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 ...
, as it prevents or "checks" the flow in one direction. Modern
control valves 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 a ...
or
flow
Flow may refer to:
Science and technology
* Fluid flow, 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 a set
* Flow (psyc ...
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 crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
, 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 ductwork
Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, ''supply air'', ''return air'', and ''exhaust air''. Ducts commonly also deliver '' ...
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 ...
valves, such as
taps for
tap water, 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 ...
s and
dishwashers, safety devices fitted to
hot water systems, and
poppet valves 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 and umbilical veins, both of which carry oxygenated ...
controlling the
blood circulation, and
heart valves controlling the flow of blood in the
chambers of the heart and maintaining the correct
pumping action.
Valves may be operated manually, either by a
handle,
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...
, 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 a ...
,
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
, or flow. These changes may act upon a
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
or a
piston which in turn activates the valve, examples of this type of valve found commonly are
safety valves fitted to hot water systems or
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central ...
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 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 control signal) a ...
. 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 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 dispensers and
aerosol can
Aerosol 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 ...
s.
A common use of the term ''valve'' refers to the
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
*
Pneumatic
*
Manual
Manual may refer to:
Instructions
* User guide
* Owner's manual
An owner's manual (also called an instruction manual or a user guide) is an instructional book or booklet that is supplied with almost all technologically advanced consumer ...
*
Solenoid valve
*
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 (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 or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
.
Brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...
,
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 suc ...
,
gunmetal,
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 impuri ...
,
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
,
alloy steels 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 r ...
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, petrochemical, power generation, and plastics industries. ...
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
inconel 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 fluoropolymer produced by the polymerization of vinylidene difluoride.
PVDF is a specialty plastic used in applications requiring the highest pu ...
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 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 valves 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 used in plumbing and electrical conduit systems to join two tubes or thin-walled pipes together. In instances where two pipes made of dissimilar materials are to be joined (most commonly PVC and copper), t ...
s,
glue,
cement
A cement is a binder, a chemical substance used for construction that 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 (aggregate) together. Cement mixe ...
,
flange
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
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 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 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 control signal) a ...
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 ...
s and
relief valves 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), 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 (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 ...
). 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 valves use spherical rotors with a cylindrical hole drilled as a fluid passage.
Plug valves 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 ...
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, 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 PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chem ...
or various
elastomers such as
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
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 object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...
, 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 th ...
, 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 ...
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
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 r ...
,
titanium
Titanium is a chemical element with the 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, resistant to corrosion i ...
,
Stellite,
Hastelloy,
brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...
, or
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
. 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 fluoropolymer produced by the polymerization of vinylidene difluoride.
PVDF is a specialty plastic used in applications requiring the highest pu ...
.
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 h ...
for spring-loading, to normally shift the disc into some position by default but allow control to reposition the disc.
Relief valves commonly use a spring to keep the valve shut, but allow excessive pressure to force the valve open against the spring-loading.
Coil springs 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 r ...
, 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
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 valves 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 valves''. 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 a ...
, 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, vap ...
. 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 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
Sample or samples may refer to:
Base meaning
* Sample (statistics), a subset of a population – complete data set
* Sample (signal), a digital discrete sample of a continuous analog signal
* Sample (material), a specimen or small quantity of ...
without affecting the pressure of a hydraulic system and to avoid
degassing (no leak, no gas loss or air entry, no external contamination)....
Control
Many valves are controlled manually with a
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
An actuator is a component of a 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 control signal) a ...
s attached to the stem. They can be electromechanical actuators such as an
electric motor
An electric motor is an 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 wire winding to generate f ...
or
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
, 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 (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars ...
, or
hydraulic 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 a ...
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 quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
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 a ...
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
The Pressure Equipment Directive (PED) 2014/68/EU (formerly 97/23/EC) of the EU sets out the standards for the design and fabrication of pressure equipment ("pressure equipment" means steam boilers, pressure vessels, piping, safety valves a ...
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
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 conc ...
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 (on vertical line)
Image:Nasa-space-18408-l.jpg, Large butterfly valve
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 impuri ...
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
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 ...
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
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 ...
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 ...
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
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 ...
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
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 ...
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 ...
, 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 ...
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 ...
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
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 ...
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 ...
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
*
Plumbing
Water industry