Flush Toilet

A typical flush toilet is a vitreous ceramic bowl containing water plus special plumbing made to be rapidly filled with more water. The back of the toilet bowl is connected to a hollow drain pipe shaped like a upside down U connecting the drain from the bowl to a hollow siphon tube longer than the water in the bowl is high. The siphon tube connects to the drain. The bottom of the upside down U shaped drain pipe limits the height of the water in the bowl before it flows down the drain. If water is poured slowly into the toilet bowl it simply flows down the drain–the toilet does not flush. The water in the bowl both acts as a barrier to sewer gas entering and as a receptacle for waste. Sewer gas is vented though a vent pipe attached to the sewer line. At the top of the toilet bowl is a rim built into the toilet with many slanted drain holes connected to the toilet tank to fill, rinse and induce swirling in the toilet bowl when it is flushed. Mounted above the toilet is a large holding tank with about (now) 1.6 US gallons (6.1 L) to 1.2 US gallons (4.5 L) of water. This tank is built with a large drain 2.0 inches (5.1 cm) to 3.0 inches (7.6 cm) diameter hole at its bottom covered by a flapper valve that allows the water to rapidly leave the tank. The toilet’s plumbing is built to allow entry of the toilet tank’s water into the toilet in a very short period of time. This water enters through the holes in the rim and a siphon jet hole about 1.0 inch (2.5 cm) diameter in the bottom of the toilet. Other toilets use a large hole in the front of the rim to allow rapid filling of the toilet bowl. When a user flushes a toilet he/she opens the flapper valve and allows the tank’s water to quickly enter the toilet bowl. This rapid influx of water into the toilet bowl of the tank water causes the swirling water in the bowl to rapidly rise and fill the upside down U shaped drain and the siphon tube mounted in the back of the toilet. This starts the toilet’s siphon action. Siphons work by the molecular attraction that keeps the liquid’s molecules bound to each other such that a falling continuous column of liquid falling below the height of a liquid will “pull” the liquid up and over a rim. This siphon action rapidly (5-7 seconds) “pulls” nearly all of the water and waste in the bowl and the on-rushing tank water down the drain—it flushes. When most of the liquid has been pulled down the drain the continuous column of water up and over the bottom of the upside down U shaped drain pipe is broken when air gets into the siphon tube and the toilet gives its characteristic gurgle as the siphon action ceases. After flushing, the flapper valve in the water tank closes the bottom of the tank and various water lines and valves connected to a input water supply refill the toilet tank and bowl. The toilet is again ready for use. A two piece movable seat and toilet bowl lid is typically mounted on the back of the toilet bowl to allow covering the toilet or sitting (or not) while using the toilet.

A toilet’s body is essentially a work of fired pottery made from vitreous china, which starts out as a thin clay mixture called a slurry slip. The clay mixture is delivered or made in the factory as a liquid. It is thinned, filtered to remove any leftover impurities, and re-thickened. It takes about 20 kilograms (44 lb) of slurry per toilet.

This liquid slurry is poured into the space between Plaster of Paris (gypsum) molds. Toilet bowl, toilet rim, toilet tank and toilet tank lid all require separate pairs or more molds. The filled molds sit for about an hour while the Plaster of Paris molds absorb moisture from the slurry slip making it semisolid next to the mold but staying liquid further from the mold. Then, the workers remove plugs that allows any excess slip to pour from the mold–this excess slurry is recycled for later use. This drained out slip leaves voids inside the fixture using less material, keeping it both lighter and easier to fire in a kiln and allows the formation of intricate waste lines in the fixture–the drain’s centers are poured out as liquid slurry slip. At this point the toilets parts look like and are about as strong as milk chocolate. After about one hour the top core mold (interior of toilet) is removed. The rim mold bottom, which includes a place to mount the holding tank is removed and has the appropriate slanted holes for the rinsing jets cut and the mounting holes for tank and seat punched into the rim piece. Large flapper valve holes for rapid water entry into the toilet are cut into the rim pieces. The exposed top of the bowl is then covered with a thick clay slurry called butter slurry and the still uncured rim is attached. The bowl and hollow rim are now a single piece. The bowl plus rim is then inverted and the toilet set on the top of the top rim mold and the rest of the molds are removed. As the clay dries further it hardens more and continues to shrink. After a few hours the casting is semisolid and self supporting, and is called greenware. After the molds are removed workers use hand tools and sponges to smooth the edges and surface of the greenware and remove evidence of mold joints. For large scale production pieces these steps may be automated. The parts are then left outside or put in a warm dry room to dry before going through a dryer set at about 200°F, (93°C), for about 20-36 hours.

After finishing the surfaces the bowls and tanks are sprayed or painted with glaze of various kinds to get different colors. The glaze is designed to shrink and contract at the same rate as the greenware while undergoing firing. The toilet bowls, tanks and lids are placed on a conveyor belt or “car” that slowly goes through a large kiln. The belt slowly moves the greenware plus glaze into the kiln, which has different temperature zones starting at about 400°F (200°C) at the front of the kiln increasing in the middle to over 2,200°F (1,200°C) degrees and exiting the kiln at about 200°F (90°C). Vitreous china with glaze is an exception to normal pottery and glazing materials in that both the clay and glaze are made to be fired together. During the firing in the kiln the greenware and glaze are vitrified (turns to a form of glass) as one finished unit. The finished toilet is now glass like, stronger, germ resistant, waterproof and stain proof through its entire thickness. The trip through the kiln takes around 23-40 hours.

When the pieces are removed from the kiln and fully cool, they are ready for inspection for cracks. After inspection, the flushing mechanism may be installed on a one piece toilet. On a two piece toilet with a separate tank the flushing mechanism may only be put on the tank with final assembly waiting installation. The seat too may be installed at this time, or the parts may be sold separately and assembled by a plumbing distributor.

Various forms of flush toilets have become widely used in modern times The amount of water used by modern toilets is a significant portion of personal water usage, totaling as much as about 90 litres (24 USgal) of water per capita per day. Modern low flush toilet designs allow the use of much less water per flush–1.6 US gallons (6.1 L) to (1.2 US gallons (4.5 L)gallons per flush–but may require the sewage treatment system be modified for the more concentrated waste. Dual flush toilet allow the use to select between a flush for urine or feces saving a significant amount of water over conventional units. You push the flush handle up for one kind of flush and down for the other. In some places users are encouraged not to flush after urination. Flush toilets, if plumbed for it, may also use greywater (water previously used for washing dishes, laundry and bathing) for flushing rather than potable water (drinking water). Some modern toilets pressurize the water in the tank which initiates flushing action with less water usage. Heads (on ships) are typically flushed with seawater.

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