A valve is a device that regulates, directs or controls the flow of liquid (gas, liquid, fluidized solids, or slurry) by opening, closing, or partially blocking the various pathways. Valves are technically complete, but are usually discussed as separate categories. In the open valve, the liquid flows in from the higher pressure to the lower pressure. This word is derived from the Latin valva , the moving part of a door, in turn from volvere , to spin, roll over.
The simplest, and very ancient, valve is simply a free hinged flap that drips to block the flow of liquid (gas or liquid) in one direction, but is pushed open by flow in opposite directions. This is called check valve, because it prevents or "checks" the flow in one direction. Modern control valves can adjust pressure or downstream flow and operate on advanced automation systems.
Valves have many uses, including water control for irrigation, industrial use for process control, use of housing such as on/off and pressure control for dishwashers and washing machines and taps at home. Even the aerosol has a small valve attached inside it. Valves are also used in the military and transportation sectors.
Video Valve
Valves are everywhere
Valves are found in almost every industrial process, including water and sewage treatment, mining, power generation, oil, gas and petroleum processing, food manufacturing, chemical and plastic manufacturing and many other fields.
People in developed countries use valves in their everyday life, including pipe valves, such as taps for tap water, gas control valves on stoves, small valves installed for washing machines and dishwashers, security devices mounted on water systems heat, and popet valves in the car. machine.
In nature there is a valve, for example a one-way valve in a blood vessel that controls blood circulation, and a heart valve that controls blood flow in the heart chambers and maintains proper pumping action.
Valves can be operated manually, either with handles, levers, pedals or wheels. Valves may also be automatic, driven by changes in pressure, temperature, or flow. This change may act upon the diaphragm or piston which in turn activates the valve, an example of the type of valve found generally is a safety valve installed in a hot water system or boiler.
More complex control systems use valves that require automatic controls based on external inputs (i.e., regulating flow through pipes to changing set point) requiring actuators. An actuator will push the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over various requirements.
Maps Valve
Variations
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.
The cost of the valve ranges from simple and cheap disposable valves to special valves that cost thousands of dollars per inch of valve diameter.
Disposable valves can be found in general household items including mini-pump dispensers and aerosol cans.
The general use of the term "valve" refers to the popet valves found in most modern internal combustion engines such as those in most fossil-fueled vehicles used to control mixed air-fuel intake and allow gas vents throw away.
Type
The valves are very diverse and can be classified into several basic types. Valves can also be classified according to how they are driven:
- Hydraulics
- Pneumatic
- Manual
- Solenoid valve
- Motor
Components
The main parts of the most common types of valves are body and bonnet . These two parts form a casing that holds the liquid through the valve.
Body
The body valve is the outer casing of most or all valves containing internal parts or trim . The hood is part of the cover that is passed by the stalk (see below) and which forms the guide and seal for the rod. Kapbor usually screwed or bolted to the body of the valve.
Valve body is usually made of metal or plastic. Brass, bronze, gunmetal, cast iron, steel, alloy steel and stainless steel are very common. Seawater applications, such as desalination plants, often use duplex valves, as well as super duplex valves, due to their rust-proof nature, especially against warm seawater. The alloy valve 20 is commonly used in sulfuric acid plants, while the monel valve is used in hydrofluoric acid plants (HF Acid). Hastelloy valves are often used in high temperature applications, such as nuclear plants, while inconel valves are often used in hydrogen applications. The plastic body is used for relatively low pressure and temperature. PVC, PP, PVDF and glass-reinforced nylon are common plastics used for valve bodies.
Bonnet
bonnet hat serves as a cover on the valve body. It is generally semi-permanently screwed into the valve body or bolted onto it. During valve manufacture, the internal parts are inserted into the body and then the bonnet is fitted to hold it all inside. To access the internal parts of the valve, the user will remove the hood, usually for maintenance. Many valves do not have ax; for example, a buffer valve usually does not have a hood. Many ball valves do not have caps because the valve body is united in different styles, such as screwed together in the center of the valve body.
Port
Port is the part that allows the liquid to pass through the valve. The port is blocked by a valve member or disc to control the flow. The most common valve has 2 ports, but may have as many as 20. Valves are almost always connected on their ports to pipes or other components. Connection methods include screw, compression fitting, glue, cement, flanges, or welding.
Handle or actuator
A handle is used to control the valve manually from outside the valve body. Automatically controlled valves often do not have a handle, but some may have a handle (or something similar) to manually override automatic controls, such as check-stop valves. An actuator is a mechanism or device to automatically or remotely control the valve from outside the body. Some valves have no handle or actuator because they automatically control themselves from within; for example, check valves and release valves may not have both.
Disc
A disc or valve member is a movable obstruction within a stationary body that deliberately limits the flow through the valve. Although disc-shaped discs come in many forms. Depending on the type of valve, the disc may move linearly inside the valve, or rotate on the rod (as in the butterfly valve), or rotate on a hinge or trunnion (as in a valve). A ball is a member of a round valve with one or more paths between ports passing through it. By turning the ball, the flow can be directed between different ports. The ball valve uses a round rotor with a cylindrical hole drilled as a liquid duct. The plug valve uses a cylinder or conical rotors rotor called spark plug . Other rounded shapes for the rotor are also possible in rotor valves , as long as the rotor can be rotated inside the valve body. However, not all round or rounded disks are rotor; for example, ball valves use ball to block backflow, but not rotor because operating the valve does not involve ball rotation.
Chair
seating is the inner surface of the body that contacts the disk to form a leaky seal. In discs that move linearly or swing on a hinge or trunnion, the discs come into contact with the seat only when the valve is closed. In a rotating disk, the seat is always in contact with the disc, but the contact area changes when the disc is turned on. Seats always remain silent relative to the body.
Chairs are classified by whether they are cut directly into the body, or whether they are made of different materials:
- Hard chair is an integral part of the valve body. Almost all metal valves sitting hard have little leakage.
- Soft seats are mounted on the valve body and are made of a softer material such as PTFE or various elastomers such as NBR, EPDM, or FKM depending on the maximum operating temperature.
Closed sealed closed valve is much easier to leak when closing while the valve sitting hard is more durable. The gates, balls, and check valves are usually hard to sit while the butterfly, ball, connector, and diaphragm valves usually sit gently.
Stem
The rod transmits motion from the handset or controller device to the disk. The trunk usually passes through the hood at this time. In some cases, rods and plates can be combined into one piece, or stalks and handles combined into one section.
The movement emitted by the rod may be a linear force, rotation torque, or some combination of these (angle valves using the torque reactor pin and the Hub Assembly). Valves and rods can be threaded in such a way that the rods can be screwed in or out of the valve by rotating them in one direction or another, thereby moving the disc back or back inside the body. Packing is often used between the stem and hood to maintain the seal. Some valves have no external control and do not require a rod like in most check valves.
The valve between the seat and the stem and where the rod moves toward the valve to close it is which usually sit or in front of the sitting . The valve that is between the disc and the rod and where the rod moves outwards from the valve to close it is reversed or sit back . These terms do not apply to valves without bars or valves using rotor.
Gasket
Gaskets are mechanical seals, or packaging, used to prevent gas or liquid leakage from the valves.
Valve ball
A ball valve is also used for heavy duty applications, high pressure, high tolerance. They are usually made of stainless steel, titanium, Stellite, Hastelloy, brass, or nickel. They can also be made of various types of plastics, such as ABS, PVC, PP or PVDF.
Spring
Many valves have springs to load springs, usually shifting the disk to multiple positions by default but allowing the control to reposition the disk. Relief valves generally use springs to keep the valve closed, but allow excess pressure to force the valve open to the loading of the spring. Coil springs are usually used. Typical spring materials include zinc-coated steel, stainless steels, and for high temperature Inconel X750 applications.
Crop
The internal elements of the valve are collectively referred to as trim valves. According to API 600 Standard, "Steel Gate Valve-Flanged and Butt-welding Ends, Bolted Bonnets", trims consist of rods, body seating surfaces, seating surfaces, bushing or welds deposited for backseat and barrow guides, a small internal which usually contacts the service fluid, excluding the pins used to make the connecting rod to the gate (this pin must be made of austenitic stainless steel).
Valve operating position
Valve positions is an operating condition determined by the position of disk or rotor in the valve. Some valves are made to operate in a gradual change between two or more positions. The return valve and the non-return valve allow the fluid to move in 2 or 1 direction.
Two-port valve
The operating position for the 2-port valve can be closed (closed) so that no flow at all flows, fully open for maximum flow, or sometimes partially open to whatever level in between. Many valves are not designed to precisely control intermediate flow rates; the valve is considered open or closed. Some valves are specially designed to vary the amount of flow. The valve has been dialed under various names such as set , throttling , meter , or needle valve . For example, the needle valve extends the cone-tapered disc and seats suitable for fine flow control. For some valves, there may be a mechanism to show how many valves are open, but in many cases another indication of flow rate is used, such as a separate flow meter.
In factories with remote controlled process operations, such as oil refineries and petrochemical plants, some 2-way valves may be designated as normally closed (NC) or normally open (NO) during normal operation. Examples of normally closed valves are sampling valves , which are only opened when samples are taken. Another example of a normally closed valve is an emergency shutter valve, which remains open when the system is operating and will be automatically closed by picking up the power supply. This occurs when there is a problem with the unit or part of the fluid system such as a leak to isolate the problem from the rest of the system. Examples of normally open valves are exhaust gas supply valves or emergency release valves. When there is a problem, these valves open (by turning it off) which causes the unit to flush and empty.
Although many 2-way valves are created where the flow can go in either direction between the two ports, when the valve is placed into a particular application, the flow is often expected to go from one particular port on the valve's upstream upstream other ports on the downstream side. The pressure regulator is a variation of the valve in which the flow is controlled to produce a certain downstream pressure, if possible. They are often used to control gas flow from gas cylinders. The back pressure regulator is a variation of the valve in which the flow is controlled to maintain a certain upstream pressure, if possible.
Three-port valve
Valves with three ports serve many different functions. Some possibilities are listed here.
A three-way ball valve comes with a T-shaped or L-shaped liquid channel inside the rotor. Valve T can be used to allow connections from one incoming channel to one or both channels or connections from two channels. Valve L can be used to allow disconnection of both or the connection of both but not both of the two channels into one outlet.
The cruise valve automatically connects high pressure inlet to outlet when (in some configurations) prevents flow from one channel to another.
Single handling mixer valves produces a mixture of hot and cold water variables at variable flow rates under the control of one handle.
Thermostatic mixing valves mix hot and cold water to produce constant temperature with varying pressure and temperature on two input ports.
Four-port valve
The 4-port valve is a valve whose body has four ports with the same distance around the body and the disc has two parts to connect the adjacent port. It is operated in two positions.
This can be used to isolate and simultaneously bypass sample cylinders mounted on pressurized water channels. It is useful for taking fluid samples without affecting the pressure of the hydraulic system and to avoid degassing (no leakage, no gas loss or air ingress, no external contamination).
Control
Many valves are manually controlled with a handle attached to the rod. If the handle turns ninety degrees between the operating positions, the valve is called quarter-turn of the valve . Butterfly valves, balls, and plug valves are often a quarter-turn valve. If the handle is circular with a rod as the rotation axis in the center of the circle, then the handle is called handwheel . The valves can also be controlled by actuators attached to the rod. They can be electromechanical actuators such as electric motors or solenoid, pneumatic actuators controlled by air pressure, or hydraulic actuators controlled by liquid pressure such as oil or water. Actuators can be used for automated control purposes such as in washing machine cycles, remote controls such as the use of centralized control room, or because manual control is too difficult such as when the valve is very large. Pneumatic actuators and hydraulic actuators require air ducts or pressurized fluids to supply actuators: inlets and outlets. Pilot valve is a valve used to control other valves. The pilot valve in the actuator lane controls the air or liquid supply to the actuator.
The filling valve in the toilet water tank is a valve that is moved by the liquid level. When a high water level is reached, the mechanism closes the valve that fills the tank.
In some valve designs, the pressure from the fluid flow itself or the pressure difference of the fluid flow between the ports automatically controls the flow through the valve.
Other considerations
Valves are usually rated for maximum temperature and pressure by the manufacturer. The material moistened in the valve is usually identified as well. Some very high pressure valves are available. When a designer, engineer, or user decides to use a valve for application, he must ensure that the rated temperature and maximum pressure are never exceeded and that the moistened material is compatible with the fluid exposed to the inside of the valve. In Europe, valve design and pressure ratings are subject to statutory regulations under Pressure Equipment Directive 97/23/EC (PED).
Some fluid system designs, especially in chemical or power generation, are schematically represented in piping and instrumentation diagrams. In such diagrams, various types of valves are represented by certain symbols.
Valves in good condition should be leak free. However, the valve may eventually wear out of use and develop leaks, either between the inside and outside of the valve or, when the valve is closed to stop the flow, between the disc and the seat. Particles trapped between seats and disks can also cause leaks.
Images
See also
References
External links
- ISO-15926-4 - Nearly 500 base valve classifications and definitions of ISO 15926 standard.
- Animations that Show Internal Functions Different Types of Valves, tlv.com
- Groove in Design Type Batik Valve, home.arcor.de
- Valves: Piping and Instrumentation Standard Notation Diagram, controls.engin.umich.edu
- Fundamental Handbook of the Department of Energy, Mechanical Sciences, Module 4 Valves
Source of the article : Wikipedia
0 Comments