Pipe (fluid conveyance)
A pipe is a tubular section or hollow cylinder but not of circular cross-section, used to convey substances which can flow — liquids and gases, slurries and masses of small solids. It can be used for structural applications. In common usage the words pipe and tube are interchangeable, but in industry and engineering, the terms are uniquely defined. Depending on the applicable standard to which it is manufactured, pipe is specified by a nominal diameter with a constant outside diameter and a schedule that defines the thickness. Tube is most specified by the OD and wall thickness, but may be specified by any two of OD, inside diameter, wall thickness. Pipe is manufactured to one of several international and national industrial standards. While similar standards exist for specific industry application tubing, tube is made to custom sizes and a broader range of diameters and tolerances. Many industrial and government standards exist for the production of tubing; the term "tube" is commonly applied to non-cylindrical sections, i.e. square or rectangular tubing.
In general, "pipe" is the more common term in most of the world, whereas "tube" is more used in the United States. Both "pipe" and "tube" imply a level of rigidity and permanence, whereas a hose is portable and flexible. Pipe assemblies are always constructed with the use of fittings such as elbows, so on, while tube may be formed or bent into custom configurations. For materials that are inflexible, cannot be formed, or where construction is governed by codes or standards, tube assemblies are constructed with the use of tube fittings. Plumbing Tap water Pipelines transporting gas or liquid over long distances Compressed air systems Pipe bombs Casing for concrete pilings used in construction projects High-temperature or high-pressure manufacturing processes The petroleum industry: Oil well casing Oil refinery equipment Delivery of fluids, either gaseous or liquid, in a process plant from one point to another point in the process Delivery of bulk solids, in a food or process plant from one point to another point in the process The construction of high pressure storage vessels.
Additionally, pipe is used for many purposes. Handrails and support structures are constructed from structural pipe in an industrial environment. There are three processes for metallic pipe manufacture. Centrifugal casting of hot alloyed metal is one of the most prominent process. Ductile iron pipes are manufactured in such a fashion. Seamless pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell; as the manufacturing process does not include any welding, seamless pipes are perceived to be stronger and more reliable. Seamless pipe was regarded as withstanding pressure better than other types, was more available than welded pipe. Advances since the 1970s in materials, process control, non-destructive testing, allow specified welded pipe to replace seamless in many applications. Welded pipe is formed by welding the seam; the weld flash can be removed from both outer surfaces using a scarfing blade. The weld zone can be heat-treated to make the seam less visible. Welded pipe have tighter dimensional tolerances than the seamless type, can be cheaper to manufacture.
There are a number of processes. Each of these processes leads to coalescence or merging of steel components into pipes. Electric current is passed through the surfaces. Pools of molten metal are formed where the two surfaces are connected as a strong electric current is passed through the metal. ERW pipes are manufactured from the longitudinal welding of steel; the welding process for ERW pipes is continuous, as opposed to welding of distinct sections at intervals. ERW process uses steel coil as feedstock; the High Frequency Induction Technology welding process is used for manufacturing ERW pipes. In this process, the current to weld the pipe is applied by means of an induction coil around the tube. HFI is considered to be technically superior to “ordinary” ERW when manufacturing pipes for critical applications, such as for usage in the energy sector, in addition to other uses in line pipe applications, as well as for casing and tubing. Large-diameter pipe may be EFW or Submerged Arc Welded pipe.
There are two technologies that can be used to manufacture steel pipes of sizes larger than the steel pipes that can be produced by seamless and ERW processes. The two types of pipes produced through these technologies are longitudinal-submerged arc-welded and spiral-submerged arc-welded pipes. LSAW are made by bending and welding wide steel plates and most used in oil and gas industry applications. Due to their high cost, LSAW pipes are used in lower value non-energy applications such as water pipelines. SSAW pipes are produced by spiral welding of steel coil and have a cost advantage over LSAW pipes, as the process uses coils rather than steel plates; as such, in applications where spiral-weld is acceptable, SSAW pipes may be preferr
Rust is an iron oxide, a red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable both visually and by spectroscopy, form under different circumstances. Rust consists of hydrated iron oxides Fe2O3·nH2O and iron oxide-hydroxide. Given sufficient time and water, any iron mass will convert to rust and disintegrate. Surface rust is flaky and friable, it provides no protection to the underlying iron, unlike the formation of patina on copper surfaces. Rusting is the common term for corrosion such as steel. Many other metals undergo similar corrosion, but the resulting oxides are not called rust. Other forms of rust exist, like the result of reactions between iron and chloride in an environment deprived of oxygen. Rebar used in underwater concrete pillars, which generates green rust, is an example. Although rusting is a negative aspect of iron, a particular form of rusting, known as "stable rust," causes the object to have a thin coating of rust over the top, if kept in low relative humidity, makes the "stable" layer protective to the iron below, but not to the extent of other oxides, such as aluminum.
Rust is another name for iron oxide, which occurs when iron or an alloy that contains iron, like steel, is exposed to oxygen and moisture for a long period of time. Over time, the oxygen combines with the metal at an atomic level, forming a new compound called an oxide and weakening the bonds of the metal itself. Although some people refer to rust as "oxidation", that term is much more general and describes a vast number of processes involving the loss of electrons or increased oxidation state, as part of a reaction; the best-known of these reactions involve oxygen, hence the name "oxidation". The terms "rust" and "rusting" only mean oxidation of its resulting products. Many other oxidation reactions exist which do not produce rust, but only iron or alloys that contain iron can rust. However other metals can corrode in similar ways; the main catalyst for the rusting process is water. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic pits and cracks in any exposed metal.
The hydrogen atoms present in water molecules can combine with other elements to form acids, which will cause more metal to be exposed. If chloride ions are present, as is the case with saltwater, the corrosion is to occur more quickly. Meanwhile, the oxygen atoms combine with metallic atoms to form the destructive oxide compound; as the atoms combine, they weaken the metal, making the structure crumbly. When impure iron is in contact with water, other strong oxidants, or acids, it rusts. If salt is present, for example in seawater or salt spray, the iron tends to rust more as a result of electrochemical reactions. Iron metal is unaffected by pure water or by dry oxygen; as with other metals, like aluminium, a adhering oxide coating, a passivation layer, protects the bulk iron from further oxidation. The conversion of the passivating ferrous oxide layer to rust results from the combined action of two agents oxygen and water. Other degrading solutions are sulfur dioxide in carbon dioxide in water.
Under these corrosive conditions, iron hydroxide species are formed. Unlike ferrous oxides, the hydroxides do not adhere to the bulk metal; as they form and flake off from the surface, fresh iron is exposed, the corrosion process continues until either all of the iron is consumed or all of the oxygen, carbon dioxide, or sulfur dioxide in the system are removed or consumed. When iron rusts, the oxides take up more volume than the original metal. See economic effect for more details; the rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen. The iron is the reducing agent; the rate of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effects of road salt on the corrosion of automobiles. The key reaction is the reduction of oxygen: O2 + 4 e− + 2 H2O → 4 OH−Because it forms hydroxide ions, this process is affected by the presence of acid. Indeed, the corrosion of most metals by oxygen is accelerated at low pH.
Providing the electrons for the above reaction is the oxidation of iron that may be described as follows: Fe → Fe2+ + 2 e−The following redox reaction occurs in the presence of water and is crucial to the formation of rust: 4 Fe2+ + O2 → 4 Fe3+ + 2 O2−In addition, the following multistep acid–base reactions affect the course of rust formation: Fe2+ + 2 H2O ⇌ Fe2 + 2 H+ Fe3+ + 3 H2O ⇌ Fe3 + 3 H+as do the following dehydration equilibria: Fe2 ⇌ FeO + H2O Fe3 ⇌ FeO + H2O 2 FeO ⇌ Fe2O3 + H2OFrom the above equations, it is seen that the corrosion products are dictated by the availability of water and oxygen. With limited dissolved oxygen, iron-containing materials are favoured, including FeO and black lodestone or magnetite. High oxygen concentrations favour ferric materials with the nominal formulae Fe3−xOx⁄2; the nature of rust changes with time, reflecting the slow rates of the reactions of solids. Furthermore, these complex processes are affected by the presence of other ions, such as Ca2+, which serve as electrolytes which accelerate rust formation, or combine with the hydroxides and oxides of iron to precipitate a variety of Ca, Fe, O, OH species.
Onset of rusting can be detected in laboratory with the use of ferroxyl indicator solu
Hydraulics is a technology and applied science using engineering and other sciences involving the mechanical properties and use of liquids. At a basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, cover concepts such as pipe flow, dam design and fluid control circuitry; the principles of hydraulics are in use in the human body within the vascular system and erectile tissue. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, lakes and seas, its sub-field open-channel flow studies the flow in open channels. The word "hydraulics" originates from the Greek word ὑδραυλικός which in turn originates from ὕδωρ and αὐλός.
Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient Central Asia; the Greeks constructed sophisticated water and hydraulic power systems. An example is the construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of hydraulic wheel the earliest in Europe, is the Perachora wheel; the construction of the first hydraulic automata by Ctesibius and Hero of Alexandria is notable. Hero describes a number of working machines using hydraulic power, such as the force pump, known from many Roman sites as having been used for raising water and in fire engines; the Persians constructed an intricate system of water mills and dams known as the Shushtar Historical Hydraulic System.
The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I, has been referred to by UNESCO as "a masterpiece of creative genius." They were the inventors of the Qanat, an underground aqueduct. Several of Iran's large, ancient gardens were irrigated thanks to Qanats. In ancient China there was Sunshu Ao, Ximen Bao, Du Shi, Zhang Heng, Ma Jun, while medieval China had Su Song and Shen Kuo. Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation. In ancient Sri Lanka, hydraulics were used in the ancient kingdoms of Anuradhapura and Polonnaruwa; the discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, several large-scale irrigation works had been completed.
Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control and recreational water courses and retaining structures and cooling systems were in place in Sigiriya, Sri Lanka. The coral on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa, Parakrama Samudra, Tisa Wewa, Minneriya In Ancient Rome, many different hydraulic applications were developed, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining, they were among the first to make use of the siphon to carry water across valleys, used hushing on a large scale to prospect for and extract metal ores. They used lead in plumbing systems for domestic and public supply, such as feeding thermae. Hydraulic mining was used in the gold-fields of northern Spain, conquered by Augustus in 25 BC; the alluvial gold-mine of Las Medulas was one of the largest of their mines. It was worked by at least 7 long aqueducts, the water streams were used to erode the soft deposits, wash the tailings for the valuable gold content.
In 1619 Benedetto Castelli, a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e. management of rivers in the Papal States, beginning in 1626. Blaise Pascal studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids, his discovery on the theory behind hydraulics led to the invention of the hydraulic press by Joseph Bramah, which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force.
This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the containe
Water supply network
A water supply system or water supply network is a system of engineered hydrologic and hydraulic components which provide water supply. A water supply system includes: A drainage basin. A raw water collection point where the water accumulates, such as a lake, a river, or groundwater from an underground aquifer. Raw water may be transferred using uncovered ground-level aqueducts, covered tunnels or underground water pipes to water purification facilities. Water purification facilities. Treated water is transferred using water pipes. Water storage facilities such as reservoirs, water tanks, or water towers. Smaller water systems may store the water in cisterns or pressure vessels. Tall buildings may need to store water locally in pressure vessels in order for the water to reach the upper floors. Additional water pressurizing components such as pumping stations may need to be situated at the outlet of underground or above ground reservoirs or cisterns. A pipe network for distribution of water to the consumers and other usage points.
Connections to the sewers are found downstream of the water consumers, but the sewer system is considered to be a separate system, rather than part of the water supply system. Water supply networks are run by public utilities of the water industry. Raw water is collected from a surface water source or from a groundwater source within the watershed that provides the water resource; the raw water is transferred to the water purification facilities using uncovered aqueducts, covered tunnels or underground water pipes. All large systems must treat the water. Water treatment must occur. Water purification occurs close to the final delivery points to reduce pumping costs and the chances of the water becoming contaminated after treatment. Traditional surface water treatment plants consists of three steps: clarification and disinfection. Clarification refers to the separation of particles from the water stream. Chemical addition destabilizes the particle charges and prepares them for clarification either by settling or floating out of the water stream.
Sand, anthracite or activated carbon filters refine the water stream, removing smaller particulate matter. While other methods of disinfection exist, the preferred method is via chlorine addition. Chlorine kills bacteria and most viruses and maintains a residual to protect the water supply through the supply network; the product, delivered to the point of consumption, is called potable water if it meets the water quality standards required for human consumption. The water in the supply network is maintained at positive pressure to ensure that water reaches all parts of the network, that a sufficient flow is available at every take-off point and to ensure that untreated water in the ground cannot enter the network; the water is pressurised by pumps that pump water into storage tanks constructed at the highest local point in the network. One network may have several such service reservoirs. In small domestic systems, the water may be pressurised by a pressure vessel or by an underground cistern.
This eliminates the need of a water-tower or any other heightened water reserve to supply the water pressure. These systems are owned and maintained by local governments, such as cities, or other public entities, but are operated by a commercial enterprise. Water supply networks are part of the master planning of communities and municipalities, their planning and design requires the expertise of city planners and civil engineers, who must consider many factors, such as location, current demand, future growth, pressure, pipe size, pressure loss, fire fighting flows, etc. — using pipe network analysis and other tools. As water passes through the distribution system, the water quality can degrade by chemical reactions and biological processes. Corrosion of metal pipe materials in the distribution system can cause the release of metals into the water with undesirable aesthetic and health effects. Release of iron from unlined iron pipes can result in customer reports of "red water" at the tap. Release of copper from copper pipes can result in customer reports of "blue water" and/or a metallic taste.
Release of lead can occur from the solder used to join copper pipe together or from brass fixtures. Copper and lead levels at the consumer's tap are regulated to protect consumer health. Utilities will adjust the chemistry of the water before distribution to minimize its corrosiveness; the simplest adjustment involves control of pH and alkalinity to produce a water that tends to passivate corrosion by depositing a layer of calcium carbonate. Corrosion inhibitors are added to reduce release of metals into the water. Common corrosion inhibitors added to the water are silicates. Maintenance of a biologically safe drinking water is another goal in water distribution. A chlorine based disinfectant, such as sodium hypochlorite or monochloramine is added to the wat
Solid is one of the four fundamental states of matter. In solids particles are packed, it is characterized by structural resistance to changes of shape or volume. Unlike liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does; the atoms in a solid are bound to each other, either in a regular geometric lattice or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because in gases molecules are loosely packed; the branch of physics that deals with solids is called solid-state physics, is the main branch of condensed matter physics. Materials science is concerned with the physical and chemical properties of solids. Solid-state chemistry is concerned with the synthesis of novel materials, as well as the science of identification and chemical composition; the atoms, molecules or ions that make up solids may be arranged in an orderly repeating pattern, or irregularly.
Materials whose constituents are arranged in a regular pattern are known as crystals. In some cases, the regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal. Solid objects that are large enough to see and handle are composed of a single crystal, but instead are made of a large number of single crystals, known as crystallites, whose size can vary from a few nanometers to several meters; such materials are called polycrystalline. All common metals, many ceramics, are polycrystalline. In other materials, there is no long-range order in the position of the atoms; these solids are known as amorphous solids. Whether a solid is crystalline or amorphous depends on the material involved, the conditions in which it was formed. Solids that are formed by slow cooling will tend to be crystalline, while solids that are frozen are more to be amorphous; the specific crystal structure adopted by a crystalline solid depends on the material involved and on how it was formed.
While many common objects, such as an ice cube or a coin, are chemically identical throughout, many other common materials comprise a number of different substances packed together. For example, a typical rock is an aggregate of several different minerals and mineraloids, with no specific chemical composition. Wood is a natural organic material consisting of cellulose fibers embedded in a matrix of organic lignin. In materials science, composites of more than one constituent material can be designed to have desired properties; the forces between the atoms in a solid can take a variety of forms. For example, a crystal of sodium chloride is made up of ionic sodium and chlorine, which are held together by ionic bonds. In diamond or silicon, the atoms share form covalent bonds. In metals, electrons are shared in metallic bonding; some solids most organic compounds, are held together with van der Waals forces resulting from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid result from the differences between their bonding.
Metals are strong and good conductors of both electricity and heat. The bulk of the elements in the periodic table, those to the left of a diagonal line drawn from boron to polonium, are metals. Mixtures of two or more elements in which the major component is a metal are known as alloys. People have been using metals for a variety of purposes since prehistoric times; the strength and reliability of metals has led to their widespread use in construction of buildings and other structures, as well as in most vehicles, many appliances and tools, road signs and railroad tracks. Iron and aluminium are the two most used structural metals, they are the most abundant metals in the Earth's crust. Iron is most used in the form of an alloy, which contains up to 2.1% carbon, making it much harder than pure iron. Because metals are good conductors of electricity, they are valuable in electrical appliances and for carrying an electric current over long distances with little energy loss or dissipation. Thus, electrical power grids rely on metal cables to distribute electricity.
Home electrical systems, for example, are wired with copper for its good conducting properties and easy machinability. The high thermal conductivity of most metals makes them useful for stovetop cooking utensils; the study of metallic elements and their alloys makes up a significant portion of the fields of solid-state chemistry, materials science and engineering. Metallic solids are held together by a high density of shared, delocalized electrons, known as "metallic bonding". In a metal, atoms lose their outermost electrons, forming positive ions; the free electrons are spread over the entire solid, held together by electrostatic interactions between the ions and the electron cloud. The large number of free electrons gives metals their high values of electrical and thermal conductivity; the free electrons prevent transmission of visible light, making metals opaque and lustrous. More advanced models of metal properties consider the effect of the positive ions cores on the delocalised electrons.
As most metals have crystalline structure, those ions are arranged into a periodic lattice. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model. Minerals are
A gasket is a mechanical seal which fills the space between two or more mating surfaces to prevent leakage from or into the joined objects while under compression. Gaskets allow for "less-than-perfect" mating surfaces on machine parts where they can fill irregularities. Gaskets are produced by cutting from sheet materials. Gaskets for specific applications, such as high pressure steam systems, may contain asbestos. However, due to health hazards associated with asbestos exposure, non-asbestos gasket materials are used when practical, it is desirable that the gasket be made from a material, to some degree yielding such that it is able to deform and fill the space it is designed for, including any slight irregularities. A few gaskets require an application of sealant directly to the gasket surface to function properly; some gaskets are made of metal and rely on a seating surface to accomplish the seal. This is typical of some other metal gasket systems; these joints are known as E-con compressive type joints.
Gaskets are made from a flat material, a sheet such as paper, silicone, cork, neoprene, nitrile rubber, polytetrafluoroethylene or a plastic polymer. One of the more desirable properties of an effective gasket in industrial applications for compressed fiber gasket material is the ability to withstand high compressive loads. Most industrial gasket applications involve bolts exerting compression well into the 14 MPa range or higher. Speaking, there are several truisms that allow for better gasket performance. One of the more tried and tested is: "The more compressive load exerted on the gasket, the longer it will last". There are several ways to measure a gasket material's ability to withstand compressive loading; the "hot compression test" is the most accepted of these tests. Most manufacturers of gasket materials will publish the results of these tests. Gaskets come in many different designs based on industrial usage, chemical contact and physical parameters: When a sheet of material has the gasket shape "punched out" of it, it is a sheet gasket.
This can lead to a crude and cheap gasket. In previous times the material was compressed asbestos, but in modern times a fibrous material or matted graphite is used; these gaskets can fill various different chemical requirements based on the inertness of the material used. Non-asbestos gasket sheet is durable, of multiple materials, thick in nature. Material examples are carbon or nitrile synthetic rubber. Applications using sheet gaskets involve corrosive chemicals, steam or mild caustics. Flexibility and good recovery prevent breakage during installation of a sheet gasket; the idea behind solid material is to use metals which cannot be punched out of sheets but are still cheap to produce. These gaskets have a much higher level of quality control than sheet gaskets and can withstand much higher temperatures and pressures; the key downside is that a solid metal must be compressed in order to become flush with the flange head and prevent leakage. The material choice is more difficult. An additional downside is that the metal used must be softer than the flange — in order to ensure that the flange does not warp and thereby prevent sealing with future gaskets.
So, these gaskets have found a niche in industry. Spiral-wound gaskets comprise a mix of filler material; the gasket has a metal wound outwards in a circular spiral with the filler material wound in the same manner but starting from the opposing side. This results in alternating layers of metal; the filler material in these gaskets acts as the sealing element, with the metal providing structural support. These gaskets have proven to be reliable in most applications, allow lower clamping forces than solid gaskets, albeit with a higher cost; the constant seating stress gasket consists of two components. The sealing elements are made from a material suitable to the process fluid and application. Constant seating stress gaskets derive their name from the fact that the carrier ring profile takes flange rotation into consideration. With all other conventional gaskets, as the flange fasteners are tightened, the flange deflects radially under load, resulting in the greatest gasket compression, highest gasket stress, at the outer gasket edge.
Since the carrier ring used in constant seating stress gaskets take this deflection into account when creating the carrier ring for a given flange size, pressure class, material, the carrier ring profile can be adjusted to enable the gasket seating stress to be radially uniform across the entire sealing area. Further, because the sealing elements are confined by the flange faces in opposing channels on the carrier ring, any in-service compressive forces acting on the gasket are transmitted through the carrier ring and avoid any further compression of the sealing elements, thus maintaining a'constant' gasket seating stress while in-service. Thus, the gasket is immune t
A tap is a valve controlling the release of a liquid or gas. Tap is used in the British Isles and most of the Commonwealth for any everyday type of valve the fittings that control water supply to bathtubs and sinks. Faucet is the most common term in the US, similar in use to "tap" in British English. Spigot is used by professionals in the trade, refers to an outdoor fixture. Silcock, same as "spigot", referring to a "cock" that penetrates a foundation sill. Bib, same as "spigot". Wall hydrant, same as "spigot" Tap refers to a beer tap, though appears as a descriptor in "tap water". Water for baths and basins can be provided by separate hot and cold taps. In kitchens and bathrooms, mixer taps are used. In this case and cold water from the two valves is mixed before reaching the outlet, allowing the water to emerge at any temperature between that of the hot and cold water supplies. Mixer taps were invented by Thomas Campbell of Saint John, New Brunswick, patented in 1880. For baths and showers, mixer taps incorporate some sort of pressure balancing feature so that the hot/cold mixture ratio will not be affected by transient changes in the pressure of one or other of the supplies.
This helps avoid uncomfortable chilling as other water loads occur. Rather than two separate valves, mixer taps use a single, more complex, valve controlled by a single handle; the handle moves up and down to control the amount of water flow and from side to side to control the temperature of the water. For baths and showers, the latest designs are thermostatic mixing valves that do this using a built-in thermostat, can be mechanical or electronic. There are faucets with color LEDs to show the temperature of the water. If separate taps are fitted, it may not be clear which tap is hot and, cold; the hot tap has a red indicator while the cold tap has a blue or green indicator. In the United States, the taps are also labeled with an "H" or "C". In countries with Romance languages, the letters "C" for hot and "F" for cold are used; this can create confusion for English-speaking visitors. Mixer taps may have arrows indicating which side will give hot and which cold. In most countries, there is a standard arrangement of hot/cold taps.
For example, in the United States and many other countries, the hot tap is on the left by building code requirements. Many installations exist. Mis-assembly of some single-valve mixer taps will exchange hot and cold if the fixture has been plumbed correctly. Most handles in homes are fastened to the valve shafts with screws, but on many commercial and industrial applications they are fitted with a removable key called a "loose key", "water key", or "sillcock key", which has a square peg and a square-ended key to turn off and on the water. Before the "loose key" was invented it was common for some landlords or caretakers to take off the handle of a tap, which had teeth that would meet up with the gears on the valve shaft; this tooth and cog system is still used on most modern taps. "Loose keys" may be found outside homes to prevent passers-by from using them. Taps are connected to the water supply by means of a "swivel tap connector", attached to the end of the water pipe using a soldered or compression fitting, has a large nut to screw onto the threaded "tail" of the tap, which hangs down underneath the bath, basin or sink.
A fibre washer is used between the tap tail. Tap tails are 1⁄2 " or 12 mm in diameter for sinks and 3⁄4 " or 19 mm for baths, although continental Europe sometimes uses a 3⁄8 " size; the same connection method is used for a ballcock. The term tap is used to describe the valve used to dispense draft beer from a keg, whether gravity feed or pressurized. A gas tap is a specific form of ball valve used in residential and laboratory applications for coarse control of the release of fuel gases. Like all ball valves its handle will parallel the gas line when open and be perpendicular when closed, making for easy visual identification of its status. Water and gas taps have adjustable flow: gate valves are more progressive. Turning a valve knob or lever adjusts flow by varying the aperture of the control device in the valve assembly; the result when opened in any degree is a choked flow. Its rate is independent of the viscosity or temperature of the fluid or gas in the pipe, 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. Bubbles of cool water vapor form and collapse at the restriction, causing the familiar hissing sound. At low flow settings, the viscosity of the water becomes important and the pressure drop