2 a plug for a bunghole in a cask [syn: tap]
- /spɪg.ət/ /spIg.@t/
A tap is a valve for controlling the release of a liquid or gas. In the British Isles and normally in the Commonwealth the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S. the usage is sometimes more specialised, with the term "tap" restricted to uses such as beer taps and the word faucet being used for water outlets; however some Americans use "tap" in the broader sense as well.
Mixer taps are more difficult to fit in the UK than in other countries because traditional British plumbing provides hot and cold water at different pressures.
If separate taps are fitted, it may not be immediately clear which tap is hot and which is cold. The hot tap generally has a red indicator while the cold tap generally has a blue or green indicator. In English-speaking countries, the taps are frequently also labeled with an "H" or "C". Note that in countries with Romance languages, sometimes the letters "C" for hot and "F" for cold are used, possibly creating confusion when English speakers visit these countries or vice versa. Mixer taps may have a red-blue stripe or arrows indicating which side will give hot and which cold.
In some countries there is a 'standard' arrangement of hot/cold taps: for example in the United States and Canada, the hot tap is on the left by building code requirements. This convention applies in the UK too, but many installations exist where it has been ignored. Mis-assembly of some single-valve mixer taps will exchange hot and cold even if the fixture has been plumbed correctly.
Most handles on residential homes are connected to the valve shaft and fastened down with a screw. Although on most commercial and industrial applications they are fitted with a removable key called a "loose key" or "Water key" which has a square peg and a square ended key to turn off and on the water. You can also take off the "Loose key" to prevent vandals from turning on the water. In older building before the "Loose key" was invented for some landlords or caretakers to take off the handle of a residential tap, which had teeth that would meet up with the cogs on the valve shaft. This Teeth and cog system is still used on most modern faucets. Although most of the time a "Loose key" is on industrial and commercial applications sometimes you may see a "Loose key" on homes by the seashore to prevent guests from washing the sand off their feet.
While in other contexts, depending on location, a "tap" may be a "faucet", "valve" or "spigot", the use of "tap" for beer is almost universal. This may be because the word was originally coined for the wooden valve in traditional barrels. A "beer tap" now may be one of several items: ; Portable keg tap : Sometimes, beer kegs designed to be connected to the above system are instead used on their own, perhaps at a party or outdoor event. In this case, a self-contained portable tap is required that allows beer to be served straight from the keg. Because the keg system uses pressure to force the beer up and out of the keg, these taps must have a means of supplying it. The typical "picnic tap" uses a hand pump to push air into the keg; this will cause the beer to spoil faster but is perfectly acceptable when it will be consumed in a short time. Portable taps with small CO2 cylinders are also available.
Although a gas tap may be a valve that releases any gas, the word is most commonly used to refer to taps that control the flow of fuel gas (natural gas or, historically, coal gas, syngas, etc.) in the home (for gas fires or other appliances) or in laboratories (for Bunsen burners).
Physics of taps
Most water and gas taps have adjustable flow. Turning the knob or working the lever sets the flow rate by adjusting the size of an opening in the valve assembly, giving rise to choked flow through the narrow opening in the valve. The choked flow rate is independent of the viscosity or temperature of the fluid or gas in the pipe, and depends only weakly on the supply pressure, so that flow rate is stable at a given setting. At intermediate flow settings the pressure at the valve restriction drops nearly to zero from the venturi effect; in water taps, this causes the water to boil momentarily at room temperature as it passes through the restriction. Bubbles of cool water vapor form and collapse at the restriction, causing the familiar hissing sound. At very low flow settings, the viscosity of the water becomes important and the pressure drop (and hissing noise) vanish; at full flow settings, parasitic drag in the pipes becomes important and the water again becomes quiet.
One reason that most beer taps are not designed for adjustable flow is that the beer itself is damaged by the pressure drop in a choked-flow valve: holding a beer tap partially open causes the beer to foam vigorously, ruining the pour.
The first screw-down tap mechanism was patented and manufactured by the Rotherham brass founders, Guest and Chrimes,in 1845. Most older taps use a soft rubber or neoprene washer which is screwed down onto a valve seat in order to stop the flow. This is called a "globe valve" in engineering and, while it gives a leak-proof seal and good fine adjustment of flow, both the rubber washer and the valve seat are subject to wear (and for the seat, corrosion) over time, leading to leakage (see photo). The washer can be replaced and the valve seat resurfaced (at least a few times), but globe valves are never maintenance-free.
Also, the tortuous S-shaped path the water is forced to follow offers a significant obstruction to the flow. For high pressure domestic water systems this does not matter, but for low pressure systems where flowrate is important, such as a shower fed by a storage tank, a "stop tap" or, in engineering terms, a "gate valve" is preferred.
Gate valves use a metal disc the same diameter as the pipe which is screwed into place perpendicularly to the flow, cutting it off. There is no resistance to flow when the tap is fully open, but this type of tap rarely gives a perfect seal when closed. In the UK this type of tap normally has a wheel-shaped handle rather than a crutch or capstan handle.
Cone valves or ball valves are another alternative. These are commonly-found as the service shut-off valves in more-expensive water systems and usually found in gas taps (and, incidentally, the cask beer taps referred to above). They can be identified by their range of motion -- only 90º -- between fully on and fully off. Usually, when the handle is in line with the pipe the valve is on, and when the handle is across the pipe it is closed. A cone valve consists of a shallowly-tapering cone in a tight-fitting socket placed across the flow of the fluid. A ball valve uses a spherical ball instead. In either case, a hole through the cone or ball allows the fluid to pass if it is lined up with the openings in the socket through which the fluid enters and leaves; turning the cone using the handle rotates the passage away, presenting the fluid with the unbroken surface of the cone through which it cannot pass. Valves of this type using a cylinder rather than a cone are sometimes encountered, but using a cone allows a tight fit to be made even with moderate manufacturing tolerances. The ball in ball valves rotates within plastic seats.
Hands free infrared proximity sensors are replacing the standard valve. Thermostatically controlled electronic dual-purpose mixing or diverting valves are used within industrial applications to automatically provide liquids as required.
Foot controlled valves are installed within laboratory and healthcare/hospitals.
Modern bathroom and kitchen taps often use ceramic or plastic surfaces sliding against other spring-loaded ceramic surfaces or plastic washers. These tend to require far less maintenance than traditional globe valves and when maintenance is required, the entire interior of the valve is usually replaced, often as a single pre-assembled cartridge.
Of the trio of well-respected faucet manufacturers in North American plumbing circles, Moen and American Standard use cartridges (Moen's being O-ring based, American Standard's being ceramic), while Delta uses easily-replaced rubber seats facing the cartridge(s). Each design has its advantages: Moen cartridges tend to be easiest to find, American Standard cartridges have nearly infinite lifespan in sediment-free municipal water, and Delta's rubber seats tend to be most forgiving of sediment in well water.
spigot in Old English (ca. 450-1100): Tæppa
spigot in Arabic: صنبور
spigot in Danish: Vandhane
spigot in German: Wasserhahn (Technik)
spigot in Spanish: Llave de paso
spigot in Persian: شیر (وسیله)
spigot in French: Robinet
spigot in Hebrew: ברז
spigot in Icelandic: Krani
spigot in Italian: Rubinetto
spigot in Dutch: Kraan (vloeistof)
spigot in Japanese: 蛇口
spigot in Polish: Kran
spigot in Portuguese: Torneira
spigot in Russian: Смеситель (сантехника)
spigot in Simple English: Tap (valve)
spigot in Finnish: Hana
spigot in Swedish: Vattenkran
spigot in Turkish: Çeşme