Sharing experience: The Fox D20 locator sends a full-close signal to the DCS, yet air leakage still occurs in the locator
Thread Content
Today I encountered this issue. First, I conducted a test: I disconnected the air pipe connection that leads from the positioner to the cylinder, and had the DCS set the opening degree between 0 and 100. I checked to see if there was no airflow at zero degree; as the degree increased to 25%, the airflow gradually increased (the air valve opened). When the DCS set the degree to 0%, air leakage started to occur. During operation, the opening from 0 to 100 worked fine, but the closing process was extremely slow. The self-tuning function of the positioner didn’t work either. I began to suspect a problem with the piezoelectric valve and planned to replace the positioner. Suddenly, I noticed that the air pressure was quite high, at 4.5 kilograms per square centimeter. By reducing the air pressure to 3.5 kilograms per square centimeter, the self-tuning function worked properly again, and no air leakage occurred when the DCS set the degree to 0%. All operations were normal. In conclusion, the high air pressure, along with leaks in the piezoelectric valve of the positioner (in simple terms, the positioner couldn’t handle a pressure of 4.5 kilograms per square centimeter), caused the air leakage. It was mistakenly thought that there was a problem with the positioner itself; however, this 1 kilogram difference in pressure cannot be ignored
The air release valve closes slowly, which means the exhaust is slow; it’s not necessarily a problem with air pressure. . .
When everything is turned off, air still enters the cylinder (so there is an additional amount of air flowing during the process of closing the valve). When the air pressure is set to 3.5 kilograms, no air flows any more and the valve closes more quickly
Exhaust: I just remembered something. It’s a corner valve – I’ve searched everywhere but couldn’t find where the exhaust is; I can’t feel any area from which exhaust is coming out. It must be the regulator that releases air; the red valve seems to be from Honeywell, right?
Foss’s new piezoelectric valves keep leaking air a bit, but the manufacturer says it’s normal. Air is leaking from the area at the bottom of the locator where there is a cover. The employees in the production department keep reporting leaks, and we keep explaining that it’s a normal phenomenon; sigh.