Valves, the actuators that move them, and the electronic circuits that control them, take a lot of abuse every day. This can cause screws to reposition, springs to weaken, and mechanical linkage to loosen. Electronic components may also experience "calibration drift" causing valves to malfunction, resulting in improper regulation of the gas or liquid they are controlling.
Avoid these problems with a preventive maintenance program. Key areas to test include:
- Valve closing to determine whether the positioner fully closes the valve at the 4.0mA current level
- Valve opening to determine at what point the valve starts to open and to assure there is no force holding the valve closed
- Span position to assess the stability of the valve in the fully open position
- Linearity of valves with linear action
- Overall operation to ensure that the valve performs smoothly without sluggishness or oscillation during the opening and closing process
These checks need to be conducted quickly to minimize down time. And when calibration drift is found, they should be followed by quick recalibration.