage tank where it is stored for use by building occupants. Elevated storage tanks are discussed later in this chapter. A typical utility-powered well system consists of a pump delivering water into a pressure tank. A pressure tank is a type of closed storage container designed to store water under pressure. In a well system, a pres- sure tank is used to hold water under pressure after it is pumped to ensure steady water pressure in the building. This type of tank is divided into two internal compartments by a flexible diaphragm or bladder. In the diaphragm pressure tank, the diaphragm separates the water storage section from a pressurized air chamber. In the bladder design, a balloon-like bladder holds pressurized air. The pressurized chamber is charged with air, which applies a force against the water, inducing and maintaining a consistent pressure in the stored water. The bladder or diaphragm separate the pressurized air from the water pumped into the tank. A pressure tank stores the energy the pump has produced in the form of pressure. Air is compressed in the pressurized air chamber. When water is drawn from a plumbing fixture, the pressure in the tank is released in the form of water flow. After about a third to half of the tank capacity is drained, a device called a pressure switch turns the pump on to restore the pres- sure in the tank. When the pressure in the tank reaches an upper limit, usually about 50 psi (340 kPa), the pump cycles off. The pressure is stored in the tank until it is needed again. A pressure tank will hold storage water on reserve under pressure so small demands do not require the pump to switch on. It extends the time between pumping cycles and therefore prolongs the life of the pump and motor. The tank must be pro- tected from freezing by locating it in a pump house or base- ment, or by burying it in a pump pit below the frost line. Well Design and Installation yield or capacity of the well is the maximum flow rate of water drawn from a well is referred to as the; it is expressed in gpm or L/m. A well yielding 10 gpm provides five times the water, as does a well yielding 2 gpm. Water demand is the amount of water required to meet the demands of the building served by the well system. equipment can be designed and space allowed in the de- sign of the project to locate the tank and equipment. Where insufficient information on well yields is available, and espe- cially where large projects will require substantial water sup- plies, it may be necessary to have test holes made so that the yield can be checked. When a large supply of water is required for the continuous operation of the project, it may be necessary to put in other wells to be certain that the water yield will be sufficient to meet the pro- jected demand. For example, if one well provides adequate water, it may be a good investment to have a second well put in to act as a backup in case the first well should fail. A backup well is usu- ally not required for residences. However, for industries or busi- nesses that require large amounts of water such as a car wash, farm, or apartment complex, it is a wise investment. When more than one well is required, the wells must be spaced so that the use of one well will not lower the water table in the other well. In general, deep wells must be 500 to 1000 ft (150 to 300 m) apart, while shallow wells must be 20 to 100 ft (6 to 30 m) apart. Because of geological variables, the minimum distance between wells can be determined only by testing. Water Towers and Elevated Storage Tanks Water towers used in community systems and elevated water storage tanks used in private systems carry a reserve capacity of water. They serve many additional purposes, including what follows: To introduce pressure to the water supply system 8 CHAPTER 12 To equalize supply and demand over periods of high consumption To supply water during equipment failure or maintenance To supply water for firefighting demand A water tower must be tall enough to deliver adequate pressure to all of the houses and businesses in the area of the tower. Each foot of water height provides 0.433 psi (pounds per square inch) of pressure. (This is discussed in Chapter 13.) A typical community water supply maintains pressures between 50 and 100 psi (344 and 688 kPa), whereas plumbing fixtures require 8 psi (55 kPa) to 30 psi (206 kPa). An example of a pri- vate water tower is shown in Photo 12.1. Water in a water tower tank must be 100 to 200 ft (30 to 60 m) above the highest plumbing fixture being served. There- fore water towers are typically located on high ground, and they are tall enough to provide the necessary pressure. In mountainous regions, a ground-level water storage tank or reservoir located on the highest hill in the area can sometimes substitute for a water tower. The capacity of a community water tower for even a small community is quite large; normally it will hold 1 000 000 gal (3 800 000 L) or more. In comparison, a typical in-ground resi- dential swimming pool might hold 20 000 gal (76 000 L). The tank of the water tower is typically sized to hold about two days of water supply. If the pumps fail during a power failure or are down for maintenance, stored water provides an adequate sup- ply under pressure. The extra supply also serves as a reserve for the high demand for water during firefighting situations. Elevated water storage tanks serve buildings that are too tall to rely on street water pressure. Water is pumped to a stor- age tank located on top of the building. An elevated storage tank that is 30 to 35 ft (10 to 12 m) above the highest plumbing fixture being served is generally required. Elevated water stor- age tanks are sized to hold one to two days of water supply plus a reserve for firefighting. An alternative to an elevated storage tank in tall buildings is a pressurized tank—a storage tank that is pressurized to the appropriate pressure. A big benefit of a water tower and elevated water storage tanks is that water pumps are sized for average rather than peak demand. During periods of high demand, water flows from the tank to the consumer while during periods of low demand the tank refills. For example, water consumption for a pumping station averaging 750 gpm (2850 L/min) is equivalent to 1 080 000 gal/ day (4 100 000 L/day). During a period of high demand such as from 7 to 8 AM, water consumption may peak at 3000 gpm (11 400 L/min) and water is removed from the tank at a greater rate than the pumping station is filling the tank. When demand drops off, say at midnight, the tank is refilled. Even though water demand peaks at 3000 gpm (11 400 L/min), the smaller 750 gpm (2850 L/min) pumping capacity is sufficient. A 3000 gpm (11 400 L/min) pumping capacity is not needed. 12.3 PIPING MATERIALS Pipe is a round, hollow channel used to transport liquids such as water or solid–liquid mixtures such as wastewater from one point to the next. In a building plumbing system, pipes transport hot and cold water and remove liquid and solid wastes. Piping in buildings is also used in transporting natural and liquefied petroleum gases, fuel oil, compressed air, refrigerants, and irri- gation water. Water pipe generally falls into one of two categories: pressure pipe, which delivers supply water; and drain, waste, and vent (DWV) pipe, which carries waste and soil water away. Both categories are sold in metal and plastic; however, metal (copper in plumbing systems) dominates the pressure category. Plastic and cast iron are the most common piping material for DWV. Pressure pipe must be heavy enough to hold continuous pressure without rupture, and all connections must be leak proof. This pipe tends to be of a smaller diameter, and it must be made of material that will not react with the chemicals or minerals in the water. DWV pipe provides a channel for waste materials to flow freely away from the fixtures and the building by the force of gravity. It is typically lighter weight with thinner walls than pres- sure pipe, and joints do not need to be as tightly sealed because there is no pressure exerted on them. DWV pipe is generally larger in size than pressure pipe to allow for free gravity flow, and it must not react to common chemicals that might be poured down a drain. In both pressure and DWV piping, fitting design and join- ing techniques must be compatible with the pressures and temper- atures encountered when the pipe is placed in service. Piping Materials Many types of piping materials most commonly used in build- ing plumbing systems as described in the following sections. Photos 12.2 to 12.7 show examples of piping materials. Table Copper Pipe and Tubing Copper tubing is traditionally the most popular water supply pipe material. It is also used in water space heating (hydronic) systems, air conditioning and refrigeration systems, sanitary drainage, and natural gas and liquid petroleum gas piping. The thin walls of copper tubing are usually soldered to fittings. This allows the pipes and fittings to be set into place before the joints are PLUMBING FUNDAMENTALS 9 connected with solder. This advantage generally al- lows faster installation of copper pipe in comparison to treaded steel or brass. The types of copper tubing available are K, L, and M, with K having the thickest walls, then L, and finally M, with the thinnest walls of this group. DWV copper tubing is used for drainage, waste, and vent piping. Types K and L are preferred for pressure applications. Type M and DWV are used for low- and no-pressure applications. Types of commercially available copper tubing are summarized in Table 12.8. They are de- scribed in the following: Type K Type K copper tube is available as either rigid (hard temper) or flexible (soft temper). Type K is used primarily for underground water service in water supply systems. It is avail- able in the following nominal diameters: 3⁄8, 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, and 8 in. Soft temper tubing 1 in and smaller is usually available in coils 60 or 100 ft (18.3 or 30.5 m) long, while 1 1⁄4 and 11⁄2 in tubing is available in 40- or 60-ft (12.2 or 18.3 m) coils. Hard temper is available in 12- and 20-ft (3.7 and 6.1 m) straight lengths. Type K copper tubing is color coded in green for quick visual identification. Type L Type L copper tube is also available in either hard or soft temper and in coils (soft temper only) and straight lengths much like Type K. It is available in the following nominal diam- eters: 3⁄8, 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, and 10 in. The soft temper tubing is often used as replacement plumbing because the flexibility of the tube allows easier installation. Hard temper tub- ing is often used for new installations, particularly in commercial work. Type L copper tubing is color coded blue. This type of tub- ing is most popular for use in water supply systems. Type M Type M copper tube is made in hard temper only and is available in straight lengths of 12 and 20 ft (3.7 and 6.1 m). It is used for branch supplies where water pressure is not too great, but it is not used for risers and mains. It is available in the following nominal diameters: 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, and 10 in. It is also used for chilled water systems, ex- posed lines in hot water heating systems, and drainage piping. Type M copper tubing is color coded red. DWV DWV copper tube is the thinnest copper tube and is used in nonpressure applications. It is made in hard temper only and is obtainable in straight lengths of 20 ft (6.1 m). It is avail- able in the following nominal diameters: 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, and 10 in. The diameter of copper pipe is expressed in nominal size. The actual size is 1⁄8 in larger than the nominal size expressed (e.g., a 1-in copper pipe has an actual outside diameter of 11⁄8 in). Regardless of type, the outside diameter does not vary for a specific nominal diameter. Inside diameter will vary with wall thickness. The inside diameter of a thin-wall pipe will be greater than the inside diameter of a thick-wall pipe. Weights and dimensions of copper tubing are provided in Table 12.9. Weights and dimensions of copper and brass pipes are provided in Table 12.10. Compared with iron or steel pipe, copper pipe has the advantage of not rusting and of being highly resistant to any accumulation of scale (particles) in the pipe. Copper tubing has a lower friction loss than wrought iron or steel, providing an additional advantage. Also, the outside dimensions of the fittings are smaller, which makes a neater, better-looking job. With wrought iron and steel pipe, the larger outside dimen- sions of the fittings sometimes require that wider walls be used in the building. Copper piping should not be installed if it will carry water having a pH of 6.8 or less, as this could cause copper to corrode from the acidic nature of the water at this pH. The ma- jority of public utilities supply water at a pH between 7.2 and 8.0. Private well water systems often have a pH below 6.8. When this it the case, it is suggested that a treatment system be installed to make the water less acidic. Brass Pipe Red brass piping, consisting of approximately 85% copper and 15% zinc, is used as water supply piping. The pipe is threaded for fitting connections, but this requires thicker walls to accommodate the threading, making installation and handling more difficult than for copper. In addition, its relatively higher total cost, installed on the job, limits its usage. Brass piping has seen limited use in new construction. Steel and Iron Pipe Steel pipe is available in the following nominal diameters: 3⁄8, 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, 10, and 12 in. It is typically sold in lengths of 21 ft. When steel pipe is forged, a black oxide scale forms on its surface that gives it a dull black finish, and as a result it is called black pipe. Because steel is subject to rust and corrosion, the pipe manufacturer also coats it with protective oil. Black pipe is most commonly used for natural gas supply lines and fire suppression sprinkler system lines. Galvanized steel pipe is covered with a protective coating of zinc that greatly reduces its tendency to corrode and thus extends its life expectancy. It is moderately corrosion resistant and suitable for mildly acid water. It was commonly used for water supply, waste, and vent lines in plumbing systems through the early 1950s. It is not frequently used for water supply lines today because the  10 CHAPTER 12 minerals in the water react with the galvaniz- ing material and form scale, which builds up over time and will eventually clog the pipe. Weights and dimensions of standard weight steel pipe are provided in Tables 12.11, 12.12, 12.13, and 12.14. Steel pipe is typically cut and threaded to fit the job. Fit- tings for this type of pipe are of malleable (soft) cast iron. They connect by screwing onto the threaded pipe, after applying a small amount of pipe joint compound on the threads. Larger diameter pipe is typically welded rather than threaded. Concerns arise as galvanized steel pipe ages: corrosion of the inner surface of the pipe restricts water flow; develop- ment of rust flakes loosen, collect, and restrict water flow in fittings and valves; and leaks form from corrosion. There- fore, galvanized steel pipe is not used extensively in water supply systems. Steel pipe is connected to its fittings with threaded connections. Steel pipe also has a higher friction loss than copper. Lightweight wrought-iron pipe, designated Standard (or Schedule 40), is the type most commonly used for water supply and fire suppression sprinkler systems. The most commonly used wrought-iron pipe is galvanized. The zinc-galvanized coating adds extra corrosion resistance. Occasionally, it is used as the service main from the community main to the riser.Wrought- iron pipe is threaded for connection to the fittings, and it can be identified by a red spiral stripe on the pipe. The higher cost of wrought-iron pipe limits its increased use. Wrought-iron pipe also has a higher friction loss than copper. Wrought-iron pipe used in buildings is available in the follow- ing nominal diameters: 3⁄8, 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, 10, and 12 in. Cast iron pipe is commonly used in gravity building and storm drain/sewer systems. Cast iron pipes and fittings are limited to gravity pressure systems. It is available in two grades: Service (SV) for above-grade installations; and, Extra Heavy (XH) for applications below grade. Cast iron pipes are available in 5 and 10 ft lengths with the following nominal diameters: 2, 3, 4, 5, 6, 8, 10, 12, and 15 in. Cast iron pipes and fittings are connected using two methods: hub (female end) and spigot (male end) that are joined by sliding the spigot into the hub; and the no-hub connection that is connected with a rubber gasket and screw-type clamp that is similar to a hose clamp. Thermoplastic Pipe Thermoplastic pipe, sometimes referred to simply as plastic pipe, is used for water supply systems because its economy and ease of installation make it popular, especially on projects such as low-cost housing or apartments where cost economy is im- portant. It is important to check the plumbing code in force in your locale because some areas still do not allow the use of plastic pipe for water supply systems. A variety of thermoplastics are used for pipe and fittings in building plumbing systems. Types of thermoplastic materials and their uses are summarized in Table 12.16. Acrylonitrile butadiene styrene (ABS) thermoplastic pipe is typically black in color. It is generally approved for use in DWV applications. It is available in two grades: Schedule 40 and Service. It is available in straight lengths in the fol- lowing nominal diameters: 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, 6, 8, and 10 in. Solvent-cement welding is used to join ABS pipe and fittings. Polybutylene (PB) pipe is a flexible (coils) thermoplastic pipe generally approved for use in potable hot and cold water supply applications. Because of several lawsuits tied to this type of pipe, it is no longer recommended for use in building plumbing systems. Interior PB pipe is easily recognized by its gray color. Underground service laterals are typically blue in color. PB is available in copper tube size (CTS) and iron pipe size (IPS). PB pipe cannot be solvent-cement welded, so special fittings are used: a brass, copper, or acetyl plastic insert fitting that slides into the pipe and a crimp ring around the outside of the pipe; a compression fitting with a nut, ring, and cone; and an instant connect fitting that involves sliding the pipe into the fitting and rotating the fitting, which causes the fitting and pipe to press together. It is available for water distribution applications in the following nominal diameters: 1⁄2, 3 ⁄4, 1, 11⁄4, 11⁄2, and 2 in. Polyethylene (PE) is a flexible (coils) thermoplastic pipe. Black PE pipe is used for buried cold building water sup- ply and irrigation (yard) piping. PE pipe is also approved for use in piping for natural gas and liquefied petroleum gas (LPG) applications, but only when it is directly buried and outside the building foundation. Fusion (melt) welding and compression and flanged connec- tions are used to join PE pipe and fittings carrying gas. PE pipe is available for water distribution applications in the following nominal diameters: 1⁄2, 3⁄4, 1, 11⁄4, 11⁄2, and 2 in IPS. PE fittings are typically copper alloy or plastic barbed insert. Cross-linked polyethylene (PEX) is a specific type of medium- or high-density polyethylene with individual molecules linking one polymer chain to another. This type of bond makes PEX stronger and more stable than PE with respect to temperature extremes, chemical attack, and creep deformation. In contrast to metal pipes, it is freeze-break resistant. As a result, PEX plas- tic pipe is ideally suited for interior potable cold and hot water plumbing applications. PEX tubing has been in use successfully in Europe for plumbing, radiant heating, and snow melt applications since the 1960s. PEX is commonly available in 1⁄2, 3⁄4, 1, 11⁄2, and 2 in out- side diameter CTS and is packaged in coils or 20 ft straight lengths. See Table 12.18. Some tubing is color coded for easy identification of hot (red) and cold (blue) lines. PEX fittings are generally made of brass, copper, and engineered plastic barbed insert fittings specifically designed for PEX. Polyvinyl chloride (PVC) is a rigid thermoplastic pipe generally approved for use in pressure applications such as cold water  PLUMBING FUNDAMENTALS 11 supply applications outside the building (e.g., the building service and in DWV and irrigation pip- ing). It is generally white or gray in color, but can be other colors. PVC is typically rated at 73°F (23°C) and 100 psi (690 kPa), so it is not suitable for potable hot water distribution. It is available in straight lengths in the following nominal diameters: 1, 11⁄4, 11⁄2, 2, 21⁄2, 3, 31⁄2, 4, 5, and 6 in. Solvent- cement welding and threaded or flanged connections are used to join PVC pipe and fit- tings. Dimensions of PVC pipe for drainage, waste, and vent systems are provided in Table 12.19. Chlorinated polyvinyl chloride (CPVC) is a rigid thermo- plastic pipe generally approved for use in potable hot and cold water supply, fire suppression sprinkler systems in residences, and in process piping. CPVC is rated at 180°F (82°C) and 100 psi (690 kPa), making it suitable for potable hot water distribution. Because of its excellent chemical resistance, it can also be used in sanitary drainage applications. CPVC tubing and fittings are beige or tan in color. CPVC pipe is available as Schedule 40 and Schedule \ 80 in straight lengths in the nominal diameters from 1⁄2 to 12 in. Dimensions of Schedule 40 and Schedule 80 CPVC pipe are provided in Table 12.19. CPVC is also available CTS, which is designed for use in hot and cold water distribution systems in buildings. Dimensions of CTS-CPVC plumbing pipe are provided in Table 12.20. CPVC pipe with a standard dimension ratio (SDR) of 13.5 is used for fire sprinkler piping (see Table 12.21). Solvent-cement welding and threaded and flanged con- nections are used to join CPVC pipe and fittings. Styrene rubber (SR) is a rigid thermoplastic pipe that is generally approved for use in septic tanks, drain fields, and storm sewers. It is available in straight lengths in the following nominal diameters: 3, 31⁄2, 4, 5, 6, and 8 in. Polypropylene (PP) is a thermoplastic pipe material that is typically used in chemical waste lines. It can also be used for hot and cold water applications. It is rarely used in building plumbing systems, likely because it is joined by heat fusion. Polyvinylidene fluoride (PVDF) is an extremely expensive thermoplastic pipe that is used in ultrapure water systems and industrial applications (e.g., pharmaceutical industry).. Reinforced thermosetting plastic pipe is a thermoplastic resin used in combination with reinforcement and fillers. The most commonly used reinforced thermosetting plas- tic pipe products are based on polyester or epoxy resins. The reinforcement may be organic (e.g., synthetic fiber) or inorganic (e.g., glass fiber). Glass fiber is the most common reinforcement used in this type of pipe. Rein- forced thermosetting plastic pipe will typically consist of 15 to 70% glass fiber, 0 to 50% filler (e.g., sand), and 30 to 75% thermosetting resin. Composite Pipe Composite pipe is a flexible pipe material that is constructed of an aluminum tube laminated between two layers of polyethyl- ene thermoplastic. It is available in 3⁄8, 1⁄2, 5⁄8, 3⁄4, and 1 in nominal diameter coils ranging from 100 to 1000 ft (30 to 30 m). Fit- tings are joined to the pipe with a compression or crimped con- nection and to fixtures and other fittings with a threaded connection. Branches can extend from a main manifold and ex- tend uninterrupted to the plumbing fixture (e.g., sink, lavatory, bathtub, and so on). It is available in two types: PE-AL-PE Pipe PE-AL-PE pipe is an aluminum (AL) tube laminated between two layers of PE plastic. It carries long-term pressure and temperature ratings of 200 psi at 73oF, and 160 psi at 140oF, which is approved for use in cold water and compressed air applications. PE-AL-PE pipe is coded dark blue in color. PEX-AL-PEX Pipe PEX-AL-PEX pipe is an aluminum (AL) tube laminated between two layers of temperature-resistant, PEX plastic. Cross-linking of PE means that the molecular chains are linked into a three-dimensional network that makes PEX remark- ably durable within a wide range of temperatures, pressures, and chemicals. It is color coded orange, light blue, or black. Black is used in exposed installations. It is approved for use in cold and hot water and high-pressure applications and can also be used in radiant floor heating systems. It has a long-term pressure rating of 125 psi at 180oF. PEX-AL-PEX pipe is more costly than PE- AL-PE pipe and tends to be used in hot water applications only. Composite pipe is extremely light; a 1000 ft (300 m) coil weighs about 40 lb (178 N). Dimensions of and bending re- quirements for PEX- AL-PEX composite pipe are provided in Table 12.22. As a flexible pipe, minimum radius requirements limit the minimum size of bend based upon the diameter of the pipe. Ease of handling and installation makes this type of pipe a cost-effective alternative to copper. Clay and Concrete Pipe Clay pipe is made from vitrified clay. Concrete pipe is cast from concrete. These pipes are traditionally used for sewage, industrial waste, storm water, and drain field applications. Con- crete pipe is also used as large water supply pipe. These materi- als are not commonly used in building plumbing systems. Pipe is normally supplied in three end styles: PE or plain end; BE, or beveled end for welding; or T&C for threaded and supplied with one coupling per length. Steel pipe can be cut to any length and sold threaded both ends (TBE) or threaded on one end 12 CHAPTER 12 only (TOE). Copper and thermoplastic pipe are sold PE only. Tubing and Pipe Sizes Historically, pipe size was based on the inside diameter of the pipe that was characteristic of the period, which was cast iron. For example, a half-inch cast iron pipe had an inside diameter (ID) that was exactly one-half inch. The thickness of its wall de- termined the outside diameter. Later, the standard was changed so that pipe size related to a specific outside diameter to ensure that all pipes and fittings would fit together for a specific size. Pipe is thick walled and available in standard iron pipe size (IPS). IPS remains the standard by which pipe size is meas- ured. With materials other than iron, the wall thickness of pipe is different. Consequently, inside diameters of pipes of different materials vary for a specific pipe size. Thus, a half-inch pipe is neither a half-inch on the inside nor the outside, but it is still called a half- inch pipe based on the nominal diameter. Under the IPS designation, female fittings are identified by FIP and male fittings are MIP. The terms nominal pipe size (NPS) and IPS are interchangeable and refer to the nominal diameter of the pipe, not the actual diameter. Pipe is distinguished from tubing by the standard by which it is measured. When copper tubing was developed, the walls were much thinner than cast iron or steel. Because of cop- per’s unique characteristics, it was not necessary that it be made in IPS sizes. A new standard called copper tube size (CTS) was developed. The actual size of CTS is much closer to its nominal size than that of pipe. The standard has evolved so that any product made in IPS size is called pipe and any product made in CTS size is called tubing, without regard to any differences in material or manu- facturing process. CPVC is an exception, being called pipe but sold in CTS. Pipe is available in a number of different thicknesses or schedules. The American Society for Testing and Materials (ASTM) establishes the standards by which they are graded. The ASTM has assigned standards to each schedule of pipe made, and those standards dictate their use. Pipe Pressure Rating With the exception of sewer and drainage pipe, all pipe is pres- sure rated. There are several different methods of determining pressure ratings: The schedule number is obtained from the expression 1000 × P/S, where P is the service pressure and S is the al- lowable stress, both being expressed in the same units. For example, on types of steel pipe with IPS sizes thru 12 in, wall thickness is assigned schedule numbers from Schedule 10 (S.10) thru Schedule 160 (S.160), which represent ap- proximate values for 1000 times the pressure–stress ratios. The SDR is calculated by dividing the outside diameter of the pipe by its wall thickness. Pipe with an SDR of 13.5 has an outside diameter that is 13.5 times thicker than the wall thickness. The pressure-level rating provides the pressure rating of the pipe at a given temperature. Pipes are available com- mercially at many pressure ratings, and the most popular of these are 50, 100, and 125 psi (340, 690, and 860 kPa); 160, 200, 250, and 315 psi (1.1, 1.4, 1.7, and 2.2 MPa). Weights designations are used for steel and iron pipe: standard wall (Std), extra strong wall (XS), and double extra strong wall (XXS). These last two designations are sometimes referred to as extra heavy wall (XH) and dou- ble extra heavy wall (XXH), respectively. Wrought-iron pipe is referred to as Std, XS, and XXS and not by sched- ule numbers. 12.4 FITTINGS AND VALVES Fittings A variety of fittings must be used to connect pipe lengths and make all the pipe turns, branch lines, couplings that join the straight runs, and stops at the end of the runs. Fittings for steel and wrought-iron pipe are made of malleable iron and cast iron. The fittings for plastic, copper, and brass pipe are made of the same materials as the pipe being connected. Elbows Elbows, usually at 45° and 90°, are angular fittings used to change the direction of a supply pipe. On a sanitary drainage system, a sanitary bend makes a more gradual turn to prevent blockage. Tees Tees are used in a supply system when a line must branch off at a straight run. A reducing tee allows different pipe sizes to be PLUMBING FUNDAMENTALS 13 joined together in a supply system. Sanitary T and sanitary Y are tee-like fittings used in sanitary drainage systems that make a more gradual turn to prevent blockage. A sanitary Y can accept two or three branches before combining flow into one pipe. Couplings Couplings are used to join straight runs of pipe. A union joins straight runs of pipe but also allows the pipes to be more easily disconnected when future piping revisions are expected or equipment needs to be replaced. A reducer is a straight fitting used to decrease the diame- ter in a pipe in a water supply system. An increaser is a straight fitting used to increase the diameter in a pipe in a sanitary drainage system. Adapters Adapters are used in a supply system where threaded pipe is being connected to copper or thermoplastic. Adapters have one threaded end to accommodate threaded pipe. Joining Pipes and Fittings Pipes and fittings are joined through a number of techniques. Pipes and fittings can be joined mechanically. Threaded joints, insert fittings with crimped connections or clamped connec- tions; hub and spigot; and flared (metal to metal) joints are pop- ular mechanical joining techniques. Fire suppression sprinkler pipes are frequently joined using a grooved Victaulic fitting. A compression fitting is a type of connection for tubing or pipe where a nut, and then a sleeve or ferrule, is placed over a copper or plastic tube, and is compressed tightly around the tube as the nut is tightened, forming a positive grip and seal without soldering. Soldering, brazing, and welding are ways of joining metal surfaces. Soldering and brazing are methods of joining two or more metal surfaces by melting nonferrous filler metal with a melting temperature well below the metals to be joined. The melted filler metal distributes itself between the surfaces to be bonded by cap- illary action. Soldering involves melting solder to a temperature below 840°F (449°C), usually in the range of 350° to 550°F (177° to 288°C). Brazing involves melting the metal filler above 430°C (800°F), usually in the range of 1100° to 1500°F (593° to 816°C), but still below the melting temperature of the metals to be joined. Soldered joints are used when the service temperature does not exceed 205°F (96°C). Brazed joints offer greater strength and should be used where operating temperatures are up to 400°F (204°C). Welding typically involves joining two or more pieces of metal by the application of heat. Unlike soldering or brazing, welding involves a partial melting of the surfaces of the metals to be joined. It offers the greatest physical strength. Solvent-cementing and fusion welding can join some plastic pipe materials. Solvent cementing involves coating the plastic surfaces with a prime coat and a solvent cement coat before they are joined. The cement cures joining the surfaces in a manner similar to the cementing technique used to attach the pieces of a plastic model airplane. Fusion welding involves heating the surfaces until they melt, allowing them to be joined. Valves Valves are used to control flow of the water throughout the system. Valves generally fall into four categories: gate, globe, check and angle. Gate Valves The gate valve is a manual valve that has a wedge-shaped leaf that, when closed, seals tightly against two metal seats that are set at slight angles. Globe Valves The globe valve is a manual, compression-type valve, commonly used where there is occasional or periodic use, such as lavatories (faucets) and hose connections (called hose bibbs). This type of valve regulates the flow of water. Design of the globe valve is such that the water passing through is forced to make two 90° turns, which greatly increases the friction loss in this valve compared with that in a gate valve. (See Figure 12.9.) Angle Valves The angle valve is a manual valve similar in operation to the globe valve, utilizing the same principle of compressing a washer against a metal seat to cut the flow of water. It is commonly used for outside hose bibbs. The angle valve has a much higher friction loss than the gate valve and about half the friction loss of the globe valve. 14 CHAPTER 12 Check Valves The check valve opens to allow the flow of water in the direction desired and prevents flow in the other direction. Swing check valve design, the pressure of the water forces the valve gate to swing open, but once the flow stops, gravity causes the gate to fall closed, preventing a reversal of the flow Spring check valve is spring loaded. Water pressure forces the gate open much like the swing type, but when the flow stops, a spring (not gravity) forces the gate closed. Ball Valves A ball valve is a manual valve that has a ball with a hole through it that is mounted between two seats. When the ball hole is in line with the valve openings, full flow of water occurs. Metered valves are designed to automatically discharge for a specific length of time and thus deliver a fixed quantity of water before closing off flow. Flushometer valve is a metered valve that discharges a predetermined quantity of water to fixtures for flushing purposes (e.g., water closets and urinals) and is closed by direct water pressures. Flow Control Valves A flow control valve automatically adjusts the rate of water flow to a predetermined flow rate as pressure in the system varies. They can be used to limit flow at a fixture outlet thereby holding demand to a required minimum. Thermostatic Valves A thermostatic valve, frequently called a tempering valve or mixing valve, is an automatic valve thermostatically blends hot and cold water to desired temperatures and to prevent scalding. Temperature-Pressure Relief Valves A temperature-pressure relief (T/P) valve is a safety valve de- signed to limit pressure of a liquid vapor or gas. These valves are specified such that the valve remains closed at normal oper- ating pressures yet it is allowed to open to release excessive pressure. They are commonly found as a safety feature on water heaters and boilers. Pressure-Reducing Valves A pressure-reducing valve is an adjustable valve designed to reduce pressure to a specific setting. Hose Bibbs A hose bibb, sometimes called a sill cock, is a valve designed to accept the threaded connection of a hose. A freezeless hose bibb has a long body that when placed in an exterior wall, cuts off the water supply near the interior wall surface. This allows water near the exterior wall surface to drain out when the valve is closed to avoid freezing of water and valve damage in severe winter temperatures. Secured hose bibbs require a specially designed knob to open the valve, which prevents use by the general public. A hose bibb is shown in Photo 12.9. Flushometer A flushometer is a valve-like device designed to supply a fixed quantity of water for flushing toilets and urinals. When operated, it automatically shuts off after a measured amount of water flow in order to conserve water. It uses pressure from the water supply system rather than the force of gravity to discharge water. Sensor-Operated Valves Modern urinals and water closets (toilets) use a sensor-operated valve that automatically flushes the fixture when a user departs. The unit uses an infrared proximity sensor to detect a user approaching the fixture, then waits until the user departs. A solenoid PLUMBING FUNDAMENTALS 15 is used to actuate the flush. Typically, a batter con- tained within the unit powers the sensor circuit. Valves referred to as standard weight are designed to withstand pressures up to 125 psi (860 kPa). High-pressure valves are also available. Most small valves have bronze bod- ies, while large valves (2 in [50 mm] and larger) have iron bod- ies with noncorrosive moving parts and seats that must be replaced periodically. They are available threaded or soldered to match the pipe or tubing used. Valves must be installed in the appropriate direction of flow. An arrow cast in the body of the valve usually indicates direction of flow. Some valves are better than others in regulat- ing flow. Gate valves and ball valves undergo excessive wear (from cavitation) when they are partially closed. Globe valves are designed to more easily and effectively regulate flow. 12.5 PLUMBING FIXTURES A plumbing fixture is an approved receptacle, device, or appli- ance that uses water and discharges wastewater such as a water closet, urinal, faucet, shower, dishwasher, drinking fountain, hose connection, hose bibb, water heater, water softener, under- ground sprinkler, hot tub, spa, and clothes washer.. Plumbing fixtures are classified according to their use. Groups of two or more like fixtures that are served by a common drainage branch are known as a group of fixtures. Types of plumbing fixtures and related design concerns are as follows. Water Closets A water closet is a plumbing fixture that serves as an indoor re- ceptacle and removal system for human waste. Although this fixture is commonly called a toilet or commode, the building code specifically refers to it as a water closet. Water closets are typically made of solid vitrified china cast with an inte- gral (built-in) trap. They are also available in stainless steel that is typically specified for high-vandalism installations such as at highway rest stops, outdoor recreation areas, jails, and detention centers. Examples of water closets are shown in Photos 12.10 and 12.11. In North America, water closets are available as single- flush, flush tank, or flush valve fixtures. Present requirements limit average water consumption to 1.6 gal (6.0 L) per flush. These are known as ultra-low flush (ULF) water closets. Infrared and ultrasonic sensors can be built into the flush valve to automatically flush and avoid nonflushing or double flushing. PHOTO 12.10 A flush tank water closet. (Used with permission of ABC) PHOTO 12.11 A wall-mounted, flush valve water closet. Note the wall cleanout cover at the floor line to the right of the water closet. (Used with permission of ABC) 16 CHAPTER 12 A flush tank water closet has a water tank as part of the fixture. (See Figure 12.12.) As the handle or button on a water closet is pushed, it lifts the valve in the tank, releasing the water to flush out the bowl. Two piece One piece FIGURE 12.12 Flush tank water closets. Floor mounted Wall mounted FIGURE 12.13 Flush valve water closets. Flush valve water closets have no tank to supply water. Instead, when the handle is pushed, the water to flush the bowl comes directly from the water supply system at a high rate of flow. When used, it is important that the water supply system be designed to supply the high flow required. Although most of the fixtures operate effectively at a pressure of 20 psi (140 kPa), the manufacturer’s specifications should be confirmed because higher pressure is often required. The dual-flush water closet, a technology first developed in the early 1980s, takes water conservation one step further by using 1.6 gal (6.0 L) of water to flush solid waste but only 0.8 gal (3.0 L) to flush liquid waste. The National Association of Home Builders Research Center (NAHB) completed performance tests on 49 popular toilet models. One element of this study provided a relative rating called the Flush Performance Index (FPI). FPI ratings ranged from 0 to 82, with lower numbers being better. Urinals Urinals are plumbing fixtures that are commonly used in public restrooms where it is desirable to reduce possible contamination of the water closet seats. They are commonly available in FIGURE 12.14 Types of flushing actions used in a water closet. Water flows into the bowl from the bowl rim. This raises the water level in the bowl to fill the gooseneck pathway. As water fills the gooseneck, the water and waste remaining in the bowl is sucked up and into the gooseneck PLUMBING FUNDAMENTALS 17 by a siphoning action. Wallhung Stall Pedestal FIGURE 12.15 Types of urinals. vitreous china and sometimes in enameled iron. They are also available in stainless steel for high-vandalism installations. Floor and trough-type urinals are no longer allowed in new construction. Examples of urinals are shown in Figure 12.15 and Photos 12.12 and 12.13. Urinals are available as flush tank or flush valve fixtures. Present requirements typically limit average water consumption to 1.0 gal (3.8 L) per flush. These are known as the ULF urinals. Special metal urinals with straight drain lines limit average water consumption to 0.5 gal (1.9 L) per flush. PHOTO 12.12 A wall-mounted, flush valve urinal. (Used with permission of ABC) 18 CHAPTER 12 PHOTO 12.13 A group of urinals separated by partitions. (Used with permission of ABC) Waterless Urinals A waterless urinal is a urinal that is specifically engineered to eliminate potable water consumption for urinal flushing. PHOTO 12.14 A waterless urinal, which represents the most water-efficient urinal option because they provide first-cost savings (e.g., eliminating the need to provide a water line and flush valve) and less maintenance (e.g., leaks, valve repairs, and water overflows) over the conventional urinals. (Courtesy of NREL/DOE) PLUMBING FUNDAMENTALS 19 Bidets Bidets are personal hygiene plumbing fixtures used for genital and perineal cleanliness. It is typically used after using the water closet. Equipped with valves for hot and cold water, the inside walls of the bowl are washed the same way as a standard toilet. Bathtubs are plumbing fixtures used for bathing. See Photos 12.15 through 12.17. They are available in enameled iron, cast FIGURE 12.16 A bidet. PHOTO 12.15 A luxurious bathtub with power jets in a residential bathroom. (Used with permission of ABC) PHOTO 12.16 A bathtub for a master bathroom. (Used with permission of ABC)  20 CHAPTER 12 PHOTO 12.17 An enameled iron bathtub stored before installation. (Used with permission of ABC) iron, or fiberglass. Tubs are available in a variety of sizes, the most common being 30 or 32 in (760 or 810 mm) wide; 12, 14, or 16 in (300, 350 or 400 mm) high; and 4 to 6 ft (1.2 to 1.8 m) long. Whirlpool bathtubs are fitted with jets that propel a current of warm water in a swirling motion. Bathtub fittings may be installed on only one end of a tub, and the end at which they are placed designates the tub. As you face the tub, if the fittings are placed on the left, it is called a left- handed tub, and if placed on the right, it is right-handed. Showers A showerhead is an overhead nozzle that sprays water down on the bather. Shower fittings may be placed over bathtubs instead of having a separate shower space; this is commonly done in residences, apartments, and motels. However, it is important that when a showerhead is used with a bathtub fixture, the walls be constructed of an impervious material such as ceramic tile. See Photos 12.18 through 12.21. Present requirements for average water consumption by a showerhead are that flow rates not exceed 2.5 gpm (9.5 L/min). These are known as low-flow showerheads. A handshower is a showerhead attached to the end of a flexible hose, which the bather can hold during bathing or showering. Shower surrounds cover the walls that enclose a shower stall. A shower enclosure consists of glass panels, either framed or frameless, used to enclose bathtubs, shower modules, shower receptors, and custom-tiled showering spaces. A receptor or shower pan is a shallow basin used to catch and contain water in the bottom of a showering space. They are available in units of porcelain enameled steel, fiberglass, tile, terrazzo, marble, cement, or molded compositions. Special PHOTO 12.18 A tub faucet with tub/shower control. (Used with permission of ABC PLUMBING FUNDAMENTALS 21 ) PHOTO 12.19 A showerhead. (Used with permission of ABC) PHOTO 12.20 A roughed-in plastic shower pan. (Used with permission of ABC) shower surrounds available include corner units and gang head units. A gang head shower has multiple showerheads extending from the top of a post. It is commonly used in institutions, schools, factories where workers must shower after work, and other locations where large numbers of people must shower. Shower surrounds and receptors of tile, concrete, or marble may be built to any desired size or shape. Typically lead or plastic sheets are site-formed into shower pans on custom-made opening. PHOTO 12.21 A three-quarter bathroom (lavatory, water closet, and shower) with glass doors on the shower stall. (Used with permission of ABC) shower designed to accommodate a 32 in by 32 in (800 mm by 800 mm) roughed-in opening, provided it has at least 900 in2 (.56 m2) of interior area. Lavatories A lavatory is a bathroom basin or sink used for personal hygiene. Lavatories are generally available in vitreous china or enameled iron, or they may be cast in plastic or a plastic com- pound with the basin an integral part of the countertop. They are also available in stainless steel for high-vandalism applications. See Figure 12.17 and Photos 12.22 through 12.24. Present requirements for nonmetered lavatory faucets limit the average water consumption to 2.2 gpm (8.4 L/min).  22 CHAPTER 12 Metered lavatory faucets are designed to shut off after a short period of time. They are used in public restrooms such as in transportation terminals, restaurants, and convention halls to ensure that water is shut off and not flowing freely. Metered faucets used on lavatories should not deliver more than 0.25 gal (1.0 L) per use. Infrared and ultrasonic sensors can be installed to operate faucets and limit waste. Lavatories are available in a large variety of sizes and the shapes are usually square, rectangular, round, or oval. The lavatory may be wall-hung, set on legs, set on a stand, or built into a cabinet. Lavatory styles are usually classified as flush- mount, self-rimming, undercounter, integral, or as units that can be wall-hung or supported on legs. Self-rimming lavatories have a finished rim that is placed directly over the countertop Countertop Corner, wall or floor mounted FIGURE 12.17 Types of lavatories. Floor mounted PHOTO 12.22 Luxurious lavatories in a residential bathroom. (Used with permission of ABC) PLUMBING FUNDAMENTALS 23 PHOTO 12.23 A pedestal lavatory. (Used with permission of ABC) PHOTO 12.24 A cast, vitrified china wall-mounted lavatory in a public restroom. (Used with permission of ABC)  24 CHAPTER 13 Undercounter lavatories are an installation in which a lavatory (or sink) is attached to the underside of a countertop. Pedestal lavatories have a basin that is supported primarily by a freestanding pedestal leg. Residential lavatories have a lift rod that opens the pop-up drain when the lift rod is depressed. When rod is lifted, the drain closes so the lavatory will retain water. Sinks Kitchen sinks are most commonly made of enameled cast iron or stainless steel. Sinks are usually available in a single- or a double-bowl arrangement; some even have a third bowl, which is much smaller. Waste disposal is typically connected to one of the sink drains. Kitchen sinks are generally flush- mounted into a plastic laminate or into a composition plastic counter. Present water conserving requirements for residential kitchen sink faucets limits the average water consumption to 2.5 gpm (9.5 L/min). A common sink width for the kitchen is 30 in. Utility or service sink has a deep, fixed basin that is supplied with hot and cold water and is used for rinsing mops and disposing cleaning water. They are often called slop sinks or mop sinks. Floor- mount sink is installed into the center of a concave floor to dispose of water. PHOTO 12.25 An enameled cast iron kitchen sink. (Used with permission of ABC) PHOTO 12.26 A stainless steel kitchen sink. (Used with permission of ABC) PHOTO 12.27 A stainless wet bar with sink. (Used with permission of ABC) BUILDING WATER SUPPLY SYSTEMS 25 PHOTO 12.28 A stainless steel service sink. (Used with permission of ABC) Laundry Tubs and Trays Laundry tubs, sometimes called trays, are a large deep sink used in laundry rooms. PHOTO 12.29 A laundry tray. (Used with permission of ABC) Drinking Fountains and Water Coolers Drinking fountains offer users a limitless supply of drinking water at any location where water and sanitary drainage are readily available. Water coolers can deliver 8 gal/hr (30 L/hr) or more of chilled drinking water. They require connections to power, water, and drainage. Drinking fountains and water coolers are available in wall-mounted and floor units. Drinking fountains and water coolers should not be installed in public restrooms. Other Fixtures Emergency fixtures include eye-face washes, drench showers, decontamination units, portables, and accessories designed for use wherever hazardous substances are present. Other types of fixtures include baptisteries, ornamental ponds, fountains, and aquariums. An emergency drench shower at a university laboratory is shown in Photo 12.31. 26 CHAPTER 13 PHOTO 12.30 A wall-mounted drinking fountain unit. Chilled water is provided to the unit. (Used with permission of ABC) PHOTO 12.31 An emergency drench shower at a university laboratory. (Used with permission of ABC) ”Approved” Fixtures Federal law mandates that all plumbing fixtures meet or exceed the minimum Energy Policy Act (EPACT) requirements based on maximum flow. Toilets 1.6 gpf (6.1 Lpf) Urinals 1.0 gpf (3.8 Lpf) Showerheads 2.5 gpm (9.5 L/min) Faucets 2.2 gpm (8.4 L/min) Metering faucets0.25 gal (1 L) per cycle Basic Design Considerations for Restrooms Restroom is a personal hygiene facility provided to allow use of a water closet by members of the public, or by patrons or customers. washroom (Canada) public toilet (Great Britain, Australia, and Hong Kong) comfort station (Africa, Middle East, and Southeast Asia). With the passage of the Americans with Disabilities Act (ADA) in 1991, public restroom facilities in the United States must be designed to accommodate people with disabilities. New commercial construction in the United States is required to comply with Title III of the ADA Standards for Accessible Design as enforced by the U.S. Department of Justice. New multifamily dwellings must meet the requirements of the Fair Housing Amendment Act (FHAA) as enforced by the U.S. Department of Housing and Urban Development. BUILDING WATER SUPPLY SYSTEMS 27 PHOTO 12.32 An accessible water closet with rear and side grab bars. (Used with permission of ABC) 12.6 CODES AND STANDARDS Building codes in the United States began as fire regulations written and enacted by several large cities during the 19th century. Standards A standard is a set of specifications written by a professional organization or group of professionals that seek to standardize materials, components, equipment, or methods of construction/ operation. Many organizations develop technical standards, specifications, and design techniques that govern the design and construction of buildings and building systems. Many organizations exist that write standards for the plumbing industry, including those that follow: American Gas Association, Inc. (AGA), a national organization that develops standards, tests, and qualifies products used in gas lines and gas appliance installations. American National Standards Institute (ANSI), a private, nonprofit organization that coordinates the work between standards writing groups in the United States (e.g., International Standard Organization, American Society of Mechanical Engineers, American Society for Testing of Materials, and so on). American Society for Testing of Materials (ASTM), an international standards-writing organization that devel- ops voluntary standards for materials, products, systems, and services. American Society of Mechanical Engineers (ASME), a national organization that develops standards for plumb- ing materials and products. American Society of Sanitary Engineering, Inc. (ASSE), a national organization that develops standards and qual- ifies products for plumbing and sanitary installations. American Water Works Association (AWWA), a national organization that promotes public health through improvement of the quality of water. Develops standards for drinking water, valves, fittings, and other equipment. Canadian Gas Association, Inc. (CGA), a Canadian as- sociation that develops standards, tests, and qualifies products used in gas lines and gas appliance installations. International Standard Organization (ISO), a world- wide standard coordinating organization that offersinternationally recognized certification for manufactur- ers that comply with high standards of quality control. Mechanical Standardization Society of the Valve and Fittings Industry, Inc. (MSS), a nonprofit technical as- sociation consisting of a group of manufacturers that develops technical codes and standards for the valve and fitting industry. National Sanitation Foundation, Inc. (NSF), a non- profit organization known for its role in developing standards for equipment, products, and services. Many standards govern drinking water treatment chemicals and plumbing system components. Underwriter’s Laboratory, Inc. (UL), a nonprofit oranization that tests and qualifies valve and fitting products under UL standards. 28 CHAPTER 13 Building Codes Building code is a local ordinance (a law) that establishes the minimum requirements for design, construction, use, renovation, alteration, and demolition of a building and its systems. The intent of a building code is to ensure health, safety, and welfare of the building occupants. Model building code is a collection of standards and specifications written and compiled by group of professionals and made available for adoption by state and local jurisdictions. Administration of the Code Where codes are in force, there will be a building department or department of building within the local governmental entity (e.g., city, county, and so forth). The governmental building department issues permits for the construction, addition, alteration, repair, occupancy, use, and maintenance of all buildings, structures, or utilities within its jurisdiction. Building inspector is a representative of a governmental entity who performs the local administration and enforcement of the codes.. 1. Underground Inspection The inspector reviews the sewer and water services coming from the city mains to the property. 2. Rough-In Inspection This is an inspection of the inte- rior drainage, waste vent, and water supply piping of the piping system is required. 3. Final Inspection This is the inspection of the final set- ting of fixtures (bathtub, water closet, lavatory, kitchen sink, and so on.). 13.1 THE BUILDING WATER SUPPLY SYSTEM Main Parts of a Water Supply System Plumbing codes require that a potable water supply be adequately furnished to all plumbing fixtures. The water supply system in a building carries cold and hot water through distribution pipes and delivers it to the plumbing fixtures. Building Supply The building supply or water service is a large water supply pipe that carries potable water from the district or city water system or other water source to the building. Water Meter A water meter is required by most district water supply systems to measure and record the amount of water used. It may be placed in a meter box located in the ground near the street or in- side the building. Building Main The building main is a large pipe that serves as the principal artery of the water supply system. It carries water through the building to the furthest riser. The building main is typically run (located) in a basement, in a ceiling, in a crawl space, or below the concrete floor slab. Riser A riser is a water supply pipe that extends vertically in the building at least one story and carries water to fixture branches. It is typically connected to the building main and runs vertically in the walls or pipe chases. Fixture Branch A fixture branch is a water supply pipe that runs from the riser or main to the fixture being connected. In a water supply system, it is any part of a piping system other than a riser or main pipe. Fixture branch pipes supply the individual plumbing fixtures. A fixture branch is usually run in the floor or in the wall behind the fixtures. Fixture Connection A fixture connection runs from the fixture branch to the fixture, the terminal point of use in a plumbing system. A shut-off valve is typically located in the hot and cold water supply at the fixture connection.  BUILDING WATER SUPPLY SYSTEMS 29 General Water Distribution System Layout The water service pipe is an underground pipe that is typically called a lateral. It extends from the underground street main that is part of a district or city water system, and delivers pres- surized potable water to a building plumbing system. Rigid-Pipe Distribution Configuration In the conventional rigid-pipe distribution configuration, the hot and cold water distribution pipes are installed parallel to one another as they convey hot and cold water to risers and branch pipes. Running pipes parallel with building walls and floors arrange pipes in an organized manner. A branch supplying water to two or more fixtures is called a zone. A zone can supply one or many fixtures on one floor or on a few floors. Fixtures are typically located in clusters called groups. There are times when the width of a wall needs to be in- creased to allow for pipes running horizontally to pass by drainage pipes (or other pipes) running vertically. These walls of increased thickness are called plumbing walls. In multistory buildings, risers are pipes that carry water vertically through walls or through enclosures called chases. A chase is a vertical opening through a floor or several floors that is enclosed with walls between floors. A chase can enclose pip- ing only or it can enclose electrical wiring and/or mechanical system ducting and/or pipes that run vertically from floor to floor through the building. Pipe tunnels may be used on large projects to provide concealed space for the passage of mechanicals at ground level and from building to building. Hangers from the top or side of the tunnel are used to support the pipes. Readily accessible valves used to close off the water sup- ply to a fixture, appliance, or system are called shut-off valves. A shut-off valve is required on the discharge side of the water meter. Homerun (Manifold) Distribution Configuration A homerun or manifold distribution configuration consists of a plastic or metal plumbing manifold and flexible plastic piping. Upfeed and Downfeed Distribution Two basic types of water supply distribution systems are used in buildings: the upfeed (or upflow) system and the downfeed (or downflow) systems. See Figures 13.4 and 13.5. Variations of these distribution systems are described in the paragraphs that follow. In a conventional upfeed system, water pressure from the water supply main is relied on to drive water flow through the system. Water pressure in building water supply mains typi- cally ranges from 40 to 80 psi (275 to 550 kPa), with 80 psi (550 kPa) considered the upper limit for most systems plumbed with metal pipe and 40 psi the upper limit for plastic pipe. (Note: psi is an abbreviation for lb/in2.) This available pressure places limits on how far water can be driven upward in a plumbing system. Part of the available pressure is expended in friction losses as the water passes through the meter and the various pipes and fittings; and part of the pressure is expended to overcome gravity, which is the pressure required to push the weight of water upward vertically (up the riser). Additionally, there must be sufficient pressure left at the remote fixture to drive flow of water through the fixture. It takes 0.433 psi to push water up 1 ft vertically or, in the SI (metric) system, 9.8 kPa to push water up 1 m vertically. Conversely, a 1.0 psi pressure can push water upward 2.31 ft vertically or, in the SI (metric) system, 1 kPa to push water up 0.144 m vertically. (This concept is further discussed later in this chapter.) Pushing water up 20 ft (6.1 m) vertically requires a pressure at the base of the riser of at least 8.68 psi (42 kPa), because 20 · 0.433 psi = 8.68 psi. If a pressure of 80 psi (550 kPa) is available at the base of a plumbing system riser, the maximum height water can rise vertically is 185 ft (56.5 m), because 80 psi · 2.31 ft = 185 ft. Depending on the exact floor-to-floor height, a pressure of 80 psi (550 kPa) would drive water about 15 stories, but only if there were no friction losses or fixture operation pressures to con- sider. When friction loss and fixture operation are taken into account, practical design limitations typically establish about 60 ft (18 m) as the standard maximum height and 40 ft (12 m) as the preferred maximum height. This limits a conventional upfeed system to buildings with a height of about 5 stories. In tall buildings, water must be supplied through a pumped upfeed distribution system. A pumped upfeed system is one in which water entering the building flows through pumps that maintain adequate water pressure throughout the structure sufficient to operate any plumbing fixture. In a high- rise building (e.g., 50 stories), water enters one or more pumps where its pressure is boosted to pressures of 150 to 250 psi (1000 to 1700 kPa) or more. A vertical riser carries this high- pressure water to fixtures at 30 CHAPTER 13 the top of the building. Such a pres- sure in the distribution system is too great to use in plumbing fixtures (e.g., lavatories and water closets). For this reason, at several zones water is removed from the vertical riser, reduced in pressure at pressure-reducing stations and distributed to the fixtures in that zone. The pressure-reducing stations, which are located about every 10 floors, monitor and adjust for any varia- tion in pressure. This ensures that water available to plumbing fixtures is always kept under a constant pressure. In buildings that cannot be adequately serviced to the top floor by an upfeed system, water is pumped to elevated storage tanks in, or on, the building, and the water is fed down into the building by gravity. This gravity system, fed from the upper stories to the lower, is called a downfeed distribution system. Water entering the building flows through pumps that develop sufficient water pressure to drive water to storage tanks serving zones of about 10 floors each. To develop adequate pressure, the storage tanks are placed above the zones that they serve. 13.2 WATER PRESSURE CONSIDERATIONS Hydrostatic Pressure Fluid (gas or liquid) molecules tend to seek equilibrium (a sta- bility of forces). When forces acting on a fluid are unequal, molecules in the fluid move in the direction of the resultant forces. Therefore, an elementary property of any fluid at rest (not flowing) is that the force exerted on any molecule within the fluid is the same in all directions. A hydrostatic force is a force exerted by the weight of the fluid against the walls of a vessel containing the fluid. Hydrostatic pressure, the hydrostatic force per unit area, is per- pendicular to the interior walls at every point. If the pressure were not perpendicular, an unbalanced force component would exist and the fluid would flow. If gravity is the only force acting on a fluid (e.g., the water in a gravity plumbing system), the hydrostatic pressure at any point in the system is directly proportional to the weight of a vertical column of that water. Additionally, the pressure is di- rectly proportional to the depth below the surface and is inde- pendent of the size or shape of the container. For example: the hydrostatic pressure at the bottom of a 6 ft (2 m) high pipe that is filled with water is the same as the hydrostatic pressure at the bottom of a tank or pool that is 6 ft (2 m) deep. A 12 ft (4 m) pipe that is filled with water, and slanted so that the top is only 6 ft (2 m) above the bottom (measured vertically), will have the same hydrostatic pressure exerted at the bottom of the 6 ft (2 m) vertical pipe even though the distance along the 12 ft (4 m) pipe is much longer. Water Pressure Water pressure difference is the driving force behind fluid flow. Water pressure available at the water service is lost as water flows through the piping of a plumbing system. This pressure loss or pressure drop in a plumbing system is from friction loss as the water moves through the system and pressure loss as water is forced to a higher elevation (e.g., from the basement to an upper story). Water pressure available at the water service is consid- ered acceptable in the range of 40 to 80 psi (275 to 550 kPa) or greater in mountainous regions. In most residential and com- mercial systems, the upper limit is 80 psi (550 kPa). Some sys- tems with thermoplastic supply piping set the upper pressure limit much lower, usually about 40 psi (275 kPa). When water service pressure is deemed too great, a pressure reducer is used to limit pressure and reduce potential for leaks in the thermo- plastic supply piping. An insufficient pressure at a plumbing fixture results in low flow of water at that fixture. An excessive pressure at a fix- ture may cause disturbingly high flow, will waste water, and may cause damage to or premature deterioration of the fixture. Residual water pressure is the pressure available at the outlet, just before a fixture. It affects water output of a fixture. The residual pressure requirement at the many types of plumb- ing fixtures varies. Code specifies that the highest (most remote outlet) fixture have a minimum pressure of 8 psi (55 kPa) for flush tanks and 15 psi (103 kPa) for fixtures with flushometer valves. Table 13.1 provides recommended residual pressure for different plumbing fixture types. Pressure Difference When forces acting on a fluid are unequal, molecules in the fluid move in the direction of the least pressure. Fluid flow is caused by a pressure difference in the fluid. A fluid will always flow from a higher pressure region to a lower pres- sure region. A pressure difference must exist at a plumbing fixture to cause water to flow—that is, water pressure at the fixture must be at a higher level than atmospheric pressure for water to flow from the fixture. Pressure difference (P) is the driving force of fluid flow. Pressure difference is negative (a loss) if the elevation change from the known pressure is upward (a positive Z) and positive if elevation change is downward (a negative Z).  BUILDING WATER SUPPLY SYSTEMS Pressure change in a plumbing system from elevation change may be computed by multiplying the vertical height of 31 the fixture outlet to the street main (a known pressure) by the pressure the water creates per foot. Conversely, a 2.31 ft of ele- vation change results in a pressure difference of 1 psi and a 0.102 m change results in a pressure difference of 1 kPa. Pressure Losses from Friction Pressure losses from friction, friction head (Pfriction), are more difficult to compute, as they are related to flow rate (gpm,influences friction loss. Pressure drop for a particular rough pipe diameter is greater than in a smooth pipe having the same inside diameter. The pressure drop chart in Figure 13.8 applies to pressure drop as water flows through a water meter. Water meter design typically reduces pressure significantly. It should not be neglected in pressure drop computations. Pressure drop charts have many lines and numbers; use them with care and review the information on the chart before using it. Along the left and right is the volumetric flow rate, and along the bottom and top is the friction loss in the pipe. On the charts provided, pressure drop from friction is expressed in psi per 100 ft. The heavy, solid lines sloping diagonally to the left represent the nominal diameters of pipe; the lines running per- pendicular (at a 90° angle) to the pipe diameter lines represent the velocity of the water in a pipe of a specific nominal diameter. Cavitation Cavitation is a physical phenomenon that occurs in a liquid when it experiences a drastic drop in pressure that causes the liquid to vaporize into small vapor bubbles. Vaporization is a problem because the liquid being vaporized expands greatly; for example, 1 ft3 (or 1 m3) of water at room temperature be- comes 1600 ft3 (or 1600 m3) of vapor at the same temperature. As the low pressure returns to normal pressure levels, these bubbles implode as the vapor changes phase back to a liquid and thus drastically decreases its volume. This implosion causes noise and high levels of erosion where the imploding bubbles contact the walls of a pipe, fitting, pump, or valve. The noise that develops sounds similar to gravel flowing through the system in the area where the cavitation is developing. Over time, the erosion results in excessive wear; this eventually man- ifests itself as pinhole leaking. Valves can develop cavitation when they are partially closed and flow is restricted. The result is noise and possible damage from erosion. Cavitation can also develop in a pump, which is noisy and can adversely affect pump performance by causing violent and damaging vibration and a sharp drop in dis- charge pressure. It occurs if the pumped liquid on the suction side of the pump drops below its vapor pressure. Eliminating this potential for cavitation is necessary because a cavitating pump can be completely damaged in a few hours of operation. As a minimum, pressure drop analysis should be per- formed to ensure that pressure available at the most remote out- let (farthest and highest fixture) is adequate. This proceeds once the layout of the plumbing system has been performed. Thus, the constant velocity method may be used in initial sizing. Cross-Connections A cross-connection is an unsatisfactory connection or arrange- ment of piping that can ca