What is the function of the feedback rod in a valve positioner, and how will the valve operate if the feedback rod comes loose?
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This post was last edited by 328104062 on 2015-10-26 at 23:41. As the title suggests: From what I remember (I disassembled them three or four years ago, so my memory is a bit fuzzy): A valve positioner can be considered a negative feedback system, consisting of a nozzle, a feedback rod, a baffle, a cam, as well as screws for adjusting the travel and zero point (mechanical type: such as those from Shanghai Valve Special, Ningxia Wuzhong, and Fisher). I’m not able to understand how intelligent positioners work once they are disassembled; please forgive me for that. 1. What is the function of the feedback rod? Is the nozzle wind force balanced by a spring? Let’s have a detailed explanation. 2. For the gas pressure controller of the heating furnace (single-loop, reverse action), the positioner operates in forward action, the actuator also operates in forward action, and the valve body as well operates in forward action. What will happen if the stem of the positioner in an FC valve comes loose? 3. What does routine valve maintenance include, and how can feedback rod detachment be prevented? Automatic control instruments
What are the consequences if the actuator stem comes loose? The control valve will move to the extreme position.
The valve positioner and the control valve form a negative feedback closed-loop control system; the feedback rod serves as the feedback element of this control loop. If the feedback rod comes loose, the system becomes an open-loop system, and the output of the positioner will reach its maximum value.
I agree with the person above; the locator acts as a negative feedback mechanism. If the valve is installed vertically, when the feedback rod moves in the direction of closing, the valve moves in the direction of opening.
If the feedback rod connecting the positioner and the control valve comes loose, the positioner loses its feedback function and becomes a pneumatic amplifier with a high amplification factor. If the actuator is direct-acting, that is, as the signal increases the output also increases, the valve stem comes loose and the output reaches its maximum value; if it is reverse-acting, the output goes to zero.
There is no setpoint rod for the gas pressure controller of the heating furnace.
1. The function of the feedback rod is to provide negative feedback, which is achieved through a linkage mechanism； 2. If the actuator stem comes loose, positive feedback is established; as the input to the actuator increases, the output also increases, and due to this positive feedback effect, the output reaches its maximum value. Conversely, as the input increases, the output decreases, until it eventually becomes zero. 3. The routine maintenance of valves focuses on checking whether the valve stem is stuck, whether all moving parts operate smoothly, whether the connecting parts are secure, and whether there is any leakage...
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