Valve positioner failure issues

There are many reasons for this. Try entering a value manually using the tester on-site; if that doesn’t work, try entering it manually using instrument air.

First, determine whether the valve is of the air-open type or air-close type. Then check the output signal of the valve actuator to figure out whether the problem lies with the actuator or the valve itself. If it’s the actuator that’s at fault, examine the distance of the nozzle baffle; you can also check the distance of the manual baffle to see if there is any change in the actuator’s output. If there is a change, the issue lies in the nozzle baffle mechanism or the electrical components; if there is no change, the problem is related to the air supply system, and it’s necessary to check whether the constant-throttle orifice is blocked or if there are issues with the amplifier.

There are many reasons. Is this a gas shut-off valve? Has current actually been supplied? Is the wiring okay? Is the air pressure sufficient?

It could be that the pressure of the air supply is insufficient, or there is sticking between the valve stem and the valve seat, which prevents smooth movement, or the air supply is pushing the valve stem against the diaphragm head. Coordination is carried out between the site and the control room, with manual operation

Based on what the poster described, it can basically be determined that it is a gas shut-off valve. For the situation described by the poster, the following solutions are provided: 1: Is this valve connected to an ESD interlock? If it is connected to an ESD interlock, there must be a solenoid valve; is this solenoid valve de-energized? Check the reason. 2: Is a hold-back relay, commonly known as a hold-back valve, installed in the air intake circuit of this valve? Is the hold-back valve activated? (Adjustable with preset pressure screws) 3: The nozzle is completely blocked; clean the nozzle (this takes some time). 4: A common issue with electrical valve positioners – the power amplifier installed behind the positioner is damaged, and in such cases, no output will be generated. The situation you mentioned must be listed above; please check carefully

Based on what the poster described, it is generally a problem with the feedback rod part of the valve positioner.

First, determine what type of valve it is – a cylinder-type or diaphragm-type valve – and check whether there is any leakage in the cylinder or diaphragm of the control valve. Check again whether it is a smart or mechanical locator. 1) If it is smart, then check the amplifier; it’s possible that the amplifier is clogged. If it still doesn’t work after cleaning the amplifier, then check whether the connections of the feedback rod or other components are loose. If it still doesn’t work, it’s basically ruined. 2) If it is a mechanical device, one can first adjust the zero setting or the range adjustment knob to see if it is possible to open the valve to other positions; if so, a signal is sent to set that position. Generally, 50% is adjusted first, followed by 100% and 0%. It’s also possible that the amplifier is blocked, the adjustment cam is loose, or the connections in other areas are not secure. There are many possible causes of the problem, and considerable practical experience is required to diagnose it

Thank you all for your helpful answers; I will go to the site tomorrow and conduct a thorough inspection based on everyone’s suggestions.

In the situation described by the original poster, for ball valves, the positioner is usually of the angular stroke type, right? :In the abnormal state, a normally open indication should indicate a valve that closes when pressurized. 1. Check at the on-site locator to see if the signal has been transmitted; this is the simplest step, but it’s one that is often overlooked. 2. Supply air to the valve’s cylinder to see if there is any response, thereby ruling out the possibility of a damaged cylinder. 3. If there is a signal generator available, use it to send signals to the locator on-site for testing. Check whether the positioner is working. If there is no response from the positioner at step 3, see if the nozzle is clogged; if so, clean the nozzle. Then check whether the power amplifier of the electric valve positioner is damaged, as it will also not produce any output if it is damaged. Additionally, I would like to remind the poster that the connecting mechanism and feedback in the positioner of the angular travel are linked through gears; it’s possible that these gears are stuck or loose. It would be better if there were a diagram to look at, OP:P

Normal use, sudden changes – in most cases it’s a problem with the feedback mechanism, or something is loose