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Contents
1 Valves everywhere 2 Variation 3 Types 4 Components
4.1 Body
4.2 Bonnet
4.3 Ports
4.4 Handle or actuator
4.5 Disc
4.6 Seat
4.7 Stem
4.8 Gaskets
4.9
Valve
Valve balls
4.10 Spring
4.11 Trim
5
Valve
Valve operating positions
5.1 Two-port valves 5.2 Three-port valves 5.3 Four-port valves
6 Control 7 Other considerations 8 Images 9 See also 10 References 11 External links
Valves everywhere
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 taps for tap water, gas control valves on
cookers, small valves fitted to washing machines 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
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, pedal or
wheel. Valves may also be automatic, driven by changes in pressure,
temperature, or flow. These changes may act upon a diaphragm 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
boilers.
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] typically
range from 0.1 mm to 60 cm.
Special
Special valves can have a
diameter exceeding 5 meters.[which?]
Valve
Valve costs range from simple inexpensive disposable valves to
specialized valves which cost thousands of
US dollars
US dollars per inch of the
diameter of the valve.
Disposable
Disposable valves may be found in common household items including
mini-pump dispensers and aerosol cans.
A common use of the term valve refers to the poppet valves 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 article: 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:
Hydraulic
Pneumatic
Manual
Solenoid
Solenoid valve
Motor
Components
Cross-sectional diagram of an open globe valve. 1. body 2. ports 3. seat 4. stem 5. disc when valve is open 6. handle or handwheel when valve is open 7. bonnet 8. packing 9. gland nut 10. fluid flow when valve is open 11. position of disc if valve were shut 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
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
Valve bodies are usually metallic or plastic. Brass, bronze, gunmetal,
cast iron, steel, alloy steels and stainless steels are very
common.[citation needed]
Seawater
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
Hastelloy valves are often used in high temperature applications, such
as nuclear plants, whilst inconel valves are often used in hydrogen
applications.
Plastic
Plastic bodies are used for relatively low pressures and
temperatures. PVC, PP,
PVDF
PVDF and glass-reinforced nylon are common
plastics used for valve bodies.[citation needed]
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 fittings, glue,
cement, flanges, or welding.
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 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 valves and relief valves may have neither.
Disc
Valve
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 valves use spherical rotors with a cylindrical hole drilled as a fluid passage. Plug valves use cylindrical or conically tapered rotors called plugs.[ambiguous] 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 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
PTFE or various elastomers such as NBR, EPDM, or
FKM depending
on the maximum operating temperature.
The shut off butterfly valve for a
Francis turbine
Francis turbine at Gordon Power
Station, Tasmania
Ball valve
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, 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] 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 valves. 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.
Inconel
Inconel X750 spring
Gaskets
Gaskets
Gaskets are the mechanical seals, or packings, used to prevent the
leakage of a gas or fluids from valves.
Valve
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 ABS, PVC, PP or PVDF.
Spring
Many valves have a spring for spring-loading, to normally shift the
disc into some position by default but allow control to reposition the
disc. Relief 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, and for high
temperature applications
Inconel
Inconel X750.
Trim
The internal elements of a valve are collectively referred to as a
valve's trim. According to API Standards 600, "
Steel
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
Valve operating positions
A seacock for cooling seawater, on a marine diesel engine.
Valve
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 meters.
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
Pressure regulators 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
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. 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 Main article: 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 without affecting the pressure of a hydraulic system and to avoid degassing (no leak, no gas loss or air entry, no external contamination).... Control
A sailor aboard a ship operates the wheel controlling a fuel valve.
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 actuators 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 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 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
Pressure Equipment Directive 97/23/EC (PED).[1]
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, 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
Globe valve
A valve controlled by a wheel
Large butterfly valve
Cast iron
Cast iron butterfly valve
Cast iron
Cast iron butterfly valve
Hastelloy
Hastelloy ball valve
Stainless steel
Stainless steel gate valve
Stainless steel
Stainless steel gate valve
Hastelloy
Hastelloy check valves
Duplex ball valve
Inconel
Inconel gate valve
Stainless steel
Stainless steel wafer check valve
Inconel
Inconel check valve
Stainless steel
Stainless steel ball valve
Cryogenic 254 SMO gate valve
Inside view of a tilting disc inconel check valve
Duplex ball valves
Cryogenic super duplex gate valve frozen up during operation
Super duplex ball valves
Flanged nozzle inconel check valve or axial check valve
Inside hastelloy check valve, wafer configuration
Large carbon steel swing check valve
Disc for an alloy check valve also known as axial check valve
Balls for alloy ball valves
Wafer check valve
Nuts and bolts for incoloy valves
Inconel
Inconel check valve springs
Ball for a titanium ball valve
See also
Hydrotest
Ball valve
Control valves
Directional control valve
Endobronchial valve, medical
Four-way valve
Piping
Plastic
Plastic
Pressure
Pressure Pipe Systems
Tap (valve)
Tubing
Valve
Valve stem
Variable
Valve
Valve Timing
Zone valve
References
^ "European Commission
Pressure
Pressure Equipment Directive (PED)".
External links
Wikimedia Commons has media related to Valves.
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
Flow in known Design Types of Shut-off Valves, home.arcor.de
Valves:
Piping
Piping and Instrumentation Diagram Standard Notation,
controls.engin.umich.edu
Department of Energy Fundamentals Handbook, Mechanical Science, Module
4 Valves
v t e
Reciprocating engines and configurations
Type
Bourke Orbital (Sarich) Piston Pistonless (Wankel) Radial Axial Rotary Split cycle Stelzer Tschudi
Stroke cycles
Two-stroke Four-stroke Five-stroke Six-stroke Two-and four-stroke
Configurations & number of cylinders
Single cylinder
Single
Two cylinders
Split-single I2 V2 F2
Inline / straight
I2 I3 I4 I5 I6 I7 I8 I9 I10 I12 I14
Flat
F2 F4 F6 F8 F10 F12 F16
V / Vee
V2 V3 V4 V5 V6 V8 V10 V12 V14 V16 V18 V20 V24
W
W8 W12 W16 W18
Other inline
H U Square four VR Opposed X X24 Junkers Jumo 222
Components
Valves
Cylinder head porting
Corliss
Intake
Exhaust
Multi
Overhead
Piston
Poppet
Side
Sleeve
Slide
Rotary valve
Variable valve timing
Camless
Desmodromic
Hydraulic
Hydraulic tappet
Fuel supplies
Carburetor Gasoline direct injection Common rail
Mechanisms
Cam Camshaft Overhead camshaft Connecting rod Crank Crankshaft Scotch yoke Swashplate Rhombic drive
Linkages
PeaucellierāLipkin Watt's (parallel)
Other
Hemi Recuperator Turbo