Valve technical requirements and species analysis
2023-02-11 04:07:15
Valves are control elements in fluid piping systems. Their main function is to isolate equipment and piping systems, regulate flow, prevent backflow, regulate and drain pressure. Because it is important to select the most suitable valve for the piping system, understanding the characteristics of the valve and the steps and the basis for selecting the valve also become crucial.
The valve industry has so far been able to produce a wide range of butterfly valves, gate valves, globe valves, ball valves, check valves, hydraulic control valves, diaphragm valves, regulating valves, pressure reducing valves, plug valves, plunger valves, steam traps, and power stations. Valves, American standard valves, hydraulic control valves and other 12 categories, more than 3,000 models, more than 4000 specifications of the valve products; the maximum working pressure of 600MPa, the maximum nominal diameter of 5350mm, the maximum operating temperature of 1200 °C, the minimum operating temperature For -196°C, the applicable medium is water, steam, oil, natural gas, highly corrosive media, flammable media (such as stupid, ethylene, etc.), toxic media (such as hydrogen sulfide), explosive media, and radioactive media (metal Sodium, - circuit water, etc.). Pressure-bearing parts for valves Cast copper, cast iron, ductile iron, high-silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless acid-resistant steel, Hastelloy, Inconel, Monel, duplex stainless steel , titanium alloys, etc. And can produce a variety of electric, pneumatic, hydraulic valve drive. Faced with so many valve types and such a variety of working conditions, we must choose the most suitable valve system for the installation of the valve product, I think, first of all should understand the characteristics of the valve; Second, we should master the steps and basis for the choice of valve; Follow the principle of selecting the valve.
1. There are two general characteristics of the valve, use characteristics and structural characteristics.
Usage characteristics: It determines the main performance of the valve and the use of the valve, belonging to the valve use characteristics are: the type of valve (closed-circuit valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.) Valve main parts (valve body, valve cover, stem, valve disc, sealing surface) materials; valve transmission methods. Structural characteristics: It determines some of the structural characteristics of the valve installation, maintenance, maintenance and other methods, belonging to the structural characteristics: the valve structure length and overall height, and the connection of the pipeline (flange connection, threaded connection, clamp connection , external thread connection, welding end connection, etc.); the form of the sealing surface (inset ring, thread ring, build-up welding, spray welding, valve body); valve stem structure (rotating rod, lifting rod).
2. The steps and basis for selecting the valve are as follows:
(1) Select Step 1 to clarify the use of the valve in the device or device to determine the valve's operating conditions: the applicable media, working pressure, operating temperature, and so on.
2 Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.
3 determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.
4 According to the pipeline conveying medium, working pressure, working temperature to determine the selected valve housing and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloys.
5 Select the type of valve: closed-circuit valve, regulating valve, safety valve and so on.
6 determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, and so on.
(2) The basis for selecting the valve While understanding the steps for selecting the valve, it is also necessary to further understand the basis for selecting the valve.
1 The use of selected valves, operating conditions and operating control methods.
2 The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, viscosity of the medium and so on.
3 requirements for valve fluid properties: flow resistance, discharge capacity, flow characteristics, seal rating, and more.
4 Installation Dimensions and Dimensions Requirement: Nominal diameter, connection to the pipe and connection dimensions, dimensions or weight restrictions.
5 Additional requirements for the valve's reliability, service life, and explosion-proof performance of electrical devices.
(At the time of parameter selection, it should be noted that 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 at closing, maximum and minimum inlet of the valve pressure.)
According to the basis and steps of selecting the valve, the internal structure of each type of valve must be understood in detail when selecting the valve rationally and correctly, so that the correct choice of valve can be made.
The final control of the pipeline is the valve. Valve opening and closing parts control the flow pattern of the medium in the pipeline. The shape of the valve flow path allows the valve to have a certain flow characteristic. This must be taken into consideration when selecting the piping system that is most suitable for installing the valve.
The following are the principles to follow when choosing a valve:
(1) Valve flow channels for cut-off and open media are straight-through valves with a low flow resistance and are usually selected as valves for shut-off and open media. Down-closed valves (stop valves, plunger valves) are less preferred because of their tortuous flow paths and higher flow resistance than other valves. Where higher fluid resistance is permitted, closed valves may be used.
(2) Valves for controlling flow rate Usually, valves that are easy to adjust the flow rate are used as control flow. A closed down valve, such as a shutoff valve, is suitable for this purpose because of the proportional relationship between its seat size and the stroke of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexible valve body valves (pinch valves, diaphragm valves) can also be used for throttling control, but they are usually only suitable for limited valve diameters. The gate valve is a disk-shaped gate that cross-cuts the circular valve seat. It can control the flow only when it is close to the closed position, so it is usually not used for flow control.
(3) Valves for commutation diverting The valve may have three or more channels depending on the need for commutation diversion. Plug valves and ball valves are more suitable for this purpose. Therefore, most of the valves used for commutation and diversion have selected one of these types of valves. However, in some cases, other types of valves can also be used for commutation diverting as long as two or more valves are properly connected to each other.
(4) Valves for media with suspended particles When the medium contains suspended particles, it is best to use a sliding valve with a wiper action along its sealing surface. If the closing member's back and forth movement of the valve seat is vertical, it is possible to hold the particles, and thus this valve is only suitable for a substantially clean medium unless the material of the sealing surface 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.
At present, whether in petroleum, chemical, or in other industries, pipeline systems, valve applications, operating frequencies and services are ever-changing, to control or eliminate even the slightest leakage, the most important and most critical equipment is also a few valves. The final control of the pipeline is the valve. The service and reliable performance of the valve in all areas is unique.
The valve industry has so far been able to produce a wide range of butterfly valves, gate valves, globe valves, ball valves, check valves, hydraulic control valves, diaphragm valves, regulating valves, pressure reducing valves, plug valves, plunger valves, steam traps, and power stations. Valves, American standard valves, hydraulic control valves and other 12 categories, more than 3,000 models, more than 4000 specifications of the valve products; the maximum working pressure of 600MPa, the maximum nominal diameter of 5350mm, the maximum operating temperature of 1200 °C, the minimum operating temperature For -196°C, the applicable medium is water, steam, oil, natural gas, highly corrosive media, flammable media (such as stupid, ethylene, etc.), toxic media (such as hydrogen sulfide), explosive media, and radioactive media (metal Sodium, - circuit water, etc.). Pressure-bearing parts for valves Cast copper, cast iron, ductile iron, high-silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless acid-resistant steel, Hastelloy, Inconel, Monel, duplex stainless steel , titanium alloys, etc. And can produce a variety of electric, pneumatic, hydraulic valve drive. Faced with so many valve types and such a variety of working conditions, we must choose the most suitable valve system for the installation of the valve product, I think, first of all should understand the characteristics of the valve; Second, we should master the steps and basis for the choice of valve; Follow the principle of selecting the valve.
1. There are two general characteristics of the valve, use characteristics and structural characteristics.
Usage characteristics: It determines the main performance of the valve and the use of the valve, belonging to the valve use characteristics are: the type of valve (closed-circuit valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.) Valve main parts (valve body, valve cover, stem, valve disc, sealing surface) materials; valve transmission methods. Structural characteristics: It determines some of the structural characteristics of the valve installation, maintenance, maintenance and other methods, belonging to the structural characteristics: the valve structure length and overall height, and the connection of the pipeline (flange connection, threaded connection, clamp connection , external thread connection, welding end connection, etc.); the form of the sealing surface (inset ring, thread ring, build-up welding, spray welding, valve body); valve stem structure (rotating rod, lifting rod).
2. The steps and basis for selecting the valve are as follows:
(1) Select Step 1 to clarify the use of the valve in the device or device to determine the valve's operating conditions: the applicable media, working pressure, operating temperature, and so on.
2 Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.
3 determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.
4 According to the pipeline conveying medium, working pressure, working temperature to determine the selected valve housing and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloys.
5 Select the type of valve: closed-circuit valve, regulating valve, safety valve and so on.
6 determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, and so on.
(2) The basis for selecting the valve While understanding the steps for selecting the valve, it is also necessary to further understand the basis for selecting the valve.
1 The use of selected valves, operating conditions and operating control methods.
2 The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, viscosity of the medium and so on.
3 requirements for valve fluid properties: flow resistance, discharge capacity, flow characteristics, seal rating, and more.
4 Installation Dimensions and Dimensions Requirement: Nominal diameter, connection to the pipe and connection dimensions, dimensions or weight restrictions.
5 Additional requirements for the valve's reliability, service life, and explosion-proof performance of electrical devices.
(At the time of parameter selection, it should be noted that 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 at closing, maximum and minimum inlet of the valve pressure.)
According to the basis and steps of selecting the valve, the internal structure of each type of valve must be understood in detail when selecting the valve rationally and correctly, so that the correct choice of valve can be made.
The final control of the pipeline is the valve. Valve opening and closing parts control the flow pattern of the medium in the pipeline. The shape of the valve flow path allows the valve to have a certain flow characteristic. This must be taken into consideration when selecting the piping system that is most suitable for installing the valve.
The following are the principles to follow when choosing a valve:
(1) Valve flow channels for cut-off and open media are straight-through valves with a low flow resistance and are usually selected as valves for shut-off and open media. Down-closed valves (stop valves, plunger valves) are less preferred because of their tortuous flow paths and higher flow resistance than other valves. Where higher fluid resistance is permitted, closed valves may be used.
(2) Valves for controlling flow rate Usually, valves that are easy to adjust the flow rate are used as control flow. A closed down valve, such as a shutoff valve, is suitable for this purpose because of the proportional relationship between its seat size and the stroke of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexible valve body valves (pinch valves, diaphragm valves) can also be used for throttling control, but they are usually only suitable for limited valve diameters. The gate valve is a disk-shaped gate that cross-cuts the circular valve seat. It can control the flow only when it is close to the closed position, so it is usually not used for flow control.
(3) Valves for commutation diverting The valve may have three or more channels depending on the need for commutation diversion. Plug valves and ball valves are more suitable for this purpose. Therefore, most of the valves used for commutation and diversion have selected one of these types of valves. However, in some cases, other types of valves can also be used for commutation diverting as long as two or more valves are properly connected to each other.
(4) Valves for media with suspended particles When the medium contains suspended particles, it is best to use a sliding valve with a wiper action along its sealing surface. If the closing member's back and forth movement of the valve seat is vertical, it is possible to hold the particles, and thus this valve is only suitable for a substantially clean medium unless the material of the sealing surface 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.
At present, whether in petroleum, chemical, or in other industries, pipeline systems, valve applications, operating frequencies and services are ever-changing, to control or eliminate even the slightest leakage, the most important and most critical equipment is also a few valves. The final control of the pipeline is the valve. The service and reliable performance of the valve in all areas is unique.
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