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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 A slurry composed of glass beads in silicone oil flowing down an inclined plane A slurry is a mixture of solids denser than water suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids, the liquid ...
) 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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
, as it prevents or "checks" the flow in one direction. Modern
control valves A control valve is a valve used to control fluid flow In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matt ...

control valves
may regulate
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
or
flow Flow may refer to: Science and technology * Flow (fluid) or fluid dynamics, the motion of a gas or liquid * Flow (geomorphology), a type of mass wasting or slope movement in geomorphology * Flow (mathematics), a group action of the real numbers on ...
downstream and operate on sophisticated
automation Automation describes a wide range of technologies that reduce human intervention in processes. Human intervention is reduced by predetermining decision criteria, subprocess relationships, and related actions — and embodying those predetermi ...
systems. Valves have many uses, including controlling water for
irrigation Irrigation is the agricultural Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated Domesti ...

irrigation
, 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 The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the filters Filter, filtering or filters may refer to: Science and technology Device * Filter (chemi ...
ductwork mechanical shaft with HVAC sheet metal ducting and copper pipe (material), piping, as well as Joint (building), "HOW" (Head-Of-Wall) joint between top of concrete block wall and underside of concrete slab, firestopped with ceramic fibre-based fi ...
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 pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delive ...

plumbing
valves, such as
tap Tap, Taps, TAP or tapped may refer to: Arts and entertainment Film * Tap (film), ''Tap'' (film), a 1989 film * Taps (film), ''Taps'' (film), a 1981 American drama film * Taps (2006 film), ''Taps'' (2006 film), a short film * Tapped (film), ''Tapp ...
s for
tap water Tap water (also known as faucet water, running water, or municipal water) is supplied through a , a water dispenser valve. Tap water is commonly used for , , , and . Indoor tap water is distributed through "indoor ", which has existed since but ...

tap water
, gas control valves on cookers, small valves fitted to
washing machine A washing machine (laundry machine, clothes washer, or washer) is a home appliance A home appliance, also referred to as a domestic appliance, an electric appliance or a household appliance, is a machine which assists in household A house ...

washing machine
s and
dishwasher A dishwasher is a machine for cleaning dishware and cutlery automatically. Unlike dishwashing, manual dishwashing, which relies largely on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, typically b ...

dishwasher
s, safety devices fitted to
hot water system 300px, A small tank water heater 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 indust ...
s, and
poppet valve A poppet valve (also called mushroom valve) is a valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries A slurry composed of glass beads in sili ...
s in car engines. In nature there are valves, for example one-way valves in
veins Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A b ...

veins
controlling the
blood circulation The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and bloo ...
, and
heart valve A heart valve is a one-way valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valv ...
s controlling the flow of blood in the
chambers of the heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...
and maintaining the correct
pump A pump is a device that moves fluids (liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the ...

pump
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 grasp A grasp is an act of taking, holding or seizing firmly with (or as if with) the hand A hand is a prehensile, multi- fingered appendage located at the end of t ...
,
lever A lever ( or ) is a simple machine A simple machine is a mechanical device that changes the direction or magnitude of a force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge o ...

lever
, pedal or wheel. Valves may also be automatic, driven by changes in
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
,
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
, or flow. These changes may act upon a
diaphragm Diaphragm may refer to: * Diaphragm (anatomy) or thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Diaphragm (optics), a stop in the light path of a lens, having an aperture that regulates the amount of light that pass ...
or a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, Hydraulic cylinder, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder ...

piston
which in turn activates the valve, examples of this type of valve found commonly are
safety valve A safety valve is a valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries A slurry composed of glass beads in silicone oil flowing down an in ...
s fitted to hot water systems or
boiler A boiler is a closed vessel in which fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order ...

boiler
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 machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power to apply ...

actuator
. 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 (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragma ...
per
inch Measuring tape with inches The inch (symbol: in or ″) is a unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television s ...
of the diameter of the valve. Disposable valves may be found in common household items including mini-pump dispensers and
aerosol canAerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. It comprises a can or bottle that contains a payload, and a propellant under pressure. When the container's valve is opened, the payload is forced out of ...
s. A common use of the term ''valve'' refers to the
poppet valves A poppet valve (also called mushroom valve) is a valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries A slurry composed of glass beads in sil ...

poppet valves
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#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is a ...
*
Pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and building ...
*
Manual
Manual
*
Solenoid valve A solenoid valve is an electromechanical In engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and build ...
*
Motor An engine or motor is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people A people is a plurality of person A person ( ...

Motor


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: Biology * Plant stem, the aboveground structures that have vascular tissue and that support leaves and flowers ** Stipe (botany), a stalk that supports some other structure ** Stipe (mycology), the stem supporting the c ...
(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 Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
lic or
plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and "artificial" * Synthetic chemical or s ...

plastic
.
Brass Brass is an alloy An alloy is an admixture of 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 appea ...

Brass
,
bronze Bronze is an alloy An alloy is an admixture of 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 appear ...

bronze
,
gunmetal Gun metal, also known as red brass in the United States, is a type of bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (such as aluminum, manganese, nicke ...
,
cast iron Cast iron is a group 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 colour when fractured: white cast iron has carbide impuritie ...
,
steel Steel is an alloy An alloy is an admixture of 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 appe ...

steel
,
alloy steel Alloy steel is steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, s ...
s and
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
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 Austenitic stainless steel is one of the five classes of stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical el ...
valves are typically used in sulphuric acid plants, whilst
monel Monel is a group of nickel alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a l ...
valves are used in
hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
(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 envi ...
valves are often used in hydrogen applications. Plastic bodies are used for relatively low pressures and temperatures.
PVC Polyvinyl chloride (colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual communication. It is the most common functional style of speech, the idiom normally employed in conversatio ...

PVC
,
PP
PP
,
PVDF Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of 1,1-Difluoroethylene, vinylidene difluoride. PVDF is a specialty plastic used in applications requ ...

PVDF
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 production of goods In economics Economics () is the social science that studies how people interact with value; in particular, the Production (economics), production, distribution (economics), distribution, and Co ...

manufacture
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 valves with cylindrical or conically tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that ...
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 fitting Fitting can refer to: * A dress fitting. ** A fitting model, the model (people), model trying on the clothes. * Any machine component, Pipe (material), piping or Tubing (material), tubing part that can attach or ...
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 binds them together and resists their separation. The use of adhesives offers certain advantag ...
,
cement A cement is a binder (material), binder, a 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 (constru ...
,
flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength Physical strength *Physical strength, as in people or animals *Hysterical strength, extreme strength occurring when people are in life ...

flange
s, or
welding Welding is a process that joins materials, usually s or s, by using high to melt the parts together and allowing them to cool, causing . Welding is distinct from lower temperature metal-joining techniques such as and , which do not the base ...

welding
.


Handle or actuator

A
handle A handle is a part of, or attachment to, an object that allows it to be grasp A grasp is an act of taking, holding or seizing firmly with (or as if with) the hand A hand is a prehensile, multi- fingered appendage located at the end of t ...
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
. An
actuator An actuator is a component of a machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power to apply ...

actuator
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
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, pr ...
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 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 pas ...

butterfly valve
), 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 T ...

hinge
or
trunnion A trunnion (from Old French Old French (, , ; French language, Modern French: ) was the language spoken in Northern France from the 8th century to the 14th century. Rather than a unified Dialect#Dialect or language, language, Old French was re ...
(as in a
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
). 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
Ball valve
s use spherical rotors with a cylindrical hole drilled as a fluid passage.
Plug valve Plug valves are valves with cylindrical or conically tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that ...
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
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 Old French (, , ; French language, Modern French: ) was the language spoken in Northern France from the 8th century to the 14th century. Rather than a unified Dialect#Dialect or language, language, Old French was re ...
, 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
leak A leak is a way (usually an opening) for fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase (matter), phase of matter and i ...
age. *Soft seats are fitted to the valve body and made of softer materials such as
PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer A fluoropolymer is a fluorocarbon Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine B: isoflurane Isoflurane, sold under the brand name Foran ...

PTFE
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, or macromolecules, composed of many Repeat unit, re ...
such as NBR,
EPDM EPDM rubber (ethylene propylene diene monomer rubber) is a type of synthetic rubber A synthetic rubber is any artificial elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is ...

EPDM
, or
FKM FKM is a family of fluorocarbon Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine B: isoflurane Isoflurane, sold under the brand name Forane among others, is a general anesthetic. It can be used to start ...

FKM
depending on the maximum
operating temperature An operating temperature is the allowable temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of ...
. 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 Bonnet may refer to: Headgear *Bonnet (headgear), a variety of headgear with the absence of a brim *Blue bonnet (hat), Blue bonnet, a distinctive woollen cap worn by men in Scotland from the 15th-18th centuries *Feather bonnet, worn by Scottish ...
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 (physics), 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 acce ...

force
, a rotational
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study. The concept originated with the studies ...

torque
, 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
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
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 Some seals and gaskets A gasket is a mechanical seal 236px, Compression seal example A mechanical seal is a device that helps join systems or mechanisms together by preventing leakage (e.g. in a pumping system), containing pressure Pres ...

Gaskets
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 a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
,
titanium Titanium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

titanium
,
Stellite Stellite is a range of cobalt-chromium alloys designed for wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion In earth science, erosion is the action of ...
, Hastelloy,
brass Brass is an alloy An alloy is an admixture of 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 appea ...

brass
, or
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
. They can also be made of different types of plastic, such as ABS,
PVC Polyvinyl chloride (colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual communication. It is the most common functional style of speech, the idiom normally employed in conversatio ...

PVC
,
PP
PP
or
PVDF Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of 1,1-Difluoroethylene, vinylidene difluoride. PVDF is a specialty plastic used in applications requ ...

PVDF
.


Spring

Many valves have a
spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a heli ...
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, pr ...
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 A tension coil spring A coil spring is a mechanical device which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed in ...
s are normally used. Typical spring materials include zinc plated steel,
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
, 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 envi ...
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
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. A needle valve is a type of valve with a small port and a threaded, needle-shaped plunger. It allows precise regulation of Fluid dynamics, flow, although it is generally only capable of relatively low flow rates. Construction ...

needle valve
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 A leak is a way (usually an opening) for fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase (matter), phase of matter and i ...
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 and MAPP gas cylinders with two-stage pressure regulators File:Pressure regulators symbols.png, Diagram symbols for pressure reduction and back pressure regulators. The conceptual difference is mainly in which side the feedback is taken from. A pr ...

Pressure regulator
s are variations of valves in which flow is controlled to produce a certain downstream
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
, 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 ...

gas cylinder
. 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. ''Tap (valve)#immutable link from Valve, 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 valves'' 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 (material), sample without affecting the pressure of a hydraulic system and to avoid degasification, degassing (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 grasp A grasp is an act of taking, holding or seizing firmly with (or as if with) the hand A hand is a prehensile, multi- fingered appendage located at the end of t ...
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 machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power to apply ...

actuator
s attached to the stem. They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
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, 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 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 hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
and
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
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 diagrams. In such diagrams, different types of valves are represented by certain symbols. Valves in good condition should be leak-free. However, valves may eventually wear out from use and develop a
leak A leak is a way (usually an opening) for fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase (matter), phase of matter and i ...
, 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 (on vertical line) Image:Nasa-space-18408-l.jpg, Large
butterfly valve A butterfly 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 solids, or slurries) by opening, closing, or partially obstructing various pas ...

butterfly valve
Image:Butterfly-valve--The-Alloy-Valve-Stockist.JPG, Cast iron butterfly valve Image:Bidirectional tight butterfly valve-The-Alloy-Valve-Stockist.jpg, Cast iron
butterfly valve A butterfly 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 solids, or slurries) by opening, closing, or partially obstructing various pas ...

butterfly valve
Image:Hastelloy Ball valve.jpg, Hastelloy ball valve Image:Valve.jpg, Stainless steel gate valve Image:Gate valve.JPG, Stainless steel gate valve Image:Swing Check valves.JPG, Hastelloy
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
s Image:Duplex-valve-A182-F51.JPG, Duplex ball valve 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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
Image:Inconel-Tilting disc check valve--The-Alloy-Valve-Stockist.JPG, Inconel
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
Image:Ball valve--The-Alloy-Valve-Stockist.JPG, Stainless steel ball valve 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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
Image:Duplex-ball-valves-The-Alloy-Valve-Stockist.JPG, Duplex ball valves 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 valves Image:Flanged-Nozzle-check-valve-The-Alloy-Valve-Stockist.JPG, Flanged nozzle inconel
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
or axial check valve Image:Inside-wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Inside hastelloy
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
, wafer configuration Image:Large-swing-check-valve-The-Alloy-Valve-Stockist.jpg, Large carbon steel swing
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
Image:Nozzle-check-valve-disc-The-Alloy-Valve-Stockist.jpg, Disc for an alloy
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
also known as axial check valve Image:Valve-balls-The-Alloy-Valve-Stockist.jpg, Balls for alloy ball valves Image:Wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Wafer
check valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
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 check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
springs Image:Ball-valve-ball-The-Alloy-Valve-Stockist.jpg, Ball for a titanium ball valve


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 Valves, * Plumbing Water industry