How to determine the forward and reverse action of a control valve? (Update)
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This post was last edited by lingguiyuan on 2010-5-17 at 21:41. The original post was posted in the Instrumentation section, but no one replied. I study process engineering, and I would like to ask whether a control valve that receives air from above is of the air-shut type How is the forward and reverse action of the said control valve determined? Could you explain why a reverse action is used for the bottom valve? Can the direction of the control valve seat be installed in reverse? What will be the outcome? How can one determine on-site whether a control valve is air-open, air-close, and its operating mode? (All air openings in our factory now enter from below, while all air closures enter from above.) It is said that a gas-operated reverse action is used at the bottom of the pressure relief tower. I can understand using a gas shut-off, but why use reaction force? ) Below is a passage found in another set of operating procedures: Air-open control valve: As the input air pressure increases, the valve opens wider. Air-close control valve: As the input air pressure increases, the valve closes more tightly. Based on the process conditions, a choice is made for safety reasons. Direct-acting control valve: Air pressure enters from the upper part of the diaphragm, causing the valve stem to move downward ； Counteraction control valve: Air pressure enters from below the diaphragm, causing the valve stem to move upward. Large-diameter control valves are mostly of direct-acting type; the mode of operation – whether it is air-open or air-close – is determined by changing the installation direction of the valve core ； Most small-diameter control valves are used in either direction, with the air-on or air-off mode being determined by changing the direction of the input signal. How to understand the ones at the back? It’s confusing everyone. . . . Could you explain it in detail?
When it’s in the open position, it’s indeed open; when it’s FC or FO, it’s closed
This post was last edited by oatobnus on 2010-5-17 at 21:21. The links below are posts related to the concept of \"action and reaction\" that have been discussed by fellow sailors; I hope they will be helpful to you. Hope to pay attention in a timely manner. Forward/reverse action of the DVC6000 valve positioner? Forward/reverse action of the controller? The forward and reverse action of valves: How do the forward and reverse actions of the actuator of a control valve interact with those of the valve positioner? Determining the forward and reverse action of regulators in cascade control and proportional control systems; adjusting for forward and reverse action; the forward and reverse action of control valves... 1 2 If the forward and reverse action of the regulator is modified, wouldn’t the negative feedback loop then become positive feedback? Excuse me, experts: in design, is there any simple and effective way to determine the forward and reverse action of the regulator in a control loop? 1 2 The forward and reverse action of a control loop – how is the forward and reverse action of a controller determined in proportional control? I have a question regarding the forward and reverse action of valve electric positioners. What about the forward and reverse action in control systems? Determination of the forward and reverse action of positioners and valves: How to determine the forward and reverse action of the control mechanism in pneumatic control valves? ... 1 2 The relationship between the forward/reverse operation of electric valve positioners and that of valve actuators; the forward/reverse operation of control valves. In cascade control systems, how to choose the forward/reverse operation of controllers. The forward/reverse operation of valves; the forward/reverse operation of control loops. The relationship between the forward/reverse operation of controllers and gain values. What are the differences and connections between the forward/reverse operation of regulators and that of valve positioners? Seeking guidance on choosing the forward/reverse operation for various components in automatic control loops. The working principle of electric-valve positioners, and its relationship with the forward/reverse operation of valves?
3# oatobnus Thank you so much
During my studies, thank you! Many thanks
DCS systems are used in various process units to achieve automated control of the production process. These systems play a crucial role in the operational processes of different types of production units; they serve as the brain and nervous system that direct and control the production process. They are essential for ensuring that process parameters are met, for maintaining safe and stable operation, for reducing energy consumption, and for optimizing operations as well as improving production management. For a DCS to fulfill its functions and deliver results that satisfy users, the degree of automation is an important indicator, and it is crucial to determine whether the control system can operate automatically, as well as to properly adjust the PID parameters. Method for determining the positive/negative action of a regulator: When an adjustment system is set to automatic mode, once the control strategy has been determined and the positive/negative action of the regulator has been identified, the most crucial aspect is how to tune the P, I, and D parameters. Based on years of field experience, I will discuss how to adjust these parameters in an adjustment system; please use this as a reference in your own projects. Before setting the P, I, and D parameters of the control system, it is necessary to ensure that the closed-loop control system operates with negative feedback, that is, Ko*Kv*Kc > 0. Block diagram of a single-loop PID control system. Control object Ko: When the valve or actuator is opened and the measured PV value increases, then Ko > 0 ； Conversely, Ko＜0 ； Adjusting valve Kv: If the valve is of direct-acting type (operates when air or electricity is applied), then Kv > 0 ； If the valve has a reverse action (air-operated, electric-operated), then Kv＜0 ； The sign of Ko and Kv is determined by the process object and production safety. Based on the signs of Ko and Kv and the condition that Ko*Kv*Kc > 0, we can determine the sign of Kc. For the regulator Kc: if Kc > 0, then the regulator operates in a feedback manner ； If Kc < 0, the regulator is positive acting ； The software configuration must be set correctly; before device commissioning, startup, and the tuning of P, I, D parameters, it is essential to check that the regulator’s forward/reverse action is set properly and without errors. Before setting the P, I, and D parameters of the control system, it is necessary to ensure accurate measurements and smooth valve operation ； When tuning the P, I, and D parameters of the control system, it is important to inform the users in advance and ask them to pay close attention to the operational conditions during production in order to ensure safe operations ； When tuning the P, I, and D parameters of the control system, start with automatic mode before moving to cascade control; start with the secondary loop before the primary loop, with the secondary loop having a coarser setting and the primary loop a finer one. On the CRT at the operation station, open the tuning screen for the regulator, change the setpoint SP or the output value OP to generate a step signal that is acceptable within the process parameters, observe the changes in the measured value PV as well as the trend chart, and continuously adjust the PID parameters – often repeating this process several times until stable control is achieved. In practice, it is generally sufficient to achieve a first-order characteristic that satisfies the process requirements.