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Information about Valve

For other uses, see Valve (disambiguation). For the electronic component, see Thermionic valve.


Enlarge picture
These water valves are operated by handles.
A valve is a device that regulates the flow of substances (either gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately.

Valves are used in a variety of applications including industrial, military, commercial, residential, transportation. Plumbing valves are the most obvious in everyday life, but many more are used.

Some valves are driven by pressure only, they are mainly used for safety purposes in steam engines and domestic heating or cooking appliances. Others are used in a controlled way, like in Otto cycle engines driven by a camshaft, where they play a major role in engine cycle control.

Application

A large variety of valves are available and have many applications with sizes ranging from small to large. The cost of valves ranges from very cheap simple disposable valves, in some items to very expensive valves for specialized applications. Often not realized by some, small valves are even inside some common household items including liquid or gel mini-pump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and laundry washers. Valves are almost as ubiquitous as electrical switches. Often a valve is part of some object, the valve body and the object made in one piece; for example, a separatory funnel. Faucets, taps, and spigots are all variations of valves. Many fluid systems such as water and natural gas lines in houses and other buildings have valves. Fluid systems in chemical and power plants and other facilities have numerous valves to control fluid flow.

Valve parts

Body

The majority of the valve consists of the valve body, including most of the exterior. The valve body is the vessel or casing that holds the fluid going through inside the valve. Valve bodies are most commonly made of various metals or plastics, although valve bodies fused with glass laboratory items in one piece are also made of glass.

Ports

The body consists of two or more openings, called ports from which movement occurs from one opening to the next. These ports are controlled by a valve. Valves with two or three ports are the most common, while valves consisting of four or more ports are not as frequently used. Extra ports that are not needed can be closed off by the valve. Manufacturing of valves often occurs with the intent that they will be connected with another specific object. These objects can vary, but generally these include some type of piping, tubing, or pump head. In some cases, a valve port is immediately connected to a spray nozzle or container. To make a connection, valves are commonly measured by the outer diameter the ports they connect to. For example, a 1-inch valve is sized to connect to 1-inch outer diameter tubing.

Combined with a valve, ports have the ability to act as faucets, taps, or spigots, all while one or more of its remaining ports are left unconnected. Most valves are built with some means of connection at the ports. This includes threads, compression fittings, glue or cement application (especially for plastic), flanges, or welding (for metals).

Discs and rotors

Inside the valve body, flow through the valve may be partly or fully blocked by an object called a disc. Although valve discs of some kinds of valves are traditionally disc-shaped, discs can come in various shapes. Although the valve body remains stationary within the fluid system, the disc in the valve is movable so it can control flow. A round type of disc with fluid pathway(s) inside which can be rotated to direct flow between certain ports can be called a rotor. Ball valves are valves which use spherical rotors, except for the interior fluid passageways. Plug valves use cylindrically-shaped or conically-tapered rotors called plugs. Other round shapes for rotors are possible too 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 valve seat is the interior surface in the body which contacts or could contact the disc to form a seal which should be leak-tight, particularly when the valve is shut (closed). If the disc moves linearly as the valve is controlled, the disc comes into contact with the seat when the valve is shut. When the valve has a rotor, the seat is always in contact with the rotor, but the surface area of contact on the rotor changes as the rotor is turned. If the disc swings on a hinge, as in a swing check valve, it contacts the seat to shut the valve and stop flow. In all the above cases, the seat remains stationary while the disc or rotor moves. The body and the seat could both come in one piece of solid material, or the seat could be a separate piece attached or fixed to the inside of the valve body, depending on the valve design.

Stem

The stem is a rod or similar piece spanning the inside and the outside of the valve, transmitting motion to control the internal disc or rotor from outside the valve. Inside the valve, the rod is joined to or contacts the disc/rotor. Outside the valve the stem is attached to a handle or another controlling device. Between inside and outside, the stem typically goes through a valve bonnet if there is one. 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 can be a linear push or pull motion, a rotating motion, or some combination of these. A valve with a rotor would be controlled by turning the stem. 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 seal fluid inside the valve in spite of turning of the stem. Some valves have no external control and do not need a stem; for example, most check valves. Check valves are valves which allow flow in one direction, but block flow in the opposite direction. Some refer to them as one-way valves.

Valves in which the 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 (also called 'front seated'). Valves in which the 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 (also called 'back seated'). These terms do not apply to valves with no stem nor to valves using rotors.

Bonnet

A bonnet basically acts as a cover on the valve body. It is commonly semi-permanently screwed into the valve body. During manufacture of the valve, the internal parts were put into the body and then the bonnet was 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.

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,

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, and nickel. They can also be made of different types of plastic, such as ABS, PVC, PP or PVDF.

Valve operating positions

Valve positions are operating conditions determined by the position the disc or rotor in the valve. Some valves are made to be operated in a gradual change between two or more positions.

2-way valves

2-port valves are commonly called 2-way valves. Operating positions for such 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, with maybe qualitative descriptions in between. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names like 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 how much the valve is open, but in many cases other indications of flow rate are used, such as separate flow meters.

In some plants with fluid systems, some 2-way valves can be designated as normally shut or normally open during regular operation. Examples of normally shut valves are sampling valves, which are only opened while a sample is taken. Examples of normally open valves are isolation valves, which are usually only shut when there is a problem with a unit or a section of a fluid system such as a leak. Then, isolation valve(s) are shut in order to isolate the problem from the rest of the system.

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 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.

3-way valves

3-way valves have three ports. 3-way valves are commonly made such that flow coming in at one port can be directed to either the second port in one position or the third port in another position or in an intermediate position so all flow is stopped. Often such 3-way valves are ball or rotor valves. Many faucets are made so that incoming cold and hot water can be regulated in varying degrees to give outcoming water at a desired temperature. Other kinds of 3-port valves can be designed for other possible flow-directing schemes and positions; for example, see Ball valve.

The "motor valve" on a domestic heating system is an example of a 3-way valve. Depending on demand the motor head rotates the spindle to control the proportion of the flow that goes to the two outlet pipes: One to radiators, one to hot water system. In a conventional system the valve usually sits just after the pump and by the cylinder ("hot tank").

In valves having more than 3 ports, even more flow-directing schemes are possible. For examples, see this external site. Such valves are often rotor valves or ball valves. Slider valves have been used also.

Control

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A valve controlled by a wheel (left).
Many valves are controlled manually with a handle attached to the valve stem. If the handle is turned a quarter of a full turn (90°) between operating positions, the valve is called a quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn valves. Valves can also be controlled by devices called 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 centralized control room, or because manual control is too difficult; for example, the valve is huge. Pneumatic actuators and hydraulic actuators need pressurized 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 commode 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. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

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.

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.

Types of valves

Images


Ball valve

Globe valve


See also

External links

A valve is a device that regulates the flow of fluids.

Valve may also refer to:
  • Valve Corporation, a computer software/games company responsible for the best-selling Half-Life games

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vacuum tube, electron tube (inside North America), thermionic valve, or just valve (elsewhere); is a device used to amplify, switch, otherwise modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space, often not
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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A solid object is in the states of matter characterized by resistance to deformation and changes of volume. At the microscopic scale, a solid has these properties :
  • The atoms or molecules that comprise the solid are packed closely together.

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Liquid is one of the four principal states of matter. A liquid is a fluid that can freely form a distinct surface at the boundaries of its bulk material.

Characteristics

A liquid's shape is determined by, not confined to, the container it fills.
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reducer, or an adapter. The term 'expander' is not used for a coupler that increases pipe size; instead 'reducer' is used. There are also fittings with stop and with out but according to this site there is no information about this.
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Industry (from Latin industrius, "diligent, industrious"), is the segment of economy concerned with production of goods. Industry began in its present form during the 1800s, aided by technological advances, and it has continued to develop to this day.
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Military has two broad meanings. In its first sense, it refers to soldiers and soldiering. In its second sense, it refers to armed forces as a whole. Over the years, military units have come in all shapes and sizes.
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Transport or transportation is the movement of people and goods from one place to another. The term is derived from the Latin trans ("across") and portare ("to carry").
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piping system in a building with intumescent firestop being installed by an insulator, Vancouver, British Columbia, Canada.]] Plumbing, from the Latin for lead, is the skilled trade of working with pipes, tubing and plumbing fixtures for potable water systems and the
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steam engine is an external combustion heat engine that makes use of the heat energy that exists in steam, converting it to mechanical work.

Steam engines were used as the prime mover in pumping stations, locomotives, steam ships, traction engines, steam lorries and other
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Appliance may refer to a device with a narrow function:
  • Home appliance, routine household tasks, using electricity or some other energy input.
  • Small appliances
  • Major appliances

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An engine is something that produces an output effect from a given input. The origin of engineering however, came from the design, building and working of (military "engines") because before such devices came to be employed in battles there were very few mechanical devices used.
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camshaft is an apparatus often used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve.
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separating funnel, also known as separation funnel, separatory funnel, or colloquially sep funnel, is a laboratory glassware used in liquid-liquid extractions to separate (partition
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tap is a valve for controlling the release of a liquid or gas. In the British Isles and normally in the Commonwealth the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S.
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tap is a valve for controlling the release of a liquid or gas. In the British Isles and normally in the Commonwealth the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S.
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gas, especially when compared to other energy sources such as electricity. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane.
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chemical plant is an industrial process plant that manufactures (or otherwise processes) chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials.
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A power station (also referred to as generating station or power plant) is an industrial facility for the generation of electric power.[1][2][3]

Power plant
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Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories.
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For structural pipe, see hollow structural section.
Pipe is a tube or hollow cylinder for the conveyance of fluid. The terms 'pipe' and 'tubing' are almost interchangeable.
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Tubing is a pipe or hollow cylinder for the conveyance of fluids (liquids or gases). The terms 'pipe' and 'tubing' are almost interchangeable, although minor distinctions exist (generally, "tubing" implies tighter engineering requirements than "pipe").
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pump is a device used to move liquids or slurries. A pump moves liquids from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system (such as a water system).
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Description

Compression fittings are used in plumbing 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), the fittings will also be made of one or more compatible materials
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Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld puddle
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A ball valve (like the butterfly valve, one of a family of valves called quarter turn valves) is a valve that opens by turning a handle attached to a ball inside the valve.
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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 fluid can flow through the plug
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A check valve is a mechanical device, 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 two openings in the body, one for fluid to enter and the other for fluid to leave.
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A check valve is a mechanical device, 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 two openings in the body, one for fluid to enter and the other for fluid to leave.
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