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A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin ''valva'', the moving part of a door, in turn from ''volvere'', to turn, roll. The simplest, and very ancient, valve is simply a freely hinged flap which swings down to obstruct fluid (gas or liquid) flow in one direction, but is pushed up by the flow itself when the flow is moving in the opposite direction. This is called a
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
, as it prevents or "checks" the flow in one direction. Modern
control valves A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of Fluid dynamics, flow rate and the consequential control of process quantitie ...
may regulate
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
or flow downstream and operate on sophisticated
automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...
systems. Valves have many uses, including controlling water for
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
, industrial uses for controlling processes, residential uses such as on/off and pressure control to dish and clothes washers and taps in the home. Even aerosol spray cans have a tiny valve built in. Valves are also used in the military and transport sectors. In
HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
ductwork and other near-atmospheric air flows, valves are instead called dampers. In compressed air systems, however, valves are used with the most common type being ball valves.


Applications

Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields. People in developed nations use valves in their daily lives, including
plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses piping, pipes, valves, piping and plumbing fitting, plumbing fixtures, Storage tank, tanks, and other apparatuses to convey fluids. HVAC, Heating and coo ...
valves, such as taps for
tap water Tap water (also known as faucet water, running water, or municipal water) is water supplied through a Tap (valve), tap, a water dispenser valve. In many countries, tap water usually has the quality of drinking water. Tap water is commonly used fo ...
, gas control valves on cookers, small valves fitted to
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and i ...
s and
dishwasher A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike dishwashing, manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying h ...
s, safety devices fitted to
hot water system Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated t ...
s, and
poppet valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...
s in car engines. In nature there are valves, for example one-way valves in
veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary vein, pulmonary and umbilical veins, both of which ca ...
controlling the
blood circulation The blood circulatory system is a organ system, system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascula ...
, and
heart valve A heart valve is a Check valve, one-way valve that allows blood flow, blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow thro ...
s controlling the flow of blood in the
chambers of the heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
and maintaining the correct
pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the metho ...
ing action. Valves may be operated manually, either by a
handle A handle is a part of, or attachment to, an object that allows it to be grasped and manipulated by hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanze ...
,
lever A lever is a simple machine consisting of a beam (structure), beam or rigid rod pivoted at a fixed hinge, or '':wikt:fulcrum, fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, l ...
, pedal or wheel. Valves may also be automatic, driven by changes in
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
,
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...
, or flow. These changes may act upon a diaphragm or a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...
which in turn activates the valve, examples of this type of valve found commonly are
safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...
s fitted to hot water systems or
boiler A boiler is a closed pressure vessel, vessel in which fluid (generally water) is heated. The fluid does not necessarily boiling, boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including ...
s. More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an
actuator An actuator is a component of a Mechanical system, machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by ...
. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.


Variation

Valves vary widely in form and application. Sizes typically range from 0.1 mm to 60 cm. Special valves can have a diameter exceeding 5 meters. Valve costs range from simple inexpensive
disposable A disposable (also called disposable product) is a product designed for a single use after which it is recycled or is disposed as solid waste. The term is also sometimes used for products that may last several months (e.g. disposable air filter ...
valves to specialized valves which cost thousands of
US dollars The United States dollar (Currency symbol, symbol: Dollar sign, $; ISO 4217, code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from Dollar, other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American ...
per
inch Measuring tape with inches The inch (symbol: in or ″) is a unit of length in the British imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelf ...
of the diameter of the valve. Disposable valves may be found in common household items including mini-pump dispensers and aerosol cans. A common use of the term ''valve'' refers to the
poppet valves A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...
found in the vast majority of modern internal combustion engines such as those in most fossil fuel powered vehicles which are used to control the intake of the fuel-air mixture and allow exhaust gas venting.


Types

Valves are quite diverse and may be classified into a number of basic types. Valves may also be classified by how they are actuated: *
Hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunne ...
*
Pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...
* Manual *
Solenoid valve A solenoid valve is an electromechanically operated valve. Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the ty ...
*
Motor An engine or motor is a machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employ ...


Components

The main parts of the most usual type of valve are the body and the bonnet. These two parts form the casing that holds the fluid going through the valve.


Body

The valve's body is the outer casing of most or all of the valve that contains the internal parts or ''trim''. The bonnet is the part of the encasing through which the
stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...
(see below) passes and that forms a guide and seal for the stem. The bonnet typically screws into or is bolted to the valve body. Valve bodies are usually
metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
lic or
plastic Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, e ...
.
Brass Brass is an alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical ...
,
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
,
gunmetal Gun metal, also known as red brass in the United States, is a type of bronze; an alloy of copper, tin and zinc. Proportions vary but 88% copper, 8–10% tin, and 2–4% zinc is an approximation. Originally used chiefly for making cannon, guns, i ...
,
cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
,
steel Steel is an alloy made up of iron with added carbon to improve its strength of materials, strength and fracture toughness, fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that ...
,
alloy steel Alloy steel is steel Steel is an alloy made up of iron with added carbon to improve its strength of materials, strength and fracture toughness, fracture resistance compared to other forms of iron. Many other elements may be present or added. ...
s and
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
s are very common. Seawater applications, like desalination plants, often use duplex valves, as well as super duplex valves, due to their corrosion resistant properties, particularly against warm seawater.
Alloy 20 Alloy 20 is an austenitic stainless steel containing less than 50% iron developed for applications involving sulfuric acid. Its corrosion resistance also finds other uses in the Chemical industry, chemical, Petrochemical industry, petrochemical, p ...
valves are typically used in sulphuric acid plants, whilst
monel Monel is a group of alloys of nickel (from 52 to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon. Monel is not a cupronickel alloy because it has less than 60% copper. Stronger than pure nickel, Monel alloys are res ...
valves are used in
hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidep ...
(HF Acid) plants. Hastelloy valves are often used in high temperature applications, such as nuclear plants, whilst
inconel Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys. Inconel alloys are oxidation-corrosion resistance, corrosion-resistant materials well suited for service in extreme env ...
valves are often used in hydrogen applications. Plastic bodies are used for relatively low pressures and temperatures. PVC, PP,
PVDF Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and so ...
and glass-reinforced nylon are common plastics used for valve bodies.


Bonnet

A bonnet acts as a cover on the valve body. It is commonly semi-permanently screwed into the valve body or bolted onto it. During
manufacture Manufacturing is the creation or Production (economics), production of goods with the help of equipment, Work (human activity), labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary secto ...
of the valve, the internal parts are put into the body and then the bonnet is attached to hold everything together inside. To access internal parts of a valve, a user would take off the bonnet, usually for maintenance. Many valves do not have bonnets; for example,
plug valve Plug valves are valve A valve is a device or Heart valve, natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageway ...
s usually do not have bonnets. Many ball valves do not have bonnets since the valve body is put together in a different style, such as being screwed together at the middle of the valve body.


Ports

Ports are passages that allow fluid to pass through the valve. Ports are obstructed by the valve member or disc to control flow. Valves most commonly have 2 ports, but may have as many as 20. The valve is almost always connected at its ports to pipes or other components. Connection methods include threadings,
compression fitting A compression fitting is a Piping and plumbing fitting, fitting used in plumbing and electrical conduit systems to join two tubing (material), tubes or thin-walled pipe (material), pipes together. In instances where two pipes made of dissimilar ...
s,
glue Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that molecular binding , binds them together and resists their separation. The use of adhesives of ...
,
cement A cement is a binder (material), binder, a chemical substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ...
,
flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the ...
s, or
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as b ...
.


Handle or actuator

A
handle A handle is a part of, or attachment to, an object that allows it to be grasped and manipulated by hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanze ...
is used to manually control a valve from outside the valve body. Automatically controlled valves often do not have handles, but some may have a handle (or something similar) anyway to manually override automatic control, such as a stop-check valve. An
actuator An actuator is a component of a Mechanical system, machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by ...
is a mechanism or device to automatically or remotely control a valve from outside the body. Some valves have neither handle nor actuator because they automatically control themselves from inside; for example,
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
s and
relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, ...
s may have neither.


Disc

A disc or valve member is a movable obstruction inside the stationary body that adjustably restricts flow through the valve. Although traditionally disc-shaped, discs come in various shapes. Depending on the type of valve, a disc can move linearly inside a valve, or rotate on the stem (as in a
butterfly valve A butterfly valve is a valve that isolates or regulates the Fluid dynamics, flow of a fluid. The closing mechanism is a Disk (mathematics), disk that rotates. Principle of operation Operation is similar to that of a ball valve, which allows fo ...
), or rotate on a
hinge A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...
or
trunnion A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. Alternatively, a trunnion is a shaft that positions a ...
(as in a
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
). A ''ball'' is a round valve member with one or more paths between ports passing through it. By rotating the ball, flow can be directed between different ports.
Ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
s use spherical rotors with a cylindrical hole drilled as a fluid passage.
Plug valve Plug valves are valve A valve is a device or Heart valve, natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageway ...
s use cylindrical or conically tapered rotors called plugs. Other round shapes for rotors are possible as well in rotor valves, as long as the rotor can be turned inside the valve body. However, not all round or spherical discs are rotors; for example, a ball
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
uses the ball to block reverse flow, but is not a rotor because operating the valve does not involve rotation of the ball.


Seat

The seat is the interior surface of the body which contacts the disc to form a leak-tight seal. In discs that move linearly or swing on a hinge or
trunnion A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. Alternatively, a trunnion is a shaft that positions a ...
, the disc comes into contact with the seat only when the valve is shut. In disks that rotate, the seat is always in contact with the disk, but the area of contact changes as the disc is turned. The seat always remains stationary relative to the body. Seats are classified by whether they are cut directly into the body, or if they are made of a different material: *Hard seats are integral to the valve body. Nearly all hard seated metal valves have a small amount of leakage. *Soft seats are fitted to the valve body and made of softer materials such as
PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied Per-_and_polyfluoroalkyl_substances, PFAS. The commonly known brand name of PTFE-b ...
or various
elastomers An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules called macromolecules, composed of many Repeat unit, ...
such as NBR, EPDM, or FKM depending on the maximum
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
. A closed soft seated valve is much less liable to leak when shut while hard seated valves are more durable. Gate, globe, and check valves are usually hard seated while butterfly, ball, plug, and diaphragm valves are usually soft seated.


Stem

The stem transmits motion from the handle or controlling device to the disc. The stem typically passes through the bonnet when present. In some cases, the stem and the disc can be combined in one piece, or the stem and the handle are combined in one piece. The motion transmitted by the stem may be a linear
force In physics, a force is an influence that can change the motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving from a Newton's first law, state of rest), i.e., to accelerate. Force can ...
, a rotational
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of the ...
, or some combination of these (Angle valve using torque reactor pin and Hub Assembly). The valve and stem can be threaded such that the stem can be screwed into or out of the valve by turning it in one direction or the other, thus moving the disc back or forth inside the body. Packing is often used between the stem and the bonnet to maintain a seal. Some valves have no external control and do not need a stem as in most
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
s. Valves whose disc is between the seat and the stem and where the stem moves in a direction into the valve to shut it are normally-seated or front seated. Valves whose seat is between the disc and the stem and where the stem moves in a direction out of the valve to shut it are reverse-seated or back seated. These terms don't apply to valves with no stem or valves using rotors.


Gaskets

Gaskets image:gaskets.jpg, Some seals and gaskets A gasket is a Seal (mechanical), mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression (physical) ...
are the mechanical seals, or packings, used to prevent the leakage of a gas or fluids from valves.


Valve balls

A valve ball is also used for severe duty, high-pressure, high-tolerance applications. They are typically made of
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
,
titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
,
Stellite Stellite is a range of cobalt-chrome, cobalt-chromium alloys designed for wear resistance. The alloys may also contain tungsten or molybdenum and a small, but important, amount of carbon. History Stellite is a trademarked name of Kennametal, Kenna ...
, Hastelloy,
brass Brass is an alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical ...
, or
nickel Nickel is a chemical element with Chemical symbol, symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and Ductility, ductile transition metal. Pure nickel is chemically reactive bu ...
. They can also be made of different types of plastic, such as ABS, PVC, PP or
PVDF Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and so ...
.


Spring

Many valves have a spring for spring-loading, to normally shift the disc into some position by default but allow control to reposition the disc.
Relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, ...
s commonly use a spring to keep the valve shut, but allow excessive pressure to force the valve open against the spring-loading.
Coil spring file:Ressorts de compression coniques.jpg, A selection of conical coil springs The most common type of spring (device), spring is the coil spring, which is made out of a long piece of metal that is wound around itself. Coil springs were in use ...
s are normally used. Typical spring materials include zinc plated steel,
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
, and for high temperature applications
Inconel Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys. Inconel alloys are oxidation-corrosion resistance, corrosion-resistant materials well suited for service in extreme env ...
X750.


Trim

The internal elements of a valve are collectively referred to as a valve's trim. According to API Standards 600, "Steel Gate Valve-Flanged and Butt-welding Ends, Bolted Bonnets", the trim consists of stem, seating surface in the body, gate seating surface, bushing or a deposited weld for the backseat and stem hole guide, and small internal parts that normally contact the service fluid, excluding the pin that is used to make a stem-to-gate connection (this pin shall be made of an austenitic stainless steel material).


Valve operating positions

Valve positions are operating conditions determined by the position of the disc or rotor in the valve. Some valves are made to be operated in a gradual change between two or more positions. Return valves and
non-return valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve A valve is a device or Heart valve, natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized ...
s allow fluid to move in 2 or 1 directions respectively.


Two-port valves

Operating positions for 2-port valves can be either shut (closed) so that no flow at all goes through, fully open for maximum flow, or sometimes partially open to any degree in between. Many valves are not designed to precisely control intermediate degree of flow; such valves are considered to be either open or shut. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names such as ''regulating'', ''throttling'', ''metering'', or ''
needle valve A needle valve is a type of valve A valve is a device or Heart valve, natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing var ...
s''. For example, needle valves have elongated conically-tapered discs and matching seats for fine flow control. For some valves, there may be a mechanism to indicate by how much the valve is open, but in many cases other indications of flow rate are used, such as separate
flow meter Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. The common types of flowmeters with industrial applications are listed below: * a) Obstruction type (differential pressure or variable area ...
s. In plants with remote-controlled process operation, such as oil refineries and petrochemical plants, some 2-way valves can be designated as normally closed (NC) or normally open (NO) during regular operation. Examples of normally-closed valves are '' sampling valves'', which are only opened while a sample is taken. Other examples of normally-closed valves are emergency shut-down valves, which are kept open when the system is in operation and will automatically shut by taking away the power supply. This happens when there is a problem with a unit or a section of a fluid system such as a leak in order to isolate the problem from the rest of the system. Examples of normally-open valves are purge-gas supply valves or emergency-relief valves. When there is a problem these valves open (by switching them 'off') causing the unit to be flushed and emptied. Although many 2-way valves are made in which the flow can go in either direction between the two ports, when a valve is placed into a certain application, flow is often expected to go from one certain port on the upstream side of the valve, to the other port on the downstream side.
Pressure regulator A pressure regulator is a valve that controls the pressure of a fluid or gas to a desired value, using negative feedback from the controlled pressure. Regulators are used for gases and liquids, and can be an integral device with a pressure setti ...
s are variations of valves in which flow is controlled to produce a certain downstream
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
, if possible. They are often used to control flow of gas from a
gas cylinder A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vapor ...
. A back-pressure regulator is a variation of a valve in which flow is controlled to maintain a certain upstream pressure, if possible.


Three-port valves

Valves with three ports serve many different functions. A few of the possibilities are listed here. '' Three-way ball valves'' come with a T- or L- shaped fluid passageways inside the rotor. The T valve might be used to permit connection of one inlet to either or both outlets or connection of the two outlets. The L valve could be used to permit disconnection of both or connection of either but not both of two inlets to one outlet. '' Shuttle valves'' automatically connect the higher pressure inlet to the outlet while (in some configurations) preventing flow from one inlet to the other. '' Single handle mixer valves'' produce a variable mixture of hot and cold water at a variable flow rate under control of a single handle. ''
Thermostatic mixing valve A thermostatic mixing valve (TMV) is a valve that blends hot water with cold water to ensure constant, safe shower and bath outlet temperatures, preventing burn#Thermal, scalding. The storage of water at high temperature removes one possible b ...
s'' mix hot and cold water to produce a constant temperature in the presence of variable pressures and temperatures on the two input ports.


Four-port valves

A 4-port valve is a valve whose body has four ports equally spaced round the body and the disc has two passages to connect adjacent ports. It is operated with two positions. It can be used to isolate and to simultaneously bypass a sampling cylinder installed on a pressurized water line. It is useful to take a fluid sample without affecting the pressure of a hydraulic system and to avoid
degassing Degassing, also known as degasification, is the removal of dissolved gases from liquid A liquid is a nearly Compressibility, incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent ...
(no leak, no gas loss or air entry, no external contamination)....


Control

Many valves are controlled manually with a
handle A handle is a part of, or attachment to, an object that allows it to be grasped and manipulated by hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanze ...
attached to the stem. If the handle is turned ninety degrees between operating positions, the valve is called a quarter-turn valve. Butterfly, ball valves, and plug valves are often quarter-turn valves. If the handle is circular with the stem as the axis of rotation in the center of the circle, then the handle is called a handwheel. Valves can also be controlled by
actuator An actuator is a component of a Mechanical system, machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by ...
s attached to the stem. They can be electromechanical actuators such as an
electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
or
solenoid file:Solenoid-1.png, upright=1.20, An illustration of a solenoid file:VFPt Solenoid correct2.svg, upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electrom ...
, pneumatic actuators which are controlled by
air pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equival ...
, or
hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunne ...
actuators which are controlled by the
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
of a liquid such as oil or water. Actuators can be used for the purposes of automatic control such as in washing machine cycles, remote control such as the use of a centralised
control room A control room or operations room is a central space where a large physical facility or physically dispersed service can be monitored and controlled. It is often part of a larger command center. Overview A control room's purpose is produc ...
, or because manual control is too difficult such as when the valve is very large. Pneumatic actuators and hydraulic actuators need pressurised air or liquid lines to supply the actuator: an inlet line and an outlet line. Pilot valves are valves which are used to control other valves. Pilot valves in the actuator lines control the supply of air or liquid going to the actuators. The fill valve in a
toilet A toilet is a piece of sanitary hardware that collects human urine and Human feces, feces, and sometimes toilet paper, usually for disposal. Flush toilets use water, while dry toilet, dry or non-flush toilets do not. They can be designed for ...
water tank is a liquid level-actuated valve. When a high water level is reached, a mechanism shuts the valve which fills the tank. In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid between the ports automatically controls flow through the valve.


Other considerations

Valves are typically rated for maximum
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...
and
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
by the manufacturer. The wetted materials in a valve are usually identified also. Some valves rated at very high pressures are available. When a designer, engineer, or user decides to use a valve for an application, he/she should ensure the rated maximum temperature and pressure are never exceeded and that the wetted materials are compatible with the fluid the valve interior is exposed to. In Europe, valve design and pressure ratings are subject to statutory regulation under the Pressure Equipment Directive 97/23/EC (PED). Some fluid system designs, especially in chemical or power plants, are schematically represented in
piping and instrumentation diagram A piping and instrumentation diagram (P&ID or PID) is a detailed diagram in the process industry which shows the piping and process equipment together with the instrumentation and control devices. Superordinate to the P&ID is the process flow dia ...
s. In such diagrams, different types of valves are represented by certain
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different ...
s. Valves in good condition should be leak-free. However, valves may eventually wear out from use and develop a leak, either between the inside and outside of the valve or, when the valve is shut to stop flow, between the disc and the seat. A particle trapped between the seat and disc could also cause such leakage.


Images

Image:Globe valve (rendered).jpg, Globe valve Image:Green tubes and valves.jpg, A valve controlled by a
wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
(on vertical line) Image:Nasa-space-18408-l.jpg, Large
butterfly valve A butterfly valve is a valve that isolates or regulates the Fluid dynamics, flow of a fluid. The closing mechanism is a Disk (mathematics), disk that rotates. Principle of operation Operation is similar to that of a ball valve, which allows fo ...
Image:Butterfly-valve--The-Alloy-Valve-Stockist.JPG,
Cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
butterfly valve Image:Bidirectional tight butterfly valve-The-Alloy-Valve-Stockist.jpg, Cast iron
butterfly valve A butterfly valve is a valve that isolates or regulates the Fluid dynamics, flow of a fluid. The closing mechanism is a Disk (mathematics), disk that rotates. Principle of operation Operation is similar to that of a ball valve, which allows fo ...
Image:Hastelloy Ball valve.jpg, Hastelloy
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
Image:Valve.jpg, Stainless steel gate valve Image:Gate valve.JPG, Stainless steel gate valve Image:Swing Check valves.JPG, Hastelloy
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
s Image:Duplex-valve-A182-F51.JPG, Duplex
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
Image:Inconel gate valve--The-Alloy-Valve-Stockist.JPG, Inconel gate valve Image:Wafer check valve--The-Alloy-Valve-Stockist.JPG, Stainless steel wafer
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
Image:Inconel-Tilting disc check valve--The-Alloy-Valve-Stockist.JPG, Inconel
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
Image:Ball valve--The-Alloy-Valve-Stockist.JPG, Stainless steel
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
Image:Cryogenic-gate-valve-The-Alloy-Valve-Stockist.JPG, Cryogenic 254 SMO gate valve Image:Inside-tilting-disc-check-valve-The-Alloy-Valve-Stockist.jpg, Inside view of a tilting disc inconel
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
Image:Duplex-ball-valves-The-Alloy-Valve-Stockist.JPG, Duplex
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
s Image:Cryogenic-stainless-steel-gate-valve-The-Alloy-Valve-Stockist.JPG, Cryogenic super duplex gate valve frozen up during operation Image:Duplex-ball-valves-The-Alloy-Valve-Stockist-side.JPG, Super duplex
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
s Image:Flanged-Nozzle-check-valve-The-Alloy-Valve-Stockist.JPG, Flanged nozzle inconel
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
or axial check valve Image:Inside-wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Inside hastelloy
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
, wafer configuration Image:Large-swing-check-valve-The-Alloy-Valve-Stockist.jpg, Large carbon steel swing
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
Image:Nozzle-check-valve-disc-The-Alloy-Valve-Stockist.jpg, Disc for an alloy
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
also known as axial check valve Image:Valve-balls-The-Alloy-Valve-Stockist.jpg, Balls for alloy
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
s Image:Wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Wafer
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
Image:Valve-nuts-bolts-The-Alloy-Valve-Stockist.jpg, Nuts and bolts for incoloy valves Image:Check-valve-springs-in-inconel-The-Alloy-Valve-Stockist.JPG, Inconel
check valve A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have t ...
springs Image:Ball-valve-ball-The-Alloy-Valve-Stockist.jpg, Ball for a titanium
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...


See also

* * * * * , medical * * * * * * * * * * * * *


References


External links


ISO-15926-4
- Nearly 500 valve base classifications and definitions from the ISO 15926 standard.
Animations showing Internal Function of Various Types of Valve
tlv.com

, home.arcor.de
Valves: Piping and Instrumentation Diagram Standard Notation
controls.engin.umich.edu
Department of Energy Fundamentals Handbook, Mechanical Science, Module 4 Valves
{{Authority control Piping * Plumbing Water industry