Flush toilet
A flush toilet is a toilet that disposes of human waste by collecting it in a bowl and then using the force of water to channel it through a drainpipe to another location for treatment, either nearby or at a communal facility. Flush toilets can be designed for sitting or squatting. Most modern sewage treatment systems are also designed to process specially designed toilet paper, and there is increasing interest for flushable wet wipes. Porcelain is a popular material for these toilets, although public or institutional ones may be made of metal or other materials.
Flush toilets are a type of plumbing fixture, and usually incorporate a bend called a trap that causes water to collect in the toilet bowl – to hold the waste and act as a seal against noxious sewer gases. Urban and suburban flush toilets are connected to a sewerage system that conveys wastewater to a sewage treatment plant; rurally, a septic tank or composting system is mostly used.
The opposite of a flush toilet is a dry toilet, which uses no water for flushing. Associated devices are urinals, which primarily dispose of urine, and bidets, which use water to cleanse the anus, perineum, and vulva after using the toilet.
Operation
A typical flush toilet is a fixed, vitreous ceramic bowl which is connected to a drain. After use, the bowl is emptied and cleaned by the rapid flow of water into the bowl. This flush may flow from a dedicated tank, a high-pressure water pipe controlled by a flush valve, or by manually pouring water into the bowl. Tanks and valves are normally operated by the user, by pressing a button, pushing down on a handle, pulling a lever or pulling a chain. The water is directed around the bowl by a molded flushing rim around the top of the bowl or by one or more jets, so that the entire internal surface of the bowl is rinsed with water.Mechanical flush from a cistern
A typical toilet has a tank fixed above the bowl which contains a fixed volume of water, and two devices. The first device allows part of the contents of the tank to be discharged rapidly into the toilet bowl, causing the contents of the bowl to be swept or sucked out of the toilet and into the drain, when the user operates the flush. The second device automatically allows water to enter the tank until the water level is appropriate for a flush.The water may be discharged through a "toilet flapper valve", or through a siphon. A float usually controls the refilling device.
Mechanical flush from a high-pressure water supply
Toilets without cisterns are often flushed through a simple flush valve or "Flushometer" connected directly to the water supply. These are designed to rapidly discharge a limited volume of water when the lever or button is pressed then released.Manual flush (pour flush)
A toilet does not need be connected to a water supply, but may be pour-flushed. This type of flush toilet has no cistern or permanent water supply, but is flushed by pouring in a few litres of water from a container. The flushing can use as little as. This type of toilet is common in many Asian countries. The toilet can be connected to one or two pits, in which case it is called a "pour flush pit latrine" or a "twin pit pour flush pit latrine". It can also be connected to a septic tank.Vacuum toilet
A vacuum toilet is a flush toilet that is connected to a vacuum sewer system, and removes waste by suction. They may use very little water or none. Some flush with coloured disinfectant solution rather than with water. They may be used to separate blackwater and greywater, and process them separately.Lavatories on trains, aircraft, buses, and ships often use vacuum toilets. The lower water usage saves weight and avoids water slopping out of the toilet bowl in motion. Aboard vehicles, a portable collection chamber is used; if it is filled by positive pressure from an intermediate vacuum chamber, it need not be kept under vacuum.
Flushing systems
The flushing system provides a large flow of water into the bowl. They normally take the form of either fixed tanks of water or flush valves.Flush tanks
Flush tanks or cisterns usually incorporate a mechanism to release water from the tank and an automatic valve to allow the cistern to be refilled automatically.This system is suitable for locations plumbed with water pipes which cannot supply water quickly enough to flush the toilet; the tank is needed to supply a large volume of water in a short time. The tank typically collects between of water over a period of time. In modern installations the storage tank is usually mounted directly above and behind the bowl.
Older installations, known as "high suite combinations", used a high-level cistern, fitted above head height, activated by a pull chain connected to a flush lever on the cistern. When more modern close-coupled cistern and bowl combinations were first introduced, these were first referred to as "low suite combinations". 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 fixed directly to the bowl. In recent decades the close coupled tank–bowl combination has become the most popular residential system, as it has been found by ceramic engineers that improved waterway design is a more effective way to enhance the bowl's flushing action than high tank mounting.
Tank fill valve
Tank fill valves are found in all tank-style toilets. The valves are of two main designs: the side-float design and the concentric-float design. The side-float design has existed for over a hundred years. The concentric design has only existed since 1957 but is gradually becoming more popular than the side-float design.The side-float design uses a float on the end of a lever to control the fill valve. The float is usually shaped like a ball, so the mechanism is often called a ball-valve or a ballcock. Historically floats were made from copper sheet, but are now usually plastic. The float is located to one side of the main valve tower or inlet at the end of a rod or arm. As the float rises, so does the float-arm. The arm connects to the fill valve that shuts off the inflow of water when the float reaches a level at which the volume of water in the tank is sufficient to provide another flush.
File:Concentric Float Valve.svg|alt=Concentric Float Valve|thumb|left|One type of concentric float valve. The concentric float valve opens when the fluid level is low, allowing more fluid to enter . When the fluid level returns to the full level, the valve is shut .|220x220px
The newer concentric-float fill valve consists of a tower which is encircled by a plastic float assembly. Operation is otherwise the same as a side-float fill valve, even though the float position is somewhat different. By virtue of its more compact layout, interference between the float and other obstacles is greatly reduced, thus increasing reliability. The concentric-float fill valve is also designed to signal to users automatically when there is a leak in the tank, by making much more noise when a leak is present than the older style side-float fill valve, which tends to be nearly silent when a slow leak is present.
Newer fill valves have a delayed action that will not start filling the tank/cistern until the flapper/drop valve has closed which saves some water.
Flapper-flush valve or drop valve
In tanks using a flapper-flush valve, the outlet at the bottom of the tank is covered by a buoyant cover, or flapper, which is held in place against a fitting by water pressure. The user pushes a lever to flush the toilet, which lifts the flush valve from the valve seat. The valve then floats clear of the seat, 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 North America and in continental Europe. From 2001, due to a change in regulations, this flush system has also become available in the UK, where prior to that the siphon-type flush was mandated.Dual flush versions of this design with push buttons are widely available. They have one level of water for liquid waste and a higher level for solid waste.
In North America, newer toilets have a flapper-flush valve. Older toilets have a flapper-flush valve. The larger flapper-flush valve is used on toilets that use less water, such as per flush. Some have a bell inlet for a faster more effective flush.
A problem with the valve type flush mechanism is that it invariably starts to leak after a couple of years use due to wear and tear of the valve, particles, etc. trapped in the valve. Quite often this leakage is barely noticeable but adds up to a considerable water wastage. In the UK it has been found that between 5 and 8% of toilets are leaking, each one between on average per day. Whilst they save more water than they leak, regular maintenance or use of a non-leaking flush mechanism will maximise water savings.
Siphon-flush mechanism
This system, invented by Albert Giblin and common in the UK, uses a storage tank similar to that used in the flapper-flush-valve system above. This flush valve system is sometimes referred to as a valveless system, since no valve as such is required.The siphon is formed of a vertical pipe that links the flush pipe to a domed chamber inside the cistern. A perforated disc, covered by a flexible plate or flap, is fitted inside this chamber and is joined by a rod to the flush lever.
Pressing the lever raises the disc, forces water over the top of the siphon into the vertical pipe, and starts the siphonic flow. Water flows through the perforated disc past the flap until the cistern is empty, at which point air enters the siphon and the flush stops.
The advantage of a siphon over the flush valve is that it has no sealing washers that can wear out and cause leaks, whereas other valve types - flapper, drop valve do leak, invariably after a couple of years of use and they have reduced water savings due to the valves not being maintained in practice. The siphon membrane will require occasional replacement.
Until 1 January 2001, the use of siphon-type cisterns was mandatory in the UK but after that date the regulations additionally allowed pressure flushing cisterns and pressure flushing valves. Siphons can sometimes be more difficult to operate than a "flapper"-based flush valve because moving the lever requires more torque than a flapper system. This additional torque is required because a certain amount of water must be lifted up into the siphon passageway in order to initiate the siphon action in the tank. Splitting or jamming of the flexible flap covering the perforated disc can cause the cistern to stop working.
Dual-flush versions of the siphon cistern provide a shorter flush option by allowing air into the siphon to stop the siphon action before the tank is empty.
The siphon system can also be combined with an air box to allow multiple siphons to be installed in a single trough cistern.