What is valve? | Applications/ Types/ Variation/ Component

Valve

A valve is a device or natural object that controls, directs, or controls the flow of liquids (gases, liquids, liquefied solids, or slurries) that open, close, or partially obstructing various pathways. Valve is technically fittings but is usually discussed as separate categories. In an open valve, the fluid flows in one direction from the higher pressure to the lower pressure. The word is derived from the Latin vulva, in the moving part of a door, which turns from a revolver, revolves.

The simplest and very ancient, the valve is simply an independently hinged flap that swings down to interrupt the fluid (gas or liquid) flow in one direction, but only when the flow is moving in the opposite direction. Is pushed up. This is called a check valve because it stops or "checks" the flow in one direction. Modern control valves can control pressure or reduce drift and operate on sophisticated automation systems.

Valve

Valves have many uses, including controlling water for irrigation, industrial use to control processes, in-house and dish, and laundry and residential uses such as on / off and pressure control for taps. Even a small valve is constructed in aerosol spray cans. Valve is also used in the military and transportation sectors. In HVAC ductwork and other near-atmospheric airflows, valves are instead called dampers. In compressed air systems, however, valves are used with the most common types of ball valves.

Applications

Valves are found in almost 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 countries use valves in their daily lives, including taps for tap water, gas control valves on cookers, small valves for washing machines and dishwashers, safety devices fitted to hot water systems, and cars. Includes valves such as poppet valves. Engine.

In nature, there are valves, for example, a one-way valve in the veins that control blood circulation, and the heart valves regulate the flow of blood into the heart's chambers and maintain the correct pumping action.

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Valves can be operated manually, either by handle, lever, paddle, or wheel. Valves can also be automatic, driven by changes in pressure, temperature, or flow. These changes can act on a diaphragm or a piston that in turn activates the valve, examples of this type of valve are commonly found that are fitted to hot water systems or boilers.

More complex control systems (ie, regulating the flow through the pipe at a changing set point) using valves requiring automatic control based on an external input require an actuator. An actuator will stroke the valve based on its input and set-up, allowing the valve to be positioned correctly, and allowing control of various requirements.

Variation

Valves vary widely in form and application. Sizes [indistinct] typically range from 0.1 mm to 60 cm. Special valves may have a diameter of more than 5 meters. [which one?]

Valves range from simple inexpensive disposable valves to specialized valves that cost thousands of US dollars per inch of valve diameter.

Disposable valves can be found in common household items including mini-pump dispensers and aerosol cans.

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A common use of the term valve refers to poppet valves found in the vast majority of modern internal combustion engines, such as most fossil fuel-powered vehicles that control the intake of fuel-air mixtures and allow exhaust gas venting. Are used to give.

Type of valves

Valves are quite diverse and can be classified into several basic types. Valves can also be classified according to how they work:

* Hydraulic

* Pneumatic

* The guide

* Solenoid valve

* Motor

Components

The main parts of the most common type of valve are the body and bonnets. These two types of parts form the casing that holds the fluids going throughout the valves.

Body

The body of a valve is the outer cover of most or all valves that have internal parts or trims. The bonnet is the part of the encasing through which the stem (see below) passes and which forms a guide and seal for the stem. The bonnet is usually bumped into the valve body.

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Valve bodies are usually metal or plastic. Brass, cast iron, bronze metal, gunmetal,  steel, alloys steel, and stainless steel are very common. Seawater applications, like desalination plants, often use duplex valves, as well as super duplex valves, due to their corrosion-resistant properties, especially against hot seawater. Alloy 20 valves are commonly used in sulfuric acid plants, while mono valves are used in hydrofluoric acid (HF acid) plants. Hastelloy valves are often used in high-temperature applications, such as nuclear plants, while Pingel valves are often used in hydrogen applications. The plastic body is used for relatively low pressures and temperature. PVC, PP, PVDF, and glass-reinforced nylon valves are common plastics used for bodies.

Bonnet

A bonnet valve acts as a cover on the body. It is usually semi-permanently screwed into the valve body or bolted to it. During the manufacture of the valve, the internal parts are inserted into the body and then the bonnet is added to hold everything inside. To access the internal parts of a valve, a user usually closes the bonnet for maintenance. Many types of valves do not have bonnets; For example, plug valves which have usually do not have bonnets. Many ball valves do not have bonnets because the valve body is held together in a different style, such as screwing together the middle of the valve body.

Ports

Ports are portions that allow fluid to pass through the valve. Ports are interrupted by the valve member or disk to control the flow. Valves typically have 2 ports, but there can be as many as 20 of them. The valve is almost always connected to pipes or other components at its ports. Connection methods include threading, compression fittings, glue, cement, flanges, or welding.

Handle or actuator

A handle or actuator is used to manually control a valve from outside the valve body. Automatically controlled valves often do not have handles, but handles (or something similar) to some can override manual controls manually, such as stop-check valves. An actuator is a mechanism or device that automatically or remotely controls a valve from outside the body. Some valves have neither a handle nor an actuator because they control themselves from the inside; For example, check valves and relief valves can be neither.

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Disk

A disc or valve member is a movable barrier inside the stationary body that restricts the adjusted flow through the valve. Although traditionally disc-shaped, discs come in different sizes. Depending on the type of valve, a disc may move linearly inside a valve, or rotate on the stem (as a butterfly valve), or on a hinge or trunion (in a check valve). is. A ball is a round valve member that has one or more paths between the passing ports. By moving the ball, the flow can be directed between different ports. Ball valve uses spherical rotors with a cylindrical hole drilled as fluid passages. Plug valves use a cylindrical or conical tapered rotor called a plug. Other round shapes for the rotor are also possible in the rotor valve, as long as the rotor cannot be replaced inside the valve body. However, not all round or circular discs are rotors; For example, a ball check valve uses the ball to block the reverse flow, but not a rotor because the operation of the valve does not involve the rotation of the ball.

Seat

The seat is the inner surface of the body that 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 closed. In a rotating disc, the seat is always in contact with the disc, but the area of ​​contact changes as the disc turns. The seat is always stationary relative to the body.

The seats are classified according to whether they are cut directly into the body, or if they are made of a different material:

Hard seats are integral to the valve seat. Almost all rigid seating metal valves have a small amount of leakage.

Soft seats are fitted to the valve body and are made of soft material such as PTFE or various elastomers such as NBR, EPDM, or FKM, depending on the maximum operating temperature.

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A closed soft seated valve is much less responsive to leakage when closed while hard-seated valves are more durable. The gate, globe, and check valves are usually hard-seated while the butterfly, ball, plug, and diaphragm valves are usually soft-seated.

Transmits the disc from the stem handle or control device. The stem usually passes through the bonnet when present. In some cases, the stem and disc can be combined into one piece, or the stem and handle can be combined into one piece.

The motion transmitted by the stem can be a linear force, a rotational torque, or some combination of these (angle reactors using torque reactor pins and hub assemblies). The valve and stem can be threaded in such a way that the valve can be moved in or out by rotating the stem in one direction or the other, thus moving the disc in or behind the body. [Unclear] packing is often used in between. Stem and bonnet to maintain a seal. Some valves have no external controls and most check valves do not require a stem.

Valves whose disks lie between the seat and the stem and where the stem moves in one direction to close the valve are normally seated or seated in front. Valves whose seat is between the disc and stem and where the stem moves in one direction to close the valve, are reverse-sited or seated behind. These terms do not apply to valves with no stem or valves using the rotor.

Gasket

Gaskets are mechanical seals or packing, which are used to prevent leakage of gas or fluid from the valve.

Valve balls

The valve ball is also used for severe duty, high pressure, high tolerance applications. They are usually made of stainless steel, titanium, starter, Hastelloy, brass, or nickel. They can also be made from different types of plastics, such as ABS, PVC, PP, or PVDF.

The spring

Many valves have a spring for spring-loading, normally to move the disk to a position by default, but allow control to regenerate the disk. Relief valves typically use a spring to keep the valve closed, but allow excessive pressure to force the valve to open against spring-loading. Coil springs are commonly used. Typical spring materials include zinc-plated steel, stainless steel, and the Inconel X750 for high-temperature applications.

Trim

The internal elements of a valve are collectively referred to as the trim of the valve. According to API Standard 600, "Steel Gate Valve-Flagged and Butt-Welding Ends, Bolted Bonnets", trim includes welds deposited for the stem, seating surface, gate seating surface, bushing, or backlight and stem hole guides. , And small internal parts that normally contact the service fluid, except for the pin used to make the gate connected to a stem (this pin will be made of an auxiliary stainless steel material).

Valve operating positioning

The valve position is the operating position determined by the position of the disc or rotor in the valve. Some valves are operated in gradual changes between two or more positions. Return and non-return valves allow the fluid to move in two or one directions, respectively.

Two-port valve

The operating position for a 2-port valve can be either closed (closed) so that any current is fully open for maximum flow, or sometimes partially open to any degree in between. Many valves are not designed to properly control intermediate degrees of flow; Such valves are considered open or closed. Some valves are specifically designed to regulate varying amounts of flow. Such valves are called by various names such as regulating, throttling, metering, or needle valves. For example, needle valves have increased conical-tapered discs and matching seats for fine flow control. For some valves, there may be a mechanism to indicate how open the valve is, but in many cases other indications of flow rate are used, such as separate flow meters.

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In plants with remote-controlled process operations, such as oil refineries and petrochemical plants, some 2-way valves may be designated normally closed (NC) or normally open (NO) during routine operation. Examples of normally closed valves are sampling valves, which are opened when taking only one sample. Other examples of normally closed valves are emergency shut-down valves, which are kept open when the system is operating and will be automatically closed by turning off the power supply. This occurs when there is a problem with a unit or a section of a fluid system such as a leak to separate the problem from the rest of the system. Examples of commonly open valves are pure-gas supply valves or emergency-relief valves. When there is a problem, these valves open (by 'closing' them) causing the unit to inflate and evacuate.

Although many 2-way valves are built, in which the flow can move in either direction between the two ports, when a valve is placed in a fixed application, the flow often moves from a certain port upstream of the valve. Looks forward to it. Downstream to another port. There are variations of pressure regulator valves in which the flow is controlled to produce a certain drift pressure, if possible. They are often used to control the flow of gas from a gas cylinder. A back-pressure regulator is a variation of a valve in which the flow is controlled to maintain a certain upstream pressure, if possible.

Three post valves

Valves with three ports perform many different functions. Some possibilities are listed here.

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Three-way ball valves come with a T or L-shaped fluid passage inside the rotor. The T valve can be used to allow the connection of either an inlet or for the connection of both outlets or both outlets. The L valve can be used to allow disconnection or connecting of the two, but not at one outlet of both inlets.

Shuttle valves automatically connect the high-pressure inlet to the outlet (while in some configurations) preventing flow from one inlet to another.

Single handle mixer valves produce a variable mixture of hot and cold water at a variable flow rate under the control of a single handle.

Thermostatic mixing valves mix hot and cold water to produce a constant temperature in the presence of variable pressure and temperature at the two input ports.

Four-port valve

A 4-port valve is a valve whose four parts of the body are evenly rounded and the disk has two passages connecting the nearby ports. It operates with two positions.

It can be used to separate and simultaneously bypass a sample cylinder installed on a pressurized water line. It is useful to sample the fluid without affecting the pressure of a hydraulic system and to avoid any gas leakage (no leakage, no gas loss or air ingress, no external contamination).

Control

Many valves are manually controlled with a handle attached to the stem. If the handle is rotated at ninety degrees between operating conditions, the valve is called a quarter-turn valve. Ball valves, Butterfly valves, and plug valves are often quarter-turn valves. If the handle is circular with the stem as the axis of rotation at the center of the circle, the handle is called a handwheel. The valve can also be controlled by the actuators attached to the stem. They may be electric motors or solenoids, pneumatic actuators such as electromechanical actuators, which are controlled by air pressure or hydraulic actuators, controlled by the pressure of a liquid such as oil or water. Actuators can be used for purposes of automatic control such as washing machine cycles, remote controls such as the use of a centralized control panel, or because manual control is too difficult such that the valve is too large. Pneumatic and hydraulic actuators need pressurized air or liquid lines to supply the actuators with an inlet line and an outlet line. Pilot valves are valves that are used to control other valves. Pilot valves in actuator lines control the supply of air or liquid going into the actuators.

The valve filled into the toilet water tank is a liquid level-activated valve. When a high water level is reached, a mechanism closes the valve that fills the tank.

In some valve designs, the pressure of the flowing fluid or the pressure difference of the flowing fluid between ports automatically controls the flow through the valve.

Other considerations

Valves are usually rated by the manufacturer for maximum temperature and pressure. Wet material in a valve is also commonly identified. Some valves with very high pressures are available. When a designer, engineer, or user decides to use a valve for an application, it should ensure that it must set the maximum temperature and the pressure should never be high and that the interior of the wet material fluid Is in contact with. In Europe, valve design and pressure ratings are subject to statutory regulation under pressure equipment directive 97/23 / EC (PED) [2].

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Some fluid system designs, especially in chemical or power plants, are schematically represented in the piping and instrumentation diagram. In such diagrams, different types of valves are represented by some symbols.

Valves must be leak-free in good condition. However, valves may eventually fall out of use and develop a leak, either inside and outside the valve or when the valve is closed to close, between the disc and the seat. A particle trapped between the seat and the disc can also cause such leakage.