How to debug mechanical and electrical valve positioners
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For ordinary mechanical valve positioners, there are only two adjustable elements: the zero adjustment knob and the range adjustment knob. Could you explain in a bit more detail how to carry out the tuning process? It seems a bit confusing. Should one first adjust the zero knob so that the valve stem is at 50%, and then determine the range by referring to the 0 and 100 marks? Is it the range adjustment knob that needs to be adjusted throughout this process?
First, send a 50% opening signal and adjust the zeroing knob to 50% valve opening. Check whether the cam mark is at the center. Try to see if the opening degrees of the 0, 25, 50, 75, 100 signal valves are appropriate. It does not meet the requirement of adjusting the range according to the circumstances. After that, conduct 50% adjustment experiments until it meets the requirements.
First, set the valve to 0-50-100. Is it aligned? Zero it out first, then run it once more. Check if the itinerary is sufficient; if not or if it’s too long, adjust it. When adjusting the stroke, it is necessary to zero it out, as changing the stroke zero point will result in changes. Just keep adjusting and trying over and over again. Once you get familiar with it, it usually takes just one or two attempts to get it adjusted properly.
The calibration method for ordinary mechanical electrical valve positioners is as follows: I. Preparation Work Prepare a pneumatically actuated control valve that has been calibrated properly (taking a straight-stroke control valve with a direct-acting actuator as an example), and connect it to the valve positioner to be calibrated. The key points are as follows: 1. Fix the outer adjustment nut at the scale corresponding to the actuator’s stroke, and place the roller inside the groove so that it can roll freely without falling out. The trough plate should be horizontal ； 2. Adjust the proportional arm position. Adjust the gas supply to 0.14 MPa and apply a 12 mA signal to make the valve stem travel 50% of its range; by adjusting the position of the valve stem up and down, bring the proportional arm into a horizontal position (this is an important step to ensure linearity). II. Valve positioner calibration 1. Zero point adjustment. With a signal of 4.0 mA, adjust the zeroing screw of the positioner so that the output pressure of the positioner is 0.02 MPa, or so that the valve stem is at the zero position of its travel ； 2. Range adjustment. With a signal of 20 mA, adjust the range setting screw on the positioner so that the output pressure of the positioner is 0.1 MPa, or so that the valve stem is at the full travel position ； 3. Repeatedly adjust the zero point and range until they are within acceptable limits ； 4. Apply signals of 4, 8, 12, 16, and 20 mA in sequence, and observe that the output pressure of the locator should be 0.02, 0.04, 00.06, 0.08, and 0.1 MPa respectively, or the valve stem stroke should be at the corresponding position (a dial indicator can be used to check the stroke displacement if higher precision is required). If there are any deviations, continue adjusting the zero point and range until all values are within the specified limits.