View source for Valve

{{About|the flow control device|the electronic component |Vacuum tube|other uses|Valve (disambiguation)}}
{{pp-semi-indef}}
{{Multiple issues|
{{refimprove|date=December 2011}}
{{one source|date=December 2011}}
}}

[[File:Water valves with spigots.jpg|thumb|300px|These water valves are operated by [[handle (grip)|rotary handle]]s.]]
A '''valve''' is a device 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 [[Piping and plumbing fittings|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 drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a [[check valve]], as it prevents or "checks" the flow in one direction.  Modern [[control valves]] may regulate [[pressure]] or [[Fluid dynamics|flow]] downstream and operate on sophisticated [[Industrial automation|automation]] systems.

Valves have many uses, including controlling water for [[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 aerosols have a tiny valve built in.  Valves are also used in the military and transport sectors.  In [[Heating, ventilation, and air conditioning|HVAC]] [[Duct (flow)|ductwork]] and other near-atmospheric air flows, valves are instead called [[Damper_(flow)|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]] valves, such as [[tap (valve)|tap]]s for [[tap water]], gas control valves on cookers, small valves fitted to [[washing machine]]s and [[dishwasher]]s, safety devices fitted to [[hot water system]]s, and [[poppet valve]]s in car engines.

In nature there are valves, for example one-way valves in [[veins]] controlling the [[blood circulation]], and [[heart valve]]s controlling the flow of blood in the [[chambers of the heart]] and maintaining the correct [[pump]]ing action.

Valves may be operated manually, either by a [[handle (grip)|handle]], [[lever]], pedal or wheel. Valves may also be automatic, driven by changes in [[pressure]], [[temperature]], or flow. These changes may act upon a [[Diaphragm (mechanical device)|diaphragm]] or a [[piston]] which in turn activates the valve, examples of this type of valve found commonly are [[safety valve]]s fitted to hot water systems or [[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 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{{Ambiguous|date=July 2011}} typically range from 0.1&nbsp;mm to 60&nbsp;cm. Special valves can have a diameter exceeding 5 meters.{{Which|date=November 2009}}

Valve costs range from simple inexpensive [[disposable]] valves to specialized valves which cost thousands of [[US dollars]] per [[inch]] of the diameter of the valve.

Disposable valves may be found in common household items including [[mini-pump dispenser]]s and [[aerosol can]]s.

A common use of the term ''valve'' refers to the [[Poppet valve#Internal combustion engine|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==
{{main|List of valves}}
Valves are quite diverse and may be classified into a number of basic types. Valves may also be classified by how they are actuated:
*[[Hydraulics|Hydraulic]]
*[[Pneumatics|Pneumatic]]
*[[Hand|Manual]]
*[[Solenoid valve]]
*[[Electric motor|Motor]]

==Components==
[[File:Valve cross-section.PNG|frame|right|Cross-sectional diagram of an open '''[[globe valve]]'''.<br>
1. '''body''' <br>
2. '''ports''' <br>
3. '''seat''' <br>
4. '''stem''' <br>
5. '''disc''' when valve is open <br>
6. '''handle''' or '''handwheel''' when valve is open <br>
7. '''bonnet''' <br>
8. '''packing''' <br>
9. '''gland nut''' <br>
10. '''fluid flow''' when valve is open <br>
11. position of disc if valve were shut <br>
12. position of handle or handwheel if valve were shut ]]

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 [[casing (borehole)|encasing]] through which the [[stem (bicycle part)|stem]] (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]]lic or [[plastic]]. [[Brass]], [[bronze]], [[gunmetal]], [[cast iron]], [[steel]], [[alloy steel]]s and [[stainless steel]]s are very common.<ref>{{cite web|url=https://www.actuation.co.uk/valve-body-types|title=Types of valve bodies and their specifications - Actuation Valves|website=www.actuation.co.uk}}</ref> 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]] valves are typically used in sulphuric acid plants, whilst [[monel]] valves are used in [[hydrofluoric acid]] (HF Acid) plants.  [[Hastelloy]] valves are often used in high temperature applications, such as nuclear plants, whilst [[Hydrogen valve|inconel]] valves are often used in hydrogen applications.  Plastic bodies are used for relatively low pressures and temperatures. [[PVC]], [[Polypropylene|PP]], [[PVDF]] and [[Fiberglass|glass-reinforced nylon]] are common plastics used for valve bodies.{{Citation needed|date=November 2009}}

===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]] 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]]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 [[Screw thread|threading]]s, [[compression fitting]]s, [[glue]], [[cement]], [[flange]]s, or  [[welding]].

===Handle or actuator===
A '''[[handle (grip)|handle]]''' 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]]''' 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]]s and [[relief valve]]s may have neither.

===Disc===
[[File:Nozzle check valve disc-The-Alloy-Valve-Stockist.JPG|150px|right|thumb|Valve 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]]), or rotate on a [[hinge]] or [[trunnion]] (as in a [[check 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]]s use spherical rotors with a cylindrical hole drilled as a fluid passage. [[Plug valve]]s use cylindrical or conically tapered rotors called '''plugs'''.{{Ambiguous|date=July 2011}}  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]] uses the ball to block reverse flow, but is not a rotor because operating the valve does not involve rotation of the ball.

===Seat===
[[File:Gordon Power Station Control Valve.jpg|150px|thumb|right|The shut off butterfly valve for a [[Francis turbine]] at [[Gordon Power Station, Tasmania]]]]
[[File:Valve-balls-The-Alloy-Valve-Stockist.jpg|150px|left|thumb|[[Ball valve]]]]

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]], 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]]age.
*'''Soft seats''' are fitted to the valve body and made of softer materials such as [[PTFE]] or various [[elastomers]] such as [[Nitrile rubber|NBR]], [[EPDM]], or [[FKM]] depending on the maximum [[operating temperature]].

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===
[[File:Check-valve-springs-in-inconel-The-Alloy-Valve-Stockist.JPG|150px|thumb|left|[[Inconel]] X750 [[Spring (device)|spring]]]]

The '''stem''' transmits motion from the handle or controlling device to the disc. The stem typically passes through the [[Hood (vehicle)|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]], a rotational [[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.{{Ambiguous|date=July 2011}} [[O-ring|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]]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]] 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]], [[titanium]], [[Stellite]], [[Hastelloy]], [[brass]], or [[nickel]]. They can also be made of different types of plastic, such as [[Acrylonitrile butadiene styrene|ABS]], [[PVC]], [[Polypropylene|PP]] or [[PVDF]].

===Spring===
Many valves have a [[Spring (device)|spring]] for spring-loading, to normally shift the disc into some position by default but allow control to reposition the disc.  [[Relief valve]]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]]s are normally used. Typical spring materials include [[Galvanization|zinc plated steel]], [[stainless steel]], and for high temperature applications [[Inconel]] 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==
[[File:Sea water cock.JPG|thumb|A [[seacock]] for cooling [[seawater]], on a marine [[diesel engine]]. Seacocks are usually ball valves, but may be other types as well.]]
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 valve]]s and [[non-return 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]]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]]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 valve]]s'', which are only opened while a sample is taken. Other examples of normally-closed valves are [[Shut down valve|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]]s are variations of valves in which flow is controlled to produce a certain downstream [[pressure]], if possible.  They are often used to control flow of gas from a [[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===
[[File:3-way.svg|120px|thumb|right|Schematic 3 way ball valve: L-shaped ball right, T-shaped left]]
Valves with three ports serve many different functions.  A few of the possibilities are listed here.

''[[Ball valve#immutable link 3-way from Valve|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 valve]]s'' 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 valve]]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===
{{Main|four-way valve}}
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==
[[File:USN sailor operates fuel valve · 070115-N-9479M-004.JPEG|thumb|300px|A sailor aboard a ship operates the wheel controlling a [[fuel valve]].]]

Many valves are controlled manually with a [[handle (grip)|handle]] 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]]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]] 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 valve]]s 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]] and [[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).<ref>{{cite web |url=http://ec.europa.eu/enterprise/sectors/pressure-and-gas/documents/ped/ |title=European Commission Pressure Equipment Directive (PED) |access-date=2010-09-13 |archive-url=https://web.archive.org/web/20100815081132/http://ec.europa.eu/enterprise/sectors/pressure-and-gas/documents/ped/ |archive-date=2010-08-15 |dead-url=yes |df= }}</ref>

Some fluid system designs, especially in chemical or power plants, are schematically represented in [[piping and instrumentation diagram]]s.  In such diagrams, different types of valves are represented by certain [[symbol]]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==
<gallery class=center>
Image:Globe valve (rendered).jpg|[[Globe valve]]
Image:Green tubes and valves.jpg|A valve controlled by a [[wheel]]
Image:Nasa-space-18408-l.jpg|Large [[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]]
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]]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]]
Image:Inconel-Tilting disc check valve--The-Alloy-Valve-Stockist.JPG|Inconel [[check 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]]
Image:Duplex-ball-valves-The-Alloy-Valve-Stockist.JPG|Duplex [[ball valve]]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]]s
Image:Flanged-Nozzle-check-valve-The-Alloy-Valve-Stockist.JPG|Flanged nozzle inconel [[check valve]] or axial check valve
Image:Inside-wafer-check-valve-The-Alloy-Valve-Stockist.JPG|Inside hastelloy [[check valve]], wafer configuration
Image:Large-swing-check-valve-The-Alloy-Valve-Stockist.jpg|Large carbon steel swing [[check valve]]
Image:Nozzle-check-valve-disc-The-Alloy-Valve-Stockist.jpg|Disc for an alloy [[check valve]] also known as axial check valve
Image:Valve-balls-The-Alloy-Valve-Stockist.jpg|Balls for alloy [[ball valve]]s
Image:Wafer-check-valve-The-Alloy-Valve-Stockist.JPG|Wafer [[check 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]] springs
Image:Ball-valve-ball-The-Alloy-Valve-Stockist.jpg|Ball for a titanium [[ball valve]]

</gallery>

==See also==
{{div col|colwidth=22em}}
*[[Ball valve]]
*[[Control valves]]
*[[Directional control valve]]
*[[Endobronchial valve]], medical
*[[Four-way valve]]
*[[Hydrotest]]
* [[Pipe (fluid conveyance)|Pipe]]
*[[Piping]]
*[[Plastic Pressure Pipe Systems]]
* [[Tap (valve)]]
* [[Tube (fluid conveyance)|Tubing]]
*[[Valve stem]]
*[[Variable Valve Timing]]
*[[Zone valve]]
{{div col end}}

==References==
{{reflist}}

==External links==
{{Commons category|Valves}}
*[http://rds.posccaesar.org/2008/05/XML/ISO-15926-4_2007/ ISO-15926-4] - Nearly 500 valve base classifications and definitions from the [[ISO 15926]] standard.
*[http://www.tlv.com/global/TI/steam-theory/types-of-valves.html Animations showing Internal Function of Various Types of Valve], tlv.com
*[http://home.arcor.de/drklaus.bauerfeind/valves/eAbsperrventil.html Flow in known Design Types of Shut-off Valves], home.arcor.de
*[https://web.archive.org/web/20120329115838/https://controls.engin.umich.edu/wiki/index.php/PIDStandardNotation#Valve_Symbols Valves: Piping and Instrumentation Diagram Standard Notation], controls.engin.umich.edu
* [http://www.constructionknowledge.net/public_domain_documents/Div_15_Mechanical/HVAC/Valves_DOE_Fundamentals.pdf Department of Energy Fundamentals Handbook, Mechanical Science, Module 4 Valves]

{{Piston engine configurations}}

[[Category:Piping]]
[[Category:Valves|*]]
[[Category:Plumbing]]
[[Category:Water industry]]