Our goal: to be a high-quality manufacturer of industrial control valves, gaining unanimous recognition from new and old customers
Our mission: To fully utilize the effectiveness of industrial control valves to achieve better results
Regulating valve, also known as control valve, is a final control element in the field of industrial automation process control that receives control signals from the regulating control unit and uses power operation to change process parameters such as medium flow, pressure, temperature, and liquid level. Generally, it consists of an actuator and a valve. According to stroke characteristics, the regulating valve can be divided into straight stroke and angular stroke; According to the power used by its equipped actuator, it can be divided into three types according to its function and characteristics: linear characteristics, equal percentage characteristics, and parabolic characteristics. The regulating valve is suitable for air, water, steam, various corrosive media, mud, oil, and other media. English name: control valve, the tag number usually starts with FV. Common classification of control valves: pneumatic control valves, electric control valves, hydraulic control valves, self operated control valves.
summary
In the automatic control of modern chemical plants, regulating valves play a very important role. The production of these plants depends on the correct distribution and control of flowing media. Whether these controls are energy exchange, pressure reduction, or simple container feeding, certain final control elements are required to complete them.
The regulating valve acts as a variable resistance in the pipeline. It changes the turbulence level of the process fluid or provides a pressure drop in laminar flow situations caused by changing valve resistance or "friction.". This pressure reduction process is commonly referred to as "throttling.". For a gas, it is close to an isothermal adiabatic state, and the deviation depends on the non ideal degree of the gas (Joule Thomson effect). In the case of liquids, pressure is consumed by turbulence or viscous friction, both of which convert pressure into heat energy, resulting in a slight increase in temperature.
A common control loop consists of three main parts. The first part is a sensitive element, which is typically a transmitter. It is a device that can be used to measure the adjusted process parameters, such as pressure, liquid level, or temperature. The output of the transmitter is sent to a regulating instrument, a regulator, which determines and measures the deviation between a given or expected value and the actual value of the process parameters, and one by one sends the correction signal to the final control element, the regulating valve. The valve changes the flow rate of the fluid, making the process parameters reach the desired value.
The regulating valve belongs to the control valve series, and its main function is to regulate the pressure, flow, temperature, and other parameters of the medium. It is the final control element in the process loop.
Basic information
The regulating valve, also known as a control valve, receives control signals from the regulating control unit and uses power operation to change the fluid flow. The regulating valve generally consists of an actuator and a valve. According to the power used by the actuator, the control valve can be divided into three types: pneumatic control valve, electric control valve, and hydraulic control valve. In addition, according to its functions and characteristics, it can be divided into three types: linear characteristics, equal percentage characteristics, and parabolic characteristics.
Valve body type
There are many types of valve bodies for regulating valves, including straight single seat, straight double seat, angular, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve, spherical, and so on.
When making specific choices, the following considerations can be made:
(1) Valve core shape and structure
It is mainly considered based on factors such as selected flow characteristics and unbalanced forces.
(2) Abrasion resistance
When the fluid medium is a suspension containing high concentrations of abrasive particles, the internal material of the valve should be hard.
(3) Corrosion resistance
Due to the corrosive nature of the medium, valves with a simple structure should be selected as far as possible.
(4) Temperature and pressure of medium
When the temperature and pressure of the medium are high and vary greatly, valves with small temperature and pressure changes in the material of the valve core and valve seat should be selected. When the temperature is ≥ 250 ℃, a radiator should be added.
(5) Prevent flash and cavitation
Flash and cavitation occur only in liquid media. In the actual production process, flash and cavitation can form vibration and noise, shortening the service life of the valve. Therefore, when selecting a valve, it is necessary to prevent flash and cavitation of the valve.
Regulating valve actuator
In order to ensure the normal operation of the regulating valve, the equipped actuator should be able to generate sufficient output force to ensure a high seal and valve opening.
For double acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The magnitude of the force is independent of its operating direction, so the key to selecting an actuator is to understand the large output force and the rotational torque of the motor. For single acting pneumatic actuators, the output force is related to the opening of the valve, and the force appearing on the regulating valve will also affect the motion characteristics. Therefore, it is required to establish a force balance across the entire opening range of the regulating valve.
After determining the output force of the actuator, select the corresponding actuator according to the process usage environment requirements. When there are explosion-proof requirements on site, pneumatic actuators should be selected. From the perspective of energy conservation, electric actuators should be selected as much as possible. If the adjustment accuracy is high, a hydraulic actuator can be selected. Such as speed regulation of transparent machines in power plants, temperature regulation and control of catalytic device reactors in refineries, etc.
The action mode of the regulating valve is only available when selecting a pneumatic actuator, and its action mode is formed by combining the positive and negative actions of the actuator and the positive and negative actions of the valve. There are four types of combinations, namely, positive and negative (air close type), positive and negative (air open type), positive and negative (air open type), and negative (air close type). The regulating valves formed through these four combinations have two modes of action: air open and air close.
The selection of the action mode of the control valve is mainly considered from three aspects: a) process production safety; b) Characteristics of the medium; c) Ensure product quality and reduce economic losses.
classification
The regulating valve can be divided into straight stroke and angular stroke according to stroke characteristics. Straight stroke includes: single seat valve, double seat valve, sleeve valve, cage valve, angle valve, three-way valve, diaphragm valve; Angular stroke includes: butterfly valve, ball valve, eccentric rotary valve, full function ultra light regulating valve.
The regulating valve can be divided into manual regulating valve, pneumatic regulating valve, electric regulating valve, and hydraulic regulating valve according to the driving mode, namely, pneumatic regulating valve using compressed air as the power source, electric regulating valve using electricity as the power source, and hydraulic regulating valve using liquid medium (such as oil) pressure as the power source;
According to the regulation form, it can be divided into: regulation type, cut-off type, regulation cut-off type;
According to flow characteristics, it can be divided into linear, logarithmic (percentage), parabolic, and fast opening.
development history
The development of control valves has a history of 80 years since the beginning of the 20th century. There have been ten major categories of control valve products, self operated valves, and positioners. The development history of control valves and control valves is as follows:
In the 1920s, the original regulating valve for stabilizing pressure came out.
In the 1930s, V-shaped regulating ball valves, represented by "V-shaped" notched double seat valves and single seat valves, were introduced.
In the 1940s, locators emerged, and new types of control valves were further developed, including diaphragm valves, angle valves, butterfly valves, and ball valves.
In the 1950s, ball valves were widely promoted and used, with three-way valves replacing two single seat valves being put into the system.
In the 1960s, after the series improvement design, standardization, and standardization of the above products were carried out in China, a complete series of products were available in China. The seven products we are still using in large quantities, namely, single seat valve, double seat valve, angle valve, three-way valve, diaphragm valve, butterfly valve, and ball valve, are still at the level of the 1960s. At this time, foreign countries began to introduce the eighth structural control valve - sleeve valve.
In the 1970s, another product with a new structure, the eccentric rotary valve, was introduced (the ninth largest type of control valve with a structure). During this period, sleeve valves were widely used abroad. In the late 1970s, the domestic joint design of sleeve valves enabled China to have its own series of sleeve valve products.
In the 1980s, during the period of reform and opening up, China successfully introduced petrochemical devices and control valve technology, making sleeve valves and eccentric rotary valves widely used. In particular, sleeve valves have a strong tendency to replace single and double seat valves, and their use is becoming increasingly widespread. At the end of the 1980s, another major development in regulating valves was the Cv3000 and precision and small regulating valves in Japan. In terms of structure, they changed the single spring pneumatic diaphragm actuator to a multi spring diaphragm actuator. The structure of the valve was only improved, not changed. Its outstanding feature is to reduce the weight and height of the regulating valve by 30%, and increase the flow coefficient by 30%.
1990s: In the 1990s, the focus of regulating valves was on tackling, improving, and improving reliability and special and difficult products. By the end of the 1990s, Hualin Company had launched the tenth structure product - a fully functional ultra light valve. Its outstanding characteristics are breakthroughs in reliability, functionality, and weight. Functional breakthrough - a fully functional product, so one product can replace many products with incomplete functions, simplifying selection, use, and variety; Breakthrough in weight - 70 to 80% lighter than leading products such as single seat valves, double seat valves, and sleeve valves, and 40 to 50% lighter than precision and small valves; Breakthrough in reliability - solves various unreliable factors such as traditional control valves, such as sealing reliability, positioning reliability, and action reliability. The advent of this product has brought China's control valve technology and application level to the level of the late 1990s; It is a major breakthrough in regulating valves; In particular, electronic full-function ultra-light valves will definitely become the mainstream of control valves in the next century.
Maintenance
The regulating valve should be maintained after normal operation. As a part of the automation control system, the maintenance of the regulating valve should be carried out simultaneously with the automation instruments and other equipment.
The maintenance of regulating valves is similar to that of general instruments, and can be divided into passive maintenance, preventive maintenance, and predictive maintenance. Passive maintenance is a maintenance method that only performs maintenance when equipment such as control valves fails. Due to equipment failures that require maintenance, the production process is often shut down, and in severe cases, equipment damage or casualties may occur. Passive maintenance is unwanted maintenance during the production process. Preventive maintenance is a maintenance method that is based on past operating experience and performed on a time basis. For example, the commonly used periodic maintenance is preventive maintenance, which establishes corresponding maintenance schedules based on the operating conditions of different equipment, and performs maintenance before the equipment fails. Since maintenance is performed without a fault occurring, the probability of a fault occurring can be greatly reduced. However, this maintenance method does not analyze the actual situation of the currently used regulating valve, and often disassembles and inspects the regulating valve that can still be used for a certain period of time, wasting time and resources. Predictive maintenance starts from analyzing the data of the currently used regulating valve, anticipating the state of the regulating valve, thereby maximizing the utilization of the regulating valve.
1、 Daily maintenance work content of control valve
The daily maintenance work of the control valve is divided into two parts: patrol inspection and regular maintenance. The patrol inspection work is as follows.
1. Ask the process operator on duty about the operation of the control valve.
2. Check the supply energy (air source, hydraulic oil, or power supply) of the regulating valve and related accessories
3. Check the operation of the hydraulic oil system.
4. Check the static and dynamic sealing points of the regulating valve for leakage.
5. Check the connecting pipelines and connectors of the control valve for looseness or corrosion.
6. Check the regulating valve for abnormal sound and large vibration, and check the supply condition.
7. Check whether the action of the regulating valve is flexible and whether it changes in time when the control signal changes
8. Listen for abnormal vibration or noise in the valve core and valve seat.
9. Timely contact and handle any problems found.
10. Make records of patrol inspections and file them.
The contents of regular maintenance work are as follows:
1. Regularly clean the outside of the regulating valve.
2. Regularly adjust the stuffing box and other sealing components of the control valve, and replace the sealing components if necessary to maintain the tightness of the static and dynamic sealing points.
3. Regularly add lubricating oil to the parts to be lubricated.
4. Regularly drain and clean the air source or hydraulic filtration system.
5. Regularly check the connection and corrosion conditions of each connection point, and replace the connecting pieces if necessary.
2、 Periodic calibration of control valves
Units that have not yet carried out predictive maintenance work on regulating valves should conduct regular calibration of regulating valves. Periodic calibration is preventive maintenance work.
According to different production processes, the periodic calibration of control valves should have different calibration cycles. The periodic calibration cycle of each regulating valve can be determined based on the information provided by the manufacturer. It can usually be carried out simultaneously with the overhaul of the process production process. When some control valves are used in high-pressure, high-pressure drop, or highly corrosive situations, the inspection cycle should be shortened.
The main content of the inspection is the static performance test of the regulating valve. If necessary, corresponding test items can be added, such as the flow characteristic test of the regulating valve. Regular calibration requires relevant testing equipment and instruments, as well as replacement parts, so it can usually be entrusted to the manufacturer.
3、 Maintenance of regulating valve
The maintenance of regulating valves includes emergency maintenance, periodic maintenance, and predictive maintenance. Emergency maintenance refers to the maintenance when the control valve fails and cannot meet the process operation requirements. Regular maintenance usually includes routine maintenance and maintenance conducted concurrently with process shutdown and overhaul. Predictive maintenance refers to targeted maintenance of relevant control valve components based on the analysis results of predictive maintenance. Emergency maintenance refers to the maintenance after the failure of the regulating valve, while regular maintenance and predictive maintenance refer to the maintenance before the failure of the regulating valve. Generally, routine maintenance of control valves is performed by instrument maintenance personnel, and periodic maintenance conducted simultaneously with major repairs is performed by manufacturing technicians.
1） The daily inspection and maintenance of the control valve includes the following:
1. Stress relief. Various stresses due to improper installation or assembly. For example, high temperature media generate thermal stress, resulting in tight installation, and stress due to unbalanced solid forces. Unbalanced stress acts on the regulating valve, causing deformation of the valve stem and guide parts, and improper alignment with the valve seat, resulting in leakage and increased variation. Therefore, stress relief maintenance should be carried out in daily maintenance.
2. Remove rust and dirt. Regularly inspect the connecting pipe of the regulating valve for rust, welding slag, dirt, etc., and promptly remove them if found. Because these contaminants can cause wear on the valve core and valve seat of the regulating valve, affecting the normal operation of the regulating valve. Generally, filter devices such as filter screens can be installed in front of the control valve and cleaned regularly.
3. Check the control valve support. The support of the regulating valve keeps the components of the regulating valve in a position that is not affected by gravity, etc. Improper support will cause the valve stem and valve seat of the control valve to be misaligned, resulting in increased variation and reduced sealing performance. Therefore, check whether the control valve support is suitable.
4. Remove the dirt that supplies energy such as air supply and hydraulic oil. Air and hydraulic sources are the energy sources for regulating valve operation. Impurities contained in instrument compressed air and hydraulic oil can clog orifices and pipes, causing failures. Therefore, it is important to regularly check the air source and hydraulic oil, and regularly drain the filter device.
5. Inspection of gear transmission device. Gear transmission devices of hand wheel mechanisms, electric actuators, and hydraulic actuators should be regularly inspected and lubricated to prevent seizure. Check whether the braking and limit devices are flexible and easy to use.
6. Packing box inspection. The wear and compression force of the packing should be checked, and the stuffing box should be replaced regularly to ensure that the packing can function as a seal while reducing its friction. Do not add lubricating oil to the stuffing box without oil lubrication.
7. Inspection of safe operation. For regulating valves and related accessories used in explosive hazardous locations, their safe operation should be checked, such as whether the sealing cap is tightened, the operation of the safety barrier, and the power supply to ensure that the regulating valves and related accessories can operate safely.
8. Transportation and storage. During transportation and storage, the regulating valve should be fixed with a special bracket to prevent loosening; Relevant accessories installed on the regulating valve, such as valve positioner, handwheel mechanism, etc., should be firm, and the feedback rod and other components connected to the regulating valve should be prevented from being damaged by external forces; Each connecting interface shall be sealed with plastic film to prevent foreign objects from entering; The connecting port of the regulating valve can be sealed with matching flanges and blind plates, or sealed with adhesive paper to prevent foreign objects from entering. During transportation, solid wooden boxes should be added, and measures should be taken to prevent the impact of adverse transportation environmental conditions such as wind, sand, rain, and dust. The environmental conditions for transportation and storage should meet the requirements of the product manual.
2） The main contents of daily maintenance of control valves and accessories are as follows:
1. Replacement of the pneumatic actuator diaphragm. The diaphragm of a pneumatic membrane actuator is subject to expansion and contraction during operation, so it is prone to fatigue damage. During replacement, rubber membranes of the same specification should be used. When tightening, the membrane should be evenly stressed to prevent leakage and damage to the membrane.
2. Grinding. Leakage occurs between the valve core and valve seat after a certain period of operation, and internal leakage can also occur between the piston and cylinder of the cylinder. Therefore, grinding should be carried out. Methods such as manual grinding, mechanical grinding, plating treatment, and bushing can be used. The grit size for grinding should be appropriate, and the grinding force should be uniform and appropriate. After grinding, it should be polished to meet the required smoothness and accuracy requirements, as well as the alignment requirements of the valve core and valve seat. After final assembly, a sealing test should be conducted.
3. Replacement of stuffing box.. When replacing the stuffing box, the same type of stuffing box should be used. When replacing, the packing should be carefully pulled out, and the packing should be properly removed to prevent damage to the valve stem. The installation of new stuffing boxes should be in accordance with the requirements of the instructions, and the cutouts should be misaligned to prevent scratching of the packing by the threads of the valve rod. The compression force of the packing should be uniform and appropriate to prevent stress and increased friction.
4. Replacement of transmission components. If the transmission components in the control valve and accessories are partially worn, they can be replaced or repaired. After replacement and repair, ensure flexible transmission and minimize transmission clearance.
5. Cleaning of pneumatic amplifiers. When the throttle hole of the pneumatic amplifier is blocked due to dirt in the compressed air for instrument use, the throttle hole should be cleaned, and suitable steel wires can be used for dredging and cleaning. During reassembly, the amplifier membrane should be evenly stressed to prevent clogging or leakage. The amplifier gain can be adjusted by adjusting the pressing force of the steel ball to prevent resonance. Shanghai Linuo Anticorrosive Valve Manufacturing Co., Ltd. is a group enterprise specializing in the production, research, development, and sales of various types of valves, pumps, and control equipment, mainly composed of Linuo Valves, Linuo Pumps, and Linuo Industries. Its headquarters are located in Huangdu Industrial Park, Jiading District, Shanghai. The main products include diaphragm valves, control valves, butterfly valves, globe valves, check valves, ball valves, gate valves, pressure reducing valves, safety valves, and American and British standard valve series. Deeply developing fluorine lined rubber lined valves, stainless steel valves, and other electrically operated valves is our long-term development goal. The products are designed and manufactured using domestic and foreign standards such as ISO, API, ANSI, BS, DIN, NF, JIS, GB, IB, etc. It is characterized by reasonable structure, exquisite manufacturing technology, complete specifications, and stable quality, and is widely used in petroleum, chemical, natural gas, electric power, metallurgy, pharmaceutical, construction, water supply, and other industries with three major performances: usability, scalability, and reliability. "We are committed to exploring the international market and are exported to countries and regions such as the United States, Canada, Germany, and the Middle East. We are deeply praised and trusted by users.".
CV value
The flow capacity Cv value () is one of the main parameters for selecting a control valve. The flow capacity of the control valve is defined as: when the control valve is fully open, the pressure difference between both ends of the valve is 0.1MPa, and the fluid density is 1g/cm3, the flow rate of the flow path control valve per hour is called the flow capacity, also known as the flow coefficient, expressed in Cv, in t/h, and the Cv value of the liquid is calculated using the following formula.
The nominal diameter DN of the regulating valve can be determined by looking up the table based on the flow capacity Cv value.
application
In the automatic control of modern chemical plants, regulating valves play a very important role. The production of these plants depends on the correct distribution and control of flowing liquid and gas. Whether these controls are energy exchange, pressure reduction, or simple container feeding, certain final control elements are required to complete them. The final control element can be considered as the "physical force" of automatic control. The final control element performs the necessary power amplification function between the low energy level of the regulator and the high energy level functions required to perform flow fluid control.
The regulating valve is a widely used type of final control element. Other final control elements include metering pumps, regulating dampers, and louvered dampers (a variant of butterfly valves), variable pitch fan blades, current regulators, and motor positioning devices that are different from valves.
Although regulating valves are widely used, other units in the regulating system probably do not require as little maintenance work as it does. In many systems, the operating conditions such as temperature, pressure, corrosion and pollution experienced by the regulating valve are more serious than those of other components. However, when it controls the flow of process fluid, it must operate satisfactorily and require less maintenance.
In the pneumatic regulating system, the pneumatic signal output by the regulator can directly drive the spring diaphragm actuator or piston actuator to make the valve act. In this case, the energy required to determine the valve position is provided by compressed air, which should be dried in outdoor equipment to prevent freezing, and should be purified and filtered.
When a pneumatic control valve and an electric regulator are used together, an electro-pneumatic valve positioner or an electro-pneumatic converter can be used. Compressed air supply systems can be considered in the same way as fully pneumatic regulation systems.
In terms of regulation theory, the regulating valve has both static and dynamic characteristics, so it affects the success or failure of the whole control circuit. The static characteristic or gain term is the flow characteristic of a valve, which depends on the size of the valve, the combined structure of the valve core and seat, the type of actuator, the valve positioner, the pressure before and after the valve, and the nature of the fluid. These will be described in detail in Chapter 5.
The dynamic characteristics are determined by a combination of actuator or valve positioner and actuator. For slower production processes, such as temperature control or liquid level control, the dynamic characteristics of the valve are generally not a limiting factor in terms of controllability. For faster systems, such as liquid flow control, the regulating valve may have significant hysteresis, and consideration must be given to the controllability of the circuit. Generally, only experts in control systems need to be concerned about the dynamic stability of regulating valves. Formal considerations regarding the application of valve positioners, as discussed in Chapter 9, will meet the needs of most regulating valve devices.
The history of automatic regulating valves can be traced back to self operated pressure regulating valves, which include a spherical valve with a weight lever used to balance the force of the valve core, thereby achieving some degree of regulation. Another early form of self operated pressure regulating pin is a pressure balanced pressure regulating valve. The pressure of the process is piped to the membrane gas chamber of the spring membrane pressure regulating valve. Whether it is a pressure reducing valve, a pressure regulating valve behind the valve, or a differential pressure regulating valve, it can be manufactured from the change of this base type valve.
The emergence of pneumatic transmitters and regulators inevitably led to the application of pneumatic throttle valves. They are essentially pressure reducing valves or pressure regulating valves that use instrument compressed air instead of the process fluid. Many companies that produce pressure reducing valves have developed into regulating valve manufacturers. The application of control valves continues to develop in terms of quantity and complexity, and improvements in the valve bodies and accessories of many valves can be used to solve various problems. The purpose of this manual is to familiarize engineers with the intricacies and factors of regulating valves, and to help instrument engineers choose valve bodies, actuators, and accessories in their applications.
The regulating valve can be divided into straight stroke and angular stroke according to stroke characteristics. Straight stroke includes: single seat valve, double seat valve, sleeve valve, angle valve, three-way valve, diaphragm valve; Angular stroke includes: butterfly valve, ball valve, eccentric rotary valve, full function ultra light regulating valve. The regulating valve can be divided into pneumatic regulating valve, electric regulating valve, and hydraulic regulating valve according to the driving mode; According to the regulation form, it can be divided into: regulation type, cut-off type, regulation cut-off type; According to flow characteristics, it can be divided into linear, equal percentage, parabolic, and fast opening. The regulating valve is suitable for air, water, steam, various corrosive media, mud, oil, and other media.
