In
plumbingPlumbing is the skilled trade of working with pipes, tubing and plumbing fixtures for drinking water systems and the drainage of waste. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as water heaters...
, a
trap is a U-, S-, or J-shaped
pipeA pipe is round tubular section or hollow cylinder used mainly to convey media. It can also be used for structural applications. In layman's terms the appelations pipe and tube are almost interchangeable, but in industry and engineering discipline the terms are uniquely defined...
located below or within a
plumbing fixtureA plumbing fixture is a device which is part of a system to deliver and drain away water, but which is also configured to enable a particular use.-Common fixtures:The most common plumbing fixtures are:...
. An S-shaped trap is also known as the
S-bend invented by
Alexander CummingsAlexander Cummings was a Scottish watchmaker who invented the flush toilet. His premises were in Bond Street, London. The first patent for the flushing toilet was issued to Cummings in 1775...
in 1775 but this was subsequently replaced with the "U-bend" following the introduction of the U-shaped trap by
Thomas CrapperThomas P. Crapper was a plumber who founded Thomas Crapper & Co. Ltd. in London. Contrary to widespread misconceptions, Crapper did not invent the toilet, nor is the word crap derived from his name...
in 1880. The new "U-bend" could not jam so it did not need an overflow, common to the "S-bend". The bend is used to prevent
sewer gasSewer gas is fundamentally methane gas, but in reality a complex mixture of toxic and non-toxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes....
es from entering buildings.
In
plumbingPlumbing is the skilled trade of working with pipes, tubing and plumbing fixtures for drinking water systems and the drainage of waste. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as water heaters...
, a
trap is a U-, S-, or J-shaped
pipeA pipe is round tubular section or hollow cylinder used mainly to convey media. It can also be used for structural applications. In layman's terms the appelations pipe and tube are almost interchangeable, but in industry and engineering discipline the terms are uniquely defined...
located below or within a
plumbing fixtureA plumbing fixture is a device which is part of a system to deliver and drain away water, but which is also configured to enable a particular use.-Common fixtures:The most common plumbing fixtures are:...
. An S-shaped trap is also known as the
S-bend invented by
Alexander CummingsAlexander Cummings was a Scottish watchmaker who invented the flush toilet. His premises were in Bond Street, London. The first patent for the flushing toilet was issued to Cummings in 1775...
in 1775 but this was subsequently replaced with the "U-bend" following the introduction of the U-shaped trap by
Thomas CrapperThomas P. Crapper was a plumber who founded Thomas Crapper & Co. Ltd. in London. Contrary to widespread misconceptions, Crapper did not invent the toilet, nor is the word crap derived from his name...
in 1880. The new "U-bend" could not jam so it did not need an overflow, common to the "S-bend". The bend is used to prevent
sewer gasSewer gas is fundamentally methane gas, but in reality a complex mixture of toxic and non-toxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes....
es from entering buildings. In
refineryA refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.-Types of refineries:Different types of refineries are as follows:...
applications, it also prevents
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
s and other dangerous gases from escaping outside through drains.
Because of its shape, the trap retains a small amount of water after the fixture's use. This water in the trap creates a
water seal that prevents
sewer gasSewer gas is fundamentally methane gas, but in reality a complex mixture of toxic and non-toxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes....
from passing from the drain pipes back into the occupied space of the building. Essentially all
plumbing fixtureA plumbing fixture is a device which is part of a system to deliver and drain away water, but which is also configured to enable a particular use.-Common fixtures:The most common plumbing fixtures are:...
s including
sinkIn plumbing, a sink or basin is a bowl-shaped fixture that is used for washing hands or small objects. In American plumbing parlance, a bathroom sink is known as a lavatory....
s,
bathtubA bath , bathtub , or tub is a plumbing fixture used for bathing. Most modern bathtubs are made of acrylic or fiberglass, but alternatives are available in enamel over steel or cast iron, and occasionally waterproof finished wood...
s, and
toiletA toilet is a plumbing fixture and disposal system primarily intended for the disposal of the bodily wastes: urine and fecal matter. Additionally, vomit and menstrual waste are sometimes disposed of in toilets in Western societies. The word toilet describes the fixture and, especially in British...
s must be equipped with either an internal or external trap.
Because it is a localized low-point in the plumbing, sink traps also tend to capture heavy objects (such as
jewelryJewellery or jewelry is an item of personal adornment, such as a necklace, ring, brooch or bracelet, that is worn by a person. It may be made from gemstones or precious metals, but may be from any other material, and may be appreciated because of geometric or other patterns, or meaningful symbols...
) that are inadvertently dropped into the sink. Traps also tend to collect
hairHair is a protein filament that grows through the epidermis from follicles deep within the dermis. The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats. Found exclusively in mammals, hair is one of the...
,
sandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
, and other debris and limit the ultimate size of objects that will pass on into the rest of the plumbing, thereby catching over-sized objects. For all of these reasons, most traps can either be disassembled for cleaning or they provide some sort of
cleanout feature. For example, the image to the right shows a removable drain screw at the bottom of each trap.
Venting and auxiliary devices
Maintaining the water seal is thus critical; traps can and do dry out, and poor
ventingIn modern plumbing, a drain-waste-vent is a system that removes sewage and greywater from a building and vents the gases produced by said waste. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped section of pipe that always contains...
can
siphonA siphon is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher, or lower, than the reservoir, the flow being driven only by the difference in hydrostatic pressure without any need for pumping...
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 pressureAtmospheric pressure is defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above...
. Plumbing codes usually provide strict limitations on how far a trap may be located from the nearest
vent stack.
When a vent cannot be provided, codes may allow the use of an air admittance valve instead. These devices avoid negative pressure in the drain pipe by venting room air into the drain pipe (behind the trap). A "
Chicago LoopThe Chicago Loop is an alternate way of venting the trap installed on an under counter island sink or other similar applications where a conventional vertical vent stack isn't feasible.-Function:...
" is another alternative.
When a trap is installed on a fixture that is not routinely used, the eventual
evaporationEvaporation is the vaporization of a liquid and the reverse, of condensation. A type of phase transition, it is the process by which molecules in a liquid state spontaneously become gaseous . Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed...
of the water in the trap must be considered. In these cases, a
trap primerA trap 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 evaporation over time...
may be installed; these are devices that automatically recharge traps with water to maintain their water seals.
Accepted traps
In many locations, "S" traps are no longer accepted by the plumbing codes and are even illegal, as these traps tend to easily siphon dry even when well-vented. It is often possible to tell whether a household uses an S or U-bend by checking for the presence of an overflow pipe outlet. Certain drum-styled traps are also discouraged or banned.
See also
- Potable cold and hot water supply
- Rainwater, surface, and subsurface water drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
- Pipe (material)
A pipe is round tubular section or hollow cylinder used mainly to convey media. It can also be used for structural applications. In layman's terms the appelations pipe and tube are almost interchangeable, but in industry and engineering discipline the terms are uniquely defined...
- Plumbing
Plumbing is the skilled trade of working with pipes, tubing and plumbing fixtures for drinking water systems and the drainage of waste. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as water heaters...
- Plumbing drainage venting
In modern plumbing, a drain-waste-vent is a system that removes sewage and greywater from a building and vents the gases produced by said waste. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped section of pipe that always contains...
- Sanitation
Sanitation is the hygienic means of promoting health through prevention of human contact with the hazards of wastes. Hazards can be either physical, microbiological, biological or chemical agents of disease. Wastes that can cause health problems are human and animal feces, solid wastes, domestic...
- Septic systems
- Septic tank
A septic tank, the key component of the septic system, is a small scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...
- Water pipe
Water pipes are pipes or tubes, frequently made of polyvinyl chloride , ductile iron, polyethylene, or copper, that carry pressurized and treated fresh water to buildings , as well as inside the building....
- Garbage disposal
A garbage disposal, garbage disposer, food waste disposal, food waste disposer, waste disposal unit, or garburator / garbarator is a device, usually electrically-powered, installed under a kitchen sink between the sink's drain and the trap which shreds food waste into pieces small enough to pass...
- Siphon
A siphon is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher, or lower, than the reservoir, the flow being driven only by the difference in hydrostatic pressure without any need for pumping...
External links