Клапаны могут использоваться для управления потоком различных типов жидкостей, таких как воздух, вода, пар, различные агрессивные среды, грязь, масло, жидкие металлы и радиоактивные среды. В связи с важностью выбора наиболее подходящей арматуры для трубопроводных систем понимание характеристик арматуры, а также этапов и критериев выбора арматуры стало решающим.

01 Классификация клапанов

В целом клапаны можно разделить на две категории: 1. Автоматический клапан. Клапан, который работает самостоятельно, полагаясь на возможности самой среды (жидкости, газа). Например, обратные клапаны, предохранительные клапаны, регулирующие клапаны, сливные клапаны, редукционные клапаны и т. д. 2. Приводной клапан Клапаны управляются вручную, электрически, гидравлически и пневматически. Такие как задвижки, шаровые клапаны, дроссельные клапаны, дроссельные клапаны, шаровые краны, пробковые клапаны и т. д.

По конструктивным характеристикам его можно разделить на: (1) Усеченную форму затвора: запирающий элемент перемещается по центру седла клапана; (2) В форме ворот: закрывающий компонент перемещается по центру вертикального седла клапана; (3) Кран и шар: закрывающий компонент представляет собой плунжер или шар, который вращается вокруг своей центральной линии; (4) Форма спирального отверстия: запирающий элемент вращается вокруг оси снаружи седла клапана; (5) Форма диска: круглый диск затвора, который вращается вокруг оси внутри седла клапана; (6) Форма шиберного клапана: запорный элемент скользит в направлении, перпендикулярном каналу. В зависимости от их применения клапаны можно разделить на: (1) Функция разъединения: используется для подключения или отключения сред трубопровода, таких как шаровые клапаны, задвижки, шаровые краны, дроссельные клапаны и т. д. (2) Обратный клапан: используется для предотвратить обратный поток среды, например, с помощью обратного клапана. (3) Регулирование: используется для регулирования давления и расхода среды, например, регулирующие клапаны и редукционные клапаны. (4) Назначение распределения: используется для изменения направления потока и распределения среды, например трехходовых заглушек, распределительных клапанов, золотниковых клапанов и т. д. (5) Предохранительный клапан: используется для сброса избыточной среды, когда давление среды превышает указанное значение. , обеспечение безопасности трубопроводных систем и оборудования, такого как предохранительные клапаны и аварийные клапаны. (6) Другие специальные цели: такие как сливные клапаны, выпускные клапаны, сливные клапаны и т. д. В зависимости от способа привода их можно разделить на: (1) Ручные: с помощью маховиков, ручек, рычагов или звездочек, он имеет ручной привод и оснащен червячными передачами, шестернями и другими понижающими устройствами при передаче большого крутящего момента. (2) Электрический: приводится в движение электродвигателем или другим электрическим устройством. (3) Гидравлический: приводится в движение (водой, маслом). (4) Пневматический: приводится в движение сжатым воздухом. В зависимости от номинального давления клапана его можно разделить на: (1) Вакуумный клапан: клапан с абсолютным давлением менее 0,1 МПа, что соответствует высоте 760 мм ртутного столба, а давление обычно выражается в мм ртутного столба или мм водяного столба. (2) Клапан низкого давления: клапаны с номинальным давлением PN ≤ 1,6 МПа (в том числе стальные клапаны с PN ≤ 1,6 МПа) (3) Клапан среднего давления: клапан с номинальным давлением PN 2,5-6,4 МПа. (4) Клапан высокого давления: клапан с номинальным давлением PN10,0-80,0 МПа. (5) Клапан сверхвысокого давления: клапан с номинальным давлением PN ≥ 100,0 МПа. В зависимости от температуры среды его можно разделить на: (1) Обычный клапан: подходит для клапанов с температурой среды от -40 ℃ до 425 ℃. (2) Высокотемпературный клапан: подходит для клапанов со средней температурой от 425 ℃ до 600 ℃. (3) Термостойкий клапан: подходит для клапанов с температурой среды выше 600 ℃. (4) Низкотемпературный клапан: подходит для клапанов со средней температурой от -150 ℃ до -40 ℃. (5) Клапан сверхнизкой температуры:подходит для клапанов с температурой среды ниже -150 ℃. В зависимости от номинального диаметра клапаны можно разделить на: (1) Клапан малого калибра: клапан номинальным диаметром DN<40 мм. (2) Клапан среднего калибра: клапан номинальным диаметром DN50–300 мм. (3) Клапаны большого калибра: клапаны номинальным диаметром DN350-1200 мм. (4) Клапан сверхбольшого диаметра: клапан с номинальным диаметром DN ≥ 1400 мм. По способу соединения с трубопроводом его можно разделить на: (1) Клапан с фланцевым соединением: корпус клапана оснащен фланцем и соединяется с трубопроводом с помощью фланца. (2) Клапан с резьбовым соединением: клапан с корпусом клапана, который имеет внутреннюю или внешнюю резьбу и соединяется с трубопроводом с помощью резьбы. (3) Клапан со сварным соединением: Корпус клапана имеет сварное соединение и соединяется с трубопроводом сваркой. (4) Клапан с хомутовым соединением: клапан с хомутом на корпусе клапана, соединенный с трубопроводом с помощью хомутов. (5) Клапан с карточной муфтой: клапан, в котором для подключения к трубопроводу используется карточная муфта.02 Characteristics of valves

There are generally two characteristics of valves: usage characteristics and structural characteristics. 1. Usage characteristics It determines the main performance and scope of use of the valve, and the characteristics of valve use include: Types of valves (closed-circuit valves, regulating valves, safety valves, etc.); Product type (gate valve, globe valve, butterfly valve, ball valve, etc.); The materials of the main components of the valve (valve body, valve cover, valve stem, valve disc, sealing surface); Valve transmission mode, etc. 2. Structural characteristics It determines some structural characteristics of valve installation, maintenance, and upkeep methods, including: The structural length and overall height of the valve, as well as the connection form with the pipeline (flange connection, threaded connection, clamp connection, external threaded connection, welded end connection, etc.); Form of sealing surface (insert ring, threaded ring, overlay welding, spray welding, valve body); Valve stem structure forms (rotating rod, lifting rod), etc.

03 Steps and criteria for selecting valves

1. Selection steps (1) Clarify the purpose of the valve in the equipment or device, determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc. (2) Determine the nominal diameter and connection method of the pipeline connected to the valve: flange, thread, welding, etc. (3) Determine the method of operating the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc. (4) Determine the materials for the shell and internal components of the selected valve based on the medium transported by the pipeline, working pressure, and working temperature: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid resistant steel, copper alloy, etc. (5) Choose the type of valve: closed-circuit valve, regulating valve, safety valve, etc. (6) Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap valve, etc. (7) Determine the parameters of the valve: For automatic valves, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole. (8) Determine the geometric parameters of the selected valve: structural length, flange connection form and size, height direction size of the valve after opening and closing, size and quantity of bolt holes for connection, overall dimensions of the valve, etc. (9) Use existing materials such as valve product catalogs and valve product samples to select appropriate valve products. 2. Basis for valve selection While understanding and mastering the steps of selecting valves, it is also necessary to further understand the basis for selecting valves. (1) The purpose, operating conditions, and control mode of the selected valve. (2) The properties of the working medium include working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable or explosive, viscosity of the medium, and so on. (3) Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc. (4) Installation dimensions and external dimensions requirements: nominal diameter, connection method and dimensions with the pipeline, external dimensions or weight limitations, etc. (5) Additional requirements for the reliability, service life, and explosion-proof performance of valve products and electric devices. When selecting parameters, attention should be paid to: If the valve is to be used for control purposes, the following additional parameters must be determined: operating method, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closing, and maximum and minimum inlet pressure of the valve. According to the above criteria and steps for selecting valves, it is necessary to have a detailed understanding of the internal structure of various types of valves when selecting valves reasonably and correctly, so as to make the correct choice for the preferred valve. The ultimate control of pipelines is valves. The valve opening and closing components control the flow of the medium in the pipeline, and the shape of the valve channel gives the valve certain flow characteristics. This must be taken into account when selecting the most suitable valve for installation in the pipeline system. Principles to be when selecting valves: (1) Valves for closing and opening media Valves with straight through flow channels have low flow resistance and are usually chosen as shut-off and open medium valves. Downward closing valves (globe valves, plunger valves) are less commonly used due to their tortuous flow paths and higher flow resistance compared to other valves. In situations where high flow resistance is allowed, closed valves can be used.

(2) Valves for controlling flow Usually, valves that are easy to adjust the flow rate are selected for controlling the flow rate. A downward closing valve (such as a globe valve) is suitable for this purpose because its seat size is proportional to the stroke of the closing member. Rotary valves (plug valves, butterfly valves, ball valves) and flex valve body valves (clamp valves, diaphragm valves) can also be used for throttling control, but are usually only applicable within a limited range of valve diameters. Gate valve is a disc-shaped gate that performs transverse movement on a circular valve seat. It can only effectively control flow when approaching the closed position, so it is usually not used for flow control. (3) Valve for directional diversion According to the needs of directional diversion, this valve can have three or more channels. Plug valves and ball valves are more suitable for this purpose, therefore, most valves used for directional diversion choose one of these types of valves. However, in some cases, other types of valves can also be used for directional diversion as long as two or more valves are appropriately connected to each other. (4) Valves for media with suspended particles When there are suspended particles in the medium, it is most suitable to use a valve with a sliding closure along the sealing surface and a wiping effect. If the back and forth movement of the closure against the valve seat is vertical, it may clamp particles, so this type of valve is only suitable for basic clean media unless the sealing surface material allows for the embedding of particles. Ball valves and plug valves have a wiping effect on the sealing surface during the opening and closing process, making them suitable for use in media with suspended particles.

04 Valve Selection Instructions

1. Selection of Gate Valves Generally, gate valves should be preferred. Gate valves are not only suitable for media such as steam and oil, but also for media containing granular solids and high viscosity, and are suitable for valves in venting and low vacuum systems. For media with solid particles, the gate valve body should have one or two blowdown holes. For low-temperature media, low-temperature dedicated gate valves should be selected. 2. Selection instructions for globe valves Globe valves are suitable for pipelines that do not have strict requirements for fluid resistance, that is, pipelines or devices that do not consider pressure loss, as well as high-temperature and high-pressure media. They are suitable for steam and other media pipelines with DN<200mm; Small valves can use globe valves, such as needle valves, instrument valves, sampling valves, pressure gauge valves, etc; Globe valves have flow regulation or pressure regulation, but do not require high regulation accuracy, and the pipeline diameter is relatively small. Globe valves or throttle valves should be selected; For highly toxic media, it is advisable to use bellows sealed globe valves; However, globe valves should not be used for media with high viscosity and media containing particles that are prone to precipitation, nor should they be used as vent valves or valves for low vacuum systems. 3. Ball valve selection instructions Ball valves are suitable for media with low temperature, high pressure, and high viscosity. Most ball valves can be used in media with suspended solid particles, and can also be used in powder and granular media depending on the sealing material requirements; Full channel ball valves are not suitable for flow regulation, but are suitable for situations that require quick opening and closing, making it easy to achieve emergency shutdown in case of accidents; Ball valves are recommended for pipelines with strict sealing performance, wear, constricted channels, rapid opening and closing actions, high pressure cutoff (large pressure difference), low noise, gasification phenomenon, low operating torque, and low fluid resistance; Ball valves are suitable for lightweight structures, low-pressure shut-off, and corrosive media; Ball valves are still the most ideal valves for low-temperature and cryogenic media. For pipeline systems and devices for low-temperature media, low-temperature ball valves with valve covers should be selected; When selecting a floating ball valve, its seat material should bear the load of the ball and working medium. Large diameter ball valves require greater force during operation, and ball valves with DN ≥ 200mm should use worm gear transmission; Fixed ball valves are suitable for larger diameters and high-pressure applications; In addition, ball valves used for the production of highly toxic materials and flammable medium pipelines should have fire-resistant and anti-static structures. 4. Selection instructions for throttle valve Throttle valves are suitable for situations where the medium temperature is low and the pressure is high. They are suitable for areas where flow and pressure need to be adjusted. They are not suitable for media with high viscosity and solid particles, and should not be used as block valves. 5. Selection Instructions for Plug Valves Plug valves are suitable for situations that require quick opening and closing, and are generally not suitable for steam and high-temperature media. They are used for media with low temperature and high viscosity, and are also suitable for media with suspended particles. 6. Butterfly valve selection instructions Butterfly valves are suitable for larger diameters (such as DN>600mm), shorter structural length requirements, and situations that require flow regulation and quick opening and closing. They are generally used for media such as water, oil, and compressed air with temperatures ≤ 80 ℃ and pressures ≤ 1.0MPa; Due to the relatively large pressure loss of butterfly valves compared to gate valves and ball valves, butterfly valves are suitable for pipeline systems with less stringent pressure loss requirements. 7. Selection instructions for check valves Check valves are generally suitable for clean media and should not be used for media containing solid particles and high viscosity. When DN ≤ 40mm, it is advisable to use a lift check valve (only allowed to be installed on horizontal pipelines); When DN=50-400mm, it is advisable to use a rotary lift check valve (which can be installed on both horizontal and vertical pipelines. If installed on a vertical pipeline, the flow direction of the medium should be from bottom to top); When DN ≥ 450mm, a buffer type check valve should be used; When DN=100-400mm, clamp type check valves can also be used; Swing check valves can be designed for high working pressures, with PN reaching up to 42MPa. Depending on the material of the shell and seal, they can be suitable for any working medium and any working temperature range. The medium includes water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196 and 800 ℃. 8. Selection Instructions for Diaphragm Valve Diaphragm valves are suitable for oil products, water, acidic media, and media containing suspended solids with working temperatures less than 200 ℃ and pressures less than 1.0MPa. They are not suitable for organic solvents and strong oxidizing agents; Grinding granular media should choose weir type diaphragm valves, and the selection of weir type diaphragm valves should refer to their flow characteristics table; Viscous fluids, cement slurries, and sedimentary media should use straight through diaphragm valves; Unless otherwise specified, diaphragm valves are not suitable for use in vacuum pipelines and vacuum equipment. The applications, operating frequencies, and services of valves are constantly changing. To control or eliminate even minor leaks, the most important and critical equipment is the valve. Learning to choose valves correctly is crucial.