Thread Content
When installing electric control valves, it is necessary to properly address the issues related to the valve as soon as it is received on site. The operator must adjust the electric control valve at each stage of its installation; handling it carelessly may cause a **delay** in the device starting up. Electric control valves are important actuator instruments in industrial automation process control, offering advantages such as stable performance, flexible operation, high reliability, and easy maintenance. What issues should users be aware of when using electric control valves? The following outlines the key points for using electric control valves, in the hope of helping users make better use of these products. Sensors and transmitters are used to detect the controlled variable and convert the detection signal into a standard signal. For example, a thermistor converts temperature changes into resistance changes, while a temperature transmitter converts the resistance signal into standard pressure or current, voltage signals, etc. The controller compares the standard signal output by the sensing and transmitting element with the setpoint signal to obtain an error signal; it then processes this error signal according to certain control rules, and the resulting output is sent to the actuator. Controllers can be implemented using analog instruments, or they can be digital controllers made up of microprocessors, such as the PID control modules used in DCS and FCS systems. The importance of control valves: Control valves are used to regulate the flow rate of the controlled variable. From the perspective of an entire control system, whether such a system functions well or not depends on the use of control valves. For the following reasons, control valves become extremely important. 1. Control valves are throttling devices and belong to the category of moving components. Compared with sensing elements, transmitters, and controllers, during the control process, control valves need to continuously change the flow area of the flow elements in order to adjust the control variable and thus adapt to changes in load or operating conditions. Therefore, higher requirements are placed on the sealing, pressure resistance, and corrosion resistance of control valve assemblies. For example, sealing can increase the friction in control valves and widen their dead zones, resulting in a decline in the control quality of the control system. 2. The moving parts of control valves are the main cause of problems such as leakage, emission, dripping, and seepage. They not only lead to waste of resources or materials but also pollute the environment and cause accidents. 3. The internal components of a control valve come into direct contact with the process medium, and the differences between these components and the sensing elements that also come into contact with the process medium are as follows: a. The medium in contact with the components of a control valve may differ from the medium in contact with the sensing elements, which imposes higher requirements on the control valve’s corrosion resistance, strength, stiffness, and material properties. b. The sensing element can be isolated from the process medium using methods such as an isolation fluid, but control valves typically come into direct contact with the process medium, making it difficult to isolate them from this medium using such methods. 4. The throttling action of the control valve results in energy being consumed within its internal components; therefore, it is necessary to make a balanced choice that takes into account reducing energy consumption, minimizing the pressure loss of the control valve, and ensuring good control quality. 5. The control valve causes noise while throttling the fluid. For example, when the pressure at the valve outlet is lower than the vapor pressure of the liquid, flash evaporation occurs ； Cavitation occurs when the pressure downstream of the valve is higher than the vapor pressure of the liquid. The noise generated by control valves is related to factors such as the design of their flow paths, operating pressure, and the properties of the medium being controlled; therefore, reducing noise and pressure losses imposes higher requirements on control valves. 6. The control valve has strong adaptability. It is installed in various production processes. Operating conditions such as low and high temperatures, high and low pressures, large and small flow rates require control valves to possess various functions, and these valves must be able to meet the demands of different stress levels. Key points for using electric control valves: (1) Control valves are field instruments; the operating temperature should be within the range of -25 to 60°C, with a relative humidity of ≤95%. If it is installed in an outdoor or high-temperature environment, waterproofing and cooling measures should be taken. In areas where there are sources of vibration, one should stay away from them or take additional vibration prevention measures. ⑵Control valves should generally be installed vertically; in special cases, they can be tilted. If the tilt angle is large or if the valve’s own weight is too great, support members should be added to protect the valve. ⑶Pipes equipped with control valves should generally not be too high above the ground or floor. When the pipe height exceeds 2 meters, a platform should be provided as much as possible to facilitate the operation of the handwheel and ease maintenance. ⑷Before installing the control valve, the pipeline should be cleaned to remove dirt and slag. After installation, to ensure that no impurities remain inside the valve body, it is necessary to clean the valve again; that is, all valves should be opened when the medium is introduced, to prevent impurities from getting stuck. After using the handwheel mechanism, it should be returned to its original neutral position. ⑸To enable the production process to continue in the event of a failure or maintenance of the control valve, a bypass line should be provided for it. Special attention should also be paid to whether the installation location of the electric control valve meets the requirements of the process. ⑹The installation of the electrical components of electric control valves shall be carried out in accordance with the relevant construction requirements for electrical equipment. In the case of flameproof products, they shall be installed in accordance with the requirements of the \"Code for Installation of Electrical Equipment in Explosive Atmospheres\". If the wires on site are of the SBH type or other six-core or eight-core rubber-insulated cables with an outer diameter of around 11.3 mm. During maintenance, it is strictly prohibited to power on and open the cover in explosive environments, as well as to pry at the flameproof surface. At the same time, avoid damaging or scratching the flameproof surface during disassembly and assembly, and restore it to its original flameproof condition after maintenance. ⑺After disassembling and repairing the reducer of the actuator, attention should be paid to lubrication by adding oil; low-speed motors generally should not be disassembled, cleaned, or lubricated. After assembly, it is also necessary to check whether the valve position matches the indication of the valve opening degree. Precautions for installing electric control valves: 1. Before installing the valve, thoroughly clean the pipes of any dirt or slag to prevent the valve core from getting stuck due to such contaminants during operation. The installation height of the valve from the ground should be appropriate, with sufficient space above and below the valve to facilitate its disassembly, assembly, and repair. 3 Avoid applying additional pressure to the valve due to improper installation, such as when the pipeline and the valve are not aligned or the flange surfaces are not parallel. The combined effect of the valve’s own weight, surrounding vibrations, and changes in the temperature of the medium and the environment can cause the flange to crack or deform. To avoid such accidents, in addition to eliminating the aforementioned external factors, the valve should be installed on a section of bent pipe; large-diameter valves need to be supported, and the valve must be installed vertically upright in the pipeline. It is recommended to consider the following 12 specific requirements: (1) The air source used to operate pneumatic control valves should be oil-free and dry, especially for valves equipped with positioners. (2) An appropriate filter should be installed on the inlet piping of small-bore control valves to filter out impurities from the piping system and prevent damage to the valves. (3) When the valve is installed in the system, the valve body should be protected from excessive pressure, which is particularly important for split-body valves. (4) Before the first start-up and after shutdown for maintenance, a filter should be installed in front of the control valve to remove scale, rust, and other debris from within the pipeline. Where possible, a short pipe fitting should be installed on the piping system, and the piping system should be flushed before installing the control valve. (5) For electric control valves operated in dusty environments, a rubber or plastic cover is fitted around the valve stem to protect its polished surface from damage. (6) It is essential to follow all the instructions provided by the manufacturer regarding the adjustment settings and the switch positions of the auxiliary equipment. For example, do not forget the bypass switch at the bypass position of the valve positioner. (7) It can be assumed that even with a good design, high-pressure fluid will inevitably accumulate upon shutdown; therefore, it is recommended that, if the potential energy of the accumulated liquid poses a significant risk, vent valves and/or discharge valves should be installed on each side of the electric control valve. (8) For valves that contain large amounts of high-pressure material, it is necessary to consider installing two vent valves and a discharge valve. Only a small amount of material accumulates between the two valves, allowing the pressure in the system to be released gradually, thereby enabling the pressure between these two discharge or vent valves to build up and be released repeatedly. Note that the control valve must be in the open position during this process. (9) If the fluid being discharged is a hazardous gas, the vent line must be connected to a safe location. (10) If the electric control valve needs to be removed from the system after installation, the isolation valve should be closed and marked. If there are hazardous fluids or contaminants inside the control valve, appropriate markings should be added to enable proper cleaning before disassembling the valve. (11) Be sure to install the control valve in accordance with the arrow indicating the flow direction. If the direction indicated by the valve arrow provided by the manufacturer is incorrect, this situation should be reported. (12) Before installation, it is necessary to consult the specific instructions from each valve manufacturer.