April 30, 2025
Control valve accessories reveal: application scenarios and functions of the full analysis
In industrial automation control systems, control valves play a key role in accurately controlling the flow, pressure, temperature and other parameters of various fluids. However, in order to operate efficiently and stably, control valves cannot be separated from the assistance of many accessories. These accessories are just like the “right-hand man” of the control valve, and they are useful in different working conditions to ensure the smooth operation of the system. Next, let us in-depth understanding of the regulating valve have what accessories, they are used in what circumstances, and what powerful functions they have.
I. Valve positioner
(A) Application Scenario
When the pressure of the fluid medium in the pipeline fluctuates greatly, it is difficult to accurately locate the valve position of ordinary control valves, at this time the valve positioner comes in handy. For example, in the petrochemical plant, the reactor feed pipeline pressure often fluctuates due to changes in the reaction process, the installation of the valve positioner can ensure that the regulating valve can be based on the control signal to act accurately.
For occasions requiring very high regulation accuracy, such as the dosage system in the pharmaceutical industry, need to accurately control the flow ratio of various raw materials, the valve positioner can increase the positioning accuracy of the regulating valve to ±0.5% or even higher, to meet the stringent requirements of the production process.
(B) Functional features
Precise positioning: Receive the standard signal (such as 4-20mA) from the controller, convert it into mechanical displacement, and then accurately control the spool position of the regulating valve, overcoming the friction of the valve stem, the unbalanced force of the medium and other interferences, to achieve precise positioning.
Improve the quality of regulation: Improve the dynamic response characteristics of the regulating valve, speed up the spool action speed, reduce the regulation hysteresis, so that the system can quickly respond to changes in the working conditions, to maintain the stability of the controlled parameters.
II. Pneumatic Relay
(A) Application Scenario
For regulating valves on long-distance transmission pipelines, due to the long transmission distance of the gas source, the signal pressure is prone to attenuation, resulting in slow action of the regulating valves. For example, in the case of natural gas long-distance pipelines, pneumatic relays need to be installed on the regulating valves at certain intervals to enhance the signal pressure and ensure that the regulating valves work properly.
Large caliber, high pressure drop control valves, switching action requires a large thrust, relying only on ordinary gas source is difficult to meet. In the metallurgical industry, blast furnace gas pipeline, large-diameter control valves with the help of pneumatic relays, the use of gas amplification principle, to provide sufficient power for the valve action.
(B) Functional characteristics
Signal amplification: the input small power control signals (such as signals from the valve positioner) for power amplification, the output of a larger pneumatic power to promote the spool of the regulating valve rapid action to enhance the valve response speed and output force.
Accelerate the speed of action: in the emergency cut-off and other demanding scenes of valve action time, the pneumatic relay can make the regulating valve in a short time to complete the fully open or fully closed action, to protect the system safety.
III. solenoid valve
(A) application scenarios
Automation control system need to remote control valve switch occasions. Such as urban water supply system pumping stations, through the remote control of the solenoid valve on and off, to realize the switching operation of the regulating valve, convenient and quick, without manual intervention.
Safety interlock system, when the system is abnormal, such as temperature, pressure exceeds the set threshold, the solenoid valve can quickly cut off the gas source, so that the regulating valve action to the safe position, to prevent accidents. For example, in the chemical production plant, once the leakage and other emergency conditions, the solenoid valve can respond immediately.
(B) Functional characteristics
Fast on and off: rely on electromagnetic force to drive the valve spool, realize the rapid connection and cut off the gas source, the response time is very short, usually between a few milliseconds to tens of milliseconds, to meet the needs of the system for rapid action.
Remote control: it can be integrated with the automation control system to remotely control its working status through electric signal, which is convenient for realizing the automated operation and centralized management of the system.
IV. Handwheel mechanism
(A) Application Scenario
In the commissioning stage, technicians need to manually operate the control valve to test its performance and whether the action is normal, the handwheel mechanism provides a convenient way for commissioning. For example, the newly installed control valve, through the handwheel can open or close the valve to different positions to check the operating conditions.
When the automation control system fails, can not be remote control of the regulating valve, the handwheel mechanism as a backup means of operation, can maintain the basic operation of the regulating valve. In the power system, when encountering unexpected conditions such as power failure of the control system, the operator can use the handwheel to operate the regulating valve manually.
(B) Functional characteristics
Manual operation: By rotating the handwheel, the valve stem is directly driven up and down to realize the switching action of the regulating valve, which is simple and intuitive to operate, and requires no external energy support.
Safe standby: as a reliable standby operation mode, there is a clutch device between the handwheel and the actuator, which disengages the handwheel and the actuator during normal operation and does not affect the automatic control; it can be switched to the manual operation in case of malfunction to guarantee the continuity of production.
V. Air Filtration Pressure Reducer
(A) Application Scenario
The quality of the air source is poor, containing impurities, moisture and oil in the environment, such as in some old factories, the air source is not strictly purified, directly used for regulating valve control, easy to lead to wear and tear of the valve parts, clogging. At this time, the installation of air filtration pressure reducer, can effectively purify the air source, to protect the regulating valve.
On the occasion of high pressure stability requirements of the air source, such as the pneumatic control system of precision instrument manufacturing workshop, need to ensure that the regulating valve air source pressure is constant. Air filter pressure reducer can stabilize the air source pressure at the set value, to ensure the stability of the regulating valve.
(B) Functional characteristics
Filtering impurities: the internal multi-layer filtration device can effectively filter out solid impurities in the air source, such as dust, rust particles, etc., and the filtration precision can reach micron level, preventing impurities from entering the regulating valve and prolonging the service life of the valve.
Pressure reducing and stabilizing: the higher pressure of the gas source is reduced to the required working pressure range of the regulating valve through the pressure reducing element, and the pressure stabilizing device is used to maintain the output pressure stable and unaffected by the fluctuation of the pressure of the gas source, which provides the regulating valve with a stable and reliable gas source.
VI. Trip Valve
(A) Application Scenario
In some occasions that do not allow sudden changes in the valve position of the control valve, such as chemical production in the distillation tower, the tower level adjustment requirements are smooth, if the gas supply is suddenly interrupted, the control valve valve position is out of control, will seriously affect the effect of distillation. Holding valve can keep the current valve position unchanged when the gas source fails.
Offshore oil platforms and other special environments, gas supply is susceptible to wind and waves and other external factors, in order to ensure the stable operation of the regulating valve, the holding valve has become an important accessory to ensure that the key regulating valves in the gas source abnormalities can still maintain the current control state.
(B) Functional features
Valve position locking: when detecting the gas source pressure is lower than the set value (such as gas source interruption), the position-holding valve will act quickly to cut off the regulating valve air circuit and lock the valve position in the current position, preventing the valve position from drifting due to the problem of the gas source, and avoiding abnormal fluctuations in the production process.
Automatic reset: after the gas source returns to normal, the holding valve automatically resets, and the regulating valve resumes normal automatic control state without manual intervention, ensuring the continuity and stability of the system operation.
