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plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delive ...
, a trap is a U-shaped portion of pipe designed to trap liquid or gas to prevent unwanted flow; most notably
sewer gas Sewer gas is a complex, generally obnoxious smelling mixture of toxic and nontoxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes, typical components of sewage. Sewer gases may inclu ...
es from entering buildings while allowing waste materials to pass through. In oil refineries, traps are used to prevent hydrocarbons and other dangerous gases and chemical fumes from escaping through drains. In heating systems, the same feature is used to prevent thermo-siphoning which would allow heat to escape to locations where it is not wanted. Similarly, some pressure gauges are connected to systems using U bends to maintain a local gas while the system uses liquid. For decorative effect, they can be disguised as complete loops of pipe, creating more than one U for added efficacy.


General description

In domestic applications, traps are typically U, S, Q, or J-shaped
pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...
located below or within a plumbing fixture. An S-shaped trap is also known as an S-bend. It was invented by
Alexander Cumming Alexander Cumming FRSE (sometimes referred to as Alexander Cummings; 1733 – 8 March 1814) was a Scottish watchmaker and instrument inventor, who was the first to patent a design of the flush toilet in 1775, which had been pioneered by Sir ...
in 1775 but became known as the U-bend following the introduction of the U-shaped trap by Thomas Crapper in 1880. The U-bend could not jam, so, unlike the S-bend, it did not need an overflow. In the United States, traps are commonly referred to as P-traps. It is the addition of a 90 degree fitting on the outlet side of a U-bend, thereby creating a P-like shape (oriented horizontally). It is also referred to as a sink trap because it is installed under most sinks. Because of its shape, the trap retains some water after the fixture's use. This water creates an air seal that prevents sewer gas from passing from the drain pipes back into the building. Essentially all plumbing fixtures including
sink A sink is a bowl-shaped plumbing fixture for washing hands, dishwashing, and other purposes. Sinks have a tap (faucet) that supply hot and cold water and may include a spray feature to be used for faster rinsing. They also include a drain t ...
s,
bathtub A bathtub, also known simply as a bath or tub, is a container for holding water in which a person or animal may bathe. Most modern bathtubs are made of thermoformed acrylic, porcelain-enameled steel or cast iron, or fiberglass-reinforced pol ...
s, and
shower A shower is a place in which a person bathes under a spray of typically warm or hot water. Indoors, there is a drain in the floor. Most showers have temperature, spray pressure and adjustable showerhead nozzle. The simplest showers have a ...
s must be equipped with either an internal or external trap.
Toilet A toilet is a piece of sanitary hardware that collects human urine and feces, and sometimes toilet paper, usually for disposal. Flush toilets use water, while dry or non-flush toilets do not. They can be designed for a sitting position popu ...
s almost always have an internal trap. Because it is a localized low-point in the plumbing, sink traps also tend to capture small and heavy objects (such as jewellery or coins) accidentally dropped down the sink. Traps also tend to collect hair, sand,
food waste Food loss and waste is food that is not eaten. The causes of food waste or loss are numerous and occur throughout the food system, during production, processing, distribution, retail and food service sales, and consumption. Overall, about o ...
and other debris and limit the size of objects that enter the plumbing system, thereby catching oversized objects. For all of these reasons, most traps may be disassembled for cleaning or provide a cleanout feature. Where a volume of water may be rapidly discharged through the trap, a vertical vented pipe called a standpipe may be attached to the trap to prevent the disruption of the seal in other nearby traps. The most common use of standpipes in houses is for clothes washing machines, which rapidly dispense a large volume of wastewater while draining the wash and rinse cycles.


History

An S-shaped trap is also known as an S-bend. It was invented by
Alexander Cumming Alexander Cumming FRSE (sometimes referred to as Alexander Cummings; 1733 – 8 March 1814) was a Scottish watchmaker and instrument inventor, who was the first to patent a design of the flush toilet in 1775, which had been pioneered by Sir ...
in 1775 but became known as the U-bend following the introduction of the U-shaped trap by Thomas Crapper in 1880. The new U-bend could not jam, so, unlike the S-bend, it did not need an overflow. Once invented, despite being simple and reasonably reliable, widespread use was slow coming. In Britain, the requirement to use traps was introduced only after the
Great Stink The Great Stink was an event in Central London during July and August 1858 in which the hot weather exacerbated the smell of untreated human waste and industrial effluent that was present on the banks of the River Thames. The problem had been m ...
in London, in the summer of 1858, when the objectionable smell of the
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
, which was effectively an open sewer, affected the nearby
Houses of Parliament The Palace of Westminster serves as the meeting place for both the House of Commons and the House of Lords, the two houses of the Parliament of the United Kingdom. Informally known as the Houses of Parliament, the Palace lies on the north ban ...
. That motivated the legislators to authorise the construction of a modern sewerage system in the city, of which the S-bend was an essential component. , only about two-thirds of the world population have access to traps, in spite of the evidence that good sewage systems significantly improve economic productivity in places that employ them.


Venting and auxiliary devices

Maintaining the water seal is critical to trap operation; traps might dry out, and poor venting can suction or blow water out of the traps. This is usually avoided by venting the drain pipes downstream of the trap; by being vented to the atmosphere outside the building, the drain lines never operate at a pressure much higher or lower than atmospheric pressure. In the United States,
plumbing code A plumbing code is a code that provides regulations for the design, installation and inspection of building plumbing and sanitary systems. In the United States, jurisdictions enact their own codes, some of which are based upon model plumbing codes ...
s usually provide strict limitations on how far a trap may be located from the nearest ''vent stack''. When a vent cannot be provided, an air admittance valve may be used instead. These devices avoid negative pressure in the drain pipe by venting room air into the drain pipe (behind the trap). A "
Chicago Loop The Loop, one of Chicago's 77 designated community areas, is the central business district of the city and is the main section of Downtown Chicago. Home to Chicago's commercial core, it is the second largest commercial business district in Nort ...
" is another alternative. When a trap is installed on a fixture that is not routinely used—such as a floor drain—the eventual evaporation of the water in the trap must be considered. In these cases, a
trap primer A trap primer (or trap seal primer) is a plumbing device or valve that adds water to traps. The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evapor ...
may be installed; these are devices that automatically recharge traps with water to maintain their water seals.


Accepted traps in the United States

In some regions of the US, "S" traps are no longer accepted by the
building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permissi ...
s as the unvented S-traps tend to siphon dry. It may be possible to determine whether a household uses an S- or U-bend by the presence of an overflow pipe outlet. What is required instead is a P-trap with proper venting. Certain drum-styled traps are also discouraged or banned. Includes several photographs of various types of drum traps.


See also

* Buchan trap, an older type of trap *
Drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic condition ...
*
Drain-waste-vent system In modern plumbing, a drain-waste-vent (or DWV) is a system that allows air to enter the plumbing system to maintain proper air pressure to enable the removal of sewage and greywater from a dwelling. Drain refers to water produced at fixtures s ...
*
Garbage disposal unit A garbage disposal unit (also known as a waste disposal unit, garbage disposer, garburator etc.) is a device, usually electrically powered, installed under a kitchen sink between the sink's drain and the trap. The disposal unit shreds food ...
*
Sanitation Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
* Septic system *
Septic tank A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater ( sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatm ...
*
Tap water Tap water (also known as faucet water, running water, or municipal water) is water supplied through a tap, a water dispenser valve. In many countries, tap water usually has the quality of drinking water. Tap water is commonly used for drinking, ...
*
Water pipe Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delive ...


References


External links

{{Toilets Plumbing Bathrooms Piping