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Tap (valve)
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Tap (valve)
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Interior water taps with aerators are commonly found in the bathroom and kitchen
Exterior spigot (also known as a "shut-off valve", "hose hydrant", "hose bib", or "silcock").
Two way water tap used in restroom.

A tap (also spigot or faucet: see usage variations) is a valve controlling the release of a fluid.

Nomenclature

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United Kingdom

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  • Tap is used in the United Kingdom and most of the Commonwealth for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks.

United States

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  • Faucet is the most common term in the US, similar in use to "tap" in British English, e.g. "water faucet" (although the term "tap" is also used in the US).
  • Spigot is used by professionals in the trade (such as plumbers), and typically refers to an outdoor fixture.[1]
  • Silcock (and sillcock), same as "spigot", referring to a "cock" (as in stopcock and petcock) that penetrates a foundation sill.
  • Bib, bibcock, or hose bib, usually a freeze-resistant version of a "spigot".
  • Wall hydrant, same as "hose bib".
  • Tap generally refers to a keg or barrel tap, though also commonly refers to a faucet that supplies either hot or cold water and not both.[citation needed] It also appears as a descriptor in "tap water" (i.e. water purified for domestic use). A single temperature tap is commonly found in a commercial or public restroom where the temperature of the water will be controlled by a separate temperature regulating valve that mixes hot and cold water. The regulating valve may be under the handwashing sink or in a separate mechanical room or service closet. These single taps are less prone to breakage from heavy use or vandalism.[citation needed]

Types

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Liquid

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Plastic taps are widely used in India due to low costs.

Water for baths, sinks and basins can be provided by separate hot and cold taps; this arrangement is common in older installations, particularly in public washrooms/lavatories and utility rooms/laundries. In kitchens and bathrooms, mixer taps are commonly used. In this case, hot 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, and patented in 1880.[2]

A North American style mixing valve uses a center handle to control both water flow and temperature (increased by clockwise rotation). Below it is a lever controlling a diverter, sending flow to the tap when positioned to the left, the shower to the right.

For baths and showers, mixer taps frequently 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 scalding or uncomfortable chilling as other water loads occur (such as the flushing of a toilet). Rather than two separate valves, mixer taps frequently use a single, more complex, valve controlled by a single handle (single handle mixer). 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. Especially for baths and showers, the latest designs are thermostatic mixing valves that do this using a built-in thermostat, and can be mechanical or electronic. There are also taps with color LEDs to show the temperature of the water.

When two pipes are installed, the hot tap generally has a red indicator while the cold tap generally has a blue or green indicator. In the United States, the taps are frequently also labeled with an "H" or "C". In countries with Romance languages, the letters "C" for hot and "F" for cold are used (from French "chaud"/Italian "caldo"/Spanish "caliente" (hot) and French "froid"/Italian "freddo"/Spanish "frio" (cold)). Portuguese would use Q (for "quente", hot) and F. This can create confusion for English-speaking visitors. Mixer taps may have a red-blue stripe or 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 where this standard has been ignored (called "crossed connections" by plumbers). Mis-assembly of some single-valve mixer taps will exchange hot and cold even if the fixture has been plumbed correctly.

In the United States, the Americans with Disabilities Act provide requirements for faucets, such as requiring less than five pounds of force to operate, and requiring that the user does not have to twist their wrist.[3]

Old metal taps were often used as decoration, as is this one at Fužine Castle, Slovenia.

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; the "loose key" can be removed to prevent vandals from turning on the water.[citation needed] 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 also be found outside homes to prevent passers-by from using them.[citation needed]

Taps are normally connected to the water supply by means of a "swivel tap connector", which is attached to the end of the water pipe using a soldered or compression fitting, and 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 (which expands when wet, aiding the seal) is used between the connector and the tap tail. Tap tails are normally 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 " (still imperial) size. The same connection method is used for a ballcock.

The term tap is widely used to describe the valve used to dispense draft beer from a keg, whether gravity feed or pressurized.

Gas

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Gas taps

A gas tap is a specific form of ball valve used in residential, commercial, and laboratory applications for coarse control of the release of fuel gases (such as natural gas, coal gas, and syngas). 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.

Physics

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Water and gas taps have adjustable flow: gate valves are more progressive; ball valves more coarse, typically used in on-off applications. 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, 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 silent.

Mechanisms

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Tap mechanism

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, also corrosion) over time, so that eventually no tight seal is formed in the closed position, resulting in a leaking tap. 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 flow rate 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 wedge with a circular face, usually the same diameter as the pipe, which is screwed into place perpendicularly to the flow, cutting it off. There is little 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 90°—between fully open and closed. Usually, when the handle is in line with the pipe the valve is open, and when the handle is across the pipe it is closed. But it could move in either direction CW or CCW perpendicular to the pipe. S=shut and O=open. A cone valve consists of a shallowly tapering cone in a tight-fitting socket placed across the flow of the fluid. In UK English this is usually known as a taper-plug cock. 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 (usually PTFE) 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, as well as in industrial settings where extremely dirty hands operating taps might leave residues on them.

Modern taps often have aerators at the tip to limit water flow and introduce air in the form of bubbles to reduce splashing. Without an aerator, water usually flows out of the tap in one big stream. An aerator spreads the water flow into many small droplets. In sanitary settings such as hospitals or laboratories "laminar flow devices" are used in place of aerators. Laminar flow devices restrict flow and direct the water into a smooth stream without introducing the surrounding air which could contain hazardous bacteria or particles.

Cross section of a shower tap

Modern bathroom and kitchen taps often use ceramic or plastic surfaces sliding against other spring-loaded ceramic surfaces or plastic washers. These taps exploit the uniquely low value of the coefficient of friction of 2 ceramic surfaces in contact, especially in the presence of water as a lubricant. These taps 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 three manufacturers in North America, Moen and American Standard use cartridges (Moen's being O-ring based, American Standard's being ceramic), while Delta uses rubber seats facing the cartridges. 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.

Backflow prevention

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Most US jurisdictions require hose spigots, hose bibs, and wall hydrants to have a vacuum breaker or backflow preventer, so that water cannot return through the spigot from the hose. This prevents contamination of the building or public water system should there be a pressure drop. In the UK, water regulations require a double check valve; this is often incorporated within the body of the tap itself.

ASME A112 Standards on Plumbing Materials and Equipment

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The American Society of Mechanical Engineers (ASME) publishes several Standards on plumbing. Some are:

  • ASME A112.6.3 – Floor and Trench Drains
  • ASME A112.6.4 – Roof, Deck, and Balcony Drains
  • ASME A112.18.1/CSA B125.1 – Plumbing Supply Fittings
  • ASME A112.19.1/CSA B45.2 – Enameled Cast Iron and Enameled Steel Plumbing Fixtures
  • ASME A112.19.2/CSA B45.1 – Ceramic Plumbing Fixtures

Brass is commonly used in the manufacture of taps because of its durability and resistance to corrosion.[4]

See also

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  • Automatic faucet – Sensor-operated water outlet
  • Drip irrigation – Irrigation system
  • Irrigation – Agricultural artificial application of water to land
  • Shower head – Place in which a person bathes under a spray of water

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Tap (valve)

View on Grokipedia
from Grokipedia
A tap, also known as a faucet or spigot, is a device used to control the release and flow of fluids, typically , from a pipe or in systems. It consists of a or that operates an internal mechanism to open, close, or regulate the passage, allowing precise adjustment of volume and, in mixing models, . Taps are essential components in residential, commercial, and industrial settings, enabling on-demand delivery while preventing leaks through sealing elements like washers, discs, or cartridges. The origins of taps trace back to , where systems using cylindrical or conical plugs with aligned holes provided basic flow control in aqueducts and . By the mid-19th century, industrialization led to the development of compression valves, which used screw mechanisms for incremental control and separate handles for hot and cold water, patented in designs like Thomas Campbell's 1880 mixing faucet. Innovations in the , such as Al Moen's single-handle cartridge inspired in 1937 and introduced in 1947, and Landis Perry's 1952 , introduced washerless systems for smoother operation and reduced maintenance. The 1973 patent for disc valves marked a significant advancement, utilizing durable plates for precise, leak-resistant sealing. Common types of tap valves include compression valves, which rely on a rubber washer pressed against a for sealing; cartridge valves, featuring a cylindrical unit for easy replacement; valves, using a perforated rotated by a for quick quarter-turn operation; and disc valves, employing two overlapping discs aligned to with minimal wear. Other variants encompass ground key faucets with plug mechanisms, loose key models for secure public use, and metering or self-closing types that limit flow for conservation. These designs vary by application, such as angle valves for 90-degree or taps for connecting service lines to mains. Modern taps prioritize durability, water efficiency, and safety, often incorporating materials like for corrosion resistance and ceramics for high-temperature tolerance. Features such as anti-scald mechanisms, pressure-balancing, and aerators reduce splashing and promote , aligning with standards for systems. Regional nomenclature differs— "tap" predominates in the UK and , while "faucet" is standard in the —but the core function remains consistent across global installations.

Nomenclature and Terminology

Regional Differences

In the , , and other countries, the term "tap" serves as the primary designation for a that regulates the flow of from pipes, reflecting its longstanding use in . In contrast, the and predominantly employ "faucet" for the same device, a term originating from the "fausset," which denoted a peg or spigot inserted into a barrel to control liquid outflow. The word "tap" traces its roots to "tæppa," also meaning a peg for plugging or drawing liquid, highlighting a shared historical concept across English variants but divergent regional adoption. These terminological differences can extend to perceptions of common features and designs, though both regions now predominantly feature mixer configurations that blend hot and cold within a single unit. Modern taps frequently incorporate such mixers, a shift from traditional separate hot and cold taps influenced by historical practices that kept potable cold mains distinct from potentially contaminated hot storage. Regional slang further illustrates these variations; in older US contexts, "spigot" commonly refers to an outdoor or hose-connected valve, evoking its etymological sense of a projecting spout. In the UK, "bib tap" denotes a wall-mounted outdoor tap with a downturned , typically used for hose attachments in or utility applications. Such nomenclature disparities have practical implications for , as they necessitate precise product labeling to align with international standards for sanitary tapware, such as EN 200, ensuring , , and across markets.

Key Technical Terms

In engineering contexts, a tap is defined as a manually operated valve designed to regulate the flow of fluids, typically liquids such as , by opening, closing, or partially obstructing a passageway, distinguishing it from automatic valves like check valves that prevent without manual intervention. Taps are commonly used in systems for precise control in residential, commercial, and industrial applications, where they differ from broader valve categories by emphasizing user-operated throttling rather than relief or directional flow. Related terms include "stopcock," often used for gate-like shutoff valves, and "bibcock," referring to angled taps for outdoor or utility use. Key components of a tap include the spindle, a rotating or linear shaft that connects the to the mechanism, allowing the user to turn or lift the to control flow; the washer, a compressible sealing element often made of rubber or synthetic material that presses against the to stop fluid passage when closed; the , a fixed surface within the body that forms the sealing interface with the washer; and the , the external or knob that provides the interface for manual operation. These elements work together to ensure leak-proof operation and durability under varying pressures. Tap mechanisms are classified as quarter-turn or multi-turn based on the rotation required for full operation: quarter-turn designs, prevalent in modern taps, achieve open or closed states with a 90-degree handle for rapid and ergonomic control, while multi-turn mechanisms require multiple s (often several full turns) for gradual adjustment, commonly found in older or high-pressure systems. This distinction influences and installation suitability, with quarter-turn taps favored for their simplicity in contemporary . An aerator is a perforated screen or mesh attachment fitted to the tap's outlet to break up water flow, reducing splashing and while conserving water by limiting flow rates; , standard aerators typically restrict output to 1.5–2.2 gallons per minute (GPM) under 60 psi pressure to comply with regulations. This feature enhances usability and environmental impact without compromising pressure delivery. The terminology for taps evolved in technical literature during the late , shifting from the archaic term ""—derived from early plug valves—to "tap" to reflect standardized amid industrialization and advancements. Regional naming preferences, such as "faucet" in versus "tap" elsewhere, occasionally appear in global standards but do not alter core technical definitions.

Types of Taps

Liquid Taps

taps, also known as faucets in some regions, are valves specifically engineered to control the flow of liquids, predominantly , in residential and light commercial settings. These devices are essential for managing in everyday applications, ensuring precise regulation while minimizing waste. Unlike taps for other fluids, liquid taps are designed to handle incompressible liquids at low to moderate pressures, prioritizing ease of use, , and . The primary subtypes of liquid taps include compression taps, ball taps, and ceramic disc taps, each employing distinct mechanisms for sealing and flow control. Compression taps, one of the oldest designs, utilize a rubber washer that compresses against a metal to stop water flow when the handle is turned, offering a simple and cost-effective solution but requiring periodic washer replacements to prevent leaks. Ball taps feature a spherical or ball with holes that aligns with the inlets via a rotating , allowing smooth adjustment of and mixing in a single operation. Ceramic disc taps, a more modern innovation, incorporate two discs—one fixed and one rotatable—that align or misalign ports to regulate flow, providing exceptional durability with resistance to wear and minimal leakage over time. In residential , liquid taps are commonly installed at sinks for tasks like and food preparation, and in bathrooms for handwashing and , where they facilitate both hot and cold water delivery. Many contemporary models integrate water-saving features, such as low-flow restrictors or aerators, which limit output to 2.2 gallons per minute (gpm) at 60 pounds per (psi), a standard established by the U.S. Department of Energy in 1998 under the authority of the Energy Policy Act of 1992 to conserve resources amid growing environmental concerns. These features reduce household water usage without compromising functionality, promoting sustainability in urban water management. Materials for liquid taps are selected for their resistance to from constant exposure and aesthetic appeal. , an of and , forms the core of high-quality taps due to its inherent corrosion resistance and strength, often enhanced with for a shiny, durable finish that resists tarnishing. In budget-friendly options, components are used for non-structural parts like handles, offering lightweight construction and reduced manufacturing costs while maintaining basic performance. The evolution of liquid taps traces back to , where lead-based systems, including rudimentary taps, distributed water through aqueducts, though high lead contamination posed health risks. Modern advancements shifted away from such materials following the Amendments of 1986, which prohibited the use of lead and exceeding 0.2% lead and exceeding 8% lead in public water systems or in facilities providing water for human consumption. Subsequent regulations, including the 2011 Reduction of Lead in Drinking Water Act, limited lead in faucet components to a weighted average of 0.25% for wetted surfaces to minimize leaching and protect . Regional design variations highlight practical adaptations, such as pillar taps prevalent in the UK, which consist of standalone pairs mounted on basins or baths for separate hot and cold controls, evoking traditional aesthetics. In contrast, U.S. preferences favor deck-mounted faucets, integrated directly into countertops or sinks with single-lever mixers for streamlined installation and modern convenience. These examples illustrate how and form factor can differ, with "taps" denoting pillar styles in and "faucets" encompassing broader deck-integrated designs in American usage.

Gas Taps

Gas taps, also known as gas valves, are specialized devices designed to regulate the flow of gases such as , , or oxygen in both industrial and domestic environments, prioritizing leak-proof seals and precise control due to the compressible nature of gases under pressure. Among the subtypes of gas taps, needle valves provide fine adjustment for low-flow applications, featuring a tapered, needle-like that seats against an orifice to enable precise throttling in settings. Butterfly valves, suitable for larger gas lines, employ a rotating disc mounted on a shaft to control flow, offering quick operation and minimal resistance in high-volume systems like pipelines. Solenoid gas taps facilitate automated shutoff through electromagnetic actuation, rapidly closing to isolate gas supply in response to electrical signals, commonly integrated into interlock systems. In applications, gas taps are essential for natural gas appliances such as stoves and heaters, where they ensure controlled delivery to burners while preventing unintended releases. They are also critical in oxygen systems, regulating flow to delivery devices with stringent requirements for spark-proof materials to avoid ignition risks in oxygen-enriched environments. Safety integrations in gas taps include built-in flame arrestors, which use mesh or barriers to quench propagating and prevent explosions, becoming mandatory following a series of early 20th-century industrial incidents that highlighted the need for such protections. regulators are often incorporated to maintain stable output despite input fluctuations, as required by standards developed in response to boiler and gas system explosions around 1914-1915. Common materials for gas taps include for corrosion resistance and durability in oxygen service, and forged iron or for robustness under pressure, with designs rated to handle up to 100 psi in certain residential distribution lines before metering. Historically, the development of gas cocks for Bunsen burners in the 1850s laboratories, refined by Peter Desaga in 1854 under , served as precursors to modern gas taps by introducing controllable gas inlets for safe flame production.

Principles of Operation

Fluid Physics

The within a tap are fundamentally governed by , which describes the along a streamline in an incompressible, . As fluid accelerates through the restricted opening of a tap, its velocity increases, leading to a corresponding decrease in to maintain the total energy constant. This pressure drop becomes more pronounced with higher flow rates, influencing the overall system performance. The principle is expressed by the equation P+12ρv2+ρgh=\constant,P + \frac{1}{2} \rho v^2 + \rho g h = \constant, where PP is the static pressure, ρ\rho is the fluid density, vv is the velocity, gg is gravitational acceleration, and hh is the elevation head. The volumetric flow rate QQ through a tap is determined by the product of the effective cross-sectional area AA of the valve opening and the average fluid velocity vv, given by Q=A⋅vQ = A \cdot v. This relationship holds for both laminar and turbulent regimes, but the flow regime is characterized by the Reynolds number, Re=ρvdμRe = \frac{\rho v d}{\mu}, where dd is the characteristic diameter (such as the valve port size) and μ\mu is the dynamic viscosity. Flows with Re<2000Re < 2000 are typically laminar, exhibiting smooth, orderly motion with lower energy dissipation, while Re>4000Re > 4000 indicates turbulent flow, marked by chaotic eddies and higher shear stresses that enhance mixing but increase losses. The transition regime between these values depends on pipe geometry and surface roughness. In liquid taps operating at high velocities, cavitation poses a significant when the local drops below the fluid's , causing the formation of vapor bubbles that subsequently collapse upon recovery. These implosions generate shock waves, resulting in audible noise, vibration, and accelerated material erosion on valve surfaces, potentially leading to premature failure. The critical threshold for cavitation onset is approximately the of the liquid at the operating , often exacerbated in partially open taps where velocity gradients are steep. For gas taps, the of the fluid introduces deviations from assumptions, particularly during throttling where rapid expansion occurs. This process triggers the Joule-Thomson effect, in which the gas decreases (cooling) as it expands isenthalpically through the , due to intermolecular forces in real gases. The magnitude of cooling depends on the gas type, initial , and ; for instance, mixtures commonly exhibit cooling rates of 6–8°F per 100 psi pressure drop. Such effects must be accounted for in cryogenic or high-pressure applications to prevent icing or performance degradation. Energy losses in tap systems arise primarily from frictional interactions between the fluid and the pipe-tap interface, quantified using the Darcy-Weisbach equation for head loss: ΔP=fLDρv22\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}, where ff is the dimensionless friction factor (dependent on and relative roughness), LL is the effective length, and DD is the . In taps, these losses are amplified by the sudden contraction and expansion, contributing to overall pressure recovery inefficiencies and requiring careful sizing to minimize system energy demands. The friction factor ff is typically obtained from the Moody diagram or empirical correlations for turbulent flows.

Valve Mechanisms

Valve mechanisms in taps refer to the internal components and designs that enable the control of flow through opening, closing, or throttling actions. These mechanisms vary in to suit different applications, balancing factors such as ease of operation, durability, and resistance to wear. Common types include compression, ceramic disc, and gate mechanisms, each employing distinct principles to seal or permit flow while minimizing leakage. The compression mechanism, prevalent in older taps, utilizes a screw-down spindle that rotates to compress a rubber washer or seal against a fixed valve seat, thereby halting flow. This , often found in traditional quarter-turn or multi-turn taps, relies on the mechanical force from the spindle threads to maintain the seal. However, repeated use leads to washer deformation and wear, resulting in drips as the seal loses over time. In contrast, the ceramic disc mechanism features two stacked ceramic discs with precisely machined ports; rotation of the stem aligns or misaligns these ports to regulate flow, achieving a drip-free operation without relying on compressible seals. This quarter-turn (90-degree) design enhances user convenience and longevity, as the hard ceramic surfaces resist erosion from water minerals and friction, often lasting decades with minimal maintenance. The lower fixed disc remains stationary while the upper disc rotates via the stem, allowing precise throttling by partial alignment. Gate mechanisms, typically employed in larger industrial or high-flow taps, involve a wedge-shaped that lifts to the flow path via a rising stem, providing full-bore opening for unobstructed passage. The , often metallic, slides within guides to seal against the valve body when lowered, effectively cutting off flow. This suits applications requiring complete isolation but is less common in residential taps due to the multi-turn operation needed for full travel. Variations in lever and handle designs, such as single-lever mixers, integrate blending of hot and cold supplies through a cam action within the cartridge, where handle movement simultaneously adjusts flow volume and temperature ratio. The cam mechanism translates lever tilt into disc or ball positioning, enabling intuitive one-handed control without separate valves. Maintenance for these mechanisms often involves disassembly to access internal components, particularly for compression types where washer replacement is routine. Technicians must adhere to limits during reassembly, typically 8-12 Nm (6-9 ft-lbs) for locknuts and stems, to prevent thread stripping or distortion while ensuring a secure seal. Over-tightening can compromise the valve body, whereas under-tightening risks leaks; always consult manufacturer specifications for precise values.

Safety Features and Standards

Backflow Prevention

Backflow prevention in taps, also known as faucets or valves, involves integrating specialized devices to safeguard potable supplies from due to reverse flow, or , which can occur through backsiphonage or backpressure. These mechanisms are essential in systems where taps connect to potential sources, such as hoses or fixtures, ensuring that hazardous substances do not enter the main line. Vacuum breakers are atmospheric devices that prevent backsiphonage by allowing air to enter the system and break the effect when downstream pressure drops below atmospheric levels. They typically feature a or float that opens an air port under negative pressure, commonly used on hose bibbs and taps. In the United States, the requires atmospheric vacuum breakers on hose bibbs to protect against contamination from attached s, with installation at least 6 inches above the flood level rim of the fixture served. Check valves serve as one-way mechanisms to block reverse flow, often incorporating a flap, ball, or disc that closes automatically upon pressure reversal, with spring-loaded variants providing enhanced sealing reliability under varying conditions. These are integrated into taps for low- to medium-hazard applications, such as residential or commercial fixtures, and form the basis of double-check assemblies with test cocks for verification. Unlike simpler designs, spring-loaded check valves ensure consistent performance even in low-flow scenarios, preventing contaminants like boiler chemicals from entering potable lines. Reduced zone (RPZ) assemblies offer advanced protection for high-hazard taps, consisting of two independent check valves separated by a reduced zone and a that discharges water if the zone falls below a safe threshold, typically 2 psi below supply . This setup detects failures in the checks and automatically vents potential contaminants, making it suitable for taps in chemical processing or systems connected to pesticides. RPZ devices are required in scenarios with severe health risks, as they provide the highest level of against both backsiphonage and backpressure. Installation guidelines for these devices emphasize placement upstream of the tap on contaminated lines to isolate hazards, with vacuum breakers and check valves positioned vertically and accessible, while RPZ assemblies require a minimum 12-inch clearance from walls and floors, plus an air-gapped drain for discharge. Many jurisdictions mandate annual testing by certified professionals to verify functionality, including pressure differentials and seating, to comply with codes and prevent system failures. The widespread adoption of backflow prevention in taps accelerated in the following documented incidents of chemical backsiphonage contaminating public water systems, such as the 1979 chlordane intrusion into municipal supplies, prompting stricter cross-connection controls under the .

Regulatory Standards

Regulatory standards for taps (valves) ensure safety, performance, and compatibility with plumbing systems, with key international and regional frameworks addressing design, materials, and installation. The ASME A112 series provides critical guidelines for plumbing supply fittings in . Specifically, ASME A112.18.1/CSA B125.1 establishes performance requirements for faucets and fittings, including maximum flow rates (typically limited to 2.2 gallons per minute at 60 psi for private lavatories), endurance testing (up to 500,000 cycles for handles and seats to simulate long-term use), and resistance to and . Complementing this, ASME A112.1.2 specifies air gaps as a method to prevent back siphonage in plumbing systems, defining minimum vertical separations (e.g., twice the supply pipe diameter or 1 inch, whichever is greater) between the flood level rim and the end of the water supply pipe to avoid contamination. On a global scale, ISO 3822 series standards focus on laboratory testing for noise emissions from water supply appliances, including hand-operated draw-off taps and mixing valves. ISO 3822-2 outlines mounting and operating conditions for accurate measurements, ensuring that acoustic performance does not exceed acceptable levels (typically below 20 dB for quiet operation under specified flow rates up to 6 liters per minute). These standards emphasize controlled test setups to evaluate for operation (limited to 0.6 Nm for ease of use) and leak rates (no visible leakage after 10,000 cycles). In the , regulations under the Directive (98/83/EC) are implemented through harmonized standards like BS EN 200, which governs sanitary tapware for water supply systems of type 1 (cold) and type 2 (mixed hot/cold). This standard mandates lead-free materials with a maximum lead content of 0.25% by weight in wetted surfaces to minimize risks, alongside requirements for thermal shock resistance in hot water taps (withstanding 100 cycles between 10°C and 65°C without cracking). In the United States, NSF/ANSI 61 certifies system components, including taps, by evaluating potential leaching of contaminants (e.g., lead limited to 5 μg/L weighted average over 18,000 liters of exposure) to protect . Since 2020, updates to these standards have strengthened low-lead provisions and begun addressing smart tap integrations. The NSF/ANSI 61-2024 edition refined leaching protocols for stricter compliance, while U.S. regulations under the (amended 2021) enforce 0.25% maximum lead in products effective 2023, with states like mandating NSF/ANSI/CAN 61 certification for all new fixtures. Emerging IoT guidelines, such as those from the (ICC) and UL standards for connected devices (e.g., UL 61010-1 for smart sensors), now incorporate cybersecurity and requirements for smart taps to prevent data breaches in water management systems.

References

  1. https://opi.cs.cmu.edu/show/tap
  2. https://asse-plumbing.org/media/wdvjmptd/asse_plumbing_dictionary_6thed.pdf
  3. https://ceramics.org/ceramic-tech-today/ceramics-in-faucets-and-plumbing/
  4. https://www.pmmag.com/articles/84097-greatest-plumbing-heating-inventions-1900-1950
  5. https://gowininc.com/faucets-vs-taps-understanding-the-real-difference/
  6. https://www.etymonline.com/word/faucet
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