Abstract: With the continuous development of modern industry, the diversity of process control and the complexity of process conditions, the demand for control valves is increasing. In the fluid pipe system, the valve is to turn on or off the pipe medium, change the flow of the medium. Direction, the pressure and flow of the media, and important control elements to protect the normal operation of the pipeline equipment.
Keywords:valve;characteristics;type selection procedure;selection specification DOI:10.16640/j.cnki.37-1222/t.2018.07.054
Gansu Yinguang Juyin Chemical Co., Ltd. has an annual output of 100,000 tons of TDI devices with tens of thousands of valves of various types, but often run, run, drip or leak due to manufacturing, use selection, improper maintenance, etc. The resulting low product quality, increased energy consumption, equipment corrosion, and even causing parking accidents have become commonplace. At this time, new requirements have been put forward for valve operators, maintenance personnel and engineering technicians. In addition to correct operation of valves and timely inspection and maintenance, the steps and basis for understanding the classification, characteristics and structure of valves, and valve selection are also It becomes crucial.
1 Classification of Valves Valves come in a variety of types, including straight-through valves (single seat, double seat), angle valves, three-way valves, ball valves, and eccentric rotary valves. The overall can be divided into two categories: automatic valves and drive valves. Automatic valves are valves that rely on the ability of the medium (liquid, gas) itself to act on its own. Drive valves are valves that operate with manual, electric, hydraulic, and pneumatic actuation.
2 valve characteristics and structure (1) valve characteristics. 1) Use characteristics: Valve categories, such as: closed-circuit valves, regulating valves, safety valves, etc.; product types, such as: gate valve, butterfly valve, ball valve, etc.; valve main parts, including: valve body, valve cover, valve stem, valve core , sealing surface and so on. 2) Structural characteristics: The structural length and overall height of the valve are connected to the pipeline, such as: flange connection, threaded connection, welding end connection, etc.; the sealing surface is in the form of: thread ring, build-up welding, spray welding, valve body Etc.; stem structure, etc.
(2) The structure of the valve. There are many kinds of valves, mainly including upper and lower valve covers, valve bodies, valve cores, valve seats, packing and other components. According to different requirements, there are many types of structures. 1) The upper valve cover of the valve. The upper valve cover is located between the actuator and the valve body. In order to adapt to different operating temperatures and sealing requirements, there are four common structures. 1 common type, suitable for high temperature places, working temperature range is -20 ~ 200 °C. 2 suction (scattered) heat type, medium working temperature is -60 ~ 450 °C, the valve cover has a number of suction (dissipation) heat film, in order to ensure the sealing packing in the allowable temperature range. 3 long-neck type, suitable for deep frozen places, medium operating temperature range -250 ~ -60 °C. 4 Bellows sealed type, the valve rod movable part adopts bellows sealing, which can avoid medium leakage and personal poisoning and explosion accidents. It is suitable for strong toxic, volatile, easy to penetrate or valuable process media. 2) spool. A straight stroke valve can be divided into five types: flat plate type, plunger type, window type, multi-stage type and sleeve type. 2 angle stroke valve core, including eccentric rotary valve core, disc type valve core and spherical valve core, wherein the spherical valve core has "O" spherical valve and "V" spherical valve.
3 valve selection procedures and principles (1) valve selection procedures. 1) First of all, confirm the use of the valve in the equipment or device to determine the working conditions of the valve including the circulating medium, working pressure, working temperature and so on. 2) The nominal path of the valve and pipe connection (flange connection, screw connection or welding, etc.) and the connected pipe. 3) Confirm the control mode (manual, electric, pneumatic or hydraulic) of the valve and the form of the valve (gate valve, globe valve, ball valve, butterfly valve, diaphragm valve, throttle valve, safety valve, pressure reducing valve, etc.). 4) When selecting the valve body component material, the factors such as the corrosivity, temperature, pressure, cavitation and erosion of the process media are mainly considered. When considering factors such as cavitation and erosion, special alloys or special structural valves may be used. In general corrosion requirements, the valve body and valve core are often made of common stainless steel (1Cr18Ni9Ti). When corrosion resistance is high, two titanium stainless steels can be used. (Cr18Ni12Mo2Ti), also available in all titanium materials suitable for most corrosive media. 5) Confirm valve parameters and valve geometry. The valve parameters include: allowable flow resistance, discharge capacity, back pressure, nominal pipe diameter, etc. The geometric parameters of the valve include: flange spacing, flange connection and dimensions, number of bolts connected, overall valve size, etc.
(2) Select the principle of the valve. With suspended particles in the medium, if the closing member's back and forth movement of the valve seat is vertical, it is possible to hold the particles, so this valve is only suitable for basic cleaning media unless the sealing surface material can allow embedded particles. . Ball valve and plug valve wipe the sealing surface in the process of opening and closing, it is suitable for use in media with suspended particles.
4 Selection instructions for various types of valves (1) Ball valves. Ball valve according to the form of the valve can be divided into "O" ball valve and "V" ball valve two. The "V" ball valve has a "V" opening in the ball valve. During operation, the actuator push rod rotates the valve core through the ball valve and changes the opening area as the ball rotates. "V" type ball valve has simple flow path and large flow capacity. The valve seat is made of soft material and has reliable sealing. It is especially suitable for fibers, pulp, low temperature and high viscosity media. Sealing material requirements can also be used for the control of powdered and granular media.
(2) Butterfly valve. Butterfly valve, also known as flap valve, is a rotary valve. Mainly by the valve body, baffle, baffle shaft and crank parts and other components. Applicable to larger diameter and short structure requirements, as well as the need for flow adjustment and opening and closing requirements for rapid occasions, because the butterfly valve than the gate valve, ball valve pressure loss, so the butterfly valve is suitable for pressure loss is not strict in the piping system.
(3) Diaphragm valve. Diaphragm valve consists of valve body, diaphragm, valve core valve cover and valve stem and other components. The film moves the valve core up and down through the valve stem to change the flow area and achieve flow regulation. Diaphragm valve has simple structure, low flow resistance and large flow capacity, and can be used for the regulation of high viscosity and suspended particle fluids. For high corrosion sites such as strong acids and alkalis, the valve body lining can be rubber or PTFE, but the diaphragm The lining material is not resistant to high temperatures and the operating temperature should not exceed 150°C.
(4) Stop valve. The cut-off valve is suitable for pipelines and devices with strict requirements on fluid resistance, high-temperature and high-pressure medium, and the adjustment accuracy is not high, and the pipe diameter is relatively small. It is particularly recommended to use a cut-off valve.
(5) Plug valves. Plug valves are suitable for applications where fast switching is required. They are suitable for low temperature, high viscosity media or media with suspended particles. It is generally not suitable for steam and high temperature medium lines.
(6) Selection of gate valve. The gate valve has a wide range of applications and is applicable not only to steam, oil and other media, but also to media containing granular solids and high viscosity and valves for emptying and low vacuum systems.
In short, the valve application, operating frequency and services are ever-changing, and it is necessary to control or eliminate even the smallest leaks. The most important and most critical equipment also counts valves. Learning to choose the correct valves is an important guarantee for ensuring the safe and smooth operation of the production line.
references:
[1] Wang Kehua. Process Instrumentation [M]. Beijing: Publishing House of Electronics Industry, 2007.
[2]Guo Haidong. Installation and Maintenance of Automation Devices [M]. Beijing: Chemical Industry Press, 2002.
[3] Zhou ZM. Process automation engineering design [M]. Beijing: Chemical Industry Press, 2011.
[4]Ren Lijing. Automation Control Instrument Operation in Chemical Industry[M]. Beijing: China University of Mining and Technology Press, 2013.
Keywords:valve;characteristics;type selection procedure;selection specification DOI:10.16640/j.cnki.37-1222/t.2018.07.054
Gansu Yinguang Juyin Chemical Co., Ltd. has an annual output of 100,000 tons of TDI devices with tens of thousands of valves of various types, but often run, run, drip or leak due to manufacturing, use selection, improper maintenance, etc. The resulting low product quality, increased energy consumption, equipment corrosion, and even causing parking accidents have become commonplace. At this time, new requirements have been put forward for valve operators, maintenance personnel and engineering technicians. In addition to correct operation of valves and timely inspection and maintenance, the steps and basis for understanding the classification, characteristics and structure of valves, and valve selection are also It becomes crucial.
1 Classification of Valves Valves come in a variety of types, including straight-through valves (single seat, double seat), angle valves, three-way valves, ball valves, and eccentric rotary valves. The overall can be divided into two categories: automatic valves and drive valves. Automatic valves are valves that rely on the ability of the medium (liquid, gas) itself to act on its own. Drive valves are valves that operate with manual, electric, hydraulic, and pneumatic actuation.
2 valve characteristics and structure (1) valve characteristics. 1) Use characteristics: Valve categories, such as: closed-circuit valves, regulating valves, safety valves, etc.; product types, such as: gate valve, butterfly valve, ball valve, etc.; valve main parts, including: valve body, valve cover, valve stem, valve core , sealing surface and so on. 2) Structural characteristics: The structural length and overall height of the valve are connected to the pipeline, such as: flange connection, threaded connection, welding end connection, etc.; the sealing surface is in the form of: thread ring, build-up welding, spray welding, valve body Etc.; stem structure, etc.
(2) The structure of the valve. There are many kinds of valves, mainly including upper and lower valve covers, valve bodies, valve cores, valve seats, packing and other components. According to different requirements, there are many types of structures. 1) The upper valve cover of the valve. The upper valve cover is located between the actuator and the valve body. In order to adapt to different operating temperatures and sealing requirements, there are four common structures. 1 common type, suitable for high temperature places, working temperature range is -20 ~ 200 °C. 2 suction (scattered) heat type, medium working temperature is -60 ~ 450 °C, the valve cover has a number of suction (dissipation) heat film, in order to ensure the sealing packing in the allowable temperature range. 3 long-neck type, suitable for deep frozen places, medium operating temperature range -250 ~ -60 °C. 4 Bellows sealed type, the valve rod movable part adopts bellows sealing, which can avoid medium leakage and personal poisoning and explosion accidents. It is suitable for strong toxic, volatile, easy to penetrate or valuable process media. 2) spool. A straight stroke valve can be divided into five types: flat plate type, plunger type, window type, multi-stage type and sleeve type. 2 angle stroke valve core, including eccentric rotary valve core, disc type valve core and spherical valve core, wherein the spherical valve core has "O" spherical valve and "V" spherical valve.
3 valve selection procedures and principles (1) valve selection procedures. 1) First of all, confirm the use of the valve in the equipment or device to determine the working conditions of the valve including the circulating medium, working pressure, working temperature and so on. 2) The nominal path of the valve and pipe connection (flange connection, screw connection or welding, etc.) and the connected pipe. 3) Confirm the control mode (manual, electric, pneumatic or hydraulic) of the valve and the form of the valve (gate valve, globe valve, ball valve, butterfly valve, diaphragm valve, throttle valve, safety valve, pressure reducing valve, etc.). 4) When selecting the valve body component material, the factors such as the corrosivity, temperature, pressure, cavitation and erosion of the process media are mainly considered. When considering factors such as cavitation and erosion, special alloys or special structural valves may be used. In general corrosion requirements, the valve body and valve core are often made of common stainless steel (1Cr18Ni9Ti). When corrosion resistance is high, two titanium stainless steels can be used. (Cr18Ni12Mo2Ti), also available in all titanium materials suitable for most corrosive media. 5) Confirm valve parameters and valve geometry. The valve parameters include: allowable flow resistance, discharge capacity, back pressure, nominal pipe diameter, etc. The geometric parameters of the valve include: flange spacing, flange connection and dimensions, number of bolts connected, overall valve size, etc.
(2) Select the principle of the valve. With suspended particles in the medium, if the closing member's back and forth movement of the valve seat is vertical, it is possible to hold the particles, so this valve is only suitable for basic cleaning media unless the sealing surface material can allow embedded particles. . Ball valve and plug valve wipe the sealing surface in the process of opening and closing, it is suitable for use in media with suspended particles.
4 Selection instructions for various types of valves (1) Ball valves. Ball valve according to the form of the valve can be divided into "O" ball valve and "V" ball valve two. The "V" ball valve has a "V" opening in the ball valve. During operation, the actuator push rod rotates the valve core through the ball valve and changes the opening area as the ball rotates. "V" type ball valve has simple flow path and large flow capacity. The valve seat is made of soft material and has reliable sealing. It is especially suitable for fibers, pulp, low temperature and high viscosity media. Sealing material requirements can also be used for the control of powdered and granular media.
(2) Butterfly valve. Butterfly valve, also known as flap valve, is a rotary valve. Mainly by the valve body, baffle, baffle shaft and crank parts and other components. Applicable to larger diameter and short structure requirements, as well as the need for flow adjustment and opening and closing requirements for rapid occasions, because the butterfly valve than the gate valve, ball valve pressure loss, so the butterfly valve is suitable for pressure loss is not strict in the piping system.
(3) Diaphragm valve. Diaphragm valve consists of valve body, diaphragm, valve core valve cover and valve stem and other components. The film moves the valve core up and down through the valve stem to change the flow area and achieve flow regulation. Diaphragm valve has simple structure, low flow resistance and large flow capacity, and can be used for the regulation of high viscosity and suspended particle fluids. For high corrosion sites such as strong acids and alkalis, the valve body lining can be rubber or PTFE, but the diaphragm The lining material is not resistant to high temperatures and the operating temperature should not exceed 150°C.
(4) Stop valve. The cut-off valve is suitable for pipelines and devices with strict requirements on fluid resistance, high-temperature and high-pressure medium, and the adjustment accuracy is not high, and the pipe diameter is relatively small. It is particularly recommended to use a cut-off valve.
(5) Plug valves. Plug valves are suitable for applications where fast switching is required. They are suitable for low temperature, high viscosity media or media with suspended particles. It is generally not suitable for steam and high temperature medium lines.
(6) Selection of gate valve. The gate valve has a wide range of applications and is applicable not only to steam, oil and other media, but also to media containing granular solids and high viscosity and valves for emptying and low vacuum systems.
In short, the valve application, operating frequency and services are ever-changing, and it is necessary to control or eliminate even the smallest leaks. The most important and most critical equipment also counts valves. Learning to choose the correct valves is an important guarantee for ensuring the safe and smooth operation of the production line.
references:
[1] Wang Kehua. Process Instrumentation [M]. Beijing: Publishing House of Electronics Industry, 2007.
[2]Guo Haidong. Installation and Maintenance of Automation Devices [M]. Beijing: Chemical Industry Press, 2002.
[3] Zhou ZM. Process automation engineering design [M]. Beijing: Chemical Industry Press, 2011.
[4]Ren Lijing. Automation Control Instrument Operation in Chemical Industry[M]. Beijing: China University of Mining and Technology Press, 2013.
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