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Flush toilet
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A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets (used in the sitting position), but many squat toilets also are made for automated flushing (as shown .) Modern toilets incorporate an 'S' bend; this 'trap' creates a water seal which remains filled.
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A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets (used in the sitting position), but many squat toilets also are made for automated flushing (as shown .) Modern toilets incorporate an 'S' bend; this 'trap' creates a water seal which remains filled. The 'S' bend also provides siphon action which helps accelerate the flushing process. Water filling up the bowl creates a high pressure area which forces the water past the S bend. At the S bend when water starts to move it creates a vacuum that pulls the water and waste out of the toilet. When no more water is left then the air stops the siphon or vacuum process. At that point the water that is going into the bowl continues to fill up the bowl to equalize the bowl and the S bend. This ends the cycle of one flush. However, since this type of toilet does not generally handle waste on site, separate waste treatment systems must be built.
Invention timeline
As with many inventions, the flush toilet did not suddenly spring into existence, but was the result of a long chain of minor improvements. Therefore, instead of a single name and date, there follows a list of significant contributors to the history of the device.
- circa 26th century BC: Flush toilets were first used in the Indus Valley Civilization. The cities of Harappa and Mohenjo-daro had a flush toilet in almost every house, attached to a sophisticated sewage system.
- circa 18th century BC: Flush toilet constructed at Knossos on Minoan Crete
- circa 15th century BC: Flush toilets used in the Minoan city of Akrotiri.
- 9th century BC: Flush toilets in Bahrain Island.
- 1st to 5th centuries AD: Flush toilets were used throughout the Roman Empire. Some examples include those at Vindolanda on Hadrian's Wall in Britain. With the fall of the Roman Empire, the technology was lost in the West.
- 1596: Sir John Harington published A New Discourse of a Stale Subject, Called the Metamorphosis of Ajax, describing a forerunner to the modern flush toilet. The design had a flush valve to let water out of the tank, and a wash-down design to empty the bowl. He installed one for his godmother Elizabeth I of England at Richmond Palace, although she refused to use it because it made too much noise. The Ajax was not taken up on a wide scale in England, but was adopted in France under the name Angrez.
- 1738: A valve-type flush toilet was invented by J. F. Brondel.
- 1775: Alexander Cummings invented the S-trap (British patent no. 814?), still in use today, which uses standing water to seal the outlet of the bowl, preventing the escape of foul air from the sewer. His design had a sliding valve in the bowl outlet above the trap.
- 1777: Samuel Prosser invented and patented the 'plunger closet'.
- 1778: Joseph Bramah invented a hinged valve or 'crank valve' that sealed the bottom of the bowl, and a float valve system for the flush tank. His design was used mainly on boats.
- 1819: Albert Giblin received British patent 4990 for the "Silent Valveless Water Waste Preventer", a siphon discharge system.
- 1852: J. G. Jennings invented a wash-out design with a shallow pan emptying into an S-trap.
- 1857: The first American patent for a toilet, the 'plunger closet', was granted.
- 1860: The first watercloset installed on the European continent was imported from England. It was installed in the rooms of Queen Victoria in castle Ehrenburg (Coburg, Germany); she was the only one who was allowed to use it.
- The first popularized water closets were exhibited at The Crystal Palace and these became the first public toilets. They had attendants dressed in white and customers were charged a penny for use. This is the origin of the phrase "To spend a penny".
- 1880s: Thomas Crapper's plumbing company built flush toilets of Giblin's design. After the company received a royal warrant, Crapper's name became synonymous with flush toilets. Although he was not the original inventor, Crapper popularized the siphon system for emptying the tank, replacing the earlier floating valve system which was prone to leaks. Some of Crapper's designs were made by Thomas Twyford. The similarity between Crapper's name and the much older word crap is merely a coincidence.
- 1885: Thomas Twyford built the first one-piece china toilet using the flush-out siphon design by J. G. Jennings.
- 1886: An early jet flush toilet was manufactured by the Beaufort Works in Chelsea, England.
- 1906: William Elvis Sloan invents the Flushometer which uses pressurized water directly from the supply line for faster recycle time between flushes. The original Royal Flushometer is still in use today in public restrooms worldwide.
- 1907: Thomas MacAvity Stewart of Saint John, New Brunswick patents the vortex-flushing toilet bowl which creates a self cleansing effect.
- 1980: Bruce Thompson, working for Caroma in Australia, developed the Duoset cistern with two buttons and two flush volumes as a water-saving measure. Modern versions of the Duoset are now available in more than 30 countries worldwide, and save the average household 67% of their normal water usage.
The bowl
The bowl, loo or pan, of a toilet is the receptacle into which body waste is excreted; the pan is usually made of porcelain, but sometimes made of stainless steel or composite plastics. Toilet bowls may be pedestal (free-standing), cantilever (wall-hung), or squat in design. There are several types of pans in common use: washdown, washout, and siphon. In less common use is the valve closet. There are "male" and "female" bowls also. Males prefer the larger, elongated (or oval) bowls for "penis clearance" while sitting for defecation. This is more sanitary since the penis is clear of the bowl, rim and usually elongated seat. The outer edge of a toilet bowl is termed the "rim". Women prefer the smaller, round bowls because these can easilly accommodate them and they take up less space in small home bathrooms.
Washout pans
Washout pans have a shallow pool of water into which waste is excreted. Waste is cleared from the pan by being swept over a trap, usually either a p trap or s trap and into a drain by water from the flush. Washout pans are popular in several countries in Europe, notably Germany and Great Britain.
The bowl siphon
The bowl of a flush toilet is a porcelain vessel; in North America this often has a built-in siphon, usually visible as a curved pipe protruding from the back (the "S-bend"). Normally, the bowl contains a small amount of water which is enough to form an air trap inside the siphon pipe, preventing foul air escaping from the sewer. When the toilet is used, liquid flows slowly through the siphon pipe as waste matter is added, but the flow volume is too small to fill the siphon. To flush the toilet, the user activates a flushing mechanism (see below) which pours a large quantity of water quickly into the bowl. This creates a flow large enough to fill the siphon tube, causing the bowl to empty rapidly due to the weight of liquid in the tube. The flow stops when the liquid level in the bowl drops below the first bend of the siphon, allowing air to enter which breaks the column of liquid.
Valve closet
The valve closet has a valve or flap at the exit of the bowl with a water-tight seal to retain a pool of water in the pan. When the toilet is flushed, the valve is opened and the water in the pan flows rapidly out of the bowl into the drains, carrying the waste with it.
The earliest type of toilet, the valve closet is now scarce as a water-flush toilet. More complicated in design than other water closets, reliability is lower and maintenance more difficult. The most common use for valve closets is now in portable closets for caravans, camping, trains, and aircraft where the flushing fluid is recycled. This design is also used in train carriages in areas where the waste is allowed to be simply dumped between the tracks (the flushing of such toilets is generally prohibited when the train is in a station).
Cultural variations
In Germany and elsewhere in Europe it is not uncommon for the toilet bowl to allow feces to rest on a ledge before being washed away by the flush to avoid the splash of water. The design of many German lavatory bowls is the reverse of that in most other Western countries, with the sewer outlet towards the front of the bowl rather than at the rear. One theory for this is that it allows the stools to be visually checked more easily for conditions such as presence of worms, or for its color, which vary depending on diet and health. This type is called Flachspüler, Washout or a shelf toilet.
In India, the "Anglo-Indian" design allows the same toilet to be used in the sitting or the squatting position.
For a review of Japanese toilet usage and history, see Toilets in Japan.
Parts
Flushing mechanisms
The bowl siphon described above is triggered by a large flow of water into the bowl, which is provided by the flushing mechanism. This is usually of one of the following designs:
Direct flush (flushometer)
In the old-style manual flush systems, the user presses a button, which opens a flush valve allowing mains-pressure water to flow into the bowl, or sometimes the user presses directly on a flush lever (a handle connected directly to a flushometer). The valve contains a pneumatic mechanism that closes it after a preset time. This system requires no storage tank, but requires high volume water for a very brief time period. Thus a 3/4 inch (19 mm) pipe at minimum, and preferably a 1 inch (25 mm) pipe, must be used, but the high volume is used only for a short duration so very little water is used for the amount of flushing efficacy delivered. Direct valves are regulated by a device called a "flushometer" that meters out a certain controlled amount of water per flush. Direct flush makes the most efficient use of water, because it uses the water at full pressure and volume. The ability of water to perform the work in removing waste matter from the toilet bowl is given by pressure times volume. Typical pressure in an urban commercial building where flushometers are usually used is around 60 pounds per square inch (400 kPa) which is enough pressure to raise the water 137 feet (42 m) above the toilet bowl. Thus, in some sense, the effectiveness of direct flush is like having the tank 137 feet (42 m) above the bowl (lots of "flush energy").
Valve tank type
A storage tank, or cistern, collects between 6 and 17 litres of water over a period of time. This system is suitable for locations plumbed with smaller diameter pipes. The actual water inlet is a 1/2" threaded connector in the UK and 3/8" on the Continent (an unusual example of an imperial standard surviving). The storage tank is kept full by a float valve or ball cock. An outlet in the bottom of the tank is covered by a buoyant plastic cover (the flush valve) which is held in place by water pressure. To flush the toilet, the user pushes a lever, which lifts the flush valve from the outlet. The valve then floats clear of the outlet, allowing the tank to empty quickly into the bowl. As the water level drops, the floating flush valve descends back to the bottom of the tank and covers the outlet pipe again. This system is common in homes in the USA. Tank type toilets waste the energy in the water by converting the potential energy of 137 feet (42 m) (the "head" of pressure in typical North American city water mains) times acceleration due to gravity, into around 18 inches (460 mm) above the bowl. Some older style toilets mitigate this waste of energy to some degree by having the tank be as high as possible (up near the bathroom ceiling), but modern tank-type toilets waste the energy in the water, and therefore either use more water than necessary for a given flushing job, or for the same amount of water, flush less effectively than direct flush.
Tanks near the ceiling are flushed by means of a dangling pull chain, often with a large ornate handle, connected to a flush lever on the cistern itself. "Pulling the chain" remains a British euphemism for flushing the toilet, although this type of cistern is now relatively uncommon.
Low-flow and High Efficiency toilets
The conventional flush-toilet or gravity-fed toilet uses 13 litres (3.4 US gallons or 2.8 imperial gallons) or more per flush. In 1992, the United States Congress passed the Energy Policy Act of 1992, which mandated that, from 1994, the common flush-toilet use only 1.6 US gallons (6 litres) of water per flush. In response to the Act, manufacturers produced low-flow toilets, which many consumers did not like. Manufacturers responded to consumers' complaints by improving the toilets. The improved products are generally identified as high efficiency toilets or HETs. HETs possess an effective flush volume of 4.8 litres (1.28 US gallons) or less. HETs may be single-flush or dual-flush. A dual-flush toilet permits its user to choose between two amounts of water. Some HETs are pressure-assisted (or power-assisted or pump-assisted or vacuum-assisted).
The performance of a flush-toilet may be rated by a Maximum Performance (MaP) score. The low end of MaP scores is 250. The high end of MaP scores is 1000. A toilet with a MaP score of 1000 should provide trouble-free service. It should remove all waste with a single flush; it should not plug; it should not harbor any odor; it should be easy to keep clean. The United States Environmental Protection Agency uses a MaP score of 350 as the minimum performance threshold for HETs.
American Standard Timed Cup Flush Valve
The flush valve is responsible for quickly emptying the tank (cistern) and driving the waste from the bowl. It is sometimes referred to as the American Standard Tilting Flush Valve.
In 1958 (citation: patent date), American Standard introduced a unique flush valve which differed from the conventional "flapper". Though no longer used in new toilets, this valve design remains an extremely popular upgrade when repairing an existing toilet.
The American Standard timed cup flush valve incorporates two cylinders mounted orthogonally, attached to a flushing disk.
Operation is best understood as follows:
1. Prior to flushing, the tank (cistern) is full of water. Both cylinders are submerged, and the flushing disk remains tightly shut due to the weight of the water pushing it against its seat.
2. With a flush, the disk is pulled away from the seat. Water escapes to the bowl. The horizontal cylinder provides buoyancy to hold the disk away from the valve seat. The vertical cylinder remains full of water.
3. As the tank empties, the buoyancy of the horizontal cylinder is compromised, but the vertical cylinder remains full of water which provides sufficient counterbalance to the flushing disk, holding it open.
4. After the tank has emptied, the water in the vertical cylinder drains through a 3/16" hole in the bottom of the cylinder. At some point after the tank has emptied, the mass of the flushing disk and horizontal cylinder exceeds the mass of the vertical (timing cup) cylinder, causing the flushing disk to fall back onto its seat.
5. The fill valve refills the tank for the next flush cycle.
A stellar benefit of the American Standard Timed Cup flush valve is that an incomplete flush is virtually impossible. Repairs are easy, generally requiring only a flushing disk.
One-Piece Fill Valve
The fill valve is responsible for refilling the tank (cistern) with water.
Toilets manufactured prior to 1990 are likely to include a "Hoover-style" ballcock, which is a fill valve employing a ball-type float mounted on an arm. As the float rises, so does the arm. The arm is connected to a linkage which blocks the water flow into the toilet tank, and thus maintains a stable level in the tank.
A one-piece fill valve consists of a tower which is encircled by a plastic float assembly. Operation is otherwise the same as a conventional Hoover ballcock, though the geometry is different. By virtue of the more compact layout, interference between the float and other obstacles (tank insulation, flush valve) is greatly minimized, thus reducing reliability issues (stuck floats, etc).
Valveless siphon tank type
This system, invented by Albert Giblin and common in the UK, uses a storage tank similar to that used in the flush valve system above. The user pushes a lever or button, forcing the water up into a siphon (not to be confused with the bowl siphon, "S-bend") which empties the entire tank into the bowl. The advantage of a siphon over the flush valve is that is has no sealing washers that can wear out and cause leaks, so it is favoured in places where there is a need to conserve water. Until recently, the use of siphon-type cisterns was mandatory in the UK to avoid the potential waste of water by millions of leaking toilets.
Older installations used a high-level cistern, or high suite, fitted above head height, that was operated by pulling a chain hanging down from a lever attached to the cistern. Some people still refer to the act of flushing a toilet (even a new low-cistern, or low suite, type) as "pulling the chain" or "flushing the chain". Modern versions have a neater-looking low-level cistern with a lever that the user can reach directly, or a 'close-coupled' cistern that is even lower down and integrated with the bowl. This lower level results in loss of potential energy in the water, as the potential energy of water pressure is converted to the potential energy of height in a less advantageous manner, due to very little height, as described above. Consequently modern toilets usually do not flush as effectively.
Pressure-assisted
Not uncommon in the United States, this system used the water pressure within a structure to compress air within a closed vessel located within the vitreous enclosure. When flushed, the compressed air pushes into the bowl at a velocity (flow rate in gallons per minute or liters per second) significantly higher than gravity flow. This system is more water efficient than a tank type and can be installed into the same fittings as the latter. It also costs 10% less than the new 3" (75 mm) gravity flapper equipped tank-type toilets. Pressure assist toilets are used in both private (single and multiple and lodging) bathrooms as well as light commercial installations (offices, etc.) They hardly ever clog and so require less maintenance, but tend to be noisier - a concern for residential settings. The inner bowl stays cleaner (in appearance) than gravity counterparts because of the larger water surface area and the toilet's forceful flush.
Automatic flush
"Automatic flush" refers to a triggering mechanism, rather than a water propulsion mechanism, although is usually implemented together with direct flush systems. Autoflush systems, as the name suggests, flush automatically once the user has left. Typically, an override button is provided if the user wishes to trigger flushing earlier or, when the system has true mechanical manual override, it can be pushed if the power source to the flush valve has failed. In retrofit installations, a self-contained battery-powered or hardwired unit can be added to an existing manual flushometer, which can automatically flush when a user departs.
There are two main kinds of machine vision systems used for sensor operated flush: passive and active. Passive systems such as passive infrared (PIR) detect infrared radiation given off by a body warmer than its surroundings. Active vision systems illuminate the target (the user of the fixture) with electromagnetic radiation (e.g., microwave or infrared) and detect energy reflected by the target. Although units usually ship with a factory-set sensor range, installers can adjust the setting to accommodate special needs or circumstances, such as for restrooms primarily used by children.
Automatic flushing cisterns may also be of the siphonic pattern, where a siphon is activated once water fills the tank and begins to run through the siphon tube; this is the most common form of automatic operation in the UK.
Manual operation
If the flush mechanism should fail in any of these systems, the bowl siphon can be activated by emptying a large bucket of water into the bowl. A domestic hose pipe will not work, as it cannot supply water fast enough to fill the siphon tube. A larger hose, or small firehose, even a 3/4 inch (2 cm) garden hose thread (GHT) firehose, provides sufficient water to flush without a bucket.
Flush Repair
For North American Valve Tank type toilets, if the handle should have to be held down to achieve a complete flush an adjustment might need to be made in the handle-float-stopper mechanism. The handle of a toilet is typically attached to a stopper via a chain. A float is attached to the chain between the handle lever and the stopper. The float acts as a counter-balance to allow a certain amount of water to escape through the flush hole in the tank. The float mechanism on the chain should be some distance under the water level of the tank so it can keep the stopper open during a flush until the tank level reaches a certain level. At a certain level the float will pop to the top of the water and the stopper will close. The float should be at a position on the chain where it is under water and does not have so much buoyancy to allow water to leak through the stopper.
For British toilets, the siphon's hidden, oblong, plastic diaphragm will tend to split after around 10 years. The effectiveness of the flush can deteriorate suddenly or gradually as the number and size of splits increase. This will often prompt owners to replace much of the system. However, the diaphragms are of a standard design and are cheap (50p) and simple to replace. Inside the cistern, unhooking the flush-handle's s-link allows the plunger and diaphragm to be removed, once the lower part of the siphon is unscrewed (it is not necessary to remove the whole assembly with some multiple part syphons -- the main outlet pipe can be left in place. Most are one piece and require removing from the cistern completely. There is also a small rubber diaphragm in the ballcock inlet assembly, which can deteriorate over a period of around 10 years -- if adjusting the water level becomes problematic, it is worth changing this inexpensive item (50p).
"The Flush"
Flushometer type toilets are much more common in commercial installations; they're almost never seen in residential installations, except for dormitory and barracks areas.
Water closet (WC)
The water closet was the original term for a room with a toilet, since the bathroom was where one was to take a bath. This term is still used today in some places, but might be a room that has both toilet and bath. Plumbing manufacturers often use the term to delineate toilets from urinals.
Flushing direction
It is a commonly held misconception that when flushed, the water in a toilet bowl swirls one way if the toilet is north of the equator and the other way if south of the equator, due to the Coriolis effect. Usually, counter clockwise in the northern hemisphere, and clockwise in the southern hemisphere. In reality, the direction that the water will take is much more determined by the geometry of the bowl and other factors and can flush in either direction in either hemisphere.
See also
External links
- (comparison between passive and active vision systems for use with plumbing fixtures, as published in Leonardo, 36(3), pp 199–120, June 2003)
- , 2005 book (link to pdf-file)
- - at Snopes
- - PM Engineer
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