Tap (valve)

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. Modern cultures continue to wear fur and fur trim as dictated by fashion trends, and it is still considered by many as a luxury item. A hole through the cone 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. The term fur is often used to refer to a fur coat, wrap, or shawl. A cone valve consists of a shallowly-tapering cone in a tight-fitting socket placed across the flow of the fluid. Fur has served as an important source of clothing for humans, especially in colder climates, since time immemorial, although its use today is controversial. They can be identified by their range of 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. Fur usually consists of two main layers:.

Cone valves are usually found in gas taps (and, incidently, the cask beer taps referred to above). Not all mammals have fur; animals without fur may be referred to as "naked", as in The Naked Ape and naked mole rat. In the UK this type of tap normally has a wheel-shaped handle rather than a crutch or capstan handle. Fur comes from the coats of animals; the animal's coat may consist of short ground hair, long guard hair, and, in some cases, medium awn hair. There is no resistance to flow when the tap is fully open, but this type of tap rarely gives a perfect seal when closed. The term fur refers to the body hair of non-human mammals also known as the pelage (like the term plumage in birds). Gate valves use a metal disc the same diameter as the pipe which is screwed into place perpendicularly to the flow, cutting it off. This is usually the visible layer for most mammals and contains most of the pigmentation.

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. Guard hair — the top layer consisting of longer straight shafts of hair that stick out through the underfur. This is called a "globe valve" in engineering and, while it gives a leak-proof seal and good fine adjustment of flow, the tortuous S-shaped path the water is forced to follow offers a significant obstruction to the flow. Ground hair or underfur — the bottom layer consisting of wool hairs which tend to be shorter, flattened, curly and denser than the top layer. Most taps use a soft washer which is screwed down onto a seat in order to stop the flow. 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.

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. Bubbles of cool water vapor form and collapse at the restriction, causing the familiar hissing sound. 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. 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.

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. Most water and gas taps have adjustable flow. 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 natural gas in the home (for gas fires) or in school science laboratories (for Bunsen burners). A "beer tap" now may be one of several items:.

This may be because the word was originally coined for the wooden valve in traditional barrels. 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 convention applies in the UK too, but many installations exist where it has been ignored. In some countries there is a 'standard' arrangement of hot/cold taps: for example in the United States the hot tap is generally on the left.

Mixer taps may have a red-blue stripe or arrows indicating which side will give hot and which cold. The cold tap generally has a blue or green indicator and/or is labeled C or Cold. In English-speaking countries, the hot tap generally has a red indicator and/or is labeled H or Hot. If separate taps are fitted, it may not be immediately clear which tap is hot and which is cold.

Latest designs do this using a built in thermostat. This is a single, more complex, valve whose handle moves up and down to control the amount of water flow and from side to side to control the temperature of the water (achieved by mixing the hot and cold water together). In kitchens, and in the US and many other places, mixer taps are often used instead. Water for baths, sinks and basins can be provided by separate hot and cold taps; this arrangement is common in the UK, particularly in toilets.

. In American English the usage is sometimes more specialised, with the term tap restricted to uses such as beer taps and the word "faucet" used for water outlets; although some Americans use "tap" in the broader sense as well. For example, in Commonwealth English the word is used for any everyday type of valve, particularly the fittings on bathtubs and sinks. A tap is a valve for controlling the release of a liquid or gas.

In an analogy to controlling the flow of a fluid, tap can also refer to drawing electricity from a certain winding in an electrical transformer. To tap a vessel containing liquid metal is to remove the liquid from the vessel, even if no valve as such is utilised in the process.