Pneumatic control valve

Personally, I think it’s most important to find 50% first, and then at zero scale

Reply to 2# 418238987: Does this value change when adjusting the range?

It will change, but not by much; it will be in much better condition

Reply to 4# 418238987: Okay! Thank you! Give it a try again! :handshake

12MA 50% is the most important, followed by the zero scale

When the valve is positioned at 50%, the feedback rod of the valve positioner should be horizontal, and the markings on this rod should correspond to the valve’s travel distance; in this way, the range can be determined fairly accurately! Once the position of the valve actuator has been determined, 12mA is used to set this at 50% position; after that, the zero point, full scale, and sensitivity can be adjusted

I think the trick is this: before making adjustments, install the positioner correctly, as mentioned earlier – ensuring that 50% of the valve’s opening angle keeps the positioner’s feedback rod in a horizontal (or nearly horizontal) position. This is very important. Why is it done this way? The fundamental purpose is to ensure the full stroke of the valve, with the feedback located within the effective area of the actuator cam. Next is zeroing and setting the range. Taking the valve operation by air as an example: (1) Zero adjustment. Enter 4mA, and adjust the zero knob to the appropriate position ； (2) Adjust the range. Enter 20mA and adjust the range knob to the appropriate position. Step 1: To what extent should it be zeroed out? The adjustment had an immediate effect; the valve was about to open, but it was fine before it did. The key is step 2: what is the appropriate setting for adjusting the range? The right cooking temperature depends on one’s own experience. After adjusting the range, the valve changes accordingly (ignore that), and the zero point also changes; therefore, once the range has been adjusted, it is necessary to return to step 1 to reset the zero. The calibration process of the positioner is only complete after 20 mA is applied, at which point the valve is in the 100% position. If the heat level isn’t controlled properly, the number of adjustments needed increases. After making the adjustments, enter 8mA, 12mA, and 16mA respectively to observe the linearity of the valve. This step is mainly intended to let you experience the results of the adjustments, and there should be no problems.

Adjusting it usually isn’t that complicated. For a new unit or one that’s in normal use, after maintenance, first send a 4-milliampere signal to check whether it has been turned off completely; then send a signal corresponding to 5% opening – if the control valve moves just a little at 5%, that’s basically sufficient. After that, send signals for 50% and 100% opening to ensure that the degree of opening is as expected. The main thing is that it can be closed tightly

In the case of an intelligent valve positioner, as long as it is not installed too far from its proper position, it can be automatically adjusted using the buttons on the positioner or a manual operator.

Reply to 9# denghl: I’ve learned it; I’ll give it a try later