Control valve positioner

Thanks I found this to be helpful and accurate.


I would like to also add compromises that positioners suffer from especially in critical ESD applications. In oil and gas applications and chemical plants for example, many process control valves only need to be moved from full open position during mandated safety testing intervals (hence the purpose of partial stroke testing). From a SIS design simplicity and SIL perspective, Positioners:

Increased dangerous failure rate
Dangerous failures of the positioner
Dangerous failures of QEVs (often need to achieve enough flow for operation, additional components that can fail...)
Limited diagnostic coverage from the inability to test solenoid valves
Susceptible to contamination
Compatible only with pneumatic actuators
Requires high level of air filtration
 
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