Plumbing is a system of pipes that carries water to and from a house or other building. The term comes from the Latin word plumbum, meaning lead. The ancient Romans used lead plumbing pipes. Today, most plumbing pipes are made of brass, cast iron, copper, plastic, or steel.
Contaminated water has long been a major cause of disease and death for people. Modern plumbing systems keep the water used in a building free from contamination. In many countries, rules called codes establish minimum standards for installing safe plumbing.
A plumbing system consists of two separate sets of pipes, a water supply system and a drain-waste-vent (DWV) system. The water supply system brings potable (fit for drinking) water to plumbing fixtures, including bathtubs, showers, sinks, and toilets. It also supplies clean water to such appliances as dishwashers, garbage disposals, hot-water heaters, washing machines, and water softeners. The DWV system carries away water, waste materials, and odors.
The water supply system and the DWV system both must function properly for a building’s plumbing to be efficient and safe. Such defects as leaking connections or dripping faucets can waste water and cause damage to a water supply system. A DWV system that leaks or overflows creates a health hazard by spilling waste materials and the bacteria they contain.
The water supply system.
Water for a plumbing system comes from two sources: (1) rivers and lakes, and (2) wells. Cities and towns draw water from these sources and pipe it to treatment plants, where it is purified. The purified water flows through large pipes called mains, which run under the streets. The mains connect with smaller pipes known as service lines, which lead into each building. In some rural and suburban areas, many houses and other buildings have private wells. See Water (City water systems) .
The water supply system of every building has a shut-off valve. This valve normally remains open, permitting water to enter the building. The valve can be closed to turn off the water for the repair of pipes or fixtures, or for some other emergency. Each plumbing fixture and appliance also should have its own shut-off valve.
In many plumbing systems, a water meter and backflow prevention device are attached to the service line. The water meter measures the amount of water used in the building. The water company or city charges the customer according to the amount of water used. The backflow prevention device stops water in a building’s plumbing system from reentering a water main or any water supply source within the building.
Water that flows into a building through the service line is cold. Pipes connected to the service line carry the water to the plumbing fixtures and appliances that use cold water. One of the pipes brings water to the hot-water heater. A cold-water inlet pipe brings water to the hot-water heater. The water is heated in the water heater tank to a temperature set on the heater’s thermostat. To prevent scalding and the build-up of lime scale, which can occur at temperatures of 140 °F (60 °C) or higher, most people set the thermostat at about 120 °F (49 °C). The heated water is drawn from the top of the tank. It flows through a hot-water outlet pipe and is carried by branch pipes to the fixtures and appliances in the building that use hot water. The hot-water heater tank in most houses holds from 30 to 50 gallons (114 to 189 liters) of water. The tank is always full. As hot water is used, cold water enters the tank to be heated.
Water expands when heated and can build high pressure in a hot-water heater tank. If the water temperature exceeds the thermostat setting or if the pressure in the tank rises above a predetermined maximum, a temperature and pressure relief (TPR) valve releases hot water from the tank. A thermal expansion tank may be connected to the cold-water entry pipe. Overheated water expands into this tank if the TPR valve fails. Some systems have a thermal expansion tank but no TPR valve. By retaining overheated water rather than releasing it, such a system conserves the energy required to heat the water.
Water in a water supply system is always under pressure. Valves in fixtures and appliances hold back the water until it is needed.
The drain-waste-vent system
carries away water that has been used, along with solid waste from sinks, toilets, garbage disposals, and other fixtures and appliances. The pipes used for drainage are larger than those of the water supply system to prevent them from becoming clogged with solid materials.
The drainpipes from the fixtures and appliances slant downward, carrying water and sewage to a vertical pipe called the soil stack. The soil stack empties into a main drain beneath the building. This drain leads to a sewer or septic tank outside. The top of the soil stack extends up through the roof of the building. In many systems, air flows through the soil stack into a network of smaller vent pipes that lead into the drainpipes of fixtures that are not near the soil stack. In most buildings, drainpipes from toilets link directly to the soil stack.
The drainpipe of each plumbing fixture and appliance empties through a P- or S-shaped bend called a trap. The water in the trap serves as a seal that prevents harmful gases from the sewer or septic tank from entering the building through a fixture or appliance. Gases instead escape through the soil stack and vent pipes. The flow of air into the drainage pipe prevents a partial vacuum from developing as water and sewage flow out. Such a vacuum would slow the passage of water and sewage from the drainage system and could siphon (pull by suction) the water from the traps and destroy the seal.
Cleanout plugs are positioned throughout a drainage system so that the homeowner or a plumber may easily clear stoppages. After removing the cleanout plug, the homeowner or plumber can insert a long, flexible tool called a drain auger, or snake into the pipe to clear it. Almost all plumbing systems have a cleanout plug where the soil stack connects to the main drain.
In many communities, sewage flows from the main drain of each building into underground pipes that carry it to a sewage treatment plant. The plant treats the sewage water and reduces the bacteria in it. The treatment plant can then pour the water into a river or other body of water with minimum damage to the waterway.
In rural and suburban areas that do not have public sewerage systems, the sewage from a building flows into a septic tank. Bacteria in the septic tank break down most of the solids in the sewage into gas and a harmless substance called humus. The gas escapes into the air, and the humus is removed periodically. The liquids run out of the tank into the surrounding soil. See Sewage .
How faucets work.
Faucets regulate the flow of water in bathtubs, showers, sinks, and certain other plumbing fixtures. Faucets are also called taps. There are two main kinds of faucets, washer-type faucets and washerless faucets.
Washer-type faucets typically have two handles, one for hot water and one for cold. The water comes out of a single spout. Older faucets have a separate handle and spout for hot and cold water. Water is turned on and off by turning one or both of the handles. A threaded stem is attached to each handle and screws into the faucet. At the bottom of each stem is a washer made of rubber or of synthetic fibers. When the faucet is turned off, the stem and washer are held tightly over a valve seat at the top of the water supply pipe. The washer prevents the flow of water into the faucet. When the faucet is turned on, the stem is unscrewed enough to lift it and the washer off the seat. Water can then flow into and through the spout.
Washerless faucets may have two handles or only one. Most have a single spout. Under the handle of a typical two-handle model is a cartridge containing two disks with several identically positioned holes in them. When the faucet is on, the holes line up with one another, enabling water to flow through them and into the spout. When the faucet is turned off, the position of the top disk changes to cover the holes of the bottom disk, preventing flow. The water temperature is regulated by turning both handles, mixing the hot and cold water.
Single-handle washerless faucets utilize either a sliding shaft within a stationary cartridge or a rotating ball. In a cartridge-type faucet, lifting the handle moves the shaft upward, which opens both hot- and cold-water passages. In a ball-type faucet, pushing the handle back turns on the water. In both types, moving the handle to the left opens wider the hot-water passage while closing the cold-water passage. Moving the handle to the right opens wider the cold-water passage while closing the hot-water passage. In a cartridge-type faucet, pushing the handle down closes off both passages, turning off the water. In a ball-type faucet, pulling the handle forward turns off the water.
How toilets work.
Most toilets consist of a bowl and a tank, both of which contain water. When the toilet is not being flushed, a stopper ball or a flapper covers an opening called the tank discharge opening at the bottom of the tank, preventing water from flowing out. When the toilet is flushed, the action of pushing down the handle lifts the stopper ball or flapper. Water then flows rapidly through the tank discharge opening and into the bowl through holes surrounding the rim and through a larger opening at the base of the bowl. The rapid flooding opens the trap and forces the water and waste products to empty from the trap. Water flowing through the rim holes cleans the sides of the bowl. When the tank has emptied, the stopper ball or flapper drops onto the discharge opening.
A refill valve in the tank is connected to the water supply pipe. This valve automatically refills the tank after the toilet is flushed. It is usually controlled by a float, which may be either a ball attached to a rod, or a device that slides up and down on the refill valve body. The float rides on the water. When the water level in the tank drops, as occurs when the toilet is flushed, the float drops as well, and the valve opens. Water from the water supply pipe then enters the tank through the refill tube. In some toilets, part of the water from the water supply pipe goes into a bowl refill tube. It then flows into an overflow tube and out the rim holes. Water flows into the tank from the refill tube until the water is about 1 inch (2.5 centimeters) from the top of the overflow tube. The refill valve prevents tank water from being drawn into the potable water system.
Since 1992, all toilets made or sold in the United States must be low-flow toilets that meet federal water conservation standards. Such toilets use less than 1.6 gallons (6.1 liters) of water per flush, about half the amount used by conventional toilets. Dual flush toilets let the user choose either a standard flush or a water-saving flush.
History.
The first plumbing systems were developed to dispose of human wastes. In the Indus Valley in what are now Pakistan and western India, most dwellings had drains for waste disposal by about 2600 B.C. A palace built on the island of Crete about 2000 B.C. had pipes to supply drinking water. It also had primitive toilets and a drainage system with air shafts that served as vents. The ancient Romans developed faucets and a sewerage system that carried waste into rivers and streams.
The quality of plumbing declined during the Middle Ages, from about the A.D. 400’s through the 1400’s. People disposed of waste materials by throwing them into the street. A type of flush toilet was developed in the 1500’s. But it did not come into wide use because of the general lack of plumbing and sewerage systems.
In 1778, Joseph Bramah, an English cabinetmaker, patented an improved flush toilet. During the first half of the 1800’s, toilets became common in England. However, most of them drained into pits called cesspools, which often overflowed. Septic tanks were invented in the mid-1800’s, and a modern sewerage system began operating in London in the 1860’s. Also in the 1860’s, Thomas Crapper, an English plumber, made improvements in the flush toilet patented by Bramah.
