Flush toilet

Flush toilet

A flush toilet or water closet (WC) is a toilet that disposes of the waste products by using water to send them through a drainpipe to another location. Modern toilets incorporate an 'S' bend which remains filled with water between flushing, thus providing a hygienic barrier by preventing foul gases from passing up the drainpipe. During flushing the 'S' bend provides siphon action which helps accelerate the flushing process. 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.

Note: due to the lack of information from other cultures, this chronology is regrettably Anglocentric. Additional information about early flush toilet technology in other parts of the world would be welcome.

• Ancient world: there are remains of flushing toilets, both private and communal, from several ancient civilisations around the world, dating from 2600 BC onwards.
• 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 15th century BC: flushing toilets were found in the remains of the Minoan city of Akrotiri.
• Roman Empire: some examples include those at Hadrian's Wall in Britain. With the fall of the Roman empire, the technology was lost.
• 1596: Sir John Harrington is said to have invented 'The Ajax', a flush toilet, for Elizabeth I of England. His design was ridiculed in England, but was adopted in France under the name Angrez. The design had a flush valve to let water out of the tank, and a wash-down design to empty the bowl.
• 1738: a valve-type flush toilet was invented by JF Brondel.
• 1775: Alexander Cummings invented the S-trap (British patent no. 814?), still used today, that used 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 was installed on the European continent and was imported from England. It has been installed in the rooms of Queen Victoria in castle Ehrenburg (Coburg, Germany) and she was the only one who was allowed to use it.
• The first popularized water closets were exhibited at Crystal Palace and they became the first public toilets, they had attendants dressed in white and they charged only a penny coining the term "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.

The bowl

The bowl, or pan, of a WC is the receptacle into which body waste is excreted, usually made of vitreous china, but sometimes made of stainless steel or composite plastics. WC bowls may be pedestal (free-standing), cantilever (wall-hung) or squat in design. There are several types of pan in common use: washdown, washout, and siphon. In less common use is the valve closet.

Washdown WC pans

Washdown WCs are the simplest in design. They take the form of a 'funnel' shape, with a broad opening at the top narrowing to a smaller outlet connected to a drain. The pan usually incorporates a water trap at the base to seal the open end of the pan from the sewer.

Washdown pans have almost vertical surfaces at the back of the pan and more gently sloping fronts to allow the outlet of the pan to be directly beneath the anus of a seated user to prevent soiling of the bowl.

Washout WC 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 weir and into a drain by water from the flush. Washout pans are not permitted in the UK.

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. 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 earliest type of WC, the valve closet is now scarce. 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 and camping.

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 WC 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.

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. 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.

Flushing mechanisms

Retrofit direct flush installation in which the flushometer has been replaced with a sensor-operated system that automatically flushes the fixture when a user departs. The system uses an infrared proximity sensor to detect a user approaching the fixture, then it waits until the user departs. A solenoid is used to actuate the flush from a 6 volt battery inside the unit that also powers the sensor circuit.

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").

Flush valves are not permitted on fixed WCs in Britain, although they are sometimes used in railway carriages.

Valve tank type

A storage tank, or cistern, collects between 6 and 9 litres of water over a period of time. This system is suitable for locations plumbed with smaller diameter pipes. 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 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.

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) 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.

Pressure assist

Not uncommon in the United States, this system (invented by Bruce Martin) uses 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. However it 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.

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. In retrofit installations a flushometer can be replaced with a self-contained battery-operated machine vision system that actuates a solenoid 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) see the body of the user by electromagnetic energy that is received by the sensor. Active vision systems provide a source of electromagnetic energy (radar, infrared, or the like) and see reflected energy from the target (the user of the fixture).

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.

"The Flush"

Flushometer type toilets are much more common in commercial installations (at least in the US); they're almost never seen in residential installations, except for dormitory and barracks areas. The installation of large numbers of toilets in buildings like sports stadiums has led to a test which is commonly performed before the final release of such a project, which is called "The Flush". It entails stationing individuals in each restroom in the facility -- in large installations this can amount to 100-400 people -- and cueing them all by radio to flush their toilets as close to simultaneously as possible.

The purpose of the test is twofold: it checks that the plumbing design engineers got their sums right on the sizes of both the main water supply to the building, and also the size of the drain piping. The test is commonly not made public before it happens, so as to avoid embarrassment in the event of a failure.

Toilet etiquette

Frequently, in public bathrooms in the United States and other countries, as a courtesy to others using the bathroom, toilet users may perform what is known as a courtesy flush, where the user flushes before they have finished, merely to minimize the exposure of others to the smell of feces.

Source: see this.

See also

• Toilet
• Ecological sanitation
• Washroom
• Squat toilet

External links

• Intelligent Bathroom Fixtures and Systems (comparison between passive and active vision systems for use with plumbing fixtures, as published in Leonardo, 36(3), pp 199–120, June 2003)
• A Brief history of Wells and Toilets, 2005 book (link to pdf-file)
• Did Thomas Crapper invent the flush toilet? - at Snopes
• "Superflushing their way to the Super Bowl" - PM Engineer